Studied by 10 people
Divisions of the nervous system
The central nervous system and the Peripheral nervous system
The central nervous system
Made up of the Brain and the spinal cord
Spinal cord= is an extension of the brain. It acts as a relay between the brain and the body. It also contains relay neurons which help us to perform quick, reflexive actions which don’t involve the brain
The Brain is made up of four main areas:
the cerebrum: main outer layer of the brain. split in two halves. divided into four main areas; frontal lobe for thought, occipital lobe for vision, motor cortex for movement and auditory cortex for speech.
the cerebellum: motor skills and balance
the diencephalon: comprises the thalamus (relay station sending nerve impulses from senses to correct area of brain for processing) and the hypothalamus (memory, hunger, thirst)
the brain stem: regulates automatic functions e.g. breathing
Peripheral nervous system
The PNS refers to all the nerves outside of the CNS. Its function is to relay impulses to and from the CNS and the rest of the body
Made up of the Autonomic nervous system and the Somatic nervous system
Autonomic nervous system= The control of involuntary actions. Some are excitatory (and involve the sympathetic division of the ANS which is involved in fight or flight) and some are inhibitory (which involve the parasympathetic division which brings the body back to a restful state after an emergency
Somatic nervous system= Made up of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The sensory receptors carry information to the spinal cord and brain and motor pathways that allow the brain to control movement and muscle responses. As well as controlling behaviour it regulates physiological processes.
Neuron
provide the nervous system a means of communication chemically and electrically. Of the 100 billion neurons, 80% are found in the brain.
Structure of a neuron
Cell body (soma) includes a nucleus which contains the genetic material of the cell
Dendrites (branch like structures) protrude from the cell body
Axon carries the impulse away from the cell body down the length of the neuron
Myelin sheath is a fatty layer that covers and protects the Axon. It speeds up electrical transmission of the impulse
Nodes of Renvier are gaps that segment the myelin sheath; these speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon
Terminal buttons are on the end of the axon and communicate with the next neuron in the chain across a gap known as the synapse
Types of neurons
Sensory
Motor
Relay
Sensory neuron
Carry messages from the PNS to the CNS. Are found in receptors such as the eyes, ears, tongue and skin and carry nerve impulses to the spinal cord and brain. When these nerve impulses reach the brain, they are translated into ‘sensations’ such as taste. However, not all neurons reach the brain, as some neurons stop at the spinal cord, allowing for reflex action.
Recognise by: Long dendrites and cell body in axon
Motor neuron
Are found in the CNS and control muscle movements. When these are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement.
Recognise by: Short dendrites & long axons
Relay neuron
Are found between sensory input and motor output/response. They are found in the brain and spinal cord and allow sensory and motor neurons to communicate
Recognise by: Short dendrites & short axons
Reflex Arc
Found in the Autonomic nervous system
Reflexes are unconscious and automatic
A stimulus can be detected by sense organs in the PNS, which convey a message along a sensory neuron. The message reaches the CNS, where it connects with a relay neuron. This then transfers the message to a motor neuron. This then carries the message to an effector, such as a muscle, which causes the muscle to contract and, hence, causes the body part to move
Electrical transmission
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
Synaptic transmission
The process by which neighbouring neurons communicate by sending chemical messages across the synapse (the gap between them).
Process of Synaptic Transmission
An Action potential (electrical charge) travels down the neuron’s axon (this neuron is the pre-synaptic neuron)
When it reaches the terminal at the end of the neuron, vesicles release the neurotransmitters they contain
Neurotransmitters (chemical messengers) travel out of the neuron, across the synaptic gap into receptors on the dendrites of the receiving neuron (the post-synaptic neuron)
Here, the chemical message is converted back into an electrical impulse and the process of transmission begins again, from this neuron
Reuptake of neurotransmitters
After the messages have been sent, any leftover neurotransmitters can be recycled.
Reuptake refers to the process in the brain of neurons to retrieve chemicals that were not received by the next neuron.
The neurotransmitter has greater effect during the time it is in the synaptic gap – the effect is lessened when the message has been received by the postsynaptic neuron and during reuptake when it is taken back into the vesicles of the presynaptic neuron
Excitation and Inhibition
Neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neuron:
Excitatory= increases positive charge in post-synaptic neuron that it sends the message to. This increases the chances of another action potential to fire and messages to continue to be transmitted
eg. Adrenaline is released during a response to stress, causing more firing and us to feel hyper-alert, excited, maybe anxious.
Inhibitory= increases negative charge in post-synaptic neuron that it sends the message to. This decreases the chances of another action potential occurring and messages slow down or stop being transmitted
eg. serotonin makes us feel calm and regulates sleep & appetite
Summation
The excitatory or inhibitory influences are summed (or totalled).
If the total effect on the post-synaptic neuron is inhibitory (negative in total) then the neuron is less likely to fire.
If the total effect is excitatory (positive in total), the neuron will be more likely to fire
The endocrine system
The endocrine system is a collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep and mood. It works alongside the nervous system to control vital functions in the body. The endocrine system acts more slowly than the nervous system but has very widespread and powerful effects. The endocrine system uses blood vessels to transport hormones around the body to a specific target cell and different hormones produce different effects. Glands in the body produce hormones
Hypothalamus
a collection of specialised cells that is located in the lower central part of the brain, is the main link between endocrine and nervous systems. Connected to the pituitary gland. It is responsible for stimulating or controlling the release of hormones from the pituitary gland
Pituitary gland
“the master gland”. Hormones released from this control and stimulate the release of other hormones from other glands. The anterior lobe releases tropic hormone (ACTH) which stimulates the adrenal cortex and the release of cortisol. The posterior lobe released oxytocin, which is responsible for uterus contractions during childbirth
Thyroid gland
releases thyroxine which affects metabolism
Pineal gland
releases melatonin, responsible for important biological rhythms e.g. sleep-wake cycle
Adrenal glands
divided into the adrenal medulla and the adrenal cortex. The adrenal medulla releases adrenaline and noradrenaline. The adrenal cortex releases cortisol which stimulates the release of glucose while suppressing the immune system
Ovaires
release oestrogen which control the regulation of the female reproductive system, including the menstrual cycle and pregnancy
Testes
releases androgens, which include the main hormone testosterone
Negative feedback loop
The endocrine system receives feedback from the hormones secreted by the target gland. The hormones are detected and the hypothalamus responds by shutting down secretion of releasing hormones, making the pituitary gland shut down secretion of stimulating hormones. Thereby, the endocrine system works via a negative feedback loop.
Fight or flight response
Stress can be acute or chronic
During fight or flight the endocrine system and Autonomic nervous system work together
Stressor perceived by hypothalamus which activates the pituitary gland- sympathetic brand of the ANS
Parasympathetic actives once the threat has passed
Sympathetic Adrenal-Medullary Pathway
The SAM pathway involves the amygdala sensing danger and alerting the hypothalamus. Via the CNS using electrical systems
This commands the ANS to activate the sympathetic branch (a change from its resting parasympathetic state)
This sends a message to the adrenal medulla, part of the adrenal gland in the kidneys.
The adrenal medulla then releases adrenaline (stress hormone) and noradrenaline into the bloodstream, stimulating the body and making it work faster and more efficiently, to deal with the stress.
This will activate the fight or flight response
When the threat has passed, the parasympathetic nervous system dampens down the stress response, bringing the body back to normal.
Sympathetic
Increases heart rate
Increases blood pressure
Widens the bronchi in the lungs
Releases glucose into blood
Dilates pupils
Slows digestion
Saliva production inhibited
Parasympathetic
Decreases heart rate
Decreases blood pressure
Narrows bronchi
Stores glucose in the liver as glycogen
Contracts pupils
Returns digestion to normal
AO3 EVALUATION: Flight or fight theory
Gender bias- Taylor (2000) suggested that, for females, behavioural responses to stress are more characterised by a pattern of ‘tend and befriend’ than fight or flight. This involves protecting themselves and their young through nurturing behaviours (tending) and forming protective alliances with other women (befriending). As fleeing at signs of danger would put offspring at risk, this would make sense as females tend to be primary caregivers for their children. Also females have higher levels of oxytocin. As research has only been conducted on males, so may misrepresent the behaviour of females. This is an example of beta bias in research.
Fight, Flight, FREEZE- Gray (1988) argued that, prior to responding with attacking or running away, most animals (including humans) typically display the ‘freeze response’ to avoid confrontation. The adaptive advantages of this response for humans are that ‘freezing’ focuses attention and makes them look for new information in order to make the best response for that particular threat. This limits the validity of the original theory.
Localisation of the brain
The brain is divided into two halves; right & left hemispheres.
This is known as lateralisation – there is a difference in some physical and psychological functions controlled by each hemisphere.
Generally the left side of the body is controlled by the right hemisphere; and the right side of the body by the left hemisphere.
Different areas of the brain are responsible for different functions or behaviours.
An example of this is that the occipital lobes control visual function or that the motor cortex is specialised to allow movement.
Damage to a particular area of the brain would mean that only a particular function or behaviour would be affected.
Frontal lobe
manages thinking, emotions, personality, judgement, self-control, muscle control and movements and memory storage
Parietal lobe
vital for sensory perception and integration, including the management of taste, hearing, sight, touch, and smell. It is home to the brain's primary somatosensory cortex, a region where the brain interprets input from other areas of the body
Occipital lobe
visual processing area of the brain. It is associated with visuospatial processing, distance and depth perception, colour determination, object and face recognition, and memory formation
Temporal lobe
The temporal lobe is responsible for interpreting sounds and speech from the ears, and for understanding meaningful speech. The temporal lobe also plays a key role in language use and communication.
Language centres- Broca’s area
Responsible for Speech production.
Identified by Broca in 1880, in the left frontal lobe.
Damage to this area causes Broca’s Aphasia, which is characterised by speech that is slow, laborious, and lacking in fluency.
Broca’s patients had difficulty finding words and naming certain objects.
Patients with Broca’s Aphasia have difficulty with prepositions and conjunctions (e.g. ‘a’, ‘the’, ‘and’).
E.g. Broca’s patient ‘Tan’ - who, after a stroke, could only use the word ‘tan’. In a post mortem damage was found in an area of his left temporal lobe - now known as the Broca’s area
Language centres- Wernicke’s Area
Responsible for language comprehension.
Identified by Wernicke in the 1880’s in the back of the temporal lobe.
Patients produce language but have problems understanding it, so they produce fluent but meaningless speech.
Patients with Wernicke’s Aphasia will often produce nonsense words (neologisms) as part of the content of their speech.
Motor Cortex
The motor area is located towards the back of the frontal lobe (in both hemispheres)and is responsible for voluntary movements by sending signals to the muscles in the body.
Hitzig and Fritsch (1870) first discovered that different muscles are coordinated by different areas of the motor cortex by electrically stimulating the motor area of dogs.
This resulted in muscular contractions in different areas of the body depending on where the probe was inserted.
The regions of the motor area are arranged in a logical order, for example, the region that controls finger movement is located next to the region that controls the hand and arm and so on.
Somatosensory cortex
The somatosensory area is located in the front of the parietal lobe and receives incoming sensory information from the skin to produce sensations related to pressure, pain, temperature, etc.
Different parts of the somatosensory area receive messages from different locations of the body, and the amount of somatosensory area devoted to a particular body part denotes its sensitivity.
Robertson (1995) found that this area of the brain is highly adaptable, with Braille readers having larger areas in the somatosensory area for their fingertips compared to normal sighted participants.
Visual Centres of the brain
At the back of the brain, in the occipital lobe is the visual area, which receives and processes visual information.
Information from the right-hand side visual field is processed in the left hemisphere, and information from the left-hand side visual field is processed in the right hemisphere.
The visual area contains different parts that process different types of information including colour, shape or movement.
Auditory centres of the brain
The auditory area is located in the temporal lobe and is responsible for analysing and processing acoustic information, (speech based information).
Information from the left ear goes primarily to the right hemisphere and information from the right ear goes primarily to the left hemisphere.
The auditory area contains different parts, and the primary auditory area is involved in processing simple features of sound, including volume, tempo and pitch.
AO3 Evaluation: Localisation of the brain
Equipotentiality (Challenge to localisation theory)- The idea of localisation is reductionist - equipotentiality is the idea that it is not the location of damage that causes deficits, but instead the extent of damage. Lashley removed areas of the cortex (up to 50%) in rats learning the route through a maze. Learning required all of the cortex rather than being confined to a particular area. This suggests that higher cognitive processes (e.g. learning) are not localised but are distributed in a more holistic way in the brain
Evidence/ Support from research-
Tan (Broca’s area)
Phineas Gage (Amygdala/frontal lobe)
Clive Wearing (hippocampus)
HM (hippocampus)
Petersen et al (1988) - Used brain scans to identified activity in the Wernicke’s areas during listening tasks and the Broca’s areas during reading tasks
Tulving et al (1994) identified that semantic and episodic memory are located in different areas of the prefrontal cortex.
Hemispheric Lateralisation
Hemispheric lateralisation is the theory that each hemisphere of the brain has specific functions.
Certain functions are controlled by one hemisphere of the brain and not the other
This is due to a large body of evidence supporting these claims – eg. The ‘speech centres’, Broca’s area and Wernicke’s area appear only to exist in the left hemisphere
Contralateral organisation
Hemispheres control opposite sides of the body
Information from our right visual field (RVF) is processed in our left hemisphere
Information from our left visual field is processed in the right hemisphere
The two hemispheres communicate via the Corpus Callosum
Corpus Callosum
The Corpus Callosum connects the two hemispheres of the brain and allows us to use both sides together
Eg. Talking about things (speech = left hemisphere) that are experienced in the right hemisphere
Split brain research
Unique research opportunities have arisen, where patients whose Corpus Callosum have been cut and information from each hemisphere couldn't’ pass between the two
When cut, this would disable some functions that are only available in one hemisphere such as speech
This allows psychologists to observe how the brain can work when information from hemispheres cannot be communicated in the usual way
Such research provides strong evidence for the case that our brains are lateralised (each hemisphere has specific functions) and we are able to function effectively (with a ‘whole’ brain) because of the Corpus Callosum
Sperry’s split brain research
Procedure:
Quasi-experiments
11 split-brain patients (due to severe epilepsy)
Performance on tasks compared with people without split-brain
This involved blindfolding one of the participant’s eyes and then asking them to fixate with the seeing eye on a point in the middle of a screen. The researchers would then project a stimulus on either the left or right hand side of the fixation point for less than 1/10 of a second
As language is processed in the left hemisphere, when a stimulus is presented to the left visual field of a split-brain patient they should not be able the name of the stimulus
Findings:
Patients can verbalise an image shown to their right visual field (because the left hemisphere contains the speech centres)
Patients cannot verbalise an image shown to their left visual field (because the right hemisphere processes this but contains no speech centre) BUT they can draw it with their left hand (the right hemisphere has dominant motor function)
If a patient is shown an image in both visual fields, they will say they’ve seen the one in the Right visual field (processed by the left hemisphere), but draw the image they’ve seen in the LVF, with their left hand.
Overall findings of Sperry’s split brain research
Sperry’s research shows that if a split-brain patient is shown an image to their right visual field, they can state what this is (as info from RVF passes directly to the left hemisphere where the brain’s speech centres are).
However, the left visual field would connect directly to the right hemisphere, where there is no speech centre. In a ‘normal’ brain, this info would pass across the corpus callosum to the left hemisphere speech centre so the information can be verbalised.
In a split-brain patient, there is no connection to cross, so the information goes nowhere and the person cannot verbalise the image. They could however, draw it, as their motor control is unaffected
AO3 EVALUATION: Split brain research
Methodology - Sperry’s research was very well designed with standardised procedures. As he made use of presenting information to one eye whilst the other was blindfolded and he flashed the image up extremely quickly he had properly controlled which hemisphere was being exposed. His procedure could be replicated so his findings could be validated. However, he used small samples so we can’t generalise. And they had epilepsy, which was medicated with drug therapy, which could act as a confounding variable. They were compared with non-epileptics. This suggests some of the results may have been due to participant variables, making the results ungeneralisable in wider population. The split-brain procedure is rarely carried out these days, replication is rare. Therefore patients who have had this procedure are rarely encountered in sufficient numbers to be useful for research.
Lateralisation changes with age- Lateralisation of function appears not to stay exactly the same throughout an individual’s lifetime, but changes with normal ageing. Across many types of tasks and many brain areas, lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults. Szaflarski et al (2006) found that language became more lateralised to the left hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of life.
Idiographic vs Nomothetic- the theory of lateralisation is nomothetic as it assumes that everyone’s brain is similar in that it is lateralised. However, it can be considered idiographic as it uses idiographic research to support its claims, evident from Sperry’s split brain patients used for his research. Psychologist shouldn’t be supporting a nomothetic theory with idiographic research. Additionally, lateralisation does not take into account individuals born with half a brain.
Plasticity
The brain’s ability to change and adapt (modify its structure) as a result of experience.
Research shows that the brain continues to create new neural pathways and alter existing ones in order to adapt to new experiences as a result of learning.
As we age, rarely used connections are deleted and frequently used connections are strengthened in a process known as cognitive pruning.
Plasticity as a result of real life experiences
When we learn something, new pathways in the brain develop (especially through repetition).
We can prune these pathways when we stop using certain skills too.
The brain constantly adapts to a changing environment; as we gain new experiences, neuronal pathways that are used frequently develop stronger connections whereas those that are rarely or never used eventually die
For example: Boyke et al. (2008) – found evidence of brain plasticity in 60 year-olds taught a new skill – juggling. They found increases in grey matter in the visual cortex (although when practising stopped this was reversed)
Plasticity in playing video games
Playing video games makes many complex cognitive and motor demands
Kuhn et al. (2014) – participants trained for at least 30 mins a day for 2 months on Super Mario. Significant increase in grey matter in several areas of the brain (this did not happen for a control group). Video game training resulted in new synaptic connections in brain areas involved in spatial navigation, strategic planning, working memory and motor performance.
Plasticity in meditation
Davidson et al. (2004) – 8 Tibetan monks and 10 volunteers who had never meditated before were asked to meditate for short periods
Measured gamma wave activity (important because they coordinate neuron activity) and found much greater gamma wave activity in the monks than the students, even before meditation began.
They concluded that meditation not only affects the brain in the short-term but may also produce negative changes
How can plasticity be negative?
Prolonged drug use leading to poorer cognitive functioning (e.g. marijuana linked with excess dopamine release, Ketamine linked with permanent memory issues, via pruning in the hippocampus).
Old age being associated with dementia .
Phantom Limb Syndrome
AO3 Evaluation: Plasticity
Research support from Animal Studies- Studies using rats have shown that environment and life experience positively influence plasticity in relevant areas of the brain. Kempermann (1998) found that rats living in complex environments showed increased neuronal activity in the hippocampus, responsible for spatial awareness and new memory formation, compared to rats living in lab cages. This research suggests the brain will adapt and become active in response to environmental pressures, showing direct evidence for plasticity in rat brains.
Research support from Human Studies- Maguire’s (2000) research showed London taxi drivers had increased grey matter and neural activity in the hippocampus, which is responsible for spatial awareness, navigation and other skills they will have in abundance due to the demands of their job. Increasing the importance of this evidence, was the finding that time working as a taxi driver was positively correlated with hippocampal volume. This is significant evidence that the brain changes and develops in response to the environment and that plasticity continues to occur to meet the specific demands of our individual lifestyles.
Plasticity and Age- The brain has a greater ability to reorganise in childhood - as it is constantly adapting to new experiences and learning. However, plasticity does still occur (although somewhat slower) throughout our lifespan (Bezzola et al, 2012).
Nomothetic- Assumption that all human brains function in the same way. Investigates plasticity using brain imagining and large groups which is easily generalisable. However, would benefit from an interactionist approach with more idiographic evidence from individuals
Functional Recovery
Following physical injury or other forms of trauma such as infection or the experience of a stroke, unaffected areas are sometimes able to adapt or compensate for those areas that are damaged.
The functional recovery that occurs in these cases is an example of neural plasticity.
Recovery can be done through axon sprouting, stem cells and denervation super sensitivity
Axon sporuting
Growth of new nerve endings which connect with undamaged cells to form new neural pathways
Denervation super sensitivity
This occurs when axons that do a similar job become aroused to a higher level to compensate for the ones that are lost
However, it can have the negative consequence of oversensitivity to messages such as pain
Stem Cells
Stem cells are unspecialised cells that can take on the characteristics of different cells, including nerve cells.
They may provide treatment for brain damage; there are three possible views on how:
Stem cells implanted into the brain directly replace dead/dying cells
Transplanted stem cells secrete growth factors that ‘rescue’ the damaged cells
Transplanted cells create a network linking an uninjured brain site, where new stem cells are made, to the damaged region
AO3 Evaluation: Functional Recovery
Research support- Tajiri et al (2013) provided evidence for the role of stem cells in recovery from brain injury in rats. They randomly assigned rats with traumatic brain injury to one of 2 groups. One group received transplants of stem cells into the region of the brain affected by traumatic injury. The control group received a solution infused into the brain containing no stem cells. Three months after the brain injury, the brains of stem cell rats showed clear development of neuron-like cells in the area of injury. This was accompanied by a solid stream of stem cells migrating to the brain’s site of injury. This was not the case with the control group.
Age differences in functional recovery- Functional recovery reduces with age. Some studies have suggested that even abilities commonly thought to be fixed in childhood can still be modified in adults with intense retraining. However, the capacity for neural reorganisation is much greater in children than in adults, as demonstrated by the extended practice that adults require in order to produce changes.
Biologically Deterministic- Functional recovery is deterministic as it suggested that recovery is only determined by biological mechanisms such as axon sprouting. This is deterministic as it ignores other external factors that can help with recovery, such as positive support from others which encourages the patient to be motivated in getting better. However, this biological determinism may be a positive as people who lack the willingness to recover by physiotherapy or regular doctor appointments now know that despite attending these treatments, the body will naturally help them to recover anyway, so don’t need to be worried about not seeking treatment.
Spatial (location) validity/resolution
how accurately the brain scan can show exactly which area of the brain is actively involved in an a specific function
Temporal (time) validity/resolution
how quickly the brain scan can detect brain activity (does it show activity in real time, or after an event & how long after?)
Ways of studying the brain
fMRI
EEG
ERP
Post Mortem examinations
fMRI Scans
Gives an image of the brain, showing the structure, and which structures are active during a specific task (function). This will help us to understand localisation of function.
Blood flow: fMRI measures blood flow whilst a person is performing a specific task.
Oxygen: If an area of the brain becomes more active those neurons in the brain use the most energy and require more oxygen.
Magnetic: Oxygen is released for use by these active neurons, at which point the haemoglobin (which carries oxygen in the blood) becomes deoxygenated. Deoxygenated haemoglobin has a different magnetic quality than oxygenated haemoglobin, and the magnetic scan can detect and show an image of this (haemodynamic response).
EEG examinations
EEGs record the measurement of the (general) electrical activity of the brain over time. EEG is often used as a diagnostic tool, as unusual patterns of activity may indicate neurological abnormalities (epilepsy, tumours etc.)
Electrical impulses are used by neurons to communicate messages (action potentials) - it’s these communications that are being measured. This shows function.
Electrodes are attached to the scalp to measure electrical activity of neurons (action potentials).
The electrodes detect the size and intensity of the electrical activity, as well as the frequency (or rate) of that activity.
The electrical signals from the different electrodes are plotted on a graph in the form of waves (Alpha, Beta, Delta, Theta waves identified)
ERP Examinations
Using electrodes to measure very small voltage changes within the brain, when patients are presented with a stimulus, such as a sound or a picture which requires cognitive processing. This shows function in the brain.
Specific: ERPs study the brain by measuring very small voltage changes in the brain that are triggered by specific stimulus.
Averaged: to establish a specific response to a specific event or stimulus requires many presentations of the stimulus, and these responses can then be averaged together.
Filtered out: using statistical averaging techniques all background brain activity from the original EEG is filtered out so that only the ERP is left.
Post Mortem Examinations
Examination of the structure of the brain after death
Study an individual’s behaviour when they are alive (esp if they behave abnormally, so have been referred to a doctor/psychiatrist).
Study the brain after death. When the person dies, the researchers can examine the brain to look for abnormalities and lesions in the brain. They then compare this to a typical/normal brain in order to identify any differences.
Analysis of the brain allows researchers to form a correlation between the abnormal behaviours of the patient and the particular areas of the brain that appear different to a typical brain.
AO3 Evaluation: Ways of studying the brain
fMRI:
Example- Maguires Taxi drivers study
Shows structure and function of the brain
Strengths- spatial resolution is high (1-2 mm) which gives more accurate insight. No radiation/risk to patients
Weaknesses- temporal resolution is low (1-4 secs). Delay is harder to detect when an activity starts. Expensive (£1-3 million for fMRI equipment)
EEG:
Example- Dement and Kleitman’s sleep stages study
Shows function of the brain
Strengths- temporal resolution is high (1-10 milliseconds). Effective tools for diagnosis of certain brain disorders e.g. tumors or epilepsy
AO3 Evaluation: Ways of studying the brain
ERP:
Shows function of the brain
Strengths- temporal resolution is high (1-10 milliseconds). Cheaper than fMRI
Weaknesses- spatial resolution is low. Can only detect activity accurately (e.g. hippocampus/hypothalamus activity is inaccessible to EEGs)
Post Mortem Examinations:
Example- Broca’s Study of Tan
Shows he structure of the brain
Strengths- excellent spatial resolution (to any depth of brain area). helps generate hypotheses for future study.
Weaknesses- no temporal resolution. Correlational outcomes (only cause and effect can be inferred from damage only). Also ethical complications from studying brains from people who have passed, issues with consent
Biological Rhythms
A biological rhythm is a cyclical change in body processes
All rhythms are controlled by 2 things: endogenous pacemakers (internal biological clock) and exogenous zeitgebers (external changes in the environment)
There are three types of rhythm: circadian, ultradian, infradian
Circadian Rhythms
Circa = about
Dian = day
A biological rhythm that takes about one day (24 hrs) to complete a cycle.
E.g. Sleep/Wake cycle and body temperature cycle
Endogenous Pacemakers
Internal body clocks that regulate our biological rhythms:
E.g. Hormones and Areas in the brain
Exogenous Zeitgebers
External cues that influence and reset our internal body clocks through entrainment:
E.g. Light/dark, Other people, Diet, Exercise
Sleep/Wake Cycle
Our main biological clock (EP) is in a small area in the hypothalamus called the SCN (suprachiasmatic nucleus).
As light (an EZ) enters the eye, it travels to the SCN (an EP).
The SCN then regulates the activity of the pineal gland
When light decreases (i.e. dusk), the SCN triggers the pineal gland to increase levels of melatonin.
When light increases (e.g. dawn), the SCN triggers the pineal gland to decrease levels of melatonin
Case study- Michel Siffre- Sleep/wake cycle
In 1962 Michel Siffre spent 2 months living in French caves with no exogenous zeitgebers (no sunlight, no clocks, no other people).
He monitored his activities, paying special attention to when he felt tired, hungry and when he slept.
To see the extent to which exogenous zeitgebers really affect circadian rhythms.
Findings:
Despite the absence of natural daylight he maintained a regular sleep/wake cycle of around 25 hrs (he woke up and went to sleep at regular times) - this was fairly erratic at first, but settled down to this regular rhythm.
It was found that we must have an internal body clock (EP) that controls our circadian rhythm to an extent.
But this shows the need we have for exogenous zeitgebers such as light to regulate and reset our 24 hr sleep/wake cycle.
AO3 EVALUATION: Circadian Rhythms
Individual Differences- Sleep/wake cycles may vary widely from person to person. Duffy (2001) found that some people have a natural preference for going to bed early and rising early (‘Larks’) whereas others prefer the opposite (‘Night Owls’). Sleep/wake cycle preferences also change due to age. So, generalisations about sleep/wake patterns are difficult to make.
Research Support- Use the Michel Siffre Study. However a counterpoint to his study is the Limited use/reliability of case studies with small samples, these may not be representative, so generalisations cannot be made. In addition, Poor control in studies e.g. Siffre used an artificial lamp and phoned his findings, so did speak with other humans.
Biological Determinism- The idea that the sleep-wake cycle is purely controlled by the SCN is determinist because it is assumed humans have no choice over their sleeping patterns. However, it may be that we do have free will and choice over our sleep-wake cycle because some people are able to work at night and sleep during the day.
Practical Application- Practical application to shift work. Desynchronisation can occur as a result of shift work. Night workers suffer a circadian trough at around 6am, making mistakes and accidents more likely. Relationship between shift work and poor health. Economic implications of worker productivity
Ultradian Rhythms
Biological rhythms that take less than a day (you have more than one cycle within 24 hours)
E.g. Sleep Stages
Sleep stages
There are 5 distinct stages of sleep that altogether span 90 minutes.
Each stage has a different level of brain activity (which can be monitored with an EEG)
Stages 1 & 2 - light sleep - alpha and theta waves
Stages 3 & 4 - deep sleep - delta waves
REM sleep - dreaming - very light sleep.
Dement and Kleitman (1957):
Conducted a sleep study using EEG scans.
Used a small sample of participants
Pps were allowed to eat normally during the day (but not allowed caffeine or alcohol).
When pps were woken during REM, 80% remembered their dreams, when pps were woken in non-REM sleep only 7% remembered their dreams.
Basic rest activity cycle (BRAC)
Kleitman has also suggested that we have a similar 90 minute cycle that continues throughout the daytime too. This is characterised by a period of alertness followed by a spell of psychological fatigue- every 90 minutes.
AO3 EVALUATION: Ultradian Rhythms
Individual differences in Sleep Stages- One limitation of Ultradian Rhythms research is that there is significant variation between people. Tucker (2007) found large differences in participants in terms of the duration of each of the sleep stages. This could be determined by; hormones, age, activity or biological differences.
Nature vs Nurture- Ultradian Rhythms is nature because it suggests we have these innate biologically driven sleep stages that everyone goes through during their sleep cycle. However it can be considered nurture as there may be other factors such as caffeine and alcohol that affect our sleep stages. As well as environment factors such as the type of area you live in e.g. urban or rural, and if your location receives more daylight for long periods of time
Infradian Rhythms
A biological rhythm that takes more than 24 hours to complete
E.g. The menstrual cycle - A series of physical and hormonal changes that prepare the female body for pregnancy. the time from the first day of a period to the day before the next period ≃ 28 days.
The Menstrual Cycle
In the first half of the menstrual cycle levels of the hormone oestrogen rise, which causes the ovary to develop and release an egg (ovulation).
Here the lining of the womb thickens.
In the second half of the menstrual cycle levels of progesterone rise, this helps to maintain the lining of the womb in preparation for implantation of a developing embryo.
If pregnancy does not occur, the womb lining leaves the body (menstruation)
Role of Endogenous Pacemakers:
Oestrogen and Progesterone
Pituitary gland and FSH
Role of Exogenous Pacemakers:
Diet
Exercise
Stress
Synching up with others
AO3 EVALUATION: Infradian Rhythms
Research support for the role of Exogenous Cues (Synching)- McClintock (1988) A ten-year longitudinal study that involved 29 women 20-35 years, with a history of irregular, spontaneous ovulation. Samples of pheromones were gathered from nine of the women at certain points in their menstrual cycles by placing pads of cotton under their arms. Each pad was then treated with alcohol and frozen. These pads were then wiped under the noses of the 20 other women on a daily basis. 68% of the women responded to the pheromones. Menstrual cycles were either shortened from 1 to 14 days or lengthened from 1 to 12 days, depending on when in the menstrual cycle the pheremones had been collected. This is known as Synching.
Exogenous Pacemakers
Internal body clock that regulate many of our biological rhythms such as the influence of the suprachiasmatic nucleus on the sleep/wake cycle
Suprachiasmatic nucleus
The main endogenous pacemaker is located in the suprachiasmatic nucleus (SCN), which lies in the hypothalamus (in the optic chiasm).
The SCN obtains information on light from the optic nerve, even when our eyes are shut. Light penetrates the eyelids, and special photoreceptors in the eyes pick up light signals and carry them to the SCN.
This information influences the sleep/wake circadian rhythm
The Pineal gland- Endogenous pacemakers
The SCN passes the information on day length and light that it receives to the pineal gland.
During the night (in low light) the pineal gland increases production of melatonin (hormone that induces sleep)
During the day (in bright light) the pineal gland decreases the production of melatonin.
Exogenous Zeitgebers
External Factors affect our biological rhythms such as the influence of light on the sleep/wake cycle
Light as an exogenous zeitgeber
This is the 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 sleep/wake cycle.
Light has an impact upon melatonin production and therefore sleep/wakefulness.
Light also has an indirect influence on key processes in the body that control such functions as hormone circulation and blood circulation.
Social cues as an exogenous zeitgeber
Is the idea that our biological rhythms are entrained through social convention.
We are influenced by the norms of people around us as to what time we wake and sleep.
Yawning may also be a social cue.
AO3 EVALUATION: Endogenous Pacemakers and exogenous zeitgebers
Supporting evidence for the role of the SCN- DeCoursey et al (2000), destroyed the SCN connections in the brains of 30 chipmunks (and had a control group of 20 normal chipmunks) - who were then radio collared and tracked for 30 days. They found more SCN damaged chipmunks were killed by predators - because their SCN damage affected their sleep patterns.
Research evidence- Jet lag study. Klein and Wegmann (1974) found that the circadian rhythms of air travellers adjusted more quickly if they went outside more at their destination. This was thought to be because they were exposed to the social cues of their new time zone, which acted as a zeitgeber.
Environmental Observations- One limitation is that EZ’s do not have the same effect in all environments. The experiences of people who live in places where there is very little darkness in the summer, and very little light in winter tell a different story from the usual narrative. For instance, people who live in the Arctic Circle have similar sleep patterns all year round, despite spending 6 months in almost total darkness. This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light
Biological reductionist- Despite all the research support for the role of endogenous pacemakers and exogenous zeitgebers, the argument could still be considered biologically reductionist. For example, the behaviourist approach would suggest that bodily rhythms are influenced by other people and social norms, i.e. sleep occurs when it is dark because that is the social norm and it wouldn’t be socially acceptable for a person to conduct their daily routines during the night. The research discussed here could be criticised for being reductionist as it only considers a singular biological mechanism and fails to consider the other widely divergent viewpoints.
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