internal: Flashcards
Neurons:
the cells making up the nervous system, which conduct electrical impulses
Sensory neuron:
neuron carrying sensory information into the CNS from the body’s sensory receptors
Central nervous system:
major part of the nervous system, made up of the brain and the spinal cord
Relay neuron:
neuron within the CNS that interconnects different parts of the CNS
Motor neuron:
neuron carrying motor commands out from the CNS to the skeletal muscles of the body, allowing for movement
Synapse:
a tiny gap between two neurons, across which nerve impulses are passed
Neurotransmitters:
packets of chemicals stored within the axon; they enable nerve impulses to pass across the synapse to the postsynaptic neuron
What is a neuron?
-neurons are special cells in the nervous system that send electrical called nerve impulses
-they have a cell body, dendrites to receive signals, and an axon to send them
-these signals are called action potentials, travel from the dendrites, through the cell body, and along the axon
-they have the same basic properties in all neurons but can vary in sped and pattern, which carry information
-neurons can send signals up to 400 times per second and the brain’s complexity comes from its 100 billion neurons working together
Dendrite: function
receives the nerve impulses or signal from adjacent neurons
Cell body: function
contains the nucleus which contains the genetic material
Axon: function
carries impulse away from the cell body
Myelin sheath: function
cover the axon, and speeds up electrical transmission, also protects the axon
Nodes of Ranvier: function
gaps in the myelin sheath -> helps the impulse more as it jumps across gaps on the axon
Axon terminals: function
communicate with the next neuron across a synapse
Saltatory Conduction:
-in advanced animals such as us and mammals, many of the neuron making up the nervous system are covered in a fatty cover called the myelin sheath, which is not found in the nervous system in more primitive animals
-there are gaps in the sheath, known as the nodes of Ranvier, where the neuronal cell membrane is exposed
-action potentials have the property of being able to jump from gap to gap; this is known as saltatory conduction, and is many times faster than the standard continuous conduction along the neuronal axon
-faster transmission means faster information processing, and has led to the development of complex human cognitive abilities
Sensory, Relay, and Motor neurons:
-sensory neurons carry information from the sense organs into the CNS
-we have sensory receptors all over our skin, for touch, pain, pressure, etc.
-information from these receptors is carried by a sensory neuron into the spinal cord and then on to the brain
-from there the axon runs into the spinal cord where it will synapse onto a relay or interneuron
-the particular function of the relay neuron is to interconnect sensory and motor pathways, and also different parts of the CNS
-relay neurons lie entirely within the CNS, and much of the brain is made up of relay neurons
-motor neurons carry commands from the motor cortex of the brain out to the muscles of the skeleton
-the final motor neuron in the pathway has its cell body within the spinal cord, and a long axon running to the muscles of the skeleton
Synaptic Transmission:
-neurons are not physically connected to one another, between the axon terminal and the next neuron is a tiny gap, the synapse, which is visible only under an electron microscope
-although tiny, this gap presents an obstacle to the nerve impulse as it cannot automatically jump across
-transmission of nerve impulses across the synapse is chemical
-stored within the axon or presynaptic terminal are packets of chemicals known as neurotransmitters
-as nerve impulses travelling down the axon reach the axon terminal, they stimulate the release of neurotransmitter molecules into the synapse
-the synaptic gap is so small that the molecules can diffuse over to the postsynaptic membrane of the following neuron, located on this membrane are synaptic receptors
Synaptic receptors:
-synaptic receptors are specialised molecules that bind to neurotransmitter
-when neurotransmitters bind briefly to these receptors on the postsynaptic membrane, they change its biochemical state, increasing the likelihood of triggering a nerve impulse
-nerve impulses follow an “all or nothing” rule: they either happen or not
-to trigger an impulse, enough neurotransmitters must be released from the presynaptic terminal
-once they bind to the receptors and the threshold is crossed, the impulse travels along the postsynaptic neuron and continues through the next synapses
The purpose of the synapse:
-the synapse enables information processing in the nervous system
-for a signal to cross the synapse, enough neurotransmitters must be released in a short time
-if too few impulses arrive, the postsynaptic membrane won’t fire, and the information is lost
-each neuron can connect up to 1,000 others, creating a complex network essential for processing
-there are limited types of neurotransmitters (e.g. dopamine, serotonin) and receptors
-synapses are often defined by the neurotransmitter they use
-understanding their chemical nature helps explain how drugs affect behaviour, as some drugs alter neurotransmitter release or receptors interaction
Excitation:
synapses in the nervous system can be excitatory or inhibitory; excitatory synapses activate the postsynaptic neuron increasing neural activation in the central nervous system
Inhibition:
synapses in the nervous system can be excitatory or inhibitory; inhibitory synapses inhibit activity in the postsynaptic neuron, decreasing neural activation in the CNS; inhibitory circuits are vital to the balance between excitation and inhibition in the nervous system
Excitation and Inhibition:
-synapses can be excitatory or inhibitory based on the neurotransmitter’s effect on the postsynaptic receptor
-excitatory neurotransmitters, like dopamine and serotonin, make nerve impulses more likely, while inhibitory ones, like GABA, decrease the likelihood of an impulse
-GABA stabilises the postsynaptic membranes, inhibiting action potentials
-increased GABA activity reduces activity in other systems, like serotonin, leading to calming effect, anti-anxiety drugs such as benzodiazepines stimulate GABA release
-normal brain function depends on a balance between excitatory and inhibitory signals, imbalances such as excessive excitation or inhibition, may lead to conditions like epilepsy
Peripheral nervous system:
consists of the 31 pairs of spinal nerves, which carry sensory and motor pathways of the somatic nervous system, and motor pathways of the autonomic nervous system; connects the CNS with the body and with the outside world
Somatic nervous system:
part of the PNS, the SNS is made up of sensory pathways from the sensory receptors on the body surface, and motor pathways controlling skeletal muscle; maintains communication between the CNS and the outside world
Autonomic nervous system:
part of the PNS, the ANS is made up of motor pathways controlling the activity of internal body systems such as the heart and circulatory system, the intestines, and various glands; it has two branches, the sympathetic and the parasympathetic
Divisions of the nervous system:
-the nervous systems consists of billions of neurons and is highly organised
-the brain is the key processor of information but relies on sensory input from receptors like eyes, ears, and skin to connect with the external world
-sensory pathways carry this input to the brain via the spinal cord, except for vision and hearing, which connect directly to the brain
-the brain also control movement and internal systems like the heart and digestive system through motor pathways
-these pathways are made up of motor neurons, while sensory neurons handle incoming signals, relay neurons, or interneurons connect different parts of the CNS and form the majority of neurons in the brain
-the CNS includes the brain and spinal cord, while the PNS consist of spinal nerves that link the CNS to the rest of the body
-together, they manage sensory input and motor responses
Hindbrain and Midbrain:
-the hindbrain is made up of the medulla, pons and cerbellum a.k.a the brainstem
-the brainstem is essentially a continuation of the spinal cord within the brain, with sensory and motor pathways carrying information to an from higher brain centres
-also buried in within the brainstem is the ascending reticular formation, a network of neurons vital to sleep and arousal functions of the brain
-the brainstem also contains major autonomic centres; autonomic pathways travel down from these centres through the spinal cord and are distributed throughout the body by the spinal nerves
-the cerbellum is a large structure located on the back surface of the brain stem
-its major functions relate to the control of movement, and damage results in a loss of motor coordination
Forebrain: diencephalon
-this is the largest division of the brain, and is subdivided into two major components, the diencephalon and the telencephalon (also known as the cerebral hemispheres or cerebrum)
Diencephalon:
-this subdivision of the forebrain contains two main structures, the thalamus and hypothalamus
-the thalamus is an important sensory structure, relaying sensory information from pathways ascending up through the spinal cord and the brainstem on to the cortex
-the hypothalamus lies at the base of the brain, through its control over the putuitary gland, which lies just below it, and the autonomic centres in the brainstem, the hypothalamus is involved in many of the body’s physiological functions
Forebrain: telencephalon or cerebral hemispheres
-the cerebral hemispheres contain the systems and structures of most interest to psychologists
-high-level cognitive and emotional processes are controlled from these areas, although it must be remembered that all parts of the brain are heavily interconnected, especially the subsystems of the hemispheres
-three major systems make up the cerebral hemispheres: the limbic system, the basal ganglia, and the cerebral cortex
limbic system, basal ganglia + cerebral cortex
-limbic system: this consists of a set of interconnected structures, including the hippocampus, amygdala, septum, and cingulate + they are involved in functions such as learning, memory, and especially emotions
-basal ganglia: the basal ganglia have important functions in relation to movement and motor control, they include the caudate nucleus, the putamen, and the globus pallidus + damage to the basal ganglia results in movement disorders such as Parkinson’s disease
-cerebral cortex: this is the most recently evolved part of the brain, and the amount of cortex distinguishes humans from other species + it contains within it the highest cognitive functions, such as planning and problem-solving, languagem consciousness, and personality, as welll as perception and control of movement
Peripheral nervous system (PNS):
-the PNS is made up for the 31 spinal nerves
-these contain millions of sensory (afferent) and motor (efferent) pathways allowing the brain to be aware of what is going on in the body and outside worlds, and to control our various response systems
-although highly complicated, the millions of pthaways making up the spinal nerves can conveniently be divided into the somatic and autonomic nervous systems
PNS: the somatic nervous system- first component
-the SNS is made up of two components:
-the first is made up of sensory or afferent pathways from the sensory receptors of the body - touch, pain, pressure, temperature
-these systems have specialised sensory receptors in the skin that respond to various stimuli by trigerring action potentials (nerve impulses) in sensory neurons
-these neurons carry the sesnory information into the spinal cord via the spinal nerves
-in the spinal cord they make synaptic connections onto neurons that carry the information up the spinal cord to the brain, where it is processed
PNS: the somatic nervous system-second component
-the second component is made up of motor or efferent pathways
-the axons of motor neurons travel in spinal nerves out to the skeletal muscles of the body, allowing the brain to control bodily movement
-commands to move our muscles are formulated in the cerebral cortex of the forebrain, and then travel down through the brain and spinal cord to the spinal nerves
-we can see the two components of the SNS as integrating the brain with the outside world, sensory pathways carry information from the environemtal stimuli, but we also have an internal environment to regulate, and for this we have another division of the spinal nerves
PNS: the autonomic nervous system
-the ANS plays a central role in states of bodily arousal
-ANS centres are located in the brainstem
-from here, ANS pathways run down through the spinal cord and are distributed throughout the body by the spinal nerves
-the ANS is concerned with the regulation of our internal environment, controlling vital functions such as body temperature, heart rate, and blood pressure
-the ANS is central to homeostasis, the maintenance of a constant internal environment, e.g. the way we keep a constant body temperature
-without homeostasis, snakes and other reptiles, for example, become inactive in the cold and spend as much time as they can in the sunshine to increase their body temperature, homeostasis allows an animal to become independent of the environment
-the ANS is vital to homeostasis as it constantly monitors and controls the internal environemnt
PNS: the ANS -two branches
-to carry out its functions, the ANS has two separate branches, the sympathetic and the parasympathetic
-nerve fibres from both branches connect with internal structures such as various glands, the heart and circulatory system, and the digestive system
-sympathetic arousal or dominance leads to a pattern of bodily arousal, with increases in heart rate and blood pressure and a decrease in activity in the digestive system
-parasympathetic dominance leads to the opposite pattern, one of the physiology calm, with lower heart rate and blood pressure and increased digestive activity
PNS: ANS- sympathetic arousal
-usually the two branches are in balance, but under certain circumstances the balance shifts and one branch becomes dominant
-these shift are determined by the body’s physiological requirements
-physical exercise need energy, and this is provided by sympathetic arousal
-similarly, if a dangerous or threatnening situation is perceived, higher brain centres signal the hypothalamus, a key structure buried deep in the brain to activate the sympathetic branch of the ANS
-this provides energy in case we need to respond physically to the situation, therefore, sympathetic arousal is an important part of the body’s response to stress- the fight or flight response
Adrenaline:
hormone released from the adrenal medulla, acts on heart and circulatory system to increase heart rate and blood pressure; important part of fight or flight response
Hormone:
chemical released from endocrine glands into the bloodstream that acts on target structures to alter their functions or to release other hormones
Gland:
body organ that releases hormones into the bloodstream
The endocrine system:
network of glands throughout the body releasing hormones to affect and organise the body’s physiological systems; the pirtuitary gland is the ‘master’ gland in the endocrine system
The function of the endocrine system:
-hormones are chemical message or substances, usually released from glands, which can control or regulate the activity of particular cells or organs in the body
-the network of glands is called the endocrine system
-glands making up the endocrine system secrete hormones directly into the bloodstream or circulatory system
-the arousal produced by adrenaline is one of the most obvious normal effects, but in fact the range of hormones and their effects is enormous, and they plan an important part in many areas of behaviour
Thyroxine: endocrine gland + effects
-endocrine gland: thyroid
-effects: regulates the body’s metabolic rate and protein synthesis
Adrenaline and nonadrenaline: endocrine gland + effects
-endocrine gland: adrenal medulla
-effects: fight or flight response, increased heart rate and blood flow to brain and muscles, release of stored glucose and fats for use in fight or flight response
Glucocorticoids: examples, endocrine gland + effects
-examples: cortisone, cortisol, and corticotesterone
-endocrine gland: adrenal cortex
-effects: further release of stored glucose and fats for energy expenditure, suppression of the immune system and the inflammatory response
Mineralocorticoids: endocrine gland + effects
-endocrine gland: adrenal cortex
-effects: these regulate the water balance of the body through water and sodium reabsorption in the kidneys
Androgens: example, endocrine gland + effects
-main example: testosterone
-endocrine gland: testes
-effects: development of male secondary sexual characteristics at puberty + promotes muscle mass and muscle growth
Oestrogens: main example, endocrine gland + effects
-main example: oestradiol
-endocrine gland: ovaries
-effects: regulation of female reproductive system, menstrual cycle and pregnancy
Melatonin: endocrine gland + effects
-endocrine gland: pineal
-effects: regulation of arousal, biological rhythms and the sleep-wake cycle
Pituitary:
-the ‘master gland’ is the pituitary, it is known as this because many of the hormones released by the pituitary gland control the secretions of other endocrine glands, rather than having direct effects on cells and tissues in the body
-the pirtuitary is located in the cranial cavity, just below the hypothalamus, to which it is directly connected
-the pirtuitary releases oxytocin and vasopressin, release of pirtuitary hormones into the bloodstream is directly controlled by the hypothalamus
-note that the hypothalamus controls the release of hormones from the pirtuitary gland, and can therefore be seen to control and regulate the endocrine system in general
Hormones released by the pirtuitary gland and their effects:
-the endocrine system therefore has a vital role in the internal physiological regulation of the body
-it works closed with the ANS in this regard
-although the contribution of the endocrine system is essentially to regulate the internal physiological processes of the body, some aspects do become important to psychologists when we look at situations such as stress and threats
(Anterior pirtuitary) ACTH: target organs and/or effects
adrenocortical trophic hormone
-adrenal cortex, stimulating release of glucocorticoids such as cortisone and corticotesterone + key component in the stress response
(Anterior pirtuitary) TSH: target organs and/or effects
thyroid stimulating hormone
-thyroid gland, stimulating release of thyroxine
(Anterior pirtuitary) Prolactin: target organs and/or effects
-mammary glands, stimulating milk production and release
(Anterior pituitary) FSH: target organs and/or effects
follicle stimulating hormone
-ovaries and testes, stimulating release of ovarian follicles and promoting spermatogenesis
(Posterior pirtuitary) ADH: target organs and/or effects
vasopressin or antiduretic hormone
-involved in regulating the water balance of the body, stimulates water reabsorption by kidney and increases blood volume
(Posterior pirtuitary) Oxytocin: target organs and/or effects
-important in promoting uterine contractions in childbirth and lactation after birth
Fight or flight response:
The body’s physiological reactions to threat or danger, involved activation of the hypothalamic-pirtuitary-adrenal cortex pathways and the sympathetic-adrenal-medullary system; designed to provide energy and arousal for rapid responses to threat and danger
Fight or flight: information
-HPA and SAM activation results in high blood levels of glucose and fats such as, triglycerides, along with an increased heart rate and blood pressure
-in the case of animals, these energy reserves are burnt up in muscle activity and, once it has escaped, blood levels return to normal and blood pressure and heart rate fall
-for modern humans, we experience major life stressors, for example, exams, relationships, redundancy, and bereavement, these stressors are equally as effective in activating the HPA and SAM system
-the response to such stressors does not usually require a huge energy expenditure, even though our bloodstream is flooded with glucose and fats
-it is the negative effects of this high level of bodily arousal that have been associated with stress-related illnesses
-the body’s fight or flight response begins with appraisal of the situation, followed by the activation of the two key pathways
Appraisal:
-appraisal or evaluation of the situation depends upon the sensory processing systems, such as vision and hearing, and stored memories of previous encounters with the situation
-key structures in the brain include higher cortical centres and parts of the limbic system, especially those involved with emotional memory such as amygdala and hippocampus
-if the situation is appraised as potentially dangerous, the hypothalamus at the base of the brain is alerted
-they hypothalamus controls to major systems that have central roles in bodily arousal, the hypothalamic-pirtuitary-adrenal axis (HPA) and the sympathetic adrenomdedullary (SAM) pathway
The hypothalamic-pirtuitary-adrenal axis (HPA):
-the pirtuitary gland sits just beneath the brain, connected to the hypothalamus by a short stalk, the pirtuitary is the master gland of the body, releasing a number of hormones into the bloodstream
-they key pirtuitary stress hormone is adrenocortitropic hormone (ACTH)
-the hypothalamus stimulates the release of ACTH from the anterior pirtuitary into the bloodstream
-the hormone travels to the adrenal cortex, part of the adrenal gland (we have 2 adrenal glands, located close to the kidney on each side of the body)
-when ACTH reaches the adrenal cortex, it stimulates the release of glucorcoticoids, especially those such as cortisol and corticosterone, into the bloodstream
-these hormones, in turn, have a major effect on the body
the sympathetic adrenomedullary pathway (SAM):
-the sympathetic nervous system (SNS) is one part of the automatic nervous system that controls our internal organs
-nerve pathways of the SNS originate in the brainstem and travel via the spinal cord and spinal nerves to the various body organs
-one of these pathways runs to the adrenal medulla, which along with the adrenal cortex makes up the adrenal gland
-when appraisal processes in higher brain centres detect a stressful situation, the hypthalamus is instructed to stimulate ACTH release from the pirtuiry
-in addition, the hypothalamus also activates the SNS centres in the brainstem and the pathways running to the adrenal medulla (SAM pathway)
-this results in the increased release of adrenaline and noradrenaline into the bloodstream
role of hormes in fight or flight:
-the hormones that are flooded into the bloodstream following a dangerous and stressful situation have a number of effects on the body, mainly designed to provide for energy expenditure used in responses to stress, such as confrontation or escape
-the SNS itself has direct connections to the heart and activation speeds up heart rate and raises blood pressure
-these effects are increased and sustained by the release of adrenaline and, to a lesser extent, noradrenaline from the adrenal medulla via the SAM pathway
-adrenaline in particular acts on the heart muscles to increase the heart rate, and also on blood vessels to constrict them and so raise blood pressure
-the end result is that oxygen is rapidly bumped to the muscles of the skeleton, allowing for increased physical activity
the role of hormones in the fight or flight response 2.0:
-the body’s energy are largely in the form of glycogen stored in the liver and fat reserves in fatty tissue
-a major effect of circulating adrenaline released in response to SAM is the increased release or mobilisation of these energy reserves; this in the form or raised blood levels of glucose (from glycogen) and fatty acids such as triglycerides (from our fat reserves)
-raised levels of corticosteroids, if sustained over a long period, also have the interesting effect of supressing the body’s immune system
-this system is the body’s defensw against infection, and cosists of a variety of complex subsystems vital in keeping the person healthy
stress-related illness:
-it is now thought that stress-related illnesses are not cause by exhaustion of the body’s physiological stress response, but rather it is the effect of chronic or long-term raised levels of stress hormones that evenatually lead to illness
-long-term raised levels of sugars and fats in the bloodstream, these can contribute to the furring-up and narrowing of blood vessels, known as astherosclerosis
-the effects of adrenaline and noradrenaline in raising heart rate and blood pressure, this can physicially damage blood vessels in the long term, by eroding the lining of blood vessels and causing hermorrhages where the lining of blood vessels is weakened
-long-term raised levels of corticosteroids, these supress the body’s immune system + leaves us vulnerable to infections and disease
cortical functions:
learn it
context:
-Franz Gall, a German physician, accidentally began the debate over localisation of function in the human brain in the early 1800s
-he proposed that a person’s personality was reflected in bumps on the skull that in turn reflected functions of the brain lying underneath; this theory was called phrenology
-Gall’s idea that certain functions were localised to specific regions of the brain eventually became extremly influential
-the opposing view was that the brain functions in a more holistic manner, with all or large parts of the brain involed all behaviours
Broca and Wernicke:
-in 1861, Broca, on the basis of his case studies of brain-damaged patients, has concluded that speech production was localised to an area in the frontal lobe, now known as ‘Broca’s area’
-Wernicke (1874) followed this up by showing that damage localised to a small area of the temporal lobe resulted in a loss of speech comprehension
localisation of function in the brain:
-by the end of the 19th century, other researhers had shown in cats, dogs, and monkeys, that damage could have highly specific effects on movement and perception
-overall, these studies seem to show conclusively that the brain is organised in a highly systematic way, with functions localised to specific areas
-by the middle of the 20th century, we could map out a number of functions localised in the cortex of the brain
electrical stimulation in the brain:
-electrical stimulation of these areas can produce the appropiate sensation: visual images from the visual cortex, sound sensation from the auditory cortex, the sesantion of touch or pressure from stimulation of somatosensory cortex, and movement of skeletal muscles from stimulation of the motor cortex
somatosensory cortex:
-the somatosensory cortex receives sensory input from receptors in the skin, including touch, pain, pressure, and temperature from all areas of the body surface
-the body surface is represented systematically in the somatosensory cortex
-head areas are represented at the bottom of the postcentral gyrus, and legs and feet at the top: that is, it is a map of the body surface, though upside down
motor cortex:
-the motor cortex in the precental gyrus is also organised systematically, with the muscles of the legs and feet at the top and the masculature of our vocal apparatus (muscles of the mouth and tongue, larynx and pharynx) at the bottom
-stimulation of tiny areas of the motor cortex can produce movement of individual muscle fibres in the appropiate part of the body
auditory areas of the cortex:
-the visual area receives input directly from eyes and the auditory areas from the ears, damage to them can lead to blindness and deafness
-they are known as the primary visual and auditory cortex, but visual perception, for example, requires additional processing in neighbouring cortical areas (secondary visual areas)
-it is in these areas that sensation is converted into perception, we know this because damage to these secondary visual areas does not lead to blindness, but can lead to loss of specific aspects of visual perception
-for example, propagnosia and achromatopsia
research on lateralisation of the brain:
-research on sensory and motor processes supports Gall’s original idea that functions were localised in the brain
-however, the debate on localisation was revived by the work of Lashley in the 1920s
-Lashley was interested in how learning was organised in the brain, and he studied how rats learned mazes, he found that large lesions on visual areas impaired maze learning, but that smaller lesions covering the same brain areas had no effect and it seemed that the size of the lesion was critical
2 main laws:
-law of mass action: as effects on learning were proportional to the amount of cortex damaged, Lashley concluded that behavioural functions such as learning were spread widely across cortical areas, they were not localised to specific regions
-law of equipotentiality: related to the law of mass action, this law states that different areas of cortex have similar capacities to process learning, so that one area can take over functions if another area is damaged, therefore only large lesions affect learning
Hemispheric lateralisation:
-the idea that some functions are found only in one hemisphere, e.g. language is usually lateralised to the left and Sperry demonstrated that some visual-spatial functions are lateralised to the right hemisphere
Broca’s area:
-area at the base of the left frontal involved in speech production, thought to contain the motor plans for words; first identified by Paul Broca in the 19th century
Wernicke’s area:
-area in the temporal lobe thought to contain our store of words; Wernicke showed in the 19th century that damage to Wernicke’s area resulted in receptive aphasia
Language and Hemispheric lateralisation:
-sensory and motor processes are organised in an extremely orderly way
-somatosensory and motor pathways are crossed, connecting the left hemisphere to the right side of the body and the right hemisphere to the left side of the body
-however, the cortical organisation is the same in each hemisphere
-visual and auditory systems are more complicated
-however, the organisation is perfectly orderly, and visual and auditory areas in the left hemisphere are matched by visual and auditory areas in the right hemisphere
-another way of putting is that a description of sensory and motor cortical areas in the left hemisphere can be applied equally to the right hemisphere
-the hemispheres are symmetrical, or mirror images of each other, with respect to sensory and motor cortical functions
Language:
-Broca and Wernicke also made a profound contribution to our understanding of hermispheric lateralisation of function
-this is the idea that some functions might be found only in one hemisphere rather than in both (lateralised -> to one side)
Broca and ‘Tan’:
-Broca, a French physician, was interested in the brain areas involved in language
-in 1861, he heard about a patient with a particularly striking language impairment
-this patient has suffered brain damage many years earlier that resulted in him being only able to speak one word, ‘tan’
-he could understand speech, following instructions and clearly understanding that was spoken to him
-tan, as he became known as, unfortunately died a week or so after Broca first met him, though this did mean Broca could perform an autopsy on his brain
-he found substantial damage to an area towards the base of the frontal lobe
-over the next four years, Broca accumulated a dozen or so cases where the symptoms were the same as in Tan, namely a lack of speech production but intact speech comprehension
-in all cases, autopsies revealed damage to the same area at the base of the frontal lobe, the damage in all cases was only in the left hemisphere
-Broca concluded that this area of the left hemisphere, now known as Broca’s area, was responsible for speech production
-the syndrome where speech is lost but comprehension is intact became known as ‘Broca’s aphasia’ or ‘expressive aphasia’
Wernicke:
-at around the same time as Broca, Wernicke was studying patients with the opposite syndrome to Tan’s-they could not understand speech, failing to follow instructions, but could produce some fluent speech
-autopsy findings were that these patients all had damage in an area of the left hemisphere at the top of the temporal lobe, near the auditory cortex, known as Wernicke’s area
-the syndrome of intact speech production but loss of speech comprehension became known as Wernicke’s aphasia or receptive aphasia
-an early simple model of speech saw Wernicke’s area as containing out store of words (the lexicon)
-when we want to speak, the word is located and activated in Wernicke’s area and the information is transmitted to Broca’s area
-this contains the motor plans for words: that is, patterns of muscle activation that allow us to speak a particular word
-this pattern is transmitted to the motor cortex, where the muscles of our vocal apparatus are activated and the word is spoken
Reading and writing:
-later research investigated reading and writing
-reading in particular involved the visual system
-the word we read is transmitted to the visual cortex for initial processing, then passed to the angular gyrus
-this structure then passes the information to Wernicke’s area and our internal lexicon where the word can be recognised, for writing, the word is activated in Wernicke’s area then passed to Broca’s area where the motor plan for writing the word can be transmitted to the motor cortex
-on rare occasions the angular gyrus is damaged
-as it is part of our reading system, this means that the person cannot read; this is called alexia
-however, Wernicke’s and Broca’s areas are intact, so the person cannot read, this is called alexia
-however, Wernicke’s and Broca’s areas are intact, so the person can write
-this produces a syndrome where someone can write, but cannot read what they have just written
-this is called alexia without a graphic (the inability to write), or pure word blindness
Split brain:
an operation used in some cases of servere epilepsy; the technical term for the operation is ‘commissurotomy’
Divided field:
technique devised by Sperry to present visual stimuli to either left or right hemisphere in his studies of split-brain patients; can also be used with neurotypical participants
Brain surgery and psychology reserach on epilepsy:
-patient HM -> studied after surgery caused profound amnesia
-split brain research -> examined effects of separating brain hemispheres
Epilepsy overview:
-a condition caused by uncontrolled electrical activity in the brain
-symptoms: convulsions and loss of consciousness (severe cases), milder cases often controlled with medication
-causes: sometimes unclear but can include: an imbalance in brain’s excitatory and inhibitory processes, scar tissue, brain damage, or previous surgeries (referred to as focus)
-surgical options: if a focus for epilepsy is identified, it can be possible to surgically remove it (as seen in the case of HM) if case is severe and disabling, however, if a focus cannot be identified, or it is in part of the brain that can’t be safely reached surgically, then another operation is possible
Epilepsy and split-brain:
-the two hemispheres of the brain are connected by the corpus callosum -> a bundle of 200-300 million fibres
-besides its normal functions, the corpus callosum also allows epilsepy discharges to travel down from one hemisphere to the other
-this means epilepsy can involve the whole brain
-in the 1940s, an operation was devised to cut the corpus callosum, preventing the epileptic discharges involving both hemispheres, and so reducing the severity of the attack
-this operation was called a commissurotomy as it was cutting a pathway connecting two hemispheres
-this operation was not very successful at reducing the symptoms of epielpsy, however, patients did not suffer ill effects from the operation, which was surprising as they had lost one of the major pathways in the brain
Sperry and the split brain:
-in the 1950s, Roger Sperry studied split-brain patients to explore brain hemispheres functions
-his earlier work with monkeys showed that both hemispheres have similar behavioural capacities, such as learning simple tasks
Human hemishphere functions:
-in humans, key functions like language are typically lateralised to the left hemisphere, which also controls the right hand
-the left hemisphere is considered dominant, while the right is seen as a minor partner
Split-brain patients and research challenges:
-Sperry saw split-brain patients (post-commissurotomy) as an opportunity to study hemisphere specialisation in humans
-a challenge arose because each eye sends information to both hemispheres, even when the hemispheres are separated
-Sperry had to design a method for projecting stimuli to each hemisphere separately
-based on earlier research into the visual systems of non-human animals,and he was able to apply his knowledge of visual systems to the problem of the split brain patient
-he devised an experimental procedure known as the divided field
Split brain information:
-divided field is based on the organisation of the human visual system, and the systematic arrangement of the visual pathways from each eye to the hemispheres
-note that the right side of the right eye and the right side of the left eye both connect to the right hemisphere; similarly to the left side of the left eye and the left side of the right eye both connect to the left hemisphere
-Sperry realised that with a split-brain patient focusing their eyes straight ahead, a stimulus presented out to their right (called right visual field or RVF) would be regstered only by the left side of each eye
-the left side of the eye projects to the left himpshere so the stimulus would be transmitted to the left hemisphere
-similarly, a sitmulus presented out to the left of the patient would be registered by the right side of each eye and projected to the right hemisphere
Split-brain procedure:
-in the intact human participant, a stimulus presented either to the right or the left hemisphere would immediatelt be conducted across the corpus callosum to the other hemisphere, so both hemispheres would be aware of the stimulus
-in split-brain patients, the corpus callosum has been cut, so a stimulus sent to the right hemisphere cannot be transmitted to the left hemisphere, and is effectively confined to the right hemisphere
-in this way, Sperry knew that he could present stimuli to each hemisphere separately by presenting them in either right or left visual field
-one limitation to the procedure was the natural tendency for the paticipant to move their eyes towards the stimulus, if the eyes move too much the stimulus is likely to be picked up by both hemispheres
-to prevent this happening, the stimulus could only be presented for a very brief period of time, for example around 200 miliseconds
-this meant in effect that Sperry could only present single words or pictures, even so, he was able to demonstrate some dramatic effecs in these early experimens
Key: study Sperry
1965
-Sperry studied split brain patients (with severed corpus callosum) to see how the brain’s hemispheres function independtly
-he found the left hemisphere controls language and speech, while the right hemisphere handle spatial and visual tasks
-this proved the brain is lateralized, with each side having specialized functions
research findings with the split brain- visual processing:
-Sperry’ss study reinforced the idea that language was mainly a left hemisphere function
-what really changed the view on lateralisation of functions across the hemishperes were the findings were the findings of studies using non-bverbal stimuli
-Sperry and his collaborators (Gazzaniga, 2005) repeated the divided field study with split-brain patients, but this time using faces as the simuli rather than words
-in one such study, a different face was presented to each hemisphere at the same time, then the split brain patient was fiven a set of faces, including the ones presented, and asked to choose the one that they had seen earlier
-they would choose the one presented to the the right hemisphere
-in a series of similar studies, Sperry demonstrated that the right hemisphere was better at identifying faces than the left hemisphere
-he was also able to show that the right hemisphere was better at matching shapes, and in general the right hemisphere showed a superiority over the left hemisphere in what we call visualspatial tasks
-so, one result of the splitbrain studies was a change in the way we viewed the two hemispheres
-no longer did we have a dominant right hemisphere and a minor left hemisphere, but instead we have a verbal left hemisphere and a visuospatial right hemisphere
Key study: Turk et al.
2002
-Turk et al- studied a split-brain patient (JW) to explore the right hemisphere’s role in language
-unlike Sperry’s findings, JW’s right hemisphere could process written words and even produce speech, suggesting that language abilities are not always limited to the left hemisphere
-this challenged the idea of strict lateralization in language processing
evaluation of split-brain research:
-the word of Sperry and others on split-brain patients patients was groundbreaking and changed our views in hemispheric function
-however, there are considerable issues with split-brain research:
-there are very few of these patients, and only between 10 and 15 have been subjected to extensive systematic study, this is a very small sample size
-those studied are an extremly varied group, they differ in age and sometimes gender and handedness, age at which they develop epilepsy, age at which they had the sommissurotomy, and age at which they were tested
-their operations were not always comparable, besides the corpus callosum, there are smaller pathways connecting the two hemispheres, such as the anterior commissure
-in some cases this was cut along with the corpus callosum, but in other cases it was left intact, possibly allowing for some communication between hemispheres
2.0 evaluation of split brain research:
-given these issues, we cannot be confident in building a model of hemispheric lateralisation using only split-brain research
-there is confidence behind language lateralisation because of the extensive case studies on language impariment after brain damage
-additionally, since Sperry’s word in the 1960s and 1970s, his techniques have been modified for use with intact (neurotypical) patients
-using Sperry’s divided field, the neurotypical participants is presented with two stimuli at the same time, one to each hemisphere
-the stimulus in the RVF is transmitted to the left hemisphere, while the sitmulus in the LVF is transmitted to the right hemisphere
-with brief presentation, about 200 ms, the participant will usually report only one of the stimuli
-if the stimuli are words, the one presented in the RVF is the one most likely to be reprted; this is called a right visual field advantage for words
-if the stimuli are faces or drawings, then the one presented in the LVF is most likely to be reported; this is called a left visual field advantage for visuospatial stimuli
split brain research overview:
-stimulated by split-brain research, findings from a variety of studies have lef to a general model of hemispheric specialisation
-the left hemisphere is seen as verbal and the right hemisphere as visuospatial
-to process language we need to break down incoming speech into separate words spread out over a stime interval (e.g. listening as a friend talks to you)
-it is only at the end of a sentence that we put everything together to understand what was said
-therefore the left hemisphere is also seen as analytical, working best when stimuli need to be broken down into their components parts
-the right hemisphere is better at processing faces, faces are not taken in bit by bit, but usually as one whole stimulus. therefore the right hemisphere is seen as holistic or Gestalt processor
