Biopsychology (A-level Psychology)

These revision notes cover the Biopsychology subtopic (3.2.2) from the AQA A-level Psychology syllabus: Paper 2: Psychology in Context.

They are structured to distinguish between AO1 (demonstrate knowledge and understanding) and AO3 (analyse, interpret, and evaluate).

Note: A-level students need to understand all these topics. AS students only need to understand the first 4 – i.e. they do not need to learn about the brain’s physiology or biological rhythms.

1. Divisions of the Nervous System: Central and Peripheral (Somatic and Autonomic)

AO1: Knowledge & Understanding

The nervous system coordinates actions by transmitting signals to and from different parts of the body.

Central Nervous System (CNS):

The central nervous system (CNS) which consists of the brain and the spinal cord.  This where all the complex processing of information is done and decisions are made.

Brain

The brain is the centre of awareness. It is divided in two hemispheres. The cortex is more developed in humans than in all other animals.

Spinal Cord

The spinal cord is an extension of the brain. It transports messages to and from the brain to the peripheral nervous system.

It is also responsible for reflexes.

Peripheral Nervous System (PNS):

The peripheral nervous system (PNS) is critical for connecting the central nervous system (CNS) to the rest of the body.

The PNS brings information from the senses to the CNS and transmit information from the CNS to the muscles and glands.

It is essential for bodily functions such as movement, sensation, and autonomic processes.

Somatic Nervous System (SNS):

The somatic nervous system (SNS) is part of the peripheral nervous system (PNS) and is associated with activities traditionally thought of as conscious or voluntary, such as walking.

The somatic nervous system consists of motor neurons and sensory neurons, which respectively transmit motor and sensory signals to and from the central nervous system (CNS).

The somatic nervous system controls voluntary movements, transmits and receives sensory information (e.g., sight, taste, touch), and is involved in reflex actions without the involvement of the CNS so that the reflex can occur very quickly.

Autonomic Nervous System (ANS):

The autonomic nervous system (ANS) is a nervous system component responsible for regulating involuntary (automatic) bodily functions, such as heart rate, digestion, respiratory rate, and pupillary response.

The ANS consists of two main divisions: the sympathetic and parasympathetic systems, which often work in opposition to maintaining the body’s internal balance or homeostasis.

• Sympathetic: Involved in responses that help us deal with emergencies. Activates fight or flight, increases heart rate/blood pressure. It slows bodily processes that are less important in emergencies, such as digestion.
• Parasympathetic: Also called the “rest and digest” system, it conserves energy and promotes relaxation of the body after undergoing stress.

AO3: Analysis & Evaluation

• Adaptive Value: Quick reflexes in the SNS for responding to threats (fight or flight). ANS homeostasis ensures physiological balance. Without proper PSNS function, the body would struggle to maintain homeostasis, potentially remaining in a constant state of heightened arousal.
• Real-life Applications: Understanding ANS function helps in anxiety treatments (beta-blockers reduce sympathetic arousal).
• Reductionism Critique: While dividing the NS helps clarity, real responses involve interplay of many systems (e.g., hormonal and neural).

Exam-Style: Short Question Example

Question: Outline one difference between the somatic and autonomic nervous systems.

Answer: The somatic system controls voluntary muscle movements (e.g. picking up objects), whereas the autonomic system controls involuntary internal processes (e.g. heart rate).

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2. Structure & Function of Sensory, Relay & Motor Neurons; Synaptic Transmission

AO1: Knowledge & Understanding

Neuronal Types:

You need to know the structure and function:

• Sensory Neurons: Carry information from sensory receptors (e.g. skin, eyes) to the CNS. Typically have long dendrites, short axons.
• Relay (Interneuron) Neurons: Found mostly in the CNS; connect sensory to motor neurons, or connect to other relay neurons. Short dendrites and short or long anxon.
• Motor Neurons: Carry impulses from CNS to effectors (muscles/glands). Short dendrites, long axons. Short dendrites and long axons.

Structure of a Typical Neuron:

• Cell Body (Soma): Contains nucleus.
• Dendrites: Branchlike structures receiving signals from other neurons.
• Axon: Long projection carrying electrical impulse (action potential) away from soma. Often myelinated.
• Myelin Sheath: Insulates axon, speeding conduction. Nodes of Ranvier are gaps in myelin facilitating saltatory conduction.
• Axon Terminal: Releases neurotransmitters into the synapse.

The cell body contains the nucleus (chromosomes), from the cell body . The dendrites extend from the cell body.

They carry  electrical impulses from other neurons towards the cell body. The axon is an extension of the neuron, it carries the impulses away from the cell  body. It is covered by a sheath of myelin,  a fatty substance.

The main purpose of the myelin sheath is to increase the speed at which impulses propagate.  There are  breaks of  between 0.2 and 2 mm. in the myelin sheath, these are called nodes of Ranvier. 

Action potentials  (nerve impulses) travelling down the axon “jump” from node to node. This speeds up the transmission.

Synaptic Transmission:

Neurons do not make direct contact. There is a very small gap between neurons called a synapse.

The signal needs to cross this gap to continue on its journey to, or from, the CNS.

This is done using chemicals which diffuse across the gap between the two neurons. These chemicals are called neurotransmitters.

1. When action potential arrives at pre-synaptic terminal, it triggers neurotransmitter release. An electrical impulse travels along the axon of the transmitting neuron.
2. This triggers the nerve-ending of the pre-syanptic neuron to release chemical messengers called neurotransmitters.
3. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the post-synaptic receptors.
4. The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse.
5. Neurotransmitters can be excitatory (increase likelihood of firing) or inhibitory (decrease likelihood of firing). E.g., serotonin often inhibitory, adrenaline excitatory.
6. Reuptake: the neurotransmitter is reabsorbed in the vesicles of the pre-synaptic neuron after it has performed its function of transmitting a neural impulse (or broken down by enzymes).

Action potentials

When a neuron is not sending a signal, it is “at rest.” When a neuron is at rest, the inside of the neuron is negative relative to the outside. 

When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a short time, this is the action potential/ it creates the electrical impulse that travels through the axon to the end of the neuron.

Some neurotransmitters act by making the neuron more negatively charged so less likely to fire. This is an inhibitory effect.  This is the case for serotonin.

Other neurotransmitters  increase the positive charge  so make the neuron more likely to fire. This is the excitatory effect. Adrenalin is which is both a neurotransmitter and a hormone has an excitatory effect.

AO3: Analysis & Evaluation

• Research & Support: Foundational experiments by Loewi (chemical transmission) support synaptic approach. Modern scanning (e.g., PET, fMRI) confirm neural pathways.
• Biological Reductionism: Explaining behavior purely by neuronal activity might ignore environment, cognition.
• Therapeutic Applications: Drugs targeting neurotransmitters, e.g., SSRIs for depression, show real-life value.

Exam-Style: Short Question Example

Question: Explain what is meant by ‘inference’ in relation to cognitive measures of reaction time.
Answer: Inference involves drawing conclusions about internal mental processes from observable evidence (e.g. reaction times), since mental processes themselves cannot be directly observed.

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3. The Function of the Endocrine System: Glands and Hormones

AO1: Knowledge & Understanding

Endocrine System:

The endocrine system consists of glands which produce hormones which are released in the blood stream to the target organs which contain receptors for  specific hormones.

Hormones are chemical messengers, travel in blood to target organs. E.g., Adrenaline, Testosterone.

Hormones  work  more slowly than nerve impulses but often together with the nervous system.

• Pituitary Gland: Master gland. Controls the release of hormones from all the other endocrine glands.
• Adrenal Gland: Adrenal medulla secretes adrenaline/noradrenaline, crucial in fight-or-flight.
• Thyroid Gland: Produces thyroxine; regulates metabolism.
• Pancreas: Produces insulin, regulates blood sugar.
• Ovaries/Testes: Secrete sex hormones (estrogen, progesterone, testosterone).

AO3: Analysis & Evaluation

• Speed & Duration: Hormonal communication is slower but longer-lasting than neural impulses.
• Real-Life Relevance: Hormones help explain stress, aggression, sexual development, etc.
• Interactive System: Nervous & endocrine systems often work together (e.g. hypothalamus → pituitary → cortisol release).

Exam-Style: Short Question Example

Question: Briefly outline the role of adrenaline in the fight-or-flight response.

Answer: Adrenaline, released by the adrenal medulla, increases heart rate, redirects blood to muscles, and readies the body for rapid action in response to threat.

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4. Fight or Flight Response (Role of Adrenaline)

AO1: Knowledge & Understanding

Fight or Flight:

The fight or flight response is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival.

It prepares your body to either confront (fight) or flee from the threat by triggering changes like increased heart rate, quickened breathing, and heightened alertness.

The fight-or-flight mechanism is an acute stress response regulated by the sympathetic ANS and adrenal medulla.

Once the hypothalamus detects a threat, it signals the adrenal medulla to release adrenaline, causing increased heart rate, etc. Then the parasympathetic system reverses these changes.

1. Threat perceived → hypothalamus activates sympathetic ANS.
2. Adrenal medulla releases adrenaline.
3. Adrenaline → increased heart rate, blood pressure, pupil dilation, glycogen → glucose.
4. Post-threat, parasympathetic branch returns body to normal (rest & digest).

AO3: Analysis & Evaluation

• Adaptive: Useful in short-term threats. A strength is that it is an evolutionary adaptation for dealing with real physical threats.
  
  However, in modern life many stressors are psychological, causing prolonged adrenaline release that may lead to illness.
  
  Additionally, the model is considered limited: research shows that women sometimes respond with ‘tend and befriend’. Therefore, while fight or flight is crucial, it may not account for all stress responses.
• Maladaptive in Modern Life: Chronic activation can damage health (hypertension).
• Gender Differences: ‘Tend and befriend’ vs. fight or flight in some theories.
• Reductionist: Ignores freeze response or social influences.

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5. Localisation of Function in the Brain & Hemispheric Lateralisation

A-Level Students Only

AO1: Knowledge & Understanding

Hemispheric Lateralisation:

The brain is divided into two symmetrical halves.

The right and left hemispheres of the brain are joined by a bundle of fibers called the corpus callosum that delivers messages from one side to the other.

Each hemisphere controls the opposite side of the body. Some of our physical and psychological functions are controlled or dominated by a particular hemisphere – this is called laterisation.

• Left hemisphere often dominates language, right hemisphere handles visual-spatial tasks.
• Split Brain Research (Sperry): In patients with severed corpus callosum, info to one hemisphere not shared to the other. Demonstrated lateralised functions (e.g., naming objects presented to right visual field processed by left hemisphere).

Localisation of Function:

The idea that specific areas of the brain are responsible for specific functions (versus a more holistic view).

• Motor Cortex (frontal lobe): Regulates voluntary movement.
• Somatosensory Cortex (parietal lobe): Processes sensory info (touch, pressure, pain) from skin.
• Visual Cortex (occipital lobe): Each visual field projects to the opposite visual cortex.
• Auditory Cortex (temporal lobe): Processes sound info.
• Language Centres: Typically in the left hemisphere:
  • Broca’s Area (left frontal): Speech production. Damage → Broca’s aphasia (slow, laborious speech).
  • Wernicke’s Area (left temporal): Language comprehension. Damage → nonsense words.

AO3: Analysis & Evaluation

• Support for Localisation: Phineas Gage’s frontal lobe injury → personality changes; Petersen’s scanning.
  
  Phineas Gage (1848) was an America railway construction foreman. During an accident a large iron rod was driven completely through his head, destroying much of his brain’s left frontal lobe. He survived the accident but his personality changed, he became unstable and is reported not to have been able to hold down a job.
  
  This supports the localisation of functions theory as it shows that control of social behaviour is located in the frontal cortex.
  
  However, we are uncertain of the extent and nature of his injuries and the reports concerning his subsequent change in behaviour are anecdotal so this lacks validity.
• Support for Localisation: Brocca found that damage of a small area in the frontal part of the left hemisphere of the brain lead to difficulties in the generation of articulate speech.
• Critiques: Lashley found learning is holistic in rats. Brain plasticity can reassign functions.
  
  Lashley (1950), removed sections of rat brains after teaching them to run a maze. None of the brain injuries impaired their ability to perform the task although he tried removing tissue in almost every area that allowed the rat to remain alive.
  
  Lashley concluded that memories had to be spread all over the brain, throughout the tissue. This suggests that learning requires the involvement of the whole brain.
  
  This challenges the brain localisation theory but running a maze is a complex behaviour which requires many different areas so it could be that just disrupting a few is not enough to disrupt the whole behaviour.
  
  Furthermore, this study was carried out on rats so we cannot extrapolate to human whose brain might be organised differently.
• Critiques: Not all psychologists agree with hemispheric lateralisation. 
  
  Some psychologists argue that the two hemispheres form a highly integrated system rather than functioning in isolation as most everyday tasks involve a mixture of left and right skills, (e.g. when listening to speech we analyse both the words and the pattern of intonation) this involves  the two hemispheres working together.
• Split Brain: Key in showing lateralised functions, but sample sizes small, epileptic brains atypical.
  
  Split-brain  surgery, is used to alleviate epileptic seizures. It involves severing the corpus callosum.
  
  After a split-brain surgery the two hemispheres cannot exchange information. This allows researchers to study the extent to which brain function is lateralised.
• Split Brain Research: Sperry (1968) investigated the effects of hemisphere disconnection and to show that each hemisphere has different functions.
  
  The participants were 11 ‘split-brain’ patients, they were patients who had undergone disconnection of the cerebral hemispheres because of severe epilepsy which did not respond to other treatments.
  
  One eye was blindfolded and the Ps were asked to fixate with the other eye on a point in the middle of a screen. 
  
  The researchers would then project a stimulus on either the left or right hand side of the fixation point for less than 1/10 of a second. 
  
  The presentation time is so brief to ensure that the Ps did not have time for eye movement as this would ‘spread’ the information across both sides of the visual field and therefore across both sides of the brain.

Another argument against brain localisation is brain plasticity: see next section

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6. Plasticity and Functional Recovery of the Brain after Trauma

A-Level Students Only

AO1: Knowledge & Understanding

Plasticity:

Neuroplasticity is the ability of the brain to change and adapt in structure and function in response to experience na learning.

During the first few years of life, the brain grows rapidly. As each neuron matures, it sends out multiple branches, this increases the number of synaptic contacts from neuron to neuron.

At birth, each neuron in the cerebral cortex has approximately 2,500 synapses. By the time an child is three years old, the number of synapses is approximately 15,000 synapses per neuron (Gopnick, et al. 1999).

As we mature the connections we do not use are deleted and the ones we use frequently are strengthened this is called neural pruning. This process continues throughout our life.

Functional Recovery:

After brain injury such as accidents or stroke the unaffected brain areas can adapt and take over the functions of the affected parts.

During the recovery period the brain rewires and reorganises itself. It forms new synaptic connections avoiding the damaged areas.

Existing neural pathways that are inactive or used for other purposes take over and carry out functions lost because of the injury.

Brain reorganisation takes place by mechanisms such as “axonal sprouting”, where undamaged axons grow new nerve endings to reconnect the neurons, whose links were severed through damage.

Undamaged axons can also sprout nerve endings and connect with other undamaged nerve cells, thus making new links and new neural pathways to accomplish what was a damaged function. 

This process can vary in speed but it can be fast in the first few weeks (phase of spontaneous recovery) then it becomes slower.

It can be helped  by rehabilitation , the nature of rehabilitation programmes varies with the type of injury from retraining some types of movement to speech therapy.

Recruitment of homologous areas

Although each brain hemisphere has its own functions, if one brain hemisphere is damaged, the intact hemisphere can sometimes take over some of the functions of the damaged one. 

AO3: Analysis & Evaluation

• Positive Applications: Neurorehabilitation, therapy helps new connections form.
• Individual Differences: Age, education, perseverance affect recovery.
• Negative Plasticity: Phantom limb pain, drug misuse reorganizes brain in maladaptive ways.

Evidence for neuroplasticity:

Maguire et al. (2000) studied 16 London taxi drivers and found an increase of the volume of grey matter in the posterior hippocampus compared to a control group.

This area of the brain is involved  in short term memory and spatial navigation.

Mechelli et al (2004) found that learning a second language increases the density of grey matter in the left inferior parietal cortex and that the degree of structural reorganization in this area is modulated by the fluency attained and the age at which the second language was learnt.

Evidence for functional recovery:

Hart (2014) found that the recovery was slower as age increases and was influenced by the severity of the impairment caused by the injury.

Scheider et al. (2014) carried out a retrospective study of 769 participants who had suffered moderate to severe brain injury and found that patients with the equivalent of college education were 7 times more likely to achieve a disability-free recovery than those who did not finish high-school.

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7. Ways of Studying the Brain

A-Level Students Only

AO1: Knowledge & Understanding

Functional magnetic resonance imaging (fMRI)

It is a technique for measuring brain activity. It works by detecting the changes in blood oxygenation and  blood flow that occur in response to neural activity.

It is based on the assumption that when a brain area is more active it consumes more oxygen and to meet this increased demand blood flow increases to the active area.

fMRI can be used to produce activation maps showing which parts of the brain are involved in a particular mental process. This allows us to study localisation of mental processes.

fMRI: Tracks blood flow changes (active regions use more oxygen).

AO3: Analysis & Evaluation

Advantages of fMRI

It is non-invasive and doesn’t involve radiation, making it safe for the subject and the test is relatively easy  to use.

The images can are given in high resolution for very small areas, however this scanning technique does not show the activity of single neurons.

Disadvantages of fMRI

It is an expensive technique compare to other scanning techniques.

The data needs to be interpreted by the researcher.

The data undergo statistical analysis which include thousands of comparisons, so at least some of them will come out positive, even if they are not real. These are called false positives.

Corrections must be applied but this can lead to false negatives.

Bennett (2009) carried out  a spoof experiment on a dead salmon and he found that the standard techniques showed “brain activity” in the dead fish.

AO1: Knowledge & Understanding

EEG:

An electroencephalogram (EEG) is a recording of electrical brain activity via scalp electrodes.

During the test, small sensors are attached to the scalp to pick up the electrical signals produced when brain cells send messages to each other. These signals are recorded by a machine.

The electrodes cannot pick up signals for individual neurons. The recording shows the electrical activity from small areas of the brain.

EEG is used to show the presence or absence of specific brain activity in specific areas of the brain. 

AO3: Analysis & Evaluation

Strengths:

• Excellent temporal resolution (ms).
• It is an easy and low –cost technique.
• It is often used to supplement neuroimaging such as fMRI.
• It provides direct rather than indirect evidence (fMRI provides indirect information as it only measures the use of oxygen and the blood flow not neural activity).
• May be the only test that shows abnormalities in epileptic patients.

Weaknesses:

• Poor spatial resolution.
• Relatively low sensitivity and specificity (does not show the functioning of very small areas of the brain).
• Influenced by state of alertness and drugs.
• Small or deep lesions might not produce an EEG  abnormality as EEG only picks up neural activity in the cortex.

AO1: Knowledge & Understanding

ERPs:

An event-related potential (ERP) is the brain response that results from a sensory, cognitive or motor event.

The individual is connected to an EEG machine and presented with various stimuli.

The resulting EEG trace is then analysed. The EEG trace has first to be filtered in order to detect the change in types of neural activity.

AO3: Analysis & Evaluation

Strengths:

Identifies brain’s response to events with high temporal precision.

EPRs have high temporal resolution as they can detect brain activity to within one millisecond. So they are used in the study of cognitive functions.

Weaknesses:

• Multiple trials needed, noise must be filtered.
• Lack of standardisation in ERP research makes if difficult to compare the results of different studies.
  
  EEG picks up data of all the neurological activity so background noise and extraneous variables need to be eliminated, which is very difficult and time-consuming to achieve.

AO1: Knowledge & Understanding

Post-Mortem Examinations:

This is the study of people’s brain after their death.

This method is widely used to study the link between function and structure of the brain, linking structural abnormalities to behavior.

For example Brocca found that damage of a small area in the frontal part of the left hemisphere of the brain lead to difficulties in the generation of articulate speech.

It is still used today to study the anomalies associated with disorders such as Alzheimer’s disease and motor neurone disease.

The structure of the brain of people who present with these types of disorders are examined and compared with “normal” brains and a correlation is made between the differences found and the disorder.  

AO3: Analysis & Evaluation

Strengths:

• Detailed anatomical analysis. Postmortem studies allows for researchers to gain information into the processes involved in particular disorders.
• This might lead to improvement in the treatment of patients with the same disorder and the prevention of the disorder in other people. This can allow researcher to prioritise areas of study.

Weaknesses:

• It is difficult to obtain consent from the family of patients.
• Retrospective, no cause-effect clarity. The lesions observed might be caused by other processes and other factors during the patient’s life than the disorders studied.
• The state of the brain is influenced by the cause of death and the method of storage after death. These factors act as confounding variables. 

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8. Biological Rhythms: Circadian, Infradian & Ultradian

A-Level Students Only

AO1: Knowledge & Understanding

Biological rhythms are cyclical changes (that occur in cycle) in our behaviour and physiology. 

They are thought to have evolved to because the environment in which we live has cyclic changes e.g. day and night, seasons.

3 types of biological rhythms:

1. Circadian: ~24-hour cycle (e.g. sleep/wake).

2. Infradian: Longer than 24 hours (e.g. menstrual cycle, seasonal affective disorder).

3. Ultradian: Less than 24 hours (e.g. stages of sleep ~90 mins).

Endogenous Pacemakers

Endogenous Pacemakers: Internal body clocks (e.g., SCN in hypothalamus) controlling circadian rhythm.

Internal pacemaker: The suprachiasmatic nucleus, it is a small group of neurons situated in the hypothalamus, the SCN is connected to the optic nerves and control the circadian cycles.

It influences physiological and behavioural rhythms which take place over a 24-hour period, e.g. the sleep/wake cycle, temperature, blood pressure and the release of melatonine, the sleep hormone.

Exogenous Zeitgebers

External cues (light, social factors) which regulate our internal body clock, in order to remain in time with the environment’s fluctuating rhythm.

The process of resetting the biological clock using exogenous zeitgebers is called entrainment.

One of the main factors is light.

There light-sensitive cells in the eye which act as light detectors they communicate with the SCN in order to synchronise the internal control with the outside world.

AO3: Analysis & Evaluation

• Circadian Evidence: Siffre’s cave study (~25h free-running). Suggests strong internal clock, limited by small samples.
  
  Michel Siffre spent two months in a cave in the French Alps with no natural light. he had no clock or means to check the time. He had verbal contact with the outside world.  The absence of natural light allowed his biological clock to run at its natural rate
  
  The findings were that his sleep-wake cycle settled naturally at around 25 hours. This supports an innate, biologically determined circadian rhythm because he maintained this rhythm in the absence of external zeitgebers.
  
  However this was a case study so the results cannot be genralised as age, gender and past experience (e.g. waking up at a particular time to go to work) could have affected  the results.
• Circadian Evidence: Our circadian rhythms are influenced by individual characteristics.
  
  Duffy et al (2001) some individuals have  a natural preference for sleeping early and waking early (larks), whereas other people prefer the opposite (owls). Age: according to research, teenagers’ circadian rhythms begin two hours after those of adults.
  
  This has practical applications as this implies that school starts too early and students are asked to focus and learn when their body still needs sleep.
  
  Kelley (2010) carried out a study on thousands of 14-16-year-olds. They started their lessons at 10.00 in a High School in North Tyneside for two years. The results showed an increase from 34% to 53% in the number of students pupils scoring five A*-C grades .
• Disruption of circadian rhythms:  many studies of the disruption of circadian rhythms (e.g. though night shift) show that it can have negative effects on physical health – night shift workers are three times more likely to develop cardiac problems but also on mental health such as anxiety and decreased alertness and vigilance.
  
  This lack of concentration, increased irritability and feelings of tiredness are thought to have been involved in both the near-disaster at the Three Mile Island nuclear plant and the Chemobyl nuclear disaster, they were associated with decision failures on the part of shift workers operating between 1.30 am and 4.30 am.
• Infradian: Menstrual cycle studies (e.g., McClintock). Confounding variables (stress, diet) limit generalization.
  
  The menstrual cycle lasts around 28 days. It is controlled by internal factors, the levels of oestrogen and progesterone, produced by the ovaries. 
  
  These cause physiological changes including the release of one egg (ovum) from the ovaries and the thickening of the lining of the uterus. If the egg is not fertilised then the lining of uterus is shed and menstruation occurs.
• Infradian: Seasonal affective disorder is a type of depression that comes and goes in a seasonal pattern.  It is also known as “winter depression” because the symptoms are more severe during the winter. The symptoms often begin in the autumn as the days get shorter.
  
  At night low light levels stimulate the production of melatonin, this triggers sleepiness.  During the winter low levels of light have a similar effect. SAD is classified in the DSM-5.
  
  The symptoms are low mood, general lack of activity and interest. It is a circannual cycle as it follow the annual rhythm of the seasons but can also be considered as a circadian rhythm as it also disrupt the sleep-wake cycle.
• Ultradian: Sleep stages supported by EEG data (Dement & Kleitman). Lab-based measures but artificial.
  
  Dement and Kleitman (1957) studied 9 participants over 61 nights, during which their brain activity was monitored by EEG, they were also woken up to report their dreams.
  
  The results show that all Ps had stages of REM sleep every night, REM was correlated to EEG patterns and to the content of dreams as reported by the Ps. This study has been replicated many times with similar findings.
• Pacemakers: SCN important, but exogenous cues like light also crucial. Real-world application to shift work/jet lag.

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Final Tips

• For AO1, present accurate, concise definitions, structures, and processes.
• For AO3, evaluate with clear arguments, referencing research and applying to real-life or other viewpoints.
• When asked to apply knowledge, explicitly link psychological terms/theories to the scenario.

These notes combine definitions, deeper analysis, and an exam-question style to help structure your revision.