Biopsychology

Introduction

Biopsychology (also called biological psychology or behavioural neuroscience) examines how biological structures and processes influence behaviour and mental processes. This section covers the structure and function of the nervous system, neurons and synaptic transmission, localisation of function in the brain, plasticity and functional recovery, methods of studying the brain, and biological rhythms.

Key Concepts

The Nervous System

The nervous system is a complex network of cells that carries information throughout the body. It is divided into two main systems:

1. Central Nervous System (CNS):

• Brain: The centre of conscious awareness and higher cognitive functions. Composed of the cerebral cortex (responsible for higher mental functions), cerebellum (motor coordination and balance), and brainstem (vital functions: breathing, heart rate).
• Spinal cord: A bundle of nerve fibres that connects the brain to the peripheral nervous system. Responsible for simple reflexes (fast, involuntary responses that bypass the brain) and relaying information between the brain and the body.

2. Peripheral Nervous System (PNS):

• Somatic nervous system: Controls voluntary movement of skeletal muscles and receives sensory information from the external environment.
• Autonomic nervous system (ANS): Controls involuntary functions (heart rate, digestion, breathing). Divided into:
  • Sympathetic nervous system: Activates the body for action (“fight or flight”). Increases heart rate, dilates pupils, inhibits digestion, releases adrenaline.
  • Parasympathetic nervous system: Returns the body to a calm, resting state (“rest and digest”). Decreases heart rate, constricts pupils, stimulates digestion.

The fight or flight response:

1. A threat is perceived.
2. The hypothalamus activates the sympathetic branch of the ANS.
3. The adrenal medulla releases adrenaline and noradrenaline.
4. Physiological changes: increased heart rate, increased blood flow to muscles, dilated pupils, increased sweating, inhibited digestion.
5. Once the threat passes, the parasympathetic nervous system returns the body to its resting state.

Neurons

Neurons are nerve cells that transmit electrical and chemical signals throughout the nervous system. There are approximately 86 billion neurons in the human brain.

Structure of a neuron:

• Cell body (soma): Contains the nucleus and genetic material.
• Dendrites: Branch-like structures that receive signals from other neurons.
• Axon: A long fibre that carries electrical impulses away from the cell body.
• Myelin sheath: A fatty layer that insulates the axon, speeding up transmission. Gaps in the myelin sheath are called nodes of Ranvier — the impulse “jumps” between these nodes (saltatory conduction).
• Axon terminals (terminal buttons): Branches at the end of the axon that connect to other neurons or to muscles/glands.

Types of neurons:

• Sensory (afferent) neurons: Carry information from the senses (receptors) to the CNS. Long dendrites, short axons.
• Relay (inter) neurons: Connect sensory and motor neurons within the CNS. Short dendrites and short axons. Make up approximately 97% of all neurons.
• Motor (efferent) neurons: Carry signals from the CNS to muscles and glands. Short dendrites, long axons.

Electrical transmission: Neurons transmit signals electrically within the cell. At rest, the inside of the neuron is negatively charged relative to the outside (resting potential, approximately −70mV). When stimulated, the membrane becomes permeable to sodium ions, which rush in, depolarising the cell. This creates an action potential — an electrical impulse that travels along the axon. After firing, the neuron enters a brief refractory period during which it cannot fire again, ensuring impulses travel in one direction only.

Synaptic Transmission

A synapse is the junction between two neurons. The tiny gap between them is the synaptic cleft. Neurons do not physically touch — signals are transmitted chemically across the synapse.

Process:

1. An electrical impulse (action potential) reaches the axon terminal.
2. This triggers the release of neurotransmitters from tiny sacs called vesicles.
3. Neurotransmitters diffuse across the synaptic cleft and bind to receptor sites on the postsynaptic neuron.
4. The neurotransmitter either excites the postsynaptic neuron (making it more likely to fire) or inhibits it (making it less likely to fire).
5. The signal is terminated by reuptake (the neurotransmitter is reabsorbed by the presynaptic neuron), enzymatic degradation (the neurotransmitter is broken down by enzymes), or diffusion (the neurotransmitter drifts away from the synapse).

Key neurotransmitters:

Neurotransmitter	Function	Effect
Serotonin	Mood regulation, sleep, appetite	Generally inhibitory — low levels associated with depression
Dopamine	Reward, motivation, voluntary movement	Generally excitatory — high levels associated with schizophrenia
Acetylcholine (ACh)	Muscle contraction, memory, attention	Excitatory — involved in the neuromuscular junction; low levels in Alzheimer’s
Noradrenaline	Arousal, alertness, fight or flight	Excitatory — involved in stress response
GABA	Anxiety reduction, relaxation	Inhibitory — the brain’s main inhibitory neurotransmitter

Excitatory and inhibitory neurotransmitters: Excitatory neurotransmitters (e.g., glutamate) increase the likelihood that the postsynaptic neuron will fire. Inhibitory neurotransmitters (e.g., GABA) decrease the likelihood of firing. The net effect on the postsynaptic neuron depends on the sum of excitatory and inhibitory inputs — this is called summation.

Localisation of Function

The principle that specific areas of the brain are responsible for specific functions. This contrasts with the holistic theory (Flourens, Lashley), which proposed that all parts of the brain contribute equally to all functions.

The cerebral cortex is divided into four lobes:

Frontal lobe:

• Motor cortex (precentral gyrus): Controls voluntary movement. The body is represented contralaterally (the left motor cortex controls the right side of the body and vice versa) and disproportionately (more cortex is devoted to areas requiring fine motor control, such as the hands and face — the motor homunculus).
• Broca’s area (left frontal lobe): Speech production. Damage causes Broca’s aphasia — slow, non-fluent speech with difficulty finding words but good comprehension. Identified by Paul Broca (1861) from his patient “Tan” (who could only say the word “tan”).

Parietal lobe:

• Somatosensory cortex (postcentral gyrus): Processes sensory information from the skin (touch, temperature, pain). Like the motor cortex, it is contralateral and has a sensory homunculus.

Temporal lobe:

• Auditory cortex: Processes auditory information. Different regions respond to different frequencies.
• Wernicke’s area (left temporal lobe): Language comprehension. Damage causes Wernicke’s aphasia — fluent but meaningless speech with poor comprehension. Identified by Carl Wernicke (1874).

Occipital lobe:

• Visual cortex: Processes visual information from the eyes. Different regions process different aspects of vision (colour, motion, shape).

Other important areas:

• Hypothalamus: Regulates the pituitary gland, hunger, thirst, temperature, and the autonomic nervous system.
• Amygdala: Processes emotional responses, particularly fear and aggression.
• Hippocampus: Essential for forming new long-term memories and spatial navigation.
• Basal ganglia: Motor control, procedural learning, habit formation.
• Cerebellum: Balance, coordination, and fine motor control.

Evidence for localisation:

• Case studies: Phineas Gage (1848) — an iron rod passed through his frontal lobe, destroying it. He survived but his personality changed dramatically (from responsible and well-mannered to impulsive and aggressive), demonstrating the role of the frontal lobe in personality and decision-making.
• Broca and Wernicke: Patients with specific brain damage showed specific language deficits, supporting localisation of language functions.
• Brain scanning: fMRI and PET studies show specific brain regions are active during specific tasks.

Evaluation: Evidence from brain scanning and case studies supports localisation. However, Lashley’s (1950) research on rats found that memory was not localised to a single area but distributed across the cortex. The brain often works holistically, with multiple areas contributing to complex functions. Furthermore, there is significant individual variation in the precise location of functional areas.

Plasticity and Functional Recovery

Plasticity refers to the brain’s ability to change and adapt as a result of experience. This occurs throughout life but is greatest during childhood.

Types of plasticity:

• Synaptic plasticity: The strengthening or weakening of synaptic connections. Repeated stimulation leads to long-term potentiation (LTP) — the strengthening of synaptic connections, which is the neural basis of learning. Lack of stimulation leads to long-term depression (LTD) — the weakening of connections.
• Structural plasticity: Physical changes in brain structure, such as the growth of new dendrites, the formation of new synapses (synaptogenesis), or changes in the size of brain regions.

Evidence:

• Maguire et al. (2000) found that London taxi drivers had significantly larger posterior hippocampi than control participants, and the size of the hippocampus correlated with the number of years spent driving. This was attributed to the extensive spatial navigation required by “The Knowledge” (the test of London streets that taxi drivers must pass).
• Draganski et al. (2004) found that medical students showed increases in grey matter in the posterior hippocampus and parietal cortex after three months of intensive studying for exams.
• Professional musicians have a larger auditory cortex and more developed motor cortex areas for finger control than non-musicians.

Functional recovery after trauma: Following brain damage (e.g., from stroke, injury), the brain can reorganise itself to recover lost functions. This occurs through several mechanisms:

• Axonal sprouting: New nerve endings grow from surviving neurons to connect with damaged areas.
• Recruitment of homologous areas: The equivalent area on the opposite side of the brain takes over the function (e.g., if Broca’s area is damaged on the left, the corresponding area on the right may take over language production).
• Neural reorganisation: Surviving neurons reorganise their connections to compensate for damaged ones.
• Diaschisis: The shock to the brain immediately after injury causes wider dysfunction than the damage alone. As this shock wears off, some functions may return.

Recovery is most effective in the first few months after injury and is more complete in younger individuals. However, the capacity for recovery is limited, and not all functions are recovered.

Ways of Studying the Brain

Method	How it works	What it measures	Strengths	Limitations
fMRI (functional Magnetic Resonance Imaging)	Detects changes in blood oxygenation; active brain areas use more oxygen	Brain activity in real time	Non-invasive; high spatial resolution; no radiation	Expensive; poor temporal resolution; cannot establish causation
EEG (Electroencephalogram)	Electrodes on scalp detect electrical brain activity	General brain activity patterns	Non-invasive; high temporal resolution (real-time)	Poor spatial resolution; cannot identify deep brain activity
ERP (Event-Related Potentials)	EEG data filtered to show responses to specific stimuli	Brain responses to specific events	High temporal resolution; useful for studying cognitive processes	Requires many trials; background noise; poor spatial resolution
Post-mortem examination	Physical examination of the brain after death	Brain structure and abnormalities	Detailed anatomical analysis; can study areas deep in the brain	Cannot study living brain function; cause of death may affect results; retrospective
CAT (Computerised Axial Tomography)	X-rays taken from multiple angles to create cross-sectional images	Brain structure	Good for identifying tumours, lesions, and structural damage	Involves radiation; only shows structure, not function

Biological Rhythms

Circadian rhythms: 24-hour cycles. The sleep-wake cycle is the most well-studied circadian rhythm.

• Endogenous pacemakers (internal clocks): The suprachiasmatic nucleus (SCN) in the hypothalamus is the body’s master clock. It receives light information via the optic nerve (even in blind individuals, some light-detecting cells in the retina project to the SCN). The SCN regulates melatonin production by the pineal gland — melatonin promotes sleepiness and is produced in darkness.
• Exogenous zeitgebers (external time-givers): Light is the primary zeitgeber. Other zeitgebers include social cues (mealtimes, work schedules), temperature, and exercise.

Evidence:

• Siffre (1975) spent 6 months in a cave with no external time cues. His circadian rhythm settled to approximately 25 hours (slightly longer than 24 hours), demonstrating the role of endogenous pacemakers and the need for zeitgebers to entrain the rhythm to 24 hours.
• Aschoff and Wever (1976) placed participants in a bunker with no external time cues. Most settled into a rhythm of 24–25 hours, but some extended to 29 hours, supporting the role of endogenous pacemakers.

Ultradian rhythms: Cycles shorter than 24 hours. The sleep cycle is the most studied ultradian rhythm. Sleep consists of five stages:

• Stage 1: Light sleep; theta waves; easy to wake.
• Stage 2: Deeper sleep; sleep spindles and K-complexes.
• Stage 3: Deep sleep; delta waves begin.
• Stage 4: Deepest sleep; delta waves; growth hormone released; hard to wake.
• REM (Rapid Eye Movement) sleep: Brain activity similar to waking; dreaming occurs; muscles paralysed (atonia).

One complete sleep cycle takes approximately 90 minutes. Across the night, REM periods lengthen and deep sleep periods shorten.

Infradian rhythms: Cycles longer than 24 hours. The menstrual cycle is the best example, lasting approximately 28 days. Regulated by the interaction of hormones (oestrogen, progesterone, FSH, LH) from the pituitary gland and ovaries.

McClintock and Stern (1998): Found that women’s menstrual cycles synchronised when living in close proximity, suggesting the presence of pheromones (chemical signals) as an exogenous influence. However, this finding has been challenged by subsequent research (e.g., Yang and Schank, 2006).

Seasonal affective disorder (SAD): A type of depression that follows a seasonal pattern, commonly occurring in winter when daylight hours are short. Treated with phototherapy (bright light exposure), supporting the role of the zeitgeber light in regulating mood and circadian rhythms.

Key Studies

Study	Researcher(s)	Year	Method	Key Findings	Evaluation
Taxi drivers	Maguire et al.	2000	Natural experiment (MRI)	Taxi drivers had larger posterior hippocampi; size correlated with driving experience	Supports plasticity; correlational; small sample; individual differences
Broca’s patient Tan	Broca	1861	Case study	Patient could understand language but not speak; damage to left frontal lobe	Supports localisation; single case; other areas also involved in speech
Cave study	Siffre	1975	Case study (self-experiment)	Circadian rhythm extended to 25 hours without external cues	Supports endogenous pacemakers; single participant; individual differences
Brain plasticity in students	Draganski et al.	2004	Longitudinal (MRI)	Medical students showed increased grey matter after studying	Supports plasticity; small sample; specific learning context
Kennard principle	Kennard	1938	Case studies (monkeys)	Younger monkeys recovered more function after brain damage	Supports age-dependent recovery; animal research; limited generalisability
SCN and circadian rhythms	Morgan	1995	Animal experiment	SCN-lesioned hamsters lost circadian rhythms; transplanted SCN from donors restored them	Strong evidence for SCN as master clock; animal research; ethical concerns

Key Terminology

Term	Definition
Central nervous system	The brain and spinal cord
Peripheral nervous system	All nerves outside the CNS (somatic and autonomic)
Autonomic nervous system	Controls involuntary functions (heart rate, digestion)
Sympathetic nervous system	Activates the body for fight or flight
Parasympathetic nervous system	Returns the body to a resting state
Neuron	A nerve cell that transmits electrical and chemical signals
Synapse	The junction between two neurons
Neurotransmitter	A chemical messenger that transmits signals across a synapse
Action potential	An electrical impulse that travels along a neuron
Myelin sheath	A fatty insulating layer around the axon that speeds up transmission
Localisation of function	The principle that specific brain areas are responsible for specific functions
Plasticity	The brain’s ability to change and adapt through experience
Functional recovery	The brain’s ability to recover function after damage
Circadian rhythm	A biological rhythm with a period of approximately 24 hours
Ultradian rhythm	A biological rhythm with a period shorter than 24 hours
Infradian rhythm	A biological rhythm with a period longer than 24 hours
Endogenous pacemaker	An internal biological clock (e.g., the SCN)
Exogenous zeitgeber	An external cue that synchronises biological rhythms (e.g., light)
SCN (suprachiasmatic nucleus)	The master biological clock in the hypothalamus
Melatonin	A hormone that promotes sleepiness, produced by the pineal gland

Evaluation Points

Strengths of the Biological Approach

• Scientific credibility: Uses objective, measurable methods (brain scans, drug trials, twin studies). Findings can be replicated and verified.
• Practical applications: Has led to effective drug treatments for mental disorders (SSRIs for depression, antipsychotics for schizophrenia) and informed neurological rehabilitation.
• Predictive power: Biological markers (genes, brain activity patterns) can predict susceptibility to certain disorders.

Limitations of the Biological Approach

• Biological determinism: Implies behaviour is entirely determined by biology, ignoring free will and the role of environment, cognition, and social factors.
• Reductionist: Reducing complex human behaviour to genes, neurotransmitters, and brain regions oversimplifies the rich complexity of human experience.
• Correlational evidence: Brain scans (fMRI) show correlations between brain activity and behaviour but cannot prove causation.
• Ethical concerns: Animal research in biopsychology raises significant ethical issues. Post-mortem studies require informed consent from the individual and their family.

Strengths of Localisation Research

• Clinical evidence: Case studies (Phineas Gage, Broca’s Tan) and brain scanning studies provide converging evidence that specific brain areas are responsible for specific functions.
• Practical applications: Understanding localisation informs neurosurgery (avoiding critical functional areas), rehabilitation programmes, and treatment of brain injuries.

Limitations of Localisation Research

• Oversimplification: Complex cognitive functions (e.g., memory, decision-making) involve multiple brain regions working together, not a single localised area.
• Plasticity: The brain can reorganise itself, with undamaged areas taking over the functions of damaged ones, challenging strict localisation.
• Individual variation: The precise location and extent of functional areas varies between individuals, limiting the generalisability of localisation findings.

Methodology

Biopsychology research uses:

• Brain imaging: fMRI (activity), EEG/ERP (electrical activity), CAT scans (structure). Provide objective data but are correlational or have limited resolution.
• Case studies: Patients with brain damage (Phineas Gage, HM, Broca’s Tan). Rich data but cannot be generalised; cannot control variables.
• Animal studies: Lesion studies, drug studies, neural recording. Allow causal inferences but raise ethical concerns and may not generalise to humans.
• Post-mortem studies: Physical examination of brain tissue after death. Provide detailed anatomical data but are retrospective and confounded by cause of death.

Common Pitfalls

1. Confusing endogenous pacemakers and exogenous zeitgebers: Endogenous = internal (SCN, melatonin). Exogenous = external (light, temperature, social cues). Endogenous pacemakers generate the rhythm; exogenous zeitgebers entrain it to the correct period.
2. Confusing Broca’s and Wernicke’s areas: Broca’s area (frontal lobe) = speech production (damage = slow, non-fluent speech). Wernicke’s area (temporal lobe) = language comprehension (damage = fluent but meaningless speech). Both are commonly in the left hemisphere.
3. Overstating brain scanning evidence: fMRI shows correlations between brain activity and behaviour, not causation. Just because an area is active during a task does not mean it causes that behaviour. Always note this limitation.

Worked Examples

Example 1: 16-Mark Essay

Question: Discuss localisation of function in the brain. Refer to evidence in your answer. [16 marks]

Model Answer:

Localisation of function is the principle that specific areas of the brain are responsible for specific functions, such as language, motor control, and vision. This view contrasts with the holistic theory of brain function, which proposes that all parts of the brain contribute equally to all behaviours. The concept of localisation has been supported by clinical case studies, brain imaging research, and neurosurgical evidence.

The cerebral cortex is divided into four lobes, each associated with different functions. The frontal lobe contains the motor cortex, which controls voluntary movement. The body is represented contralaterally — the left motor cortex controls the right side of the body and vice versa — and disproportionately, with more cortical area devoted to body parts requiring fine motor control, such as the hands and face. The parietal lobe contains the somatosensory cortex, which processes tactile information (touch, temperature, pain).

Language functions are predominantly localised to the left hemisphere. Broca’s area, in the left frontal lobe, is responsible for speech production. Paul Broca (1861) identified this area through his work with patient “Tan,” who could understand language but could only produce the syllable “tan.” A post-mortem revealed a lesion in the left frontal lobe. Damage to Broca’s area results in Broca’s aphasia — slow, effortful, non-fluent speech with relatively intact comprehension. Wernicke’s area, in the left temporal lobe, is responsible for language comprehension. Carl Wernicke (1874) identified patients who could produce fluent speech but could not understand language. Damage results in Wernicke’s aphasia — fluent but meaningless speech with poor comprehension.

One of the most dramatic pieces of evidence for localisation comes from the case of Phineas Gage (1848). An iron rod passed through his frontal lobe when an explosion drove it through his skull. Remarkably, Gage survived, but his personality changed profoundly — from a responsible, well-mannered man to an impulsive, aggressive individual who could no longer hold down his job. This case demonstrated that the frontal lobe plays a critical role in personality, decision-making, and social behaviour.

Modern brain imaging techniques have provided further support for localisation. fMRI studies consistently show that specific brain regions are activated during specific tasks. For example, the visual cortex is activated when viewing images, the auditory cortex when listening to sounds, and the motor cortex when making movements. Petersen et al. (1988) used PET scans to demonstrate that different brain regions were activated during different language tasks — listening to words activated Wernicke’s area, while speaking words activated Broca’s area.

However, the localisation view has been criticised as oversimplified. Lashley (1950) investigated the neural basis of memory by removing different areas of the cerebral cortex in rats trained to navigate a maze. He found that memory was not localised to a single area but was distributed across the cortex, with the degree of impairment determined by the amount of tissue removed rather than its location. This supports a more holistic view of brain function, at least for some cognitive processes.

Plasticity also challenges strict localisation. Following brain damage, the brain can reorganise itself, with healthy areas taking over the functions of damaged ones. For example, in some stroke patients, language functions can transfer from the damaged left hemisphere to the right hemisphere. This demonstrates that the brain is not rigidly organised and that functions are not permanently fixed to specific locations.

Furthermore, complex cognitive functions such as decision-making, creativity, and consciousness involve the coordinated activity of multiple brain regions working together as networks, not single localised areas. The modern view is that while some basic functions are localised, higher cognitive functions are distributed across the brain.

In conclusion, there is strong evidence from clinical case studies and brain imaging that specific brain areas are responsible for specific functions, particularly for basic sensory, motor, and language functions. However, the localisation view is incomplete — plasticity, distributed processing, and the holistic nature of complex cognition mean that a strict localisation account is an oversimplification. The truth lies somewhere between strict localisation and complete holism.

Example 2: 16-Mark Essay

Question: Discuss the role of endogenous pacemakers and exogenous zeitgebers in the control of circadian rhythms. [16 marks]

Model Answer:

Circadian rhythms are biological rhythms with a period of approximately 24 hours. The most well-studied circadian rhythm is the sleep-wake cycle, which is regulated by the interaction of endogenous pacemakers (internal biological clocks) and exogenous zeitgebers (external time cues).

The primary endogenous pacemaker in mammals is the suprachiasmatic nucleus (SCN), a small group of cells located in the hypothalamus above the optic chiasm. The SCN acts as the body’s master clock, generating a circadian rhythm of approximately 24–25 hours even in the absence of external cues. The SCN receives light information via the optic nerve, even in individuals who are cortically blind but have intact retinal ganglion cells that project to the SCN. The SCN regulates the pineal gland, which produces melatonin — a hormone that promotes sleepiness. Melatonin levels rise in the evening (promoting sleep) and fall in the morning (promoting wakefulness).

Morgan (1995) provided compelling evidence for the role of the SCN. He removed the SCN from hamsters, which abolished their circadian rhythms. When SCN tissue from donor hamsters was transplanted into the SCN-lesioned hamsters, circadian rhythms were restored — and the rhythms matched those of the donors. This demonstrates that the SCN is both necessary and sufficient for circadian rhythm generation.

Siffre (1975) conducted a series of self-experiments in which he lived in caves with no external time cues. In one study, he spent six months in a Texas cave with no clocks, daylight, or other time indicators. His circadian rhythm settled to approximately 25 hours (slightly longer than 24 hours), demonstrating that the body has an internal clock that runs without external cues but that it needs regular calibration by zeitgebers to maintain a 24-hour cycle. In a later study, Siffre (1999) spent two months in a cave and found that his days lengthened to 48 hours — he would sleep for 16 hours and be awake for 32 hours, without realising it.

The primary exogenous zeitgeber is light. Light entering the eye activates retinal ganglion cells that project to the SCN, resetting the internal clock each day and entraining it to the 24-hour day-night cycle. Other zeitgebers include social cues (mealtimes, work schedules), temperature, exercise, and medication.

A strength of the endogenous pacemaker explanation is its strong biological basis. The SCN has been conclusively identified as the master clock through animal lesion studies (Morgan, 1995) and human case studies. Individuals with damage to the SCN or its neural pathways show disrupted circadian rhythms, supporting its causal role.

However, the entrainment process is not solely dependent on light. Other zeitgebers, such as social cues, mealtimes, and exercise, also play a role. In situations where light cues are unavailable (e.g., blind individuals, shift workers), non-photic zeitgebers can partially compensate. This suggests that the circadian system is flexible and responsive to multiple environmental signals, not just light.

Furthermore, individual differences in circadian rhythms are well documented. Some people are “morning types” (larks) and others “evening types” (owls), with different peak performance times. Age also affects circadian rhythms — adolescents tend to have delayed circadian rhythms (preferring later bedtimes and wake times), while older adults tend to have advanced rhythms. Duffy et al. (2001) found that these differences have a biological basis, with different patterns of melatonin production and body temperature.

The interaction between endogenous pacemakers and exogenous zeitgebers has important practical implications. Shift work and jet lag disrupt the normal alignment between the internal clock and external cues, leading to fatigue, cognitive impairment, and health problems. Boivin et al. (1996) found that shift workers have higher rates of cardiovascular disease, digestive disorders, and accidents. Understanding the role of zeitgebers has led to interventions such as bright light therapy for shift workers and for individuals with seasonal affective disorder (SAD).

In conclusion, circadian rhythms are generated by the SCN (endogenous pacemaker) and entrained to the 24-hour day primarily by light (exogenous zeitgeber). The interaction between the two ensures that biological processes are optimally timed relative to the external environment. However, the system is more complex than a simple clock-and-zeitgeber model, with multiple zeitgebers, individual differences, and the effects of modern lifestyles all influencing circadian timing.

Summary

Biopsychology examines the biological basis of behaviour:

• The nervous system is divided into the CNS (brain and spinal cord) and PNS (somatic and autonomic). The ANS controls the fight or flight response.
• Neurons transmit signals electrically (action potentials) and chemically (synaptic transmission via neurotransmitters).
• Localisation of function proposes that specific brain areas serve specific functions (e.g., Broca’s area for speech production, Wernicke’s area for comprehension).
• Plasticity enables the brain to change through experience, and functional recovery allows the brain to reorganise after damage.
• Brain scanning methods (fMRI, EEG, ERP, post-mortem) each have specific strengths and limitations.
• Biological rhythms (circadian, ultradian, infradian) are regulated by endogenous pacemakers (SCN) and entrained by exogenous zeitgebers (light).