Year 2 Biopsychology Flashcards
(148 cards)
1
Q
What is the nervous system?
A
The nervous system is a specialised network of cells in the human body and is our primary internal communication system.
2
Q
What does the nervous system consist of?
A
It consists of the central nervous system and the peripheral nervous system.
3
Q
What are the two main functions of the nervous system?
A
- To collect, process and respond to information in the environment.
- To co-ordinate the working of different organs and cells in the body.
4
Q
What is the central nervous system made up of?
A
The brain and the spinal cord.
5
Q
Define CNS.
A
The CNS consists of the brain and the spinal cord and is the origin of all complex commands and decisions.
6
Q
Describe the brain.
A
The brain is the centre of all conscious awareness.
Its outer layer, the cerebral cortex, is highly developed in humans and is what distinguishes our higher mental functions from those of animals.
The brain is divided into two hemispheres.
7
Q
What is the spinal cord responsible for?
A
The spinal cord is an extension of the brain.
It is responsible for reflex actions, like pulling your hand away from a hot plate.
8
Q
What does the CNS do?
A
It passes messages to and from the brain and connects nerves to the peripheral nervous system.
9
Q
What is the role of the peripheral nervous system?
A
It sends information to the central nervous system from the outside world, and transmits messages from the central nervous system to muscles and glands in the body.
10
Q
What does the PNS do?
A
The PNS transmits messages, via millions of neurons, to and from the central nervous system.
11
Q
What is the peripheral nervous system split into?
A
- Autonomic nervous system
- Somatic nervous system
12
Q
What is the role of the autonomic nervous system?
A
It governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses.
It transmits information to and from internal bodily organs. It is autonomic as the system operates involuntarily.
13
Q
What is the autonomic nervous system split into?
A
- The sympathetic nervous system
- The parasympathetic nervous system
14
Q
What does the somatic nervous system do?
A
It controls muscle movement and receives information from sensory receptors.
It transmits information from receptor cells in the sense organs to the central nervous system. It also receives information from the CNS that directs muscles to act.
15
Q
How is the human nervous system split up?
A
The human nervous system is split into the peripheral nervous system and the central nervous system.
The central nervous system is then split into the brain and spinal cord.
The peripheral nervous system splits into the autonomic nervous system and the somatic nervous system.
The autonomic nervous system then splits into the sympathetic nervous system and the parasympathetic nervous system.
16
Q
What is the endocrine system?
A
One of the body’s major information systems that instructs glands to release hormones directly into the bloodstream. These hormones are then carried towards target organs in the body.
17
Q
What does the endocrine system work alongside?
Why does it do this?
A
The endocrine system works alongside the nervous system to control vital functions in the body.
The endocrine system acts much more slowly than the nervous system but has very widespread and powerful effects.
18
Q
What is a gland?
A
A gland is an organ in the body that synthesises substances like hormones.
19
Q
What are hormones?
A
Chemical substances that circulate in the bloodstream and only affect target organs. They are produced in large quantities but disappear quickly.
Their effects are very powerful.
20
Q
What do glands do?
A
Glands in the body produce hormones.
21
Q
Where do hormones go?
A
Hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for that particular hormone.
Most hormones affect cells in several organs or throughout the entire body, leading to many diverse and powerful responses.
22
Q
What does the thyroid gland produce?
What does it do?
A
The thyroid gland produces the hormone thyroxine.
This hormone affects cells in the heart (increases heart rate). It also affects cells throughout the body increasing metabolic rates, this in turn affects growth rates.
23
Q
What are the main glands in the endocrine system?
A
Hippothalamus Pituitary Thyroid Parathyroid Adrenal Pancreas Ovaries Testes
24
Q
What is the major endocrine gland?
What does it do?
A
The major endocrine gland is the pituitary gland, located in the brain.
It is often called the master gland because it controls the release of hormones from all other endocrine glands in the body.
25
What two parts of the nervous system work together in fight or flight?
Often the endocrine system and the autonomic nervous system work in parallel with one another when preparing someone for fight or flight.
26
What happens during fight or flight?
When a stressor is perceived the first thing that happens is a part of your brain called the hypothalamus triggers activity in the sympathetic branch of the autonomic nervous system.
The ANS changes from its normal resting state (the parasympathetic state) to the physiologically aroused, sympathetic state.
The stress hormone adrenaline is released from the adrenal medulla (part of the adrenal gland) into the bloodstream.
Adrenaline triggers physiological changes in the body which creates the physiological arousal necessary for the fight or flight response.
The all happens in an instant as soon as the threat is detected.
27
What happens after the threat has passed in fight or flight?
Finally, once the threat has passed, the parasympathetic nervous system returns the body to its resting state.
The parasympathetic branch of the ANS works in opposition to the sympathetic nervous system, it acts as a brake and reduces the activities of the body that were increased by the sympathetic branch.
This is sometimes referred to as the rest and digest response.
28
Define adrenaline.
A hormone produced by the adrenal glands which is part of the human body's immediate stress response system.
Adrenaline has a strong effect on the cells of the cardiovascular system - stimulating the heart rate, contracting blood vessels and dilating air passages.
29
Give examples of biological changes associated with the sympathetic state.
```
Increases heart rate
Increases breathing rate
Dilated pupils
Inhibits digestion
Inhibits saliva production
Contracts rectum
```
30
Give examples of biological changes associated with the parasympathetic state.
```
Decreases heart rate
Decreases breathing rate
Constricts pupils
Stimulates digestion
Stimulates saliva production
Relaxes rectum
```
31
Define neuron.
The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.
32
How many neurons are in the nervous system?
There are 100 billion neurons (nerve cells) in the human nervous system, 80% of which are located in the brain.
33
What do neurons do?
By transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication.
34
How many types of neurons are there?
| Name them.
There are three types of neurons.
Motor neurons
Sensory neurons
Relay neurons
35
What do sensory neurons do?
| Describe their structure.
Sensory neurons carry messages from the PNS to the CNS.
| They have long dendrites and short axons.
36
What do relay neurons do?
| Describe their structure.
Relay neurons connect the sensory neurons to the motor or other relay neurons.
They have short dendrites and short axons.
37
What do motor neurons do?
| Describe their structure.
Motor neurons connect the CNS to effectors such as muscles and glands.
They have short dendrites and long axons.
38
How big are neurons?
Neurons vary in size from less than a millimetre to up to a metre long, but all share the same basic structure.
39
What is the cell body on a neuron?
The cell body (soma) includes a nucleus, which contains the genetic material of the cell.
40
What are the dendrites on a nucleus?
Branch-like structures called dendrites protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body.
41
What is the axon on a neuron?
The axon carries the impulses away from the cell body down the length of the neuron.
42
What is the axon covered in?
| What does it do?
The axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse.
If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse. Thus, the myelin sheath is segmented by gaps called nodes of Ranvier.
43
What are nodes of Ranvier?
Nodes of Ranvier are the gaps in myelin sheath.
| They speed up the transmission of the impulse by forcing it to 'jump' across the gaps along the axon.
44
What are terminal buttons?
At the end of the axon are terminal buttons that communicate with the next neuron in the chain across a gap known as the synapse.
45
Describe electric transmission (the firing of a neuron).
When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur. This creates an electrical impulse that travels down the axon towards the end of the neuron.
46
Define synaptic transmission.
The process by which neighbouring neurons communicate with each other sending chemical messages across the gap (the synaptic cleft) that separates them.
47
Define neurotransmitter.
Brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another. Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.
48
Define excitation.
When a neurotransmitter (e.g. adrenaline) increases the positive charge of the postsynaptic neuron. This INCREASES the likelihood that the neuron will fire and pass on the electrical impulse.
49
Define inhibition.
When a neurotransmitter (e.g. serotonin) makes the charge of the postsynaptic neuron more negative. This DECREASES the likelihood that the neuron will fire and pass on the electrical impulse.
50
How do neurons communicate with each other?
Neurons communicate with each other within groups known as neural networks.
51
What are neurons separated by?
Each neuron is separated from the next by a synapse. The synapse includes the space between them (synaptic cleft) as well as the presynaptic terminal and postsynaptic receptor site.
52
How are signals transmitted by neurons?
Signals within neurons are transmitted electrically.
Signals between neurons are transmitted chemically by synaptic transmission.
53
What happens to impulses at the end of a neuron?
When the electrical impulse (this is in terms of chemical transmission) reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.
54
What are neurotransmitters?
Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.
55
What happens to the neurotransmitter once it crosses the gap (the synapse)?
Once the neurotransmitter crosses the gap, it is taken up by the postsynaptic receptor sites (the dendrites of the next neuron).
Here, the chemical message is converted back into an electrical impulse and the process of transmission begins again in this other neuron.
56
What makes neurotransmitters unique?
Several dozen types of neurotransmitter have been identified in the brain, as well as the spinal cord and some glands. What makes them unique is that each neurotransmitter has its own specific molecular structure that fits perfectly into a post-synaptic receptor site (like a lock and key).
Neurotransmitters also have specialist functions, e.g. acetylcholine (ACh) is found at each point where a motor neuron meets a muscle, and upon its release, it will cause muscles to contract.
57
What two effects can neurotransmitters have on neighbouring neurons?
Either a excitatory effect or inhibitory effect.
58
What is summation?
Whether a postsynaptic neuron fires or not is decided by the process of summation.
This is where the excitatory and inhibitory influences are summed: if the net effect on the postsynaptic neuron is inhibitory then the postsynaptic neuron is less likely to fire.
If the net effect is excitatory it is more likely to fire - and momentarily, the inside of the postsynaptic neuron becomes positively charged.
Once the electrical impulse is created, it travels down the neuron.
Therefore, the action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold.
59
What is localisation of function?
The theory that different areas of the brain are responsible for different behaviours, processes or activities.
60
What did Paul Broca and Karl Wernicke discover during the 19th century?
During the 19th century, scientists such as Paul Broca and Karl Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions.
61
What did scientists think before the discovery of localisation of function?
Before scientists generally supported the holistic theory of the brain - that all parts of the brain were involved in the processing of thought and action.
62
What did Broca and Wernicke argue for?
| How the brain functions
Broca and Wernicke argued for localisation of function (sometimes referred to as cortical specialisation). This is the idea that different parts of the brain perform different tasks and are involved with different parts of the body. It follows then, that if a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected.
63
How is the brain split?
The brain is divided into two symmetrical halves called left and right hemispheres.
64
What is lateralisation?
The theory that some of our physical and psychological functions are controlled or dominated by a particular hemisphere.
65
How does each hemisphere control the body?
As a general rule, activity on the left hand side of the body is controlled by the right hemisphere and activity on the right hand side of the body is controlled by the left hemisphere.
66
What is the outer layer of the both hemispheres called?
| What does this do?
The outer layer of both hemispheres is the cerebral cortex. This is about 3mm thick and is what separates us from other animals because the human cortex is much more developed.
The cortex appears grey due to the location of cell bodies, the phrase grey matter is used to describe the surface appearance of the brain.
67
How is the cortex of both hemispheres divided?
| Name them.
The cortex of BOTH hemispheres is sub-divided into four lobes which are named after the bones beneath which they lie: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe.
Each lobe is associated with different functions.
68
Where is the motor area?
What does this control?
What happens if this area is damaged?
At the back of the frontal lobe (in both hemispheres) is the motor area.
This controls voluntary movement in the opposite side of the body.
Damage to this area of the brain may result in a loss of control over fine movements.
69
Where is the somatosensory area?
What does this area do?
What does damage to this area cause?
At the front of both parietal lobes is the somatosensory area which is separated from the motor area by a valley called the central sulcus.
The somatosensory area is where sensory information from the skin is represented. The amount of somatosensory area devoted to a particular body part denotes its sensitivity (receptors for our face and hands occupy over half of the somatosensory area).
Damage to this area could cause numbness or a tingling sensation in certain parts of the body.
70
Where is the visual area?
What does this area do?
What does damage to this area cause?
In the occipital lobe at the back of the brain is the visual area (or visual cortex). Each eye sends information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex.
This means damage to the left hemisphere can produce blindness in part of the right visual field of both eyes.
71
Where is the auditory area?
What does the area do?
What does damage to this area cause?
The temporal lobes house the auditory area.
This area analyses speech-based information.
Damage may produce partial hearing loss; the more extensive the damage, the more extensive the loss.
Also, damage to a specific area of the temporal lobe - Wernicke's area - may affect the ability to comprehend language.
72
Which side of the brain is language restricted to?
Language is restricted to the left side of the brain in most people.
73
Where is Broca's area?
What is this area responsible for?
What does damage to this area cause?
In the 1880s, Paul Broca, a surgeon, identified a small area in the left frontal lobe responsible for speech production.
Damage to Broca's area causes Broca's aphasia which is characterised by speech that is slow, laborious and lacking in fluency.
E.g. Tan, one of Broca's patients who could only say the word tan.
74
Where is Wernicke's area?
What does this area do?
What does damage to this area cause?
Around the same time as Broca, 1880s, Karl Wernicke described patients who had no problem producing language but severe difficulties understanding it, such that the speech they produced was fluent but meaningless.
Wernicke identified a region (Wernicke's area) in the left temporal lobe as being responsible for language comprehension.
Damage to this area would cause Wernicke's aphasia, this is characterised as producing nonsense words (neologisms) as part of the content of their speech.
75
Evaluate localisation of function in the brain.
- Brain scan evidence of localisation, wealth of evidence supporting the idea that neurological functions are localised. Petersen et al 1988 used brain scans to demonstrate how Wernicke's area was active during a listening task and Broca's during a reading task, suggesting that those areas of the brain have different functions. Also, a LTM study by Tulving et al 1994 revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. There now exists a number of highly sophisticated and objective methods for measuring activity in the brain which provide sound scientific evidence of localisation of brain function.
- Neurosurgical evidence, surgically removing or destroying areas of the brain to control aspects of behaviour developed in the 1950s. Walter Freeman developed the lobotomy, this was brutal and imprecise and involved severing connections in the frontal lobe in an attempt to control aggressive behaviour. Neurosurgery is still used today sparingly in extreme cases of OCD and depression. E.g. Dougherty et al 2002 reported on 44 OCD patients who had undergone a cingulotomy - a procedure that lesions the cingulate gyrus. At post-surgical follow up after 32 weeks, a third met the criteria for successful response and 14 percent for partial response. The success of the procedures strongly suggest that symptoms and behaviours associated with serious mental disorders are localised.
- Case study evidence, unique cases of neurological damage support localisation theory. E.g. Phineas Gage, an accident on a railroad caused a pole to go through Gage's left eye and exit his skull from the top of his head taking a portion of his brain with it (most of his left frontal lobe). Damage to his brain left a mark on his personality - he turned from someone who was calm and reserved to someone who was quick-tempered and rude. The change in his temperament following the accident suggests that the frontal lobe may be responsible for regulating mood.
- Lashley's research, the work of Karl Lashley 1950 suggests that higher cognitive functions (processes in learning) are not localised but distributed in a more holistic way in the brain. Lashley removed areas of the cortex (10 - 50%) in rats learning a maze. No area was proven to be more important than any other in terms of the rats ability to learn the maze. The process of learning appeared to require every part of the cortex, rather than being confined to a particular area. This suggests that learning is too complex to be localised and requires the involvement of the whole brain.
- Plasticity, when the brain has become damaged and a particular function has been compromised or lost, the rest of the brain appears to be able to reorganise itself in an attempt to recover the lost function. Lashley described this as the law of equipotentiality, whereby surviving brain circuits chip in so the same neurological action can be achieved. Although this does not happen every time, there are cases of stroke victims being able to recover those abilities that were seemingly lost.
76
Define plasticity.
(Also known as neuroplasticity or cortical remapping).
Plasticity describes the brain's tendency to change and adapt (functionally or physically) as a result of experience and new learning.
77
Define functional recovery.
A form of plasticity.
Functional recovery is the brain's ability to redistribute or transfer functions following damage through trauma. Functions usually performed by a damaged area will be transferred to other undamaged areas.
78
What happens to synaptic connections during infancy?
During infancy, the brain experiences a rapid growth in the number of synaptic connections it has, peaking at approx. 15,000 at age 2 - 3 years (Gopnick et al 1999). This equates to about twice as many as there are in the adult brain.
79
What happens to synaptic connections as we age?
| What is this called?
As we age rarely used connections are deleted and frequently used connections are strengthened. This is a process known as synaptic pruning.
80
What age does plasticity start and stop?
It was originally thought that such changes (synaptic pruning) were restricted to the developing brain within childhood, and that the adult brain, having moved past a critical period, would remain fixed and static in terms of function and structure.
However, more recent research suggests that at any time in life existing neural connections can change, or new neural connections can be formed, as a result of learning and experience (plasticity).
81
Describe Eleanor Maguire's study into plasticity.
Eleanor Maguire et al 2000 studied the brains of London taxi drivers and found significantly more volume of grey matter in the posterior hippocampus than in a matched control group.
This part of the brain is associated with the development of spatial and navigational skills in humans and other animals. As part of their training, London cabbies must take a complex test called the knowledge, which assess their recall of the city streets and possible routes. It appears that the result of this learning experience is to alter the structure of the taxi drivers' brains.
It is also noteworthy that the longer they had been in the job, the more pronounced was the structural difference (a positive correlation).
82
Describe Draganski et al's study into plasticity.
Draganski et al 2006 imaged the brains of medical students three months before and after their final exams. Learning-induced changes were seen to have occurred in the posterior hippocampus and the parietal cortex presumably as a result of the exam.
83
What did Mechelli et al find (related to plasticity)?
Mechelli et al 2004 found a larger parietal cortex in the brains of people who were bilingual compared to matched monolingual controls.
84
Describe what happens during functional recovery of the brain after trauma.
Following physical injury, or other forms of trauma such as the experience of a stroke, unaffected areas of the brain are often able to adapt and compensate for those areas that are damaged.
The functional recovery that may occur in the brain after trauma is another example of neural plasticity. Healthy brain areas may take over the functions of those areas that are damaged, destroyed or even missing.
Neuroscientists suggest that this process can occur quickly after trauma (spontaneous recovery) and then slow down after several weeks or months. At this point the individual may require rehabilitative therapy to further their recovery.
85
What happens to the brain during recovery?
The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage. Secondary neural pathways that would not typically be used to carry out certain functions are activated to enable functioning to continue, often in the same way as before (Doidge 2007). This process is supported by a number of structural changes in the brain;
- axonal sprouting
- reformation of blood vessels
- recruitment of homologous (similar) areas on the opposite sides of the brain
86
What are the structural changes in the brain that happen alongside functional recovery?
Explain them.
- Axonal sprouting: The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways.
- Reformation of blood vessels.
- Recruitment of homologous (similar) areas on the opposite side of the brain to perform specific tasks, e.g. if Broca's area was damaged on the left side of the brain, the right-side equivalent would carry out its functions. After a period of time, functionality may then shift back to the left side.
87
Evaluate plasticity and functional recovery of the brain after trauma.
- Practical application, understanding the processes in plasticity has contributed to the field of neurorehabilitation. Following illness or injury to the brain, spontaneous recovery tends to slow down after a number of weeks so forms of physical therapy may be required to maintain improvements in functioning. This shows that, although the brain may have the capacity to fix itself to a point, this process requires further intervention if it is to be completely successful.
- Negative plasticity, the brain's ability to rewire itself can sometimes have maladaptive behavioural consequences. Prolonged drug use, for example, has been shown to result in poorer cognitive functioning as well as an increased risk of dementia later in life (Medina et al 2007). Also 60 - 80% of amputees have been known to develop phantom limb syndrome - the continued experience of sensations in the missing limb as if it were still there. These are unpleasant, painful and thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss (Ramachandran and Hirstein 1998).
- Age and plasticity, functional recovery tends to reduce with age. The brain has a greater propensity for reorganisation in childhood as it is constantly adapting to new experiences and learning. However, Ladina Bezzola et al 2012 demonstrated how 40 hours of golf training produced changes in the neural representation of movement in participants aged 40 - 60. Using fMRI, the researchers observed reduced motor cortex activity in the novice golfers compared to a control group, suggesting more efficient neural representations after training. This shows that neural plasticity does continue throughout the lifespan.
- Support from animal studies, early evidence of neuroplasticity and functional recovery was derived from animal studies. Hubel and Wiesel 1963 sewed one eye of a kitten shut and analysed the brain's cortical responses. It was found that the area of the visual cortex associated with the shut eye was not idle (as had been predicted) but continued to process information from the open eye.
- The concept of cognitive reserve, evidence suggests that a person's educational attainment may influence how well the brain functionally adapts after injury. Schneider et al 2014 discovered that the more time brain injury patients had spent in education - which was taken as an indicator of their cognitive reserve - the greater their chances of a disability-free recovery. Two-fifths of patients studied who achieved DFR had more than 16 years' education compared to about 10% of patients who had less than 12 years' education.
88
Using the example of meditation, what effect can this have on plasticity?
A number of recent neuroscientific studies have examine the effects of prolonged periods of meditation on the brain. Some of these studies have more specifically explored thee concept of mindfulness. Being linked to reduced everyday tension and stress, meditation and mindfulness may also alter the structure and function of the brain.
Lazar et al 2005, using MRI scans, demonstrated how experienced meditators had a thicker cortex than non-meditators, particularly in areas related to attention and sensory processing. Individuals who took part in an 8-week Mindfulness-Based Stress Reduction course showed an increase in grey matter in the left hippocampus, a part of the brain strongly associated with learning and memory (Holzel et al 2011).
Finally, Tang et al 2012 found that four weeks of meditation resulted in an increase in white matter in the anterior cingulate cortex, a part of the brain that contributes to self-regulation and control (a key aspect of meditational practice).
89
What are some of the techniques used in physical therapy when talking about functional recovery?
Techniques may include movement therapy and electrical stimulation of the brain to counter the deficits in motor and/ or cognitive functioning that may be experienced following a stroke, for instance.
90
Describe the case of Gabby Giffords.
| How does this relate to functional recovery?
Gabby Giffords is a former US Democratic politician who survived an assassination attempt in 2011 when she was shot in the head from point blank range. Doctors placed Giffords into a waking coma and within months she had made staggering progress. With the aid of physical rehabilitation, Giffords was able to walk under supervision with perfect control of her left arm and leg, and able to write with her left hand. She could read, understand and speak in short phrases.
Doctors suggested that Gifford's progress would place her in the top 5% of people recovering from serious brain injury - an example of the brain's ability to heal itself.
91
Define hemispheric lateralisation.
The idea that the two halves (hemispheres) of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere than the other.
E.g. language, this is localised as well as lateralised.
92
Define split-brain research.
A series of studies which began in the 1960s involving epileptic patients who had experienced a surgical separation of the hemispheres of the brain. This allowed researchers to investigate the extent to which brain function is lateralised.
93
How is language lateralised?
The ability to produce and understand language for most people is controlled by the left hemisphere. This suggests that for the majority of us, language is subject to hemispheric lateralisation.
94
Describe the aim and background to Roger Sperry's split-brain research.
Sperry's 1968 studies involved a unique group of individuals, all of whom had undergone the same surgical procedure - an operation called a commissurotomy. This is where the corpus callosum and other tissues which connect the two hemispheres were cut down the middle in order to separate the two hemispheres and control frequent and severe epileptic seizures.
This meant that the main communication line between the two hemispheres was removed.
This allowed Sperry and his colleagues to see the extent to which the two hemispheres were specialised for certain functions, and whether the hemispheres performed tasks independently of one another.
95
What was the procedure in Sperry's split-brain research?
Sperry devised a general procedure in which an image or word could be projected to a patient's right visual field (processed by the left hemisphere) and the same, or different, image could be projected to the left visual field (processed by the right hemisphere).
In the normal brain, the corpus callosum would immediately share the information between both hemispheres giving a complete picture of the visual world. However, presenting the image to one hemisphere of a split-brain patient meant that the information could not be conveyed from that hemisphere to the other.
96
Explain the finding 'describing what you see' from Sperry's split-brain research.
When a picture of an object was shown to a patient's right visual field, the patient could easily describe what was seen. If, however, the same object was shown to the left visual field, the patient could not describe what was seen, and typically reported that there was nothing there.
For most people language is processed in the left hemisphere. Thus, the patient's inability to describe objects in the left visual field (processed in the right hemisphere) was because of the lack of language centres in the right hemisphere.
In the normal brain, messages from the right hemisphere would be relayed to the language centres in the left hemisphere.
97
Explain the finding 'recognition by touch' from Sperry's split-brain research.
Although patients could not attach verbal labels to objects projected in the left visual field, they were able to select a matching object from a grab-bag of different objects using their left hand (linked to right hemisphere). The objects were placed behind a screen so as not to be seen, the left hand was also able to select an object that was most closely associated with an object presented to the left visual field (e.g. an ashtray was selected in response to a picture of a cigarette).
In each case the patient was not able to verbally identify what they had seen but could nevertheless 'understand' what the object was using the right hemisphere and select the corresponding object accordingly.
98
Explain the finding 'composite words' in Sperry's split-brain research.
If two words were presented simultaneously, one on either side of the visual field (e.g. a key on the left and a ring on the right), the patient would select a key with their left hand (the left visual field goes to the right hemisphere linked to the left hand) and say the word ring. The superiority of the right hemisphere in terms of drawing tasks has been shown in tests with split-brain patients. A picture is flashed to either their right or left visual field. The left hand continually outperformed the right hand in such tests despite the fact that, for all the patients, the right hand was their preferred hand.
99
Explain the finding 'matching faces' in Sperry's split-brain research.
The right hemisphere appeared dominant in terms of recognising faces. When asked to match a face from a series of other faces, the picture processed by the right hemisphere (left visual field) was consistently selected, whilst the picture presented to the left hemisphere (right visual field) was consistently ignored. When a composite picture made up of two different halves of a face was presented - one half to each hemisphere - the left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of selecting a matching picture.
100
Evaluate split-brain research into hemispheric lateralisation.
- Demonstrated lateralised brain functions, Sperry's work into split-brain research has produced a large amount of findings concluding that the left hemisphere is more geared towards analytic and verbal tasks whilst the right is more adept at performing spatial tasks and music. The right hemisphere can only produce rudimentary words and phrases but contributes emotional and holistic content to language. Research suggests the left hemisphere is the analyser whist the right is the synthesiser - a key contribution to our understanding of brain processes.
- Strengths of the methodology, the experiments used involving split-brain patients were highly specialised and standardised procedures. Sperry's method of presenting information to one hemisphere was done by asking the participants to stare at a given point (the fixation point). The image projected would be flashed up for one-tenth of a second, meaning the patients would not have time to move their eye across the image and so spread the information across both sides of the visual field and thus both sides of the brain. The allowed Sperry to make sure that only one hemisphere was receiving information at one time, meaning the procedure was useful and well-controlled.
- Theoretical basis, Sperry's work prompted a theoretical and philosophical debate about the degree of communication between the two hemispheres in everyday functioning and the nature of consciousness. Some (Roland Pucetti 1977) suggest that the two hemispheres are so functionally different that they represent a form of duality in the brain (we are all two minds and this is emphasised rather than created in split-brain patients). Others argue that the two hemispheres form a highly integrated system and are both involved in most everyday tasks.
- Issues with generalisation, split-brain patients are an unusual sample of people, only 11 took part in all variations of the basic procedure, all of whom had a history of epileptic seizures. This may have caused unique changes in the brain that may have influenced the findings. Also, some participants had experienced more disconnection of the two hemispheres as part of their surgical procedure than others. Finally, the control group Sperry used of 11 people with no epileptic history may have been inappropriate.
- Differences in function may be overstated, Sperry's work oversimplifies the functional distinction between the left and right hemispheres, modern neuroscientists contend that the actual distinction is less clear-cut and more messy than 'verbal' and 'non-verbal'. In the normal brain the two hemispheres are in constant communication when performing everyday tasks, and many of the behaviours typically associated with one hemisphere can be effectively performed by the other when the situation requires it.
101
How does the case study of Kim Peek support lateralisation?
Kim Peek was born with severe brain damage including a total absence of a corpus callosum. Although socially awkward with a low IQ of 87, Peek's powers of memory were prodigious. He had word-for-word recall of over 12,000 books. He could read two pages in around ten seconds, employing his split-brain to simultaneously read one page with his right eye and one page with his left. He knew phone books by heart, and could say what day of the week a particular date fell on going back decades. His party trick was to tell strangers the names of people who used to live next door to them years ago.
102
What are the ways of investigating the brain?
- Functional magnetic resonance imaging (fMRI)
- Electroencephalogram (EEG)
- Event-related potentials (ERPs)
- Post-mortem examinations
103
Describe functional magnetic resonance imaging (fMRI) as a way of investigating the brain.
fMRI works by detecting the changes in blood oxygenation and flow that occur as a result of neural (brain) activity in specific parts of the brain. When a brain area is more active it consumes more oxygen and to meet this increased demand, blood flow is directed to the active area (known as the haemodynamic response). fMRI produces 3-dimensional images (activation maps) showing which parts of the brain are involved in a particular mental process and this has important implications for our understanding of localisation of function.
104
Describe electroencephalogram (EEG) as a way of investigating the brain?
EEGs measure electrical activity within the brain via electrodes that are fixed to an individual's scalp using a skull cap. The scan recording represents the brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity. EEG is often used by clinicians as a diagnostic tool as unusual arrhythmic patterns of activity (i.e. no particular rhythm) may indicate neurological abnormalities such as epilepsy, tumours or disorders of sleep.
EEG had many scientific and clinical applications, in its raw form it is a crude and overly general measure of brain activity. However, within EEG data are contained all the neural responses associated with specific sensory, cognitive and motor events that may be of interest to cognitive neuroscientists.
105
Describe event-related potentials (ERPs) as a way of investigating the brain.
Researchers have developed a way of teasing out and isolating each neural response associated with specific sensory, cognitive and motor events. Using a statistical averaging technique, all extraneous brain activity from original EEG recording is filtered out leaving only those responses that relate to the presentation of a specific stimulus or performance of a specific task. What remains are event-related potentials: types of brainwave that are triggered by particular events. Research has revealed many different forms of ERP and how these are linked to cognitive processes such as attention and perception.
106
Describe post-mortem examinations as a way of investigating the brain.
This technique involves the analysis of a person's brain following their death. In psychological research, individuals whose brains are subject to a post-mortem are likely to be those who have a rare disorder and have experienced unusual deficits in mental processes or behaviour during their lifetime. Areas of damage within the brain are examined after death as a means of establishing the likely cause of the affliction the person suffered. This may also involve comparison with a neurotypical brain in order to ascertain the extent of the difference.
107
Evaluate functional magnetic resonance imaging (fMRI) (as a way of investigating the brain).
- fMRI does not rely in the use of radiation unlike other scanning techniques such as PET. If administered correctly, fMRI is virtually risk-free, non-invasive and straightforward to use.
- Produces images that have very high spatial resolution, depicting detail by the millimetre, and providing a clear picture of how brain activity is localised.
- fMRI is expensive compared to other neuroimaging techniques and can only capture a clear image if the person stays perfectly still.
- It has poor temporal resolution because there is around a 5-second time-lag behind the image on screen and the initial firing of neuronal activity.
- fMRI can only measure blood flow in the brain, it cannot home in on the activity of individual neurons and so it can be difficult to tell exactly what kind of brain activity is being represented on screen.
108
Evaluate electroencephalogram (EEG) (as a way of investigating the brain).
- EEG has proved invaluable in the diagnosis of conditions such as epilepsy, a disorder characterised by random bursts of activity in the brain that can easily be detected on screen.
- It has contributed much to our understanding of the stages involved in sleep.
- Unlike fMRI, EEG technology has extremely high temporal resolution. Today's EEG technology can detect brain activity at a resolution of a single millisecond (and even less in some cases).
- EEG signal is not useful for pinpointing the exact source of neural activity.
- It does not allow researchers to distinguish between activities originating in different but adjacent locations.
109
Evaluate event-related potentials (ERPs) (as a way of investigating the brain).
- EPRs bring much more specificity to the measurement of neural processes than could ever be achieved using raw EEG data.
- As EPRs are derived from EEG measurements, they have excellent temporal resolution, especially when compared to neuroimaging techniques such as fMRI, and this has led to their widespread use in the measurement of cognitive functions and deficits.
- Researchers have been able to identify many different types of ERP and describe the precise role of these in cognitive functioning; for instance the P300 component is thought to be involved in the allocation of attentional resources and the maintenance of working memory.
- Critics point to a lack of standardisation in ERP methodology between different research studies which makes it difficult to confirm findings.
- In order to establish pure data in ERP studies, background noise and extraneous material must be completely eliminated, and this may not always be easy to achieve.
110
Evaluate post-mortems (as a way of investigating the brain).
- Post-mortem evidence was vital in providing a foundation for early understanding of key processes in the brain.
- Paul Broca and Karl Wernicke both relied on post-mortem studies in establishing links between language, brain and behaviour decades before neuroimaging ever became a possibility.
- Post-mortem studies improve medical knowledge and help generate hypotheses for further study.
- Causation is an issue within these investigations. Observed damage to the brain may not be linked to the deficits under review but to some other unrelated trauma or decay.
- Post-mortem studies raise ethical issues of consent from the patient before death. Patients may not be able to provide informed consent, e.g. in the case of HM who lost his ability to form memories and was not able to provide such consent - nevertheless post-mortem research has been conducted on his brain.
111
Explain how fMRI has practical application in the use of lie detecting.
Many have claimed that fMRI is an ideal tool for detecting truthfulness due to its ability to effectively see inside the brain. Supporters of its use argue that the analysis of neural blood flow is preferable to tracking peripheral measures of anxiety (such as changes in pulse, skin temperature or respiration). Traditional lie detectors are widely acknowledged as 'beatable', but neural activity is more difficult to fake.
Two US companies, Cephos and No lie MRI claim to predict with over 90% accuracy whether its clients are lying. No lie MRI suggests that the technique may even be used for risk reduction in dating.
However, many neuroscientists and legal scholars doubt such claims, with some questioning whether brain scans for lie detectors will ever move beyond the research lab into the real world.
112
Define biological rhythms.
Distinct patterns of changes in body activity that conform to cyclical time periods.
Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers).
113
Define circadian rhythm.
A type of biological rhythm, subject to a 24-hour cycle, which regulates a number of body processes such as the sleep/wake cycle and changes in core body temperature.
114
What do biological rhythms have an influence over?
All living organisms are subject to biological rhythms and these exert an important influence on the way in which body systems behave.
115
What are biological rhythms governed by?
All biological rhythms are governed by two things:
- the body's internal biological clocks, called endogenous pacemakers.
- external changes in the environment called exogenous zeitgebers.
116
Give examples of biological rhythms.
- ultradian rhythms (those that occur many times a day)
- infradian rhythms (those that take longer than a day)
- circannual rhythms
- circadian rhythms (those that last for around 24 hours
117
What is a circadian rhythm?
A rhythm that lasts for around 24 hours.
| *'circa' meaning about and 'diem' meaning day.
118
What are some examples of circadian rhythms?
- The sleep/wake cycle
| - Core body temperature
119
Explain how core body temperature is a circadian rhythm.
Core body temperature varies by around two degrees centigrade during the course of a day. It is at its lowest around 4 in the morning (36 degrees) and peaks around 6 in the evening (38 degrees). Evidence suggests that body temperature may have an effect on our mental abilities: the warmer we are internally, the better our cognitive performance.
120
Describe Folkard et al's and Gupta's findings into core body temperature affecting our mental abilities.
Folkard et al 1977 demonstrated how children who had stories read to them at 3pm showed superior recall and comprehension after a week compared to children who heard the same stories at 9am.
Gupta 1991 found improved performance on IQ tests when participants were assessed at 7pm as opposed to 2pm and 9am.
121
What is the effect of daylight on our sleep/wake cycle?
The fact that we feel drowsy when it's night-time and alert during the day demonstrates the effect of daylight - an important exogenous zeitgeber - on our sleep/wake cycle.
122
What is a free-running biological clock?
When the biological clock is left to its own devices without the influence of external stimuli such as light.
123
Describe Siffre's study into biological rhythms.
Michel Siffre is a self-styled caveman who has spent several extended periods underground to study the effects on his own biological rhythms. Deprived of exposure to natural light and sound, but with access to adequate food and drink, Siffre re-surfaced in mid-September 1962 after two months in the caves of the Southern Alps believing it to be mid-August.
A decade later he performed a similar study but this time for six months in a Texan cave.
In each case, his 'free-running' biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.
124
Describe Aschoff and Wever's study into biological rhythms.
Jurgen Ashcoff and Rutger Wever convinced a group of participants to spend four weeks in a WWII bunker deprived of natural light. All but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.
125
What does Siffre's and Aschoff and Wever's studies suggest about the sleep/wake cycle?
Both Siffre's experience and the bunker study suggest that the 'natural' sleep/wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24-hour day (such as the number of daylight hours, typical meal times, etc.)
126
What research suggests that we should not overestimate the influence of environmental cues on our internal biological clock?
Describe this research.
We should not overestimate the influence of environmental cues on our internal biological clock, Simon Folkard et al 1985 studied a group of 12 people who agreed to live in a dark cave for 3 weeks, retiring to bed when the clock said 11.45pm and rising when it said 7.45am. Over the course of the study, the researcher gradually speeded up the clock (unbeknown to the participants) so an apparent 24-hour day eventually lasted only 22 hours. It was revealed that only one of the participants was able to comfortably adjust to the new regime. This would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by changes in the external environment.
127
Evaluate biological rhythms - circadian rhythms.
- Practical application to shift work, knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption (known as desynchronisation). E.g. night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes and accidents are more likely (Boivin et al 1996). Research has also suggested a relationship between shift work and poor health: shift workers are three times more likely to develop heart disease (Knutsson 2003) which may in part be due to the stress of adjusting to different sleep/wake patterns and the lack of poor quality sleep during the day. Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity.
- Practical application to drug treatments, circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels. This in turn has an effect on pharmacokinetics, the action of drugs on the body and how well they are absorbed and distributed. Research into circadian rhythms has revealed that there are certain peak times during the day or night when drugs are likely to be at their most effective. This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medications including anticancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs (Baraldo 2008).
- Use of case studies and small samples, studies of the sleep/wake cycle tend to involve small groups of participants, as in the experiment by Ashcoff and Wever, or studies of single individuals, as in the case of Siffre. The people involved may not be representative of the wider population and this limits the extent to which meaningful generalisations can be made. In his most recent cave experience in 1999, Siffre observed at the age of 60, that his internal clock ticked much more slowly than when he was a young man. This shows that even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn.
- Poor control in studies, although participants in the studies by Aschoff and Wever and Folkard were deprived of natural light, they still had access to artificial light, e.g. Siffre turned on a lamp every time he woke up which remained on until he went to bed. It was assumed by him and others that artificial light unlike daylight would have no effect on the free-running biological rhythm. However in tests Czeisler et al 1999 were able to adjust participants' circadian rhythms from 22 hours to 28 hours using dim lighting.
- Individual differences, individual differences in cycles can complicate the generalisation of findings from studies of the sleep/wake cycle. Individual cycles can vary in some cases from 13 to 65 hours (Czeisler et al 1999). Also, a study by Jeanne Duffy et al 2001 revealed that some people display a natural preference for going to bed early and rising early (larks) whereas some people prefer to do the opposite (owls). There are also age differences in sleep/wake patterns.
128
Describe a study that shows age differences in patterns of the sleep/wake cycle.
According to neuroscientists, teenagers' circadian rhythms typically begin two hours after those of adults, so current school start times mean they wake up too early and are trying to focus when their body still needs sleep. It also means, at bed time, they tend not to be as tired as they should be.
A pilot study was run at Monkseaton High School in North Tyneside in 2010. Dr Paul Kelley, who now works as a researcher associate at Oxford University's Sleep and Circadian Neuroscience Institute, which is leading the new project, was headteacher at the time. After a decade of researching all the available evidence, he decided to put the start of the school day back to 10am over a two-year period.
'There were very positive outcomes, both academic and in terms of health', said Kelley. 'Academic results went up, illness down and the atmosphere in school changed. The students were much nicer to each other'.
129
What is the average length of the sleep/wake cycle?
A researcher conducted a meta-analysis of studies that investigated the length of the sleep/wake cycle. As a result of the meta-analysis, the researcher concluded that the average length of the sleep/wake cycle is between 24 and 25 hours.
130
Define infradian rhythm.
A type of biological rhythm with a frequency of less than one cycle in 24 hours.
(takes more than a day to complete).
131
Give examples of infradian rhythms.
- menstruation
| - seasonal affective disorder
132
Define ultradian rhythm.
A type of biological rhythm with a frequency of more than one cycle in 24 hours.
(rhythms that occur multiple times a day).
133
Give examples of ultradian rhythms.
- stages of sleep
134
Describe the infradian rhythm, the menstrual cycle.
The female menstrual cycle, an example of an infradian rhythm, is governed by monthly changes in hormone levels which regulate ovulation. The cycle refers to the time between the first day of a woman's period, when the womb lining is shed, to the day before her next period. The typical cycle takes approx. 28 days to complete (though anywhere between 24 and 35 days is generally considered normal). During each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy. If pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (the menstrual flow).
135
Describe Stern and McClintock's study into menstrual cycles and how these may be influenced by exogenous factors.
Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women.
A study by Kathleen Stern and Martha McClintock 1998 demonstrated how menstrual cycles may synchronise as a result of the influence of female pheromones.
McClintock involved 29 women with a history of irregular periods. Samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycles, via a cotton pad placed in their armpit. The pads were worn for at least 8 hours to ensure that pheromones were picked up. The pads were treated with alcohol and frozen, to were to be rubbed on the upper lip of the other participants. On day one, pads from the start of the menstrual cycle were applied to all 20 women, on day two they were all given a pad from the second day of the cycle, and so on. McClintock found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor'.
136
What is seasonal affective disorder (SAD)?
SAD is a depressive disorder which has a seasonal pattern of onset, and is described and diagnosed as a mental disorder in DSM-5. As with other forms of depression, the main symptoms of SAD are persistent low mood alongside a general lack of activity and interest in life. SAD is often referred to as the winter blues as the symptoms are triggered during the winter months when the number of daylight hours becomes shorter.
137
How is SAD an infradian rhythm?
SAD is a particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle. However, it can also be classes as a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonger periods of daily darkness during winter.
138
What is the cause of SAD?
Psychologists have hypothesised that the hormone melatonin is implicated in the cause of SAD. During the night, the pineal gland secretes melatonin until dawn when there is an increase in light. During winter, the lack of light in the morning means this secretion process continues for longer. This is thought to have a knock-on effect on the production of serotonin in the brain - a chemical that has been linked to the onset of depressive symptoms.
139
What is an example of an ultradian rhythm?
| Describe it.
One of the most intensively researcher ultradian rhythms is the stages of sleep - the sleep cycle. Psychologists have identified five distinct stages of sleep that altogether span approx. 90-minutes - a cycle that continues throughout the course the night. Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG.
140
Describe the stages of sleep - the sleep cycle.
Stages 1 and 2 - are light sleep where the person may be easily woken. At the beginning of sleep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even slowing as sleep becomes deeper (theta waves).
Stages 3 and 4 - involve delta waves which are slower still and have a greater amplitude than earlier wave patterns. This is deep sleep or slow wave sleep and it is difficult to rouse someone at this point.
Stage 5 (REM sleep) - the body is paralysed yet brain actitivity speeds up significantly in a manner that resembles the awake brain. REM stands for rapid eye movement to denote the fast, jerky activity of the eyes under the eyelids at this point. Research has suggested that REM activity during sleep is highly correlated with the experience of dreaming.
141
What are hypnogogic dreams?
Hypnogogic dreams occur during stages 1 and 2, shortly after drifting off to sleep, and are those in which we may experience the feeling of being out of control or that we are falling. These dreams are significant for the fact that we often wake with a jolt (a hypnic twitch) when we are sure we are about to hit the ground.
142
Evaluate infradian and ultradian rhythms as biological rhythms.
- Evolutionary basis of the menstrual cycle, menstrual synchrony, of the kind observed in the McClintock study, is thought by many to have an evolutionary value. It may have been advantageous for females to menstruate together and therefore fall pregnant around the same time. This would mean new-borns could be cared for collectively within a social group increasing the chances of the offspring's survival. The validity of this has been challenged by Schank 2004, he argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality male (and thereby lowering the fitness of any potential offspring). From this POV, the avoidance of synchrony would appear to be most adaptive evolutionary strategy and therefore naturally selected.
- Methodological limitations in synchronisation studies, criticisms have been made of early synchronisation studies and the methods employed. Some argue that there are many factors that may effect change in a woman's menstrual cycle, including stress, changes in diet, exercise, etc... these may act as confounding variables. This means that any supposed pattern of synchronisation (McClintock's) is no more than would have been expected to occur by chance. Also, research typically involves small samples of women and relies of participants self-reporting the onset of their own cycle. Other studies (Trevathan et al 1993) failed to find any evidence of menstrual synchrony in all-female samples.
- Evidence supports idea of distinct stages in sleep, a study by Dement and Kleitman 1957 monitored the sleep patterns of nine adult participants in a sleep lab. Brainwave activity was recorded on an EEG and the researchers controlled for the effects of caffeine and alcohol. REM activity during sleep was highly correlated with the experience of dreaming, brainwave activity varied according to how vivid dreams were, and participants woken during dreaming reported very accurate recall of their dreams. Replications of this investigation have noted similar findings, though the small size of the original sample has been criticised by some. Nevertheless, the study suggests that REM (dream) sleep is an important component of the ultradian sleep cycle.
- Animal studies, knowledge of the effects of pheromones on behaviour is derived from animal studies. The role of pheromones in animal sexual selection is well-documented, e.g. sea urchins releases pheromones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously. However, evidence for the effects in human behaviour remains speculative and inconclusive.
- Practical application (SAD), one of the most effective treatments for SAD is phototherapy. This is a lightbox that stimulates very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD. This relieves symptoms in up to 60% of sufferers (Eastman et al 1998). However, the same study recorded a placebo effect of 30% using a 'sham negative-ion generator' (participants were told it was another form of treatment). This casts doubt on the chemical influence of phototherapy.
143
Describe the basic rest-activity cycle.
Evidence from EEG recordings suggests the existence of the 90-minute cycle during sleep. However, Kleitman 1969 also suggests that a similar 90-minute rhythm cycle continues during waking hours. He called this the basic rest-activity cycle (BRAC) which is characterised by a period of alertness followed by a spell of physiological fatigue. This occurs across a 90-minute cycle which then recurs during the course of the day.
Anecdotal evidence supports the existence of BRAC such as the frequent observations that students find it difficult to concentrate for periods longer than 90 minutes at a time. Similarly, most people will require a break in order to divide up their working morning and also their afternoon.
A study of prodigious violinists by Ericsson et al 1993 found that the best performers tended to practice for three sessions during the course of the day, each session lasted no more than 90 minutes, and there was a break between each in order to recharge.
144
Define endogenous pacemakers.
Internal body clocks that regulate many of our biological rhythms.
E.g. the influence of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle.
145
Define exogenous zeitgebers.
External cues that may affect or entrain our biological rhythms.
E.g. the influence of light on the sleep/wake cycle.
146
Define sleep/wake cycle.
A daily cycle of biological activity based on a 24-hour period (circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day.
147
What is the suprachiasmatic nucleus (SCN)?
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain. It is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as the sleep/wake cycle. Nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area of the cerebral cortex. The SCN lies just above the optic chiasm, it receives information about light directly from this structure. This continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
148
Describe the animal studies into the SCN.
The influence of the SCN has been demonstrated in studies involving animals. Patricia DeCoursey et al 2000 destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days. The sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep).
