new one Flashcards
The two roles of the human nervous system
To collect, process and respond to information in the environment
to co-ordinate the working of different organs and cells in the body
the two subsystems of the nervous system
peripheral nervous system
central nervous system
The divisions of the peripheral nervous system
autonomic nervous system
somatic nervous system
The autonomic nervous system function
governs all vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses
Split into the sympathetic nervous system and the parasympathetic nervous system
The parts of the central nervous system
The brain: centre of all conscious awareness, the outer layer is called the cerebral cortex and is divided into two hemispheres
The spinal cord: an extension of the brain, responsible for reflex actions
The peripheral nervous system
sends information to the CNS from the outside world and transmits messages from the CNS to muscles and glands
The central nervous system
is the origin of all complex commands and decisions
The endocrine system
One of the body’s major information systems that instructs glands to release hormones directly into the bloodstream, these hormones are carried towards target organs in the body
Gland
An organ in the body that synthesises substances such as hormones
Hormones
chemical substances that circulate in the bloodstream and only affect target organs, they are produces in large quantities but disappear quickly
The pituitary gland
The main endocrine gland, often called the master gland because it controls the release of hormones from all other endocrine glands in the body
Fight or Flight response
- when a stressor is perceived 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 into the bloodstream - adrenaline triggers physiological changes in the body e.g. increased heart rate, necessary for the response
- once the threat has passed the parasympathetic nervous system returns the body to its resting state, it acts as a break and reduces the activities of the body that were increased by the actions of the sympathetic branch, sometimes referred to as the rest and digest response
sympathetic state
- increases heart rate
- increases breathing rate
- dilates pupils
- inhibits saliva production
- contracts rectum
Parasympathetic state
- decreases heart rate
- decreases breathing rate
- contracts pupils
- stimulates digestion
- stimulates saliva production
- relaxes rectum
The structure of a neuron
- Vary in size from less than a millimeter to up to a meter long
- the cell body (or soma), dendrites, axon, myelin sheath, nodes of Ranvier and terminal buttons
Cell body (soma) of a neuron
includes a nucleus, which contains the genetic material of the cell
Dendrites
branch-like structures that protude from the neuron cell body
Axon
carries the impulses away from the cell body
Myelin sheath
fatty layer that protects the axon and speeds up chemical transmission
Nodes of Ranvier
where the myelin sheath is segmented to maintain the speed of chemical transmission
Terminal buttons
Communicate between neurons
electric transmission - 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
types of neuron
motor neurons, sensory neurons and relay neurons
neural networks
Groups of neurons communicating with each other
The synapse
includes the space between the neuron (called the synaptic cleft as well as the presynaptic terminal and post synaptic receptor site
Synaptic transmission
how signals between neurons are transmitted chemically
what happens when the electrical impulse reaches the end of the neuron
the end of the neuron is called the presynaptic terminal, it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
neurotransmitters
chemicals that diffuse across the synapse to the next neuron in the chain, they are taken up by the postsynaptic receptor sites and are then converted back into an electrical impulse
- each has its own specific molecular structure that fits perfectly into a post-synaptic receptor site
- has a specialist function
inhibition
decreases the likelihood that the neuron will fire
excitation
increases the neurons positive charge and making it more likely to fire
Localisation versus holistic theory
- Paul Broca and Karl Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions
- scientists believed that all parts of the brain were involved in the processing of thoughts and action
Localisation of function in the brain
The idea that different parts of the brain perform different tasks and are involved with different parts of the body, if a certain area of the brain becomes damaged the function associated with that area will also be affected
hemispheres of the brain
the brain is divided into two symmetrical halves called the left and right hemispheres
activity on the left-hand side of the body is controlled by the right hemisphere and vice versa
The cerebral cortex
the outer layer of both hemispheres, about 3mm thick and is what separates us from other animals as it it more developed
- appears grey due to the location of cell bodies
the sub-divisions of the cortex of the brain
named after the bones beneath which they lie; the frontal lobe, the pariental lobe, the occipital lobe and the temporal lobe
the motor area
located in the back of the frontal lobe, controls voluntary movement in the opposite side of the body and damage results in a loss of control over fine movements
the somatosensory area
located in the front of the pariental lobe, a valley separates the frontal lobe and pariental lobe called the central sulcus
it is where sensory information is represented (from the skin)
visual area
located in the occipital lobe, works in opposite to the eye
auditory area
located in the temporal lobe, analyses speech based information, damage may produce partial hearing loss
Broca’s area
responsible for speech production, damage causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency
Wernicke’s area
responsible for language comprehension, damage leads to Wernicke’s aphasia, impaired language comprehension
Brain scan evidence of localisation - Peterson et al
used brain scans to demonstrate how Wernicke’s area was active during a listening task and that Broca’s area was active during a reading task, shows different areas have different functions
Brain scan evidence of localisation - Tulving et al
long-term study revealed that semantic and episodic memories reside in different parts of the prefrontal cortex
Now a number of highly sophisticated and objective methods for measuring activity in the brain provide sound scientific evidence
Neurosurgical evidence of localisation - Dougherty et al
The practice of surgically removing and destroying areas of the brain to control aspects of behaviour, discovered in 1950s
44 OCD patients undergone angulotomy, after 32 weeks 1/3 met criteria for successful response - shows that symptoms and behaviours are localised
Lobotomy
A brutal and imprecise method of neurosurgery, only used in extreme cases of OCD and depression
Lashley’s research to disprove localisation
suggests that higher cognitive functions, such as the process of learning are not localised but distributed in a more holistic way in the brain
Karl removed areas of the cortex in rats that were learning a maze, no area was proven to be more important than any other area
The process of learning appeared to require every part of the cortex; learning is too complex to be localised and requires involvement of the whole brain
Plasticity and localisation
when the brain has become damaged the appears able to reorganise itself in an attempt to recover the lost function, known as the law of equipotentiality, stroke victims are able to recover those abilities that were seemingly lost as a result of the illness
Brain plasticity
The brain has the ability change throughout life;
during infancy, the brain experiences a rapid growth in the number of synaptic connections it has, peaking at approximately 15,000 at age 2-3 years
More and more research suggests that at any time in life existing neural connections can change or form
synaptic pruning
as we age, rarely used connections are deleted and frequently used connections are strengthened
what was originally thought about brain plasticity
changes such as synaptic pruning were restricted to the developing brain within childhood and the adult brain would remain fixed and static in terms of function and structure
Research into plasticity - Eleanor Maguire et al
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
- London cabbies must take a complex test called ‘the knowledge’ which assesses their recall of the city streets, the longer they had been in the job, the more pronounced was the structural differences (positive correlation)
Research into plasticity - Dragonski et al
Imaged the brains of medical students before and after final exams, learning-induced changes were seen to have occurred in the posterior hippocampus and the pariental cortex presumably as a result of the exam
Functional recovery after trauma
Unaffected areas of the brain are able to adapt and compensate for those areas that are damaged
it is an example of neural plasticity
healthy brain areas may take over
happens quickly after trauma - spontaneous recovery
what happens in the brain during recovery?
secondary neural pathways that would not typically be used to carry out certain functions are activated or unmasked to enable functioning to continue
- axonal sprouting
- reformation of blood vessels
- recruitment of homologous areas
axonal sprouting
the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
Practical application of plasticity and functional recovery
Understanding the processes involved in plasticity has contributed to the field of neurorehabilitation
Physical therapy may be required to maintain improvements in functioning
Although the brain may have the capacity to fix itself to a point, this process requires further intervention if it is to be completed successfully
Negative plasticity
The brains 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
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, usually unpleasant- thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss
Age and plasticity`
Functional plasticity tends to reduce with age, the brain has greater prosperity for reorganisation in childhood as it is constantly adapting to new experiences and learning
Age and plasticity - Ladina Bezzola et al
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 - more effective neural representations after training
Neural plasticity does continue throughout lifespan
Animal studies - plasticity and functional recovery
David Huber and Turton Wiesel involves sewing one eye of a kitten shut and analysing the brains cortical responses, it was found that the area of the visual cortex associated with he shut eye was not idle (as had been predicted) but continued to process information from the open eye
Hemispheric lateralisation
The ability to produce and understand language is controlled by the left hemisphere
language is subject to this
It has been investigated through a series of ingenious experiments conducted by Roger Sperry and his colleagues
Roger Sperry
Awarded the novel prize in 1981 due to his split-brain research
Split-brain studies
Involved a unique group of individuals, all whom had undergone the same surgical procedures, the separation of the two hemispheres
The communication line between the two hemispheres was removed
This allowed Sperry to seethe extent to which the two hemispheres were specialised for certain functions and whether the hemispheres performed tasks independently of one another
Commissurotomy
The corpus callosum and other tissues which connect the two hemispheres are cut down the middle in order to separate the two hemispheres and control frequent epileptic seizures
Procedure of split brain research into hemispheric lateralisation
- An image or word could be projected to the patients visual field and then processed by the opposite side of the brain
- in the normal brain, the corpus callosum would immediately share the information between both hemispheres
- 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
Key findings of split brain research - describing what you see
`When a picture of an object was shown to a patients right visual field they could easily describe what was seen but not for the left visual field, the patient typically reported that the was nothing there
Lack of language centres in the right hemisphere
Key findings of split brain research - recognition by touch
Patients are able to select a matching object from a grab bag of different objects using their left hand, was also able to select an object that was most closely associated with an object presented to the left visual field but could not verbally identify just understood what the object was
Key findings of split brain research - composite words
For example, ‘key’ on the left and ‘ring’ on the right, the patient would write with their left hand the word ‘key’ and say the word ‘ring’
Key findings of split brain research - matching faces
The right hemisphere appeared dominant, the picture consistently selected when shown to the left visual field, the left hemisphere dominated in terms of verbal description but right in selecting matching pictures
split-brain research - demonstrated lateralised brain functions
Sperry’s work has produced an impressive and sizable body of research findings, the left hemisphere is more geared towards analytical and verbal tasks whilst the right is more adept at performing spatial tasks and music, contributes to emotional and holistic content to language
Research suggests that the left hemisphere is the analyser whilst the right is the synthesiser
- a key contribution to our understanding of brain processes
split-brain research - strengths of the methodology
- experiments made use of highly specialised and standardised procedures
- typically, participants would be asked to stare at a given point, the ‘fixation point’
- the image projected would be flashed up for 1/10 of a second, meaning the split-brain patient would not have time to move their eyes across the image and so spread the information across both sides of the visual field
- this allowed Sperry to vary aspects of the basic procedure and ensured that only one hemisphere was receiving information at a time
= a very useful and well-controlled procedure
split-brain research - 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
other researchers argued that the two hemispheres form a highly integrated system and are both involved in everyday tasks
split-brain research - theoretical basis, Roland Pucetti
have suggested that the two hemispheres are so functionally different that they represent a form of duality in the brain - we are all two minds but emphasised in split-brain
split-brain research - issues with generalisation
many researchers have urged caution in their widespread acceptance, as split-brain patients constitute such an unusual sample of people - there were only 11 who 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 have influenced the findings
the control group, made up of 11 people with no history of epilepsy may have been inappropriate
functional magnetic resonance imaging (fMRI)
works by detecting the changes in blood oxygenation and flow that occur as a result of neural 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 are (known as the haemodynamic response)
produces 3D 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
Electroencephalogram (EEG)
measures electrical activity within the brain via electrodes that are fixed to an individuals 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
often used by clinicians as a diagnostic tool as an unusual arrhythmic pattern of activity may indicate neurological abnormalities such as sleep disorders, epilepsy and tumors
Event-related potentials (ERPs)
using a statistical averaging technique, all extraneous brain activity from the original EEG recording is filtered out leaving only those responses that relate to the presentation of a specific task
what remains are event-related potentials: types of brainwave that are triggered by particular events
research as revealed many different forms of ERP and how, e.g., these are linked to cognitive processes such as attention and perception
Post-mortem examinations
a technique involving the analysis of a person’s brain following their death
individuals whose brains are subject to this are likely to be those who have deficits in mental processes or behaviour during their lifetime
areas of damage within the brain are examined after death as a means of establishing a likely cause, it may involve comparison with a neurotypical brain
strengths of fMRI
- unlike other scanning techniques such as PET, it does not rely on the use of radiation. If used correctly it is virtually risk-free, non-invasive and straightforward to use
- produces images that have very high spatial resolution, depicting detail by the mm and providing a clear picture of how brain activity is localised
weaknesses of fMRI
- expensive compared to other neuroimaging techniques and can only capture a clear image if the person stays perfectly still
- it has poor temporal resolution - around 5 seconds time-lag behind the image on screen and the initial firing of neuronal activity
- can only measure blood flow - difficult to tell what kind of brain activity is being represented on screen
strengths of EEG
- proved essential in the diagnosis of conditions such as epilepsy, a disorder characterised by random bursts of energy that can only be detected on screen
- contributed to understanding of stages involved in sleep (ultradian rhythms)
- extremely high temporal resolution, can accurately detect brain activity at a resolution of a single millisecond
weaknesses of EEG
- generalised nature of the information received
- the EEG signal is not useful for pinpointing the exact source of neural activity, and does not allow researchers to distinguish between activities originating in different but adjacent locations
strengths of ERPs
- bring much more specificity to the measurement of neural processes
- excellent temporal resolution - 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
weaknesses of ERPs
- lack of standardisation in methodology between different research studies - makes it difficult to confirm findings
- in order to establish pure date in ERP studies, background noise and extraneous material must be completely eliminated, and this may not always be easy to achieve
strengths of post-mortem examinations
- 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 PME in establishing links between language, brain and behaviour, decades before neuroimaging even became a possibility
weaknesses of post-mortem examinations
- causation, observable damage to the brain may not be linked to the deficits under review but some other unrelated trauma or decay
- ethical issues, consent from the patient before death, patients may not be able to provide informed consent, e.g. HM who lost his ability to form memories and was not able to provide such consent, post-mortem studies have been conducted on his brain still
Biological rhythms
That all living organisms are subject to which exert an important influence on the way in which body systems behave
governed by two things:
- the body’s internal biological clocks which are called endogenous pacemakers
- external changes in the environment called exogenous zeitgebers
Circadian rhythms
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
the sleep/wake cycle
the fact we feel drowsy at night time and alert during the day demonstrates the effect of daylight, an important exogenous zeitgeber
free running
if our biological clock was left to its own devices without the influences of external stimuli such as light
Siffre’s cave study
Michael, deprived of exposure to natural light and sound, but with access to adequate food and drink, spent 2 months in the caves of the Southern Alps
- 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
Jurgen Ashcoff and Rutger Wever study - circadian rhythms
convinced a group of participants to spend 4 weeks in a WWII bunker deprived of natural light, all but one displayed a circadian rhythm between 24 and 24 hours, the natural sleep/wake cycle may be slightly longer than 24 hours but it is entrained by exogenous zeitgebers such as the number of daylight hours and typical meal-times
- should not overestimate the influence of environmental cues on our internal biological clock
Simon Folkard et al study - circadian rhythms
studied 12 people who agreed to live in a dark cave for 3 weeks, sleep at 11:45pm and rising at 7:45am looking at a clock, the researchers gradually sped up the clock to be a 22 hour day instead - only one participant was able to adjust to the new regime
- shows we have a strong free running circadian rhythm
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)
- night workers experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes and accidents are more likely
- significant relationship between shift work and poor health, shift workers 3x more likely t develop heart disease which may occur due to the stress of adjusting to different sleep/wake patterns and poor quality sleep during the day
= research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity
circadian rhythms - practical application to drug treatments
circadian rhythms also coordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels - an effect on pharmacokinetics, the action of drugs in the body and how well they are absorbed and distributed
- there are certain peak times during the day/night that drugs are likely to be at their most effective
- also with the development of guidelines to do with the timing of drug dosing for a whole range of medications including anti-cancer, cardiovascular, respiratory etc.
circadian rhythms - use of case studies and small samples
- studies of the sleep/wake cycle tend to involve small groups of participants
- people involved may not be representative of the wider population and limits the extent to which meaningful generalisations can be made
- Siffre observed at the age of 60 his internal clock ticked much more slowly than when he was a young man
= even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn
circadian rhythms - individual differences
individual cycles may vary, therefore generalisations can’t be made
Duffy et al - some people display a natura; preference for going to bed early (known as ‘larks’) whereas some people prefer to do the opposite (‘owls’)
there are also age differences in sleep/wake patterns
Infradian rhythms
Takes longer than a day to complete
- the menstrual cycle is an example, it is governed by monthly changes in hormone levels which regulate ovulation - refers to the time between the first day of a woman’s period to the day before her next period
- the typical cycle takes approximately 28 days to complete
- rising levels of 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
- if pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body (the menstrual flow)
Research study - the menstrual cycle, an infradian rhythm
although it is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women
- Kathleen Stem and Martha McClinton, menstrual cycles may synchronise as a result of the influence of female pheromones - 29 women with a history of irregular periods, samples of pheromones were gathered from the armpit via cotton pad placed in their armpit, the pads were then treated with alcohol and frozen, to be rubbed on the upper lips of the other women - a different pad for each day of their cycle
- 68% of the women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’
Seasonal affective disorder (SAD)
- a depressive disorder which has a seasonal pattern of onset, classified as a mental disorder using DSM-5
- referred to as the winter blues as symptoms are triggered during winter months, daylight hours are shorter
- a circannual rhythm - subject to a yearly cycle
- can be a circadian rhythm as it may be caused by a disruption of sleep/wake cycle
- the hormone melatonin is implicated in the cause, during the night the pineal gland secretes melatonin until dawn when there’s an increase in light - during the winter months a lack of light means the secretion process continues, its thought to have a knock-on effect on the production of seratonin in the brain which cause the depressive symptoms
Ultradian rhythms
occurs during the day
- psychologists identified 5 distinct stages of sleep that all together span approximately 90 minutes - a cycle that continues throughout the course of the night, each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG
stages 1 and 2 of sleep (ultradian rhythms)
the ‘sleep escalator’, are light sleep where the person can be easily woken, brainwave patterns start to become slower and more rhythmic (alpha waves) becoming even slower as sleep becomes deeper (theta waves)
stages 3 and 4 of sleep (ultradian rhythms)
involve delta waves which are slower still and have greater amplitude
this is a deep sleep or slow wave sleep and it is difficult to rouse someone
Stage 5, REM sleep ( ultradian rhythm)
the body is paralysed yet brain activity speeds up significantly resembling the awake brain
- REM = rapid eye movement, highly correlated with the experience of dreaming
evolutionary basis of the menstrual cycle
- menstrual synchrony, is thought by many to have an evolutionary value
- our ancestors thought it may have been advantageous for females to menstruate together and therefore fall pregnant at the same time
- new-borns could be cared for collectively within a social group, increasing the chances of the offspring’s survival
- the validity of the evolutionary perspective has been questioned by some, Jeffrey Schank argued that if there were too many femals cycling together within a social group, this would produce competition for the highest quality males (and thereby lowering the fitness of any potential offspring)
the avoidance of synchrony would appear to be most adaptive evolutionary strategy and therefore naturally selected
methodolgical limitations in synchronisation studies (infradian and ultradian rhythms)
criticisms have been made of early synchronisation studies and the methods employed
- argue that there are many factors that may affect change in a women’s menstrual cycle, including stress, changes in diet, exercise, etc. that may at as confounding variables, any supposed pattern of synchronisation as seen in the studies by McClintock and others is no more than would have been expected to occur by chance
- research typically involves small samples of women and relies on participants self-reporting the onset of their own cycle
- other cycles failed to find any evidence of menstrual synchrony in all-female samples
evidence supports the idea of distinct stages in sleep
- a landmark study by William Dement and Nathaniel Ideitman monitored the sleep patterns of 9 adults in a sleep lab
- Brain wave 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, brain activity varied according to how vivid dreams were
- replications have noted similar findings, though the small size of the original sample has been criticised by some
REM sleep is an important component of the ultradian sleep cycle
Animal studies (infradian rhythms)
- much of the 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 release pheromones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously
- evidence for the effects in human behaviour remains speculative and inconclusive
The superchiasmatic nucleus (SCN)
A tiny bundle of nerve cells located in the hypothalamus of each hemisphere in the brain
One of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms
The SCN receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to the changing patterns of daylight whilst we are sleep
Optic chiasm
Point at which optic nerve fibers cross in the brain on their way to the visual area of the eye (cerebral cortex)
Patricia DeCoursey et al - the SCN
(Chipmunks?)
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 had disappeared and by the end of the study a significant proportion of them had been killed by predators
Martin Ralph et al - the SCN
( Hamsters?)
Bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle
When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours
Animal studies on SCN
They emphasise the role of the SCN in establishing and maintaining the circadian sleep/wake cycle
Melatonin
A chemical that induces sleep and is inhibited during periods of wakefulnes
The pineal gland and the SCN
The SCN passed the information on day length and light that it receives to the pineal gland, during the night the pineal gland increases production of melatonin
Entrainment
The process whereby external factors in the environment can reset our biological clocks
Zeitgeber
Time giver
What happens to our sleep/wake cycle in the absence of external cues
The free-running biological clock that controls the sleep/wake cycle continues to tick in a distinct cyclical pattern, thus sleeping and wakefulness would seem to be determined by an interaction of internal and external factors
Light
A key zeitgeber in humans
It can reset the body’s main endogenous pacemaker, the SCN and thus plays a role in the maintenance of the the sleep/wake cycle
Also has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation
Scott Campbell and Patricia Murphy
Demonstrated that light may be detected by skin receptor sites even when the same information is not received by the eyes
15 participants were woken at various times and a light pad was shone on the back of their knees
The researchers managed to produce a deviation in the participants sleep/wake cycle of up to 3 hours
This suggests that light is an exogenous zeitgeber that need not necessarily rely on the eyes to influence the brain
Social cues
The schedules imposed by parents are likely to be a key influence on babies sleep/wake cycles including adult determined mealtimes and bedtimes
Infants are seldom on the sleep/wake cycle compared to the rest of the family
Their initial sleep/wake cycle is pretty much random and at about 6 weeks of age the circadian rhythms begin
By 16 weeks most babies are entrained
Jet lag…
Research suggests that adapting to local times for eating and sleeping (rather than responding to ones own feelings of hunger and fatigue) is an effective way of entraining circadian rhythms and beating this
Peripheral oscillators
There are numerous circadian rhythms in many organs and cells of the body, they are found in adrenal gland, oesophagus, lungs, liver, thymus, spleen, pancreas and skin
They can act independently but are highly influenced by the actions of the SCN
Francesa Damiola et al
Demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours whilst leaving the rhythm of the SCN unaffected
Beyond the master clock - evaluation
Suggests that there may be other complex influences on the sleep wake cycle aside from the master clock (the SCN)
Ethics in animal studies - the SCN
Issue of generalising from animal studies to humans
In DeCoursey et al study the animals were exposed to considerable harm, and subsequent risk when they were returned to their natural habitat
Whether what we learn from investigations justifies the averse procedures is a matter of debate
Influence of exogenous zeitgeber may be overstated
Laughton Miles at al - blind man from birth with a circadian rhythm of 24.9 hours, despite exposure to social cues his sleep/wake cycle could not be adjusted - took sedatives at night and stimulants in the morning to keep pace with 24-hour world
Studies of individuals in attic regions show normal sleep patterns despite the prolonged exposure to light
Methodological issues in studies - the SCN
Campbell and Murphy study yet to be replicated
Psychologists have been critical of the manner in which the study was conducted and have suggested that there may have been some limited light exposure to the participants eyes - a major confounding variable
Also isolating an exogenous zeitgeber (light) in this way does not give us an insight into the many other zeitgeber that influence the sleep/wake cycle and the extent to which these may interact
