Psychology - Biopsychology PMT

The Nervous System 

The nervous system consists of the central nervous system (CNS), made up of the brain and spinal cord, and the peripheral nervous system (PNS), which transmits information from the environment to the CNS via sensory neurones and sends signals from the CNS to effectors via motor neurones.

automatic nervous system

The PNS is divided into the autonomic nervous system, responsible for involuntary vital functions like heart rate and breathing rate, and the somatic nervous system, which receives input from sensory receptors of the five senses and stimulates effectors through motor neurones.

sympathetic and parasympathetic branches

The autonomic nervous system is further split into the sympathetic and parasympathetic branches, which function as an antagonistic pair during the ‘rest and digest’ response and help generate the physiological arousal required for the fight-or-flight response.

The sympathetic branch increases heart rate, breathing rate, causes vasoconstriction and pupil dilation, whereas the parasympathetic branch decreases heart rate, breathing rate, causes vasodilation and pupil constriction.

The Endocrine System

The endocrine system is the body’s main chemical messenger system, where glands secrete hormones into the bloodstream, which are then carried to target cells with complementary receptors.

The pituitary gland is known as the ‘master’ gland because it regulates hormone release from all other glands.

For instance, the thyroid gland releases thyroxine, which increases heart rate and promotes growth, while the adrenal gland secretes adrenaline, producing physiological arousal before the fight-or-flight response by increasing activity in the sympathetic branch of the nervous system.

Fight or Flight Response

When the body detects a stressor in the environment, such as the sound of a speeding car, sensory receptors send this information via sensory neurones in the PNS to the hypothalamus, which coordinates a response by increasing activity in the sympathetic branch of the autonomic nervous system.

The adrenal medulla in the adrenal glands then releases adrenaline, which is carried through the bloodstream to target effectors via the endocrine system.

This leads to bodily changes such as rectum contraction, inhibition of saliva production and an increase in breathing rate, creating the physiological arousal necessary for the fight-or-flight response, whose purpose is to help us escape danger and enhance survival.

Once the stressor is no longer present, the hypothalamus reduces sympathetic activity and increases parasympathetic activity, initiating the ‘rest and digest’ response, which counteracts the earlier changes.

Neurons and Synaptic Transmission

Synaptic transmission is how neurones communicate — sending information to the CNS through sensory neurones and sending responses to effectors through motor neurones.

When an action potential reaches the presynaptic membrane, it opens calcium ion channels, allowing calcium ions to enter the neurone.

This causes vesicles containing neurotransmitters to move towards and fuse with the presynaptic membrane, releasing their contents into the synaptic cleft by exocytosis.

The neurotransmitters then diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane, creating either an excitatory or inhibitory effect.

If the stimulation is strong enough, a new action potential is generated in the next neurone, continuing the signal.

Inhibitory neurotransmitters (e.g. serotonin) make a new action potential less likely by closing sodium ion channels, while excitatory neurotransmitters (e.g. dopamine) make it more likely by opening more sodium ion channels.

Localisation of Function in the Brain

Localisation theory suggests that certain areas of the brain are responsible for certain processes, behaviours and activities.

The motor area

Separated from the auditory area by the central suclus and found in the frontal lobe, this area is involved in regulating and coordinating movements. Lesions or damage in the motor area result in an inability to control voluntary fine motor movements.

The auditory area

An area of the temporal lobe, located on the superior temporal gyrus, which is responsible for processing auditory information and speech. Lesions or damage in the auditory area causes hearing loss, whereas damage to specific parts of the auditory area (Wernicke’s area) results in Wernicke’s aphasia.

The visual area

An area in the occipital lobe which is responsible for processing visual information.

The somatosensory area

An area of the parietal lobe which processes information associated with the senses e.g. touch, heat, pressure etc. Lesions in this area result in a loss of ability to denote sensitivity to particular bodily areas.

Wernicke’s Area

Responsible for speech comprehension and located in the temporal lobe (the left temporal lobe for most people). Lesions or damage (e.g. through stroke and trauma) results in Wernicke’s aphasia, which is characterised by the use of nonsensical words (called syllogisms), no awareness of using incorrect words, but no issues with pronounciation and intonation.

Broca’s area

Responsible for speech production and located in the frontal lobe, usually in the left hemisphere. Lesions or damage results in Broca’s aphasia, characterised by difficulty forming complete sentences and understanding sentences, as well as failing to understand the order of words in a sentence and who they are directed towards i.e. I, you, we, him, me etc

Overall, the left hemisphere of the brain is associated with language production and comprehension. Therefore, language is an example of a cognitive ability which is both localised and lateralised (to the left hemisphere).

Evaluation of localisation of brain function

There is evidence supporting localisation of brain function. Tulving et al. used PET scans to show that semantic and episodic memories are recalled from different sides of the prefrontal cortex. Petersen et al. (1988) similarly found that Wernicke’s area is involved in listening tasks and Broca’s area in reading tasks, confirming their distinct roles in speech comprehension and production.

Case studies such as Phineas Gage also support localisation, as damage to his prefrontal cortex led to changes in decision-making and emotional processing. However, case studies lack control and rely on small, unique samples, limiting generalisability.

A contrasting holistic view argues that complex functions involve multiple brain areas. For example, removing large sections of rat cortices did not impair maze learning, suggesting learning is too complex to be localised. Therefore, localisation may better explain simple functions than complex ones.

Further support comes from practical evidence: Dougherty et al. (2002) found that cingulotomy improved symptoms in 32–45% of OCD patients, suggesting specific brain areas contribute to OCD and that localisation research aids treatment development.

Plasticity and Functional Recovery of the brain after trauma - what is plasticity

Refers to the brain’s ability to physically and functionally adapt and change in response trauma, new experiences and learning. Neuroplasticity was demonstrated by Maguire et al (2006).

Maguires evidence

After studying the brains of London taxi drivers, Maguire et al. found a larger grey matter volume in the mid-posterior hippocampi ( and a lower volume in the anterior hippocampi) of their brains, alongside a positive correlation between an increasing grey matter volume and the longer the individuals had been taxi drivers. This may be because the hippocampus is associated with spatial awareness; an ability which taxi drivers must have when they complete The Knowledge test.

Functional Recovery

the ability of the brain to transfer the functions of areas damaged through trauma, to other healthy parts of the brain, thus allowing for normal functioning to carry on.

This is enabled through the law of equipotentiality (where secondary neural circuits surrounding the damaged area become activated), axonal sprouting (formation of new synapses and strengthening of axonal connections between damaged and healthy areas), reformation of blood vessels (as part of the haemodynamic response, where activated areas experience a higher blood deoxygenation level) and recruiting homologous areas on the opposite side of the brain. 

This means that function is not always lateralised to specific hemispheres.

Examples of functional recovery

The case of Jodi Miller, who had her entire right hemisphere removed to treat epilepsy, shows positive plasticity. Despite the removal, she regained control of the right side of her body through the brain’s ability to reorganise using cerebrospinal fluid pathways, showing neuroplasticity can also produce beneficial outcomes.

Evaluation of plasticity and functional recovery

There is evidence for positive effects of neuroplasticity. Positive plasticity is seen in the case of Jodi Miller, who recovered movement after having her right hemisphere removed by recruiting homologous brain areas, axonal sprouting and blood vessel reformations. This shows that plasticity can be adaptive.

Animal studies also support plasticity. Hubel and Wiesel (1970) sutured one eye of kittens and found that even without input to the right eye, the left visual cortex showed activity, with ocular dominance columns shifting to compensate. This suggests unstimulated brain areas can take over functions of more active areas.

Cognitive reserve further influences recovery. Schneider et al. (2014) found that patients with more years in education were more likely to achieve disability-free recovery after trauma, suggesting individuals with higher cognitive reserve form neuronal connections more efficiently, aiding functional recovery.

However, there are limits to spontaneous recovery. Although the brain can activate secondary neural circuits after injury, full recovery often requires intervention. Liepert et al. (1998) found stroke patients improved significantly only after constraint-induced movement therapy, suggesting functional recovery cannot be relied on without rehabilitation support.

Split brian research into hemispheric lateralisation - what is hemispheric lateralisation

The idea that each hemisphere (half) of the brain is mainly responsible for certain behaviours, processes and activities. This is in contrast with the holistic theory of brain function, which suggests that function is distributed across the whole brain (i.e. is global).

Split brain research

Each visual field is split into left and right, with the right hemisphere controlling the left side of the body and vice versa.

This means information from the left visual field is processed by the right hemisphere, which then coordinates responses on the left side of the body.

Sperry and Gazzaniga (1968) investigated this through split-brain research on 11 epileptic patients who had undergone corpus callosum lesioning (cerebral commissurotomy), preventing communication between the hemispheres.

This allowed researchers to present stimuli to one hemisphere at a time and assess its independent function. To ensure this, one eye was covered and images were shown for one-tenth of a second so only one visual field processed the information. The study was conducted under highly controlled laboratory conditions.

Procedure and results of split brain research

Describing what you see: When a stimulus word is shown to the right visual field, it is processed by the left hemisphere, which contains language centres, so the patient can say the word. If shown to the left visual field, it is processed by the right hemisphere, which lacks language centres but has visuo-spatial centres, so the patient can write the word with their left hand but cannot verbally describe it.

Matching words or faces: The right hemisphere dominates face-matching tasks due to its visuo-spatial centres, allowing visual identification and processing.

Words presented simultaneously: When two words are shown at once, the patient says the word in the right visual field (left hemisphere) and writes the word in the left visual field (right hemisphere).

Recognizing objects in the hands: Objects in the right hand (left hemisphere) cannot be identified because the left hemisphere lacks visuo-spatial processing, whereas objects in the left hand (right hemisphere) can be identified and matched to similar objects due to visuo-spatial centres.

Evaluation of split brain research

+Split-brain research showed clear lateralisation of function, opposing holistic brain theories. The left hemisphere dominates language tasks (the analyser), while the right hemisphere dominates visuo-spatial tasks (the synthesiser), highlighting marked functional differences between the two hemispheres.

+Split-brain research supported the ‘dual mind’ idea, showing each hemisphere represents a distinct side of the mind. However, Pucetti (1980) critiqued the work, noting that retinal anatomy means visual stimuli do not always project as assumed, sparking debate about the physiological and theoretical basis of brain function.

-Functional differences between hemispheres are not always clear-cut. While the left is often labelled the language analyser and the right the visuo-spatial synthesiser, cases such as left-handed split-brain patients using the right hemisphere for speech show that each hemisphere can compensate via homologous areas. Therefore, hemispheric functions are not strictly fixed.

Ways of investigating the brain: ERPs

Event-related potentials (ERPs) are brainwaves triggered by specific sensory, motor, or cognitive events. They are isolated from EEG data using statistical averaging, which filters out unrelated brain activity, leaving only responses linked to a particular stimulus or task.

Evaluation of ERPs

+ Excellent Temporal Resolution-Neural processes are measured more specifically than in an EEG.

+Widely used in the measurement of cognitive deficits and functions.

-Lack of standardisation in ERP methodology in different research studies.

-Background noise and extraneous material can be an obstacle.

Ways of investigating the brain: fMRI scans

fMRI relies on the haemodynamic response. Active brain areas need more oxygenated blood, increasing deoxyhaemoglobin levels. This deoxyhaemoglobin absorbs the scan signal, causing highly active areas to appear brightly coloured on the fMRI image.

Evaluation of fMRI scans

+ High spatial resolution as up to 4 images can be produced per second.

+ Can be used whilst a patient is carrying out a task, and so data from fMRI scans can help us to make inferences about brain function and localisation.

+ Does not use ionising radiation, unlike PET scans, and so is safer.

— Poor temporal resolution because there is approximately a 5 second difference between neuronal activity and the produced image.

Ways of investigating the brain: EEGs

Through the use of electrodes attached to the scalp, EEG scans measures and amplifies the electric activity across the whole brain i.e. action potentials being transmitted across the axons of neurons.

Evaluation of EEGs

+ Particularly useful in investigating the characteristics of the different stages of sleep, as demonstrated by Dement and Kleitman.

+ Much higher temporal resolution than fMRI scans, and so more appropriate for the monitoring of ongoing cerebral states and activity.

— Lower spatial resolution compared to fMRI scans, with particular difficulty in differentiating activity between adjacent areas.

+ Useful in the diagnosis of epilepsy, which is characterised by random bursts of activity.

Ways of investigating the brain: post-mortem examinations

These involve a comparison of the patient’s brain with that of a healthy, neurotypical brain. Any differences (e.g. lesions, damage, abnormally large or small areas) are assumed to have caused the neruological problem the patient faced in their lifetime.

Evaluation of post-mortem examinations

— Incorrectly makes the assumption that differences compared with the neurotypical brain must be the explanation for neurological or cognitive deficits. Prolonged drug use, stress and genetic factors may be other plausible explanations.

— Ethical issues arise because informed consent cannot always be obtained before the patient dies or from the family. The patient may be unable to give informed consent e.g. HM suffered from deficits in his short-term memory, and so would not remember having signed the document.

+ Particularly useful for advancing medical knowledge, and being the basis of further research into certain areas of the brain e.g. Broca used a post-mortem examination on his patient Tan, which led to the identification of Broca’s area and was the foundation of further research into the theory of the localisation of brain function.

Biological Rhythms

Biological rhythms are periodic fluctuations in an organism that respond to environmental changes, including core body temperature, attention, and the sleep-wake cycle.

They can be endogenous (controlled by internal clocks, e.g., the suprachiasmatic nucleus) or exogenous (controlled by external cues, e.g., sunlight). The three main types are circadian, infradian, and ultradian rhythms.

Exogenous zeitgebers

External changes in the environment which affect or ‘entrain’ our biological rhythms.

Circadian rhythms

A type of biological rhythm which completes one full cycle every 24 hours e.g. the sleep-wake cycle. Like other biological rhythms, it is affected by both endogenous pacemakers and exogenous zeitgebers.

example of exogenous zeitgeber

Light. Changes in light exposure can trigger desynchronisation of a ‘pre-set’ sleep-wake cycle.

Study into circadian rhythms

Siffre (1962) spent two months in a cave without natural light, losing track of calendar dates. His sleep-wake cycle extended to about 24.5 hours, showing that, without exogenous cues like sunlight, circadian rhythms are ‘free-running’ and regulated by an internal clock independent of the 24-hour day.

Evaluation of research into circadian rhythms

Individual differences: Circadian rhythms vary between people. For example, delaying school start times to 10 AM at Monkseaton High improved GCSE results, showing teenagers’ rhythms often differ from adults’ and can affect performance.

Artificial light as a confound: Czeisler et al. (1999) showed artificial light can shift circadian rhythms by up to 6 hours, suggesting Siffre’s cave studies may not have fully represented a truly ‘free-running’ rhythm.

Health impacts of desynchronisation: Shift work is linked to obesity, high triglycerides, and low HDL cholesterol (Karlsson et al., 2001), demonstrating how circadian disruption affects metabolism and health, with practical and economic implications for workplaces.

Limitations of case studies: Siffre’s studies used small, isolated samples and may lack ecological validity. Individual differences (e.g., changes in Siffre’s internal clock with age) could act as uncontrolled confounding variables, limiting generalisability.

Infradian rythm

One of 3 types of biological rhythms, with a frequency of one complete cycle occurring longer than 24 hours. Such rhythms are entrained by endogenous pacemakers and exogenous zeitgebers. Notable examples of infradian rhythms include the menstrual cycle and SAD (seasonal affective disorder).

Menstrual cycle

McClintock et al. (1998) showed menstrual cycle synchronisation in 29 women with irregular periods.

Pheromones collected from 9 women’s armpits were applied to the upper lips of the remaining 20.

Recipients’ cycles shortened when exposed to follicular-phase compounds (+1.7 ± 0.9 days) and lengthened when exposed to ovulatory-phase compounds (+1.4 ± 0.5 days), demonstrating the influence of pheromones on cycle timing.

SAD

Seasonal affective disorder is an example of the influence of endogenous pacemakers on the circadian sleep-wake cycle.

SAD is an infradian disorder caused by disruption to the sleep-wake cycle, and commonly occurs in the winter. Longer nights means that more melatonin is secreted from the pituitary gland, via the endocrine system, which changes the production of melatonin, leading to feelings of loneliness and depression

Ultradian rhythm

One of 3 types of biological rhythms, with a frequency of one complete cycle occurring more than once every 24 hours. A notable example are the stages of sleep, where a full sleep cycle takes 90 minutes to complete

Stages of sleep

Stages 1 and 2 represent the ‘sleep escalator’ where the participant can easily be awoken, stages 3 and 4 coincide with deeper and slower delta waves (compared to theta waves during the sleep escalator), whilst stage 5 represents REM sleep.

REM sleep is closely associated with dreaming and characterised by movement inhibition and a sensory blockade. The stages of sleep have been demonstrated by Dement and Kleitman

Evaluation of Infradian and Ultradian rhythms

Sleep stages: Dement and Kleitman (1957) demonstrated distinct sleep stages using EEG in 33 adults with controlled caffeine and alcohol intake. REM sleep was consistently recorded, and participants accurately recalled dreams when awoken during REM, linking dreaming to this stage.

Menstrual synchronisation limitations: Trevathan et al. (1993) found no evidence of menstrual synchronisation in all-female samples, suggesting extraneous factors (e.g., smoking, physical activity, alcohol) may affect cycles. McClintock et al.’s findings on pheromones are therefore less conclusive.

SAD treatment dispute: Gloth et al. (1999) found vitamin D supplements improved depression in SAD sufferers, whereas bright-light phototherapy did not, suggesting melatonin and serotonin may have limited roles in circadian rhythm entrainment for SAD.

Animal studies supporting pheromones: Luo et al. (2003) showed that pheromones in mice encode social and reproductive information via the vomeronasal system, indicating that endogenous pacemakers are crucial for entraining biological rhythms, with potential parallels to humans.

Endogenous pacemakers

Internal bodily regulators of biological rhythms, affecting or ‘entraining’ such biological rhythms to conform to certain cyclical periods e.g. one cycle every 24 hours for circadian rhythms.

SCN

The suprachiasmatic nucleus (SCN) receives light information from the eyes via the optic chiasm after processing in the occipital lobe. It regulates melatonin release from the pineal gland: high melatonin at night (low light) reduces serotonin, causing sleepiness, while low melatonin during the day (high light) increases serotonin, promoting wakefulness.

Study supporting SCN

Morgan bread mutant hamsters with circadian rhythms of 20 hrs.

Then transplated SCN from mutant hamsters to normal hamsters.

Normal hamsters then displayed circadian rhythms of 20 hrs.

SCN transplanted from normal hamsters to mutant hamsters changed their circadian rhythms back to 24hrs.

This confirms the importance of SCN in setting circadian rhythms.

Exogenous zeitgebers

External environmental changes, affecting or ‘entraining’ biological rhythms to conform to certain cyclical time periods.

Examples of exogenous zeitgebers

Exogenous zeitgebers, such as social cues like meal and bed times, help entrain biological rhythms and can reduce jet lag by aligning sleep and eating schedules with a new environment.

Light also acts as an exogenous zeitgeber: Siffre (1967) and Campbell & Murphy showed that exposing light to non-eye areas, like the back of the knees, can shift sleep-wake cycles by up to three hours.

Evaluation of endogenous pacemakers and exogenous zeitgebers

SCN influence: Damiola et al. showed that mouse liver cells can maintain a 12-hour shifted rhythm independently of the SCN, and similar ‘peripheral oscillators’ exist in organs like the adrenal glands and lungs, suggesting the SCN’s role may be less central than once thought.

Ethical and generalisation issues: Animal studies, such as DeCoursey et al., raise ethical concerns due to potential harm, and physiological differences between animals and humans limit the generalisability and ecological validity of findings on circadian rhythms.

Limits of entrainment: Cases like Miles et al. (1977), where a man’s 24.9-hour sleep-wake cycle could not be altered by stimulants or sedatives, indicate that the effects of exogenous zeitgebers and endogenous pacemakers may sometimes be overestimated.