Biopsychology

The divisions of the nervous system: central and peripheral (somatic and autonomic)

The human nervous system is a collection of neurons across the body that detects information from the environment and processes this, then directs the body to take action via the muscles and/or glands. It is split into the Central nervous system (CNS) and the Peripheral nervous system (PNS).

• The CNS is responsible for our complex processing. It consists of the brain (the centre of all conscious and most unconscious processing) and the spinal cord (this receives and transmits information).

• The PNS is the portion of the nervous system that is outside the brain and spinal cord. The primary function of the peripheral nervous system is to connect the brain and spinal cord to the rest of the body and the external environment. 

• The peripheral nervous system is split into the somatic and autonomic nervous systems

• Somatic Nervous System (SNS) connects the central nervous system with the senses and is composed of sensory nerve pathways bring information to the CNS from sensory receptors, dealing with touch, pain, pressure, temperature etc, and motor nerve pathways which control bodily movement by carrying instructions towards muscles

• Autonomic Nervous System (ANS) controls bodily arousal (how ‘excited’ or relaxed we are), body temperature, homeostasis, heart rate and blood pressure. It is composed of the sympathetic and parasympathetic nervous systems. the sympathetic ANS is involved in preparing the body for fight or flight, so causes increased arousal (e.g. increase in heart rate and blood pressure, pupil dilation, reduction in digestion and salivation)and the parasympathetic ANS is used to return our body back to its normal state after the fight or flight response, so leads to decreased arousal.

Under normal conditions there is a balance between the sympathetic and parasympathetic systems in order to maintain homeostasis.

CENTRAL NERVOUS SYSTEM (brain & spinal cord)

Similarities:

• The brainstem and spinal cord both control involuntary processes (e.g. the brain stem controls breathing and the spinal cord controls involuntary reflexes).

Differences:

• The brain provides conscious awareness and allows for higher-order thinking, while the spinal cord allows for simple reflex responses.

• The brain consists of multiple regions responsible for different functions, whereas the spinal cord has one main function.

PERIPHERAL NERVOUS SYSTEM (somatic/autonomic & sympathetic/parasympathetic)

Similarities:

• The sympathetic nervous system (part of the autonomic nervous system) and the somatic nervous system respond to external stimuli. The sympathetic nervous system responds to external stimuli by preparing the body for fight or flight and the somatic nervous system responds to external stimuli by carrying information from sensory receptors to the spinal cord and brain.

Differences:

• The autonomic nervous system consists of two sub-components, whereas the somatic nervous system only has one.

• The somatic nervous system has sensory and motor pathways, whereas the autonomic nervous system only has motor pathways.

• The autonomic nervous system controls internal organs and glands, while the somatic nervous system controls muscles and movement. 

The function of the endocrine system: glands and hormones

The Endocrine system is a series of glands located across the body which release hormones. These enter the bloodstream and send messages to other parts of the body. This is slower than the nervous system but can have stronger and longer lasting effects.

• The Hypothalamus is connected to the pituitary gland and is responsible for stimulating or controlling the release of hormones from the pituitary gland.  Therefore, the hypothalamus is the control system which regulates the endocrine system.

• The pituitary gland is sometimes known as the master gland because the hormones released by the pituitary gland control and stimulate the release of hormones from other glands in the endocrine system. The pituitary gland is also divided into the anterior (front) and posterior (rear) lobes (see right), which release different hormones. A key hormone released from the posterior lobe is oxytocin (often referred to as the ‘love hormone’) which is responsible for uterus contractions during childbirth. A key hormone released from the anterior lobe is adrenocortical trophic hormone (ACTH) which stimulates the adrenal cortex and the release of cortisol, during the stress response.

• The main hormone released from the pineal gland is melatonin, which is responsible for important biological rhythms, including the sleep-wake cycle.

• The thyroid gland releases thyroxine which is responsible for regulating metabolism. People who have a fast metabolism typically struggle to put on weight, as metabolism is involved in the chemical process of converting food into energy.

• The Pancreas releases insulin to lower blood glucose levels and releases glucagon to raise blood glucose levels.

• The adrenal gland is divided into two parts, the adrenal medulla and the adrenal cortex. The adrenal medulla is responsible for releasing adrenaline and noradrenaline, which play a key role in the fight or flight response. The adrenal cortex releases cortisol, which stimulates the release of glucose to provide the body with energy while suppressing the immune system.

• Males and females have different sex organs, and in males the testes release androgens, which include the main hormone testosterone. Testosterone is responsible for the development of male sex characteristics during puberty while also promoting muscle growth. In females, the ovaries release oestrogen which controls the regulation of the female reproductive system, including the menstrual cycle and pregnancy.

The fight or flight response including the role of adrenaline

• Stress is experienced when a person’s perceived environmental, social and/or physical demands exceed their perceived ability to cope.

• The stress response (otherwise known as the ‘fight or flight’ response) is hard-wired into our brains and represents an evolutionary adaptation designed to increase an organism’s chances of survival in life-threatening situations.

The fight or flight response involves two major systems:

• The Sympathomedullary Pathway – deals with acute (short-term, immediate) stressors such as personal attack.

• The Hypothalamic Pituitary-Adrenal System – deals with chronic (long-term, on-going) stressors such as a stressful job.

The Sympathomedullary Pathway (SAM)

• The hypothalamus also activates the adrenal medulla. The adrenal medulla is part of the autonomic nervous system (ANS).

• The ANS is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These activities are generally performed without conscious control.

• The adrenal medulla secretes the hormone adrenaline. This hormone gets the body ready for a fight or flight response. Physiological reaction includes increased heart rate.

• Adrenaline lead to the arousal of the sympathetic nervous system and reduced activity in the parasympathetic nervous system.

• Adrenaline creates changes in the body such as decreases (in digestion) and increases (sweating, increased pulse and blood pressure).

• Once the ‘threat’ is over the parasympathetic branch takes control and brings the body back into a balanced state.

• No ill effects are experienced from the short-term response to stress and it further has survival value in an evolutionary context.

The Hypothalamic Pituitary-Adrenal (HPA) System

• The stressor activates the Hypothalamic Pituitary Axis

• The hypothalamus stimulates the pituitary gland

• The pituitary gland secretes adrenocorticotropic hormone (ACTH)

• ACTH stimulates the adrenal glands to produce the hormone corticosteroid

• The adrenal cortex releases stress hormones called cortisol. This have a number of functions including releasing stored glucose from the liver (for energy) and controlling swelling after injury. The immune system is suppressed while this happens.

• Adequate and steady blood sugar levels help person to cope with prolonged stressor, and helps the body to return to normal

Evaluation

• When faced with a dangerous situation our reaction is not limited to the fight or flight response; some psychologists suggest that humans engage in an initial ‘freeze’ response. Gray (1988) suggests that the first response to danger is to avoid confrontation altogether, which is demonstrated by a freeze response. During the freeze response animals and humans are hyper-vigilant, while they appraise the situation to decide the best course of action for that particular threat.

• The fight or flight response is typically a male response to danger and more recent research suggests that females adopt a ‘tend and befriend’ response in stressful/dangerous situations. According to Taylor et al. (2000), women are more likely to protect their offspring (tend) and form alliances with other women (befriend), rather than fight an adversary or flee. Furthermore, the fight or flight response may be counterintuitive for women, as running (flight) might be seen as a sign of weakness and put their offspring at risk of danger.

• Early research into the fight or flight response was typically conducted on males (androcentrism) and consequently, researchers assumed that the findings could be generalised to females. This highlights a beta bias within this area of psychology as psychologists assumed that females responded in the same way as males, until Taylor provided evidence of a tend and befriend response.

• While the fight or flight response may have been a useful survival mechanism for our ancestors, who faced genuinely life-threatening situations (e.g. from predators), modern day life rarely requires such an intense biological response. Furthermore, the stressors of modern day life can repeatedly activate the fight or flight response, which can have a negative consequence on our health. For example, humans who face a lot of stress and continually activate the sympathetic nervous system, continually increase their blood pressure which can cause damage to their blood vessels and heart disease. This suggests that the fight or flight response is a maladaptive response in modern-day life.

Hormones involved in the response

• Adrenaline increases blood supply to the brain to allow for rapid thought processes. It prepares the body for action via increased blood supply to the muscles. It increases blood flow to these areas by dilating the blood vessels leading to the muscles and brain and by diverting blood away from the skin, kidneys, and digestive system by constricting the blood vessels leading there. It also causes increased perspiration/sweating to cool the body.

• Noradrenaline increases the formation and retrieval of memories and focuses attention. It also increases restlessness and anxiety and promotes vigilance and alertness.

The structure and function of sensory, relay and motor neurons

• Sensory neurons 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 vision, hearing, taste and touch. However, not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.

• Relay neurons are found between sensory input and motor output/response. Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.

• Motor neurons are found in the central nervous system (CNS) and control muscle movements. When motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement. 

As you can see from the diagram above, all three neurons consist of similar parts. The dendrites receive signals from other neurons or from sensory receptor cells. The dendrites are typically connected to the cell body, which is often referred to as the ‘control centre’ of the neuron, as it’s contains the nucleus. The axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal known as action potential, away from the cell body towards the axon terminals, where the neuron ends. Most axons are surrounded by a myelin sheath (except for relay neurons) which insulates the axon so that the electrical impulses travel faster along the axon. The axon terminal connects the neuron to other neurons (or directly to organs), using a process called synaptic transmission. 

The Reflex Arc

• Sensory information is detected by the sensory neuron. This information is taken from the PNS to the CNS.

• Sensory information is delivered to the relay neuron across the synapse between the sensory neuron terminal and the relay neuron dendrite. The relay neuron passes messages across the CNS.

• The motor neurone receives the message from the CNS/relay neuron and transmits this information to an effector. This could be to move a muscle or to release a hormone from a gland.  The processes involving the sensory and motor neurones are faster as these neurones have myelin sheaths across their axons (and sensory across their dendron) which speed up the rate of transmission via saltatory conduction.

The process of synaptic transmission, including reference to neurotransmitters, excitation and inhibition (you can draw a diagram for this in the exam, explain it too)

• Transmission involves impulses crossing a gap/cleft between an axon terminal and an adjacent neuron on the other side of the cleft.

• Neurotransmitters are chemicals released from vesicles on the presynaptic neuron. They diffuse across the synapse and bind to receptor sites on the postsynaptic neuron.

• The action of neurotransmitters at synapses can be:

• Excitatory neurotransmitters make a nerve impulse more likely to be triggered: for example, dopamine or serotonin which produce states of excitement/activity in the nervous system and in our mental state/behaviour.

• Inhibitory neurotransmitters make a nerve impulse less likely to be triggered: for example, GABA calms activity in the nervous system and produces states of relaxation (as with anti-anxiety medication such as Valium).

• The nerve impulse/action potential moves along the presynaptic neuron. When it reaches the axon terminal vesicles within the axon containing neurotransmitters merge with the presynaptic membrane, releasing the neurotransmitters into the synaptic cleft (gap between the presynaptic neuron and the postsynaptic neuron). The neurotransmitter then binds to the postsynaptic neuron’s membrane, generating an action potential in the postsynaptic neuron.

• Psychoactive drugs work by increasing or inhibiting transmission of neurotransmitters across the synapse such as by affecting receptor sites or influencing reuptake of neurotransmitters.

Localisation of function in the brain and hemispheric lateralisation: motor, somatosensory, visual, auditory and language centres; Broca’s and Wernicke’s areas

• The brainstem connects the brain and spinal cord and controls involuntary processes, including our heartbeat, breathing and consciousness.

• The role of the spinal cord is to transfer messages to and from the brain, and the rest of the body. The spinal cord is also responsible for simple reflex actions that do not involve the brain, for example jumping out of your chair if you sit on a drawing pin.

• The two hemispheres of the brain are connected through nerve fibres called the corpus callosum, which facilitate interhemispheric communication: allowing the left and right hemispheres to ‘talk to’ one another.

• The cerebral cortex is the outer layer of the brain.

• Contralateral is the term for the fact that the information for each side of the body is processed by the opposite side of the brain. 

• Some functions are localised whereas other take place in general brain areas.

• The frontal lobe is responsible for your higher decision-making capacity. 

• The parietal lobe integrates information from the different senses and therefore plays an important role in spatial navigation

• The occipital lobe processes visual information. 

• The temporal lobe processes sound. 

• The big gyrus (wrinkle) between the frontal and parietal lobe is called the central sulcus. In the frontal lobe by the central sulcus is the motor cortex. 

• The motor cortex allows you to control all of your voluntary movement. Each part of your body is mapped out to a different part of your motor cortex and some parts are bigger than others. The size of the area is not proportional to the size of the body part it controls. Instead it is proportional to how much control you need to have of that body part. So the area for your hands makes up around ⅓ of the motor cortex. Damage to the frontal cortex causes us to lose control of our fine movements.  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.

• In the part of the temporal lobe next to the central sulcus is the somatosensory cortex, which detects sensory information from all over the body and converts it into physical sensation. 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.

• The visual cortex is just below this area, one in each hemisphere. These deal with sight and visual perception. 

• The auditory centre is in the top part of the temporal lobe and processes information from speech. Damage to this area can lead to loss of hearing. 

• Just behind the auditory centre (in the left temporal lobe) is Wernicke’s area. It is used to interpret the meaning of speech. Damage to this area causes Wernicke’s (receptive) aphasia. This condition prevents people from being able to interpret speech properly and so start to produce nonsense words. 

• Broca’s area is in the left frontal lobe and is responsible for the production of speech. Damage to this area leads to Broca’s (expressive) aphasia which leads to slow speech which lacks fluency. 

Evaluation

• Peterson (1998) used brain scans to show that Wernicke’s area was active in a listening task, and that Broca’s area was active in a reading task, demonstrating that these functions are localised.

• Rougherty (2002) shows lateralisation of brain function in that neurosurgery can treat OCD by cutting the cingulate gyrus

• Equipotentiality theory argues that although basic brain functions such as the motor cortex and sensory functions are controlled by localised brain areas, higher cognitive functions (such as problem-solving and decision-making) are not localised. Research has found that damage to brains can result in other areas of the brain taking over control of functions that were previously controlled by the part of the brain that has been damaged. Therefore, the severity of brain damage is determined by the amount of damage to the brain rather than the particular area which has been damaged.

• The way in which brain areas are connected with each other may be as important for normal cognitive function as particular brain sites themselves. Brain sites are interdependent and damage to connections between sites may lead to the brain site not being able to function normally. For example, Dejerine (1892) found that damage to the connection between the visual cortex and Wernicke’s area lead to an inability to read (vision + comprehension).

• Gender differences have been found with women possessing larger Broca’s and Wernicke’s areas than men, presumably as a result of women’s greater use of language.

Ways of studying the brain: scanning techniques, including functional magnetic resonance imaging (fMRI); electroencephalogram (EEGs) and event-related potentials (ERPs); post-mortem examinations

Functional magnetic resonance (fMRI) A brain scanner which measures increased blood flow to brain sites when individuals are asked to perform cognitive/physical tasks. Increased blood flow indicates increased demand for oxygen in that area. Thus, fMRI can help build up a map of brain localisation. fMRI generates 3D images that can be used to locate the exact source of mental activities within the brain.

Evaluation

• Creates moving picture of brain activity allowing you to see how processes unfold in the brain

• fMRI is a non-invasive technique and does not expose the brain to potentially harmful radiation like PET scans do.

• fMRI only measures blood flow – it does not directly measure neural activity and is not, therefore, a totally objective measure of neural activity in the brain.

• fMRI may overlook the interconnectivity of brain sites. By only focusing on brain sites receiving increased blood flow, it fails to account for the importance of brain sites connecting/communicating with each other.

• Creates a very clear/high resolution image of the brain (resolution is up to 1mm)

• Very expensive

• Machines big and difficult to build

• Person must stay very still

• Takes up to 5 seconds to create the image after the brain activity has occurred

• Consciousness and personality haven’t been found to be localised to any one part of the brain. This is backed up by Lashley (1950) who found that processes involved in higher functions are not localised. Lashley removed 10-50% of the cortex of rat’s brains and found no one area that was more important for learning to navigate a maze.

Electroencephalograms (EEGs) Measures electrical activity of neurones in the brain using electrodes attached to the scalp, and measures how electrical activity in the brain varies over time/in different states (e.g. waking vs. asleep). The amplitude (size) shows the intensity of the activity. Frequency shows the speed. The 4 basic brain wave patterns are (i) alpha – awake and relaxed, (ii) beta – awake and highly aroused or in REM (rapid eye movement sleep), (iii) delta – deep sleep, (iv) theta – light sleep.

Evaluation

• Records brain activity over time and can, therefore, monitor changes as a person switches from task to task or one state to another (e.g. falling asleep). 

• EEGs have medical applications in diagnosing disorders such as epilepsy and Alzheimer’s.

• EEGs only monitor electrical activity in outer layers of the brain, therefore, cannot reveal electrical activity in deeper brain sites

• Not highly accurate – therefore cannot distinguish differences in activity between 2 closely adjacent areas.

Event Related Potential (ERP)- a similar approach to EEGs (same apparatus), but looks at responses to stimuli rather than general activity. Measures small voltages of electrical activity when a stimulus is presented. Because these small voltages are difficult to pick out from other electrical signals in the brain, the stimulus needs to be repeatedly presented (100s of times), and only signals which occur every time the stimulus is presented will be considered an ERP for that stimulus (recordings for each time are added together such that a pattern of response appears as ‘noise’ is cancelled out. This is called ‘averaging’). ERPS are of 2 types: (i) sensory ERPS - those that occur within 100 milliseconds of stimulus presentation; (ii) cognitive ERPS – those that occur 100 milliseconds or more after stimulus presentation. Sensory ERPS indicate the brain’s 1st recognition of a stimulus. Cognitive ERPS represent information processing and evaluation of the stimulus.

Evaluation

• ERPs provide a continuous measure of neural activity in response to a stimulus. Therefore, changes to the stimulus can be directly recorded: e.g. if a blue coloured slide turned green.

• Like the EEG it only takes milliseconds to take a reading, compared to several seconds for the fMRI.

• ERPs only monitor electrical activity in outer layers of the brain, therefore, cannot reveal electrical activity in deeper brain sites.

Postmortems are when the brains of the deceased are dissected after being donated for research. Brains chosen to be dissected are typically those that have had brain trauma, mental illness or some other unusual behaviour that researchers wanted to understand. Often compared to a neurotypical (standard/typical brain) to look for structural differences.

Evaluation

• Allow for detailed examinations and measurement of deep brain structures (e.g. the hypothalamus) not measurable by brain scans.

• Various factors can act as confounding variables and might confuse findings/conclusions. For example, length of time between death and post-mortem, other damage caused to the brain either during death or as a result of disease, age at death, drugs given in months prior to death, etc.

• Modern techniques such as fMRI and EEG have largely replaced post-mortems

• Brain activity cannot be measured as the person is deceased, so can only see the damage and not how it affected the functioning.

Lateralisation is the idea that the two halves of the brain are functionally different and that each hemisphere has functional specialisations, e.g. the left is dominant for language, and the right excels at visual motor tasks.

Split brain research

• Sperry and Gazzaniga (1967) were the first to investigate hemispheric lateralisation with the use of split-brain patients.

• Background: Split-brain patients are individuals who have undergone a surgical procedure where the corpus callosum, which connects the two hemispheres, is cut. This procedure, which separates the two hemispheres, was used as a treatment for severe epilepsy.

• Aim: The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions.

• Method: An image/word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere). When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut).

• Sperry and Gazzaniga conducted many different experiments, including describe what you see tasks, tactile tests, and drawing tasks.

• In the describe what you see task, a picture was presented to either the left or right visual field and the participant had to simply describe what they saw.

• In the tactile test, an object was placed in the patient’s left or right hand and they had to either describe what they felt, or select a similar object from a series of alternate objects.

• Finally, in the drawing task, participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw. 

• Conclusion: The findings of Sperry and Gazzaniga’s research highlights a number of key differences between the two hemispheres. Firstly, the left hemisphere is dominant in terms of speech and language. Secondly, the right hemisphere is dominant in terms of visual-motor tasks.

Evaluation

• Because split-brain patients are so rare, findings as described above were often based on samples of 2 or 3, and these patients often had other neurological problems which might have acted as a confounding variable. Also, patients did not always have a complete splitting of the 2 hemispheres. These factors mean findings should be generalised with care.

• It is assumed that the main advantage of brain lateralisation is that it increases neural processing capacity (the ability to perform multiple tasks simultaneously). Rogers et al. (2004) found that in a domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators). Using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions. This provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks.

• However, because this research was carried out on animals, it is impossible to conclude the same of humans. Unfortunately, much of the research into lateralisation is flawed because the split-brain procedure is rarely carried out now, meaning patients are difficult to come by. Such studies often include very few participants, and often the research takes an idiographic approach. Therefore, any conclusions drawn are representative only of those individuals who had a confounding physical disorder that made the procedure necessary. This is problematic as such results cannot be generalised to the wider population.

• Furthermore, research has suggested that lateralisation changes with age. 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. This raises questions about lateralisation, such as whether everyone has one hemisphere that is dominant over the other and whether this dominance changes with age.

• Finally, it could be argued that language may not be restricted to the left hemisphere. Turk et al. (2002) discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information presented to either side of the brain. This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.

Plasticity and functional recovery of the brain after trauma

Plasticity refers to neurological changes as a result of learning and experience. Although this was traditionally associated with changes in childhood, recent research indicates that mature brains continue to show plasticity as a result of learning.

Evaluation

• Maguire (2002) showed that London taxi drivers had more grey matter in the posterior hippocampus compared to control subjects. This area of the brain is linked to spatial awareness and navigation skills. The amount of change was positively correlated with how long they had been a London taxi driver for.

• Learning and new experiences cause new neural pathways to strengthen whereas neural pathways which are used infrequently become weak and eventually die. Thus brains adapt to changed environments and experiences. Boyke (2008) found that even at 60+, learning of a new skill (juggling) resulted in increased neural growth in the visual cortex.

• Kempermann (1998) found that rats housed in more complex environments showed an increase in neurons compared to a control group living in simple cages. Changes were particularly clear in the hippocampus – associated with memory and spatial navigation.

Compensation

• Functional recovery is the transfer of functions from a damaged area of the brain after trauma to other undamaged areas. 

• The brain is able to do this due to Neuronal unmasking. Wall (1977) noticed the brain contained ‘dormant synapses’ – neural connections which have no function. However, when brain damage occurs these synapses can become activated and open up connections to regions of the brain that are not normally active and take over the neural function that has been lost as a result of damage.

Evaluation

• Teuber (1975) 60% of soldiers <20 showed signs of improvement after trauma like moving affected areas, compared to only 20% of those over 26.

• Danielli (2003) studied a 2 ½ year old boy who had his left hemisphere removed. By 17 (and after rehabilitation) he only had minor language problems as the right hemisphere had compensated.

• Elbert et al concluded that the capacity for neural reorganisation is much greater in children than in adults, meaning that neural regeneration is less effective in older brains. This may explain why adults find change more demanding than do young people. Therefore, we must consider individual differences when assessing the likelihood of functional recovery in the brain after trauma.

• See Kuhn, Kemperman, and Maguire above

• A final strength of research examining plasticity and functional recovery is the application of the findings to the field of neurorehabilitation. Understanding the processes of plasticity and functional recovery led to the development of neurorehabilitation which uses motor therapy and electrical stimulation of the brain to counter the negative effects and deficits in motor and cognitive functions following accidents, injuries and/or strokes. This demonstrates the positive application of research in this area to help improve the cognitive functions of people suffering from injuries.

Biological rhythms: circadian, infradian and ultradian and the difference between these rhythms

The physiological processes of living organisms follow repetitive cyclical variations over certain periods of time. These bodily rhythms have implications for behaviour, emotion and mental processes.

There are 3 types of bodily rhythms:

Circadian rhythms: follow a 24-hour cycle: e.g. the sleep-waking cycle

• Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of the morning (36oC at 4:30 am) and at its highest in the early evening (38oC at 6 pm). Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.

Ultradian rhythms: occur more than once a day: e.g. the cycles of REM and NREM sleep in a single night’s sleep

• With the development of certain scientific equipment, it became possible to study sleep more objectively.

The electroencephalogram (EEG) measures electrical brain activity.

The electrooculogram (EOG) measures eye movement.

The electromyogram (EMG) measures muscle tension.

• These instruments indicate that during a single night’s sleep we experience a cyclical ultradian rhythm of different stages and types of sleep which can be roughly divided into REM (rapid eye movement) and NREM (non-rapid eye movement). REM is strongly associated with dreaming: for example, 80% of sleepers awoken from REM will report that they have been dreaming, whilst the NREM rate is only 15%, and dreams from NREM are reported as less vivid and visual. NREM can be subdivided into stages 1-4.

• Once asleep we enter stage 1 NREM then, over the next half-hour, rapidly descend through stages 2, 3 and 4. As we descend through the stages muscles progressively relax, EEGs become less active, pulse, respiration and blood pressure become slower, and it is progressively more difficult to wake the sleeper. After spending about 30 mins in stage 4 NREM the cycle reverses and we ascend back through the NREM stages 3, 2 and 1. However, instead of waking up we enter our 1st period of REM sleep. During REM, pulse, respiration and blood pressure increase but become less regular and EEG’s resemble those of the waking state - showing the brain to be highly active in terms of blood flow, oxygen consumption and neural firing.

• Major characteristics of REM are that behind the closed lids the eyeballs show rapid movement and the brain shows spontaneous activity that is strongly associated with the experience of dreaming. Firstly, hindbrain and midbrain structures normally associated with relaying visual and auditory stimuli from the outside world spontaneously generate signals: i.e. the brain is acting as if it is hearing and seeing things. Secondly, the motor cortex (responsible for bodily movement) spontaneously generates signals but these are ‘cut off’ at the top of the spine, limb commands are blocked, and we are effectively paralysed from the neck down.

• As stated earlier it is generally assumed that we almost exclusively dream in REM and that NREM is not associated with dreaming. It is possible that we dream in both NREM and REM, but we don’t recall dreams from NREM as we are more ‘deeply’ asleep in this state and dream memories cannot be recalled.

• The EP controlling REM appears to be the locus coeruleus (LC) (a patch of cells located in a brain structure called the pons) which produces noradrenaline and acetylcholine. Destruction of the LC causes REM to disappear. If neurons in a different part of the pons are destroyed, REM remains but muscle paralysis in REM disappears.

• On average, the entire cycle repeats every 90 minutes and a person can experience up to five full cycles in a night.

Infradian rhythms: occur less than once a day: e.g. menstruation (monthly) or hibernation (yearly)

• A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation. Ovulation occurs roughly halfway through the cycle when oestrogen levels are at their highest, and usually lasts for 16-32 hours. After the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus. It is also important to note that although the usual menstrual cycle is around 28 days, there is considerable variation, with some women experiencing a short cycle of 23 days and others experiencing longer cycles of up to 36 days.

• A second example of an infradian rhythm is related to the seasons. Research has found seasonal variation in mood, where some people become depressed in the winter, which is known as seasonal affective disorder (SAD). SAD is an infradian rhythm that is governed by a yearly cycle. Psychologists claim that melatonin, which is secreted by the pineal gland during the night, is partly responsible. The lack of light during the winter months results in a longer period of melatonin secretion, which has been linked to the depressive symptoms.

The effect of endogenous pacemakers and exogenous zeitgebers on the sleep/wake cycle

All bodily rhythms are controlled by an interaction of:

Endogenous pacemakers (EP’s)- Internal biological structures that control and regulate the rhythm.

• The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle.

• The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock). It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal. The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.

• The SCN sends signals to the pineal gland, which leads to an increase in the production of melatonin at night, helping to induce sleep. The SCN and pineal glands work together as endogenous pacemakers; however, their activity is responsive to the external cue of light.

Exogenous zeitgebers (time givers) (EZ’s)- External environmental factors that influence the rhythm.

• The most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24-hour cycle.

• The SCN contains receptors that are sensitive to light and this external cue is used to synchronise the body’s internal organs and glands. Melanopsin, which is a protein in the eye, is sensitive to light and carries the signals to the SCN to set the 24-hour daily body cycle. In addition, social cues, such as mealtimes, can also act as zeitgebers and humans can compensate for the lack of natural light, by using social cues instead.

Circadian Rhythms Evaluation

• The sleep-wake cycle is an example of a bodily process with a circadian rhythm. However, circadian rhythms are also influenced by EZ’s - ‘cues’ in the environment- about what time of day or night it is. In 1975 Siffre spent 6 months underground in an environment completely cut off from all EZ’s. Although he organised his time in regular patterns of sleeping and waking his body seemed to have a preference for a 25 hour rather than a 24-hour cycle. This implies that circadian rhythms are mainly controlled by EP’s rather than EZ’s.

• However, it is important to note the differences between individuals when it comes to circadian cycles. Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6am and 10pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am). This demonstrates that there may be innate individual differences in circadian rhythms, which suggests that researchers should focus on these differences during investigations.

• Additionally, it has been suggested that temperature may be more important than light in determining circadian rhythms. Buhr et al. (2010) found that fluctuations in temperature set the timing of cells in the body and caused tissues and organs to become active or inactive. Buhr claimed that information about light levels is transformed into neural messages that set the body’s temperature. Body temperature fluctuates on a 24-hour circadian rhythm and even small changes in it can send a powerful signal to our body clocks. This shows that circadian rhythms are controlled and affected by several different factors, and suggests that a more holistic approach to research might be preferable.

• Morgan (1955) bred hamsters so that they had circadian rhythms of 20 hours rather than 24. SCN neurons from these abnormal hamsters were transplanted into the brains of normal hamsters, which subsequently displayed the same abnormal circadian rhythm of 20 hours, showing that the transplanted SCN had imposed its pattern onto the hamsters. This research demonstrates the significance of the SCN and how endogenous pacemakers are important for biological circadian rhythms.

• However, this research is flawed because of its use of hamsters. Humans would respond very differently to manipulations of their biological rhythms, not only because we are different biologically, but also because of the vast differences between environmental contexts. This makes research carried out on other animals unable to explain the role of endogenous pacemakers in the biological processes of humans.

• Skene and Arendt (2007) claimed that the majority of blind people who still have some light perception have normal circadian rhythms whereas those without any light perception show abnormal circadian rhythms. This demonstrates the importance of exogenous zeitgebers as a biological mechanism and their impact on biological circadian rhythms.

• Knowing about the body’s circadian rhythms can have practical applications such as when to take drugs and how to counter jet lag and/or shift work.

• 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.

Evaluation of Infradian rhythms

• Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors). Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days. This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.

• There is further evidence to suggest that exogenous zeitgebers can affect infradian rhythms. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them. These findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.

• Evolutionary psychologists claim that the synchronised menstrual cycle provides an evolutionary advantage for groups of women, as the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time.

• There is research to suggest that infradian rhythms such as the menstrual cycle are also important regulators of behaviour. Penton-Volk et al. (1999) found that woman expressed a preference for feminised faces at the least fertile stage of their menstrual cycle, and for a more masculine face at their most fertile point. These findings indicate that women’s sexual behaviour is motivated by their infradian rhythms, highlighting the importance of studying infradian rhythms in relation to human behaviour.

• Finally, evidence supports the role of melatonin in SAD. Terman (1988) found that the rate of SAD is more common in Northern countries where the winter nights are longer. For example, Terman found that SAD affects roughly 10% of people living in New Hampshire (a northern part of the US) and only 2% of residents in southern Florida. These results suggest that SAD is in part affected by light (exogenous zeitgeber) that results in increased levels of melatonin.

Evaluation for ultradian rhythms

• Demont and Kleitman (1957) used an EEG to investigate brain activity during sleep over the course of a night. 9 participants who had not drunk caffeine or alcohol slept in a sleep lab and were tested with the EEG. They were woken at different points. If woken during REM sleep they would report dreams. This helped psychologists understand what occurs during REM sleep.

• Individual Differences: The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles.

• In addition, this study was carried out in a controlled lab setting, which meant that the differences in the sleep patterns could not be attributed to situational factors, but only to biological differences between participants. While this study provide convincing support for the role of innate biological factors and ultradian rhythms, psychologists should examine other situational factors that may also play a role.

• Additionally, the way in which such research is conducted may tell us little about ultradian rhythms in humans. When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors that measure such rhythms. This may be invasive for the participant, leading them to sleep in a way that does not represent their ordinary sleep cycle. This makes investigating ultradian rhythms, such as the sleep cycle, extremely difficult as their lack of ecological validity could lead to false conclusions being drawn.

An interesting case study indicates the flexibility of ultradian rhythms. In 1964 Randy Gardener remained awake for 264 hours. While he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep loss. After this experience, Randy slept for just 15 hours and over several nights he recovered only 25% of his lost sleep. Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very little of the other stages. These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this ultradian rhythm.