Overview – Biopsychology

Biopsychology is the study of psychology from the perspective of the underlying biology (i.e. it’s the biological approach from the approaches topic). But where the approaches section focused mainly on genetics, this biopsychology section drills down more into the physiology and biochemistry underlying behaviour:

Note: A level students need to understand all these topics. AS students only need to understand the first 2 – i.e. they do not need to learn about the brain’s physiology or biological rhythms.

The nervous system

The nervous system is the main system that controls the mind and body. It takes in information from the environment and elsewhere in the body (transmitted across neurons) and co-ordinates a wide range of conscious functions such as thinking and movement, as well as unconscious functions like the control of organs (e.g. heart rate, digestion) and glands.

Divisions of the Nervous System

In humans (and other vertebrate animals), the nervous system is divided into two parts: the central nervous system (CNS) and peripheral nervous system (PNS). These two parts are divided into further subcategories:

Nervous system diagram

Central Nervous System

The central nervous system is the main control system of the body. It consists of two parts: the brain and spinal cord.


In addition to obvious functions like thinking, the brain is also responsible for:

  • Perception (i.e. translating information from the senses so it can be understood and processed)
  • Motor control (i.e. sending commands to muscles to move)
  • Regulating bodily processes and maintaining homeostasis (e.g. maintaining temperature and hormone levels based on information from the peripheral nervous system)
  • Sleep
Spinal cord

The spinal cord connects the brain with the peripheral nervous system. In other words, it connects the brain with the rest of the body and with the external world. The spinal cord is also responsible for some unconscious movements, such as reflexes (e.g. the one where you get hit on the knee and your leg kicks).

Peripheral Nervous System

The peripheral nervous system goes beyond the central nervous system to connect it with the rest of the body and the external world. It consists of two parts: the somatic nervous system and the autonomic nervous system.


The somatic nervous system is responsible for movement (e.g. walking) and transmitting information between the central nervous system and the senses, i.e. it connects the brain to the external world.


The autonomic nervous system is responsible for transmitting information between the central nervous system and the internal organs, i.e. it connects the brain to the rest of the body.

The functions of the autonomic nervous system can be divided into two categories: sympathetic and parasympathetic, which oppose each other. For example:

Organ Sympathetic Parasympathetic
Heart Increase heart rate Decrease heart rate
Digestive system Decrease stomach acid and digestion Increase stomach acid and digestion
Eyes (iris) Dilate pupils Constrict pupils
Lungs Dilate bronchioles Constrict bronchioles

In general, sympathetic functions increase bodily activity to prepare for action – an example of this is the fight or flight response. In contrast, parasympathetic functions decrease bodily activity to conserve energy.


Neurons are the main components of the nervous system. They are how information is transmitted from one part of the nervous system to another. There are around 100 billion neurons in the brain and another 1 billion in the spinal cord.

Although there are different types of neurons, they all have the same general structure: the dendrite (receptor) receives a signal, which travels along the axon until it reaches the axon terminal (terminal buttons):

neuron structure labelled

Signals are passed within neurons electrically. At rest, the neuron is negatively charged but becomes positively charged when activated, which sends an electrical impulse through the axon.

Once this electrical signal reaches the axon terminal, synaptic transmission enables the signal to pass along to the next neuron in the chain.

Synaptic Transmission

Neurons are separated by small gaps called synapses, and synaptic transmission is the process of sending information from one neuron to another.

The gap between two neurons is called the synaptic cleft. When the electrical signal within a neuron reaches the axon terminal of that neuron, it causes the release of neurotransmitters that cross over the synaptic cleft and are taken up by receptors in the dendrites of the other neuron.

synaptic transmission diagram

Whereas signals within neurons are transmitted electrically, signals between neurons are transmitted chemically. In other words, neurotransmitters are chemicals. When a neurotransmitter is taken up by the receptor of the next neuron, it is converted back to an electrical signal which passes along the axon of that neuron until it reaches the axon terminal where the chain can continue.

Excitation and inhibition

Neurons contain many different types of neurotransmitters such as serotonin, dopamine, glutamate, GABA, and acetylcholine. These different neurotransmitters can have either excitatory or inhibitory effects:

  • Excitatory: Increase the likelihood of the neuron firing
  • Inhibitory: Decrease the likelihood of the neuron firing

For example, serotonin has a generally inhibitory effect. When serotonin binds to the receptor of a neuron, it increases the negative charge of that neuron, making it less likely to fire. In contrast, glutamate has an excitatory effect. So, if glutamate outweighs serotonin in a neuron, the net effect is increased likelihood of that neuron firing.

Types of Neurons

Neurons are classified into 3 main types according to their function within the nervous system:

The endocrine system

The endocrine system is a system of glands that are responsible for the release of hormones. The pituitary gland (the ‘master gland’) of the endocrine system is linked to the nervous system via the hypothalamus, which co-ordinates and regulates the release of hormones from glands.

endocrine system labelled

Glands and hormones

Hormones are chemicals that communicate information throughout the body. Different hormones are produced and released by different glands in the body.

The effects of hormones are significant and affect growth, sleep, mood, metabolism, and just about every other process in the body. They flow through the body and bind to specialised receptors in cells (a bit like how neurotransmitters bind to receptors in neurons). When a hormone binds to a receptor, it can cause an effect in that cell. For example:

Gland Hormone(s) Effect(s)
Pituitary Growth hormone
Growth hormone: Stimulates growth and cell division
Prolactin: Stimulates milk production (females)
Testes Testosterone Responsible for male secondary sex characteristics (e.g. body hair, deeper voice, bigger bone structure), sperm cell production, increases aggression and muscle size
Ovaries Estrogen
Estrogen: Responsible for female secondary sex characteristics (e.g. breast development, wider hips), egg maturation
Progesterone: Regulates uterus for pregnancy
Thyroid Thyroxine Increases metabolism, regulates growth and temperature
Pineal Melatonin Regulates circadian rhythm and sleep
Adrenal Cortisol
Cortisol: Maintains blood sugar, regulates inflammation and immune response
Adrenaline: see below

The endocrine system transmits information chemically, and operates much more slowly than the nervous system. It is primarily regulated via the pituitary gland (the ‘master’ gland), which connects the endocrine system to the nervous system (via the hypothalamus).

Adrenaline: Fight or Flight

You don’t need to remember all the specific glands and hormones and their effects for A level psychology. Instead, the main one the syllabus focuses on is adrenaline.

Adrenaline is responsible for the fight or flight response: an activation of the sympathetic side of the autonomic nervous system to prepare the body for action. The process for this is as follows:

  • The brain (specifically the hypothalamus) senses a threat
  • The hypothalamus sends a message to the adrenal glands (specifically the adrenal medulla) to release adrenaline
  • Adrenaline increases bodily activities to either fight or flee from the threat
    • For example, heart rate increases to improve blood flow, the bronchioles of the lungs dilate to increase oxygen intake, and the pupils dilate to increase vision. Other bodily activities that are not essential for fighting or fleeing are reduced, such as digestion
  • Once the brain senses the threat has passed, the parasympathetic nervous system returns the body to a resting state

The brain

Note: This topic is A level only, you don’t need to learn about the brain’s physiology if you are taking the AS exam only.

Areas of the brain

Early scientists tended to see the brain in a holistic way, meaning they saw all areas of the brain as used for all functions. More recent (i.e. >20th century) scientists now tend to take a more localised approach. Different areas of the brain appear to be responsible for different functions, and damaging these areas effects those functions.

Hemispheric Lateralisation

left and right brain hemispheresThe first way the brain can be divided is laterally, i.e. a left half and a right half. These halves are called hemispheres. Each of the two hemispheres can be further divided into four lobes: frontal, parietal, occipital, and temporal.

The two hemispheres are not symmetrical – they do different things. For example, the left hemisphere tends to be more involved in language processing, whereas the right hemisphere tends to be more involved in processing spatial relationships.

As a general rule, information from the left side of the body is processed by the right hemisphere and vice versa (contralateral). For example, damage to the motor cortex in the right hemisphere will affect the person’s ability to move their left side, and damage to the auditory cortex in the left hemisphere will affect a person’s hearing in their right ear.

Split-brain patients

The two hemispheres of the brain are connected by a bundle of nerve fibers called the corpus callosum.

In rare cases of extreme epilepsy, a surgeon may cut the corpus callosum (corpus callosotomy), separating the right and left hemispheres from each other. This contains any epileptic seizures to just one side of the brain, reducing their severity.

Despite the dramatic nature of the procedure, patients who’ve undergone a corpus callosotomy (split-brain patients) are able to live relatively normal lives. However, there are some effects on functioning, as observed in Sperry (1968):

  • When split-brain patients were shown an image in one half of their field of vision (e.g. the left), they did not recognise the same image when it was presented to the other half of their field of vision (e.g. the right). This is because each side of the field of vision is processed in a different hemisphere (see visual cortex). When the corpus callosum is cut, the brain cannot share information between the hemispheres.
  • Sperry also found that when an image was presented to the left-hand side of a patient’s field of vision, they were not able to describe in words what they saw. This is likely because visual information from the left side is processed in the right hemisphere, but language processing primarily occurs in the left hemisphere. In other words, visual data in the right hemisphere could not be shared to the language processing areas in the left hemisphere.

Localisation of function

Localisation of function refers to identifying specific areas of the brain that correspond to specific functions. For example, damage to the auditory cortex in the brain can damage hearing, whereas damage to the motor cortex may reduce a person’s ability to move. This suggests these functions are localised within these areas of the brain.

Motor cortex (voluntary movement)

The motor cortex of the brain is responsible for voluntary movement, such as walking. It is located in the frontal lobes of each hemisphere. However, basic involuntary movements (like coughing) are controlled by other parts of the brain.

So, damage to the motor cortex may limit a person’s motor skills. For example, a person with a damaged motor cortex may have difficulty holding a pen.

Somatosensory cortex (touch)

somatosensory cortex handThe somatosensory cortex of the brain is responsible for sensing physical sensations on the skin, like pressure and heat. It is located in the parietal lobes of each hemisphere.

The number of neurons in the somatosensory cortex differs according to body part. For example, there are many more neuronal connections dedicated to processing information from the hands than the ankles because people use their hands to feel things much more commonly than they do their ankles.

Visual cortex (seeing)

eye visual cortexThe visual cortex of the brain is responsible for processing visual information from the eyes. It is located in the occipital lobes of each hemisphere. The visual cortex is contralateral: The right hemisphere processes data from the left of a person’s field of vision (both eyes) and vice versa.

So, damage to the visual cortex of the right hemisphere may make it difficult for a person to perceive objects to the left of them.

Auditory cortex (hearing)

auditory cortex earThe auditory cortex of the brain is responsible for processing sound. It is located in the temporal lobes of each hemisphere. The auditory cortex is also contralateral: The right hemisphere processes sound from a person’s left ear and vice versa.

So, damage to the auditory cortex of the left hemisphere may cause hearing difficulties in a person’s right ear.

Language centres

As mentioned, language processing primarily happens in the left hemisphere. There are two areas that are particularly important for language: Broca’s area and Wernicke’s area.

broca's area wernicke's area brain diagram

Broca’s area (speech production)

The Broca’s area is the main area where speech is produced. It is located in the frontal lobe of the left hemisphere.

The Broca’s area was identified by and named after Pierre Paul Broca in the mid 19th Century. From post-mortem autopsies, Broca observed that patients who’d had difficulty producing words had lesions (damage) in this area of the brain.

Damage to the Broca’s area causes Broca’s aphasia (also called expressive aphasia), a condition characterised by slow speech, lack of fluency, and an inability to find the right words. Despite difficulties producing speech, people with Broca’s aphasia often have normal language comprehension – i.e. they understand what others are saying.

Wernicke’s area (speech comprehension)

Another important (but separate) area for language is Wernicke’s area. The Wernicke’s area is primarily responsible for language comprehension (both written and spoken). It is located in the temporal lobe.

Damage to the Wernicke’s area causes Wernicke’s aphasia (also called receptive aphasia). Patients with Wernicke’s aphasia typically have no problems producing speech – they speak in a fluent and effortless way – but the content of what they say often lacks meaning.

AO3 evaluation points: Localisation of function

There is lots of evidence supporting the idea that different functions within the brain are localised in specific areas. Firstly, case studies (e.g. Phineas Gage). Secondly, brain scans.

However, there is some evidence that conflicts with aspects of location of function. For example, higher cognitive processes (e.g. learning and memory)


Just like how plastic can be moulded and shaped, so too can the brain: New neuronal connections can be formed and old ones removed. Neuroplasticity is this ability of the brain to change its physical structure to perform different functions.

In childhood, the brain is highly plastic. This plasticity enables infants and children to quickly learn new skills, adapt to their environment, and recover from brain injury. Neuroplasticity reduces with age, but still remains: Unused pathways are removed, commonly used pathways are strengthened, and new pathways can be formed.

Functional recovery after trauma

Neuroplasticity enables people to recover function after trauma (e.g. brain damage caused by stroke or accident). To recover function, the brain restructures itself in the following ways:

  • Other areas of the brain adapt to take over the function of damaged areas: For example, Danelli et al (2013) describes a case study of a boy who had his entire left hemisphere removed at age 2 and a half. As described above, language function is primarily localised in this hemisphere, and the boy was initially unable to speak. However, his language skills recovered after 2 years, suggesting the right hemisphere adapted to take over this function.
  • Unused neural pathways are recruited: Wall (1977) observed that the brain contains many dormant neural connections. When healthy neural connections are damaged, these previously dormant synapses activate and form new connections to compensate for the damaged ones.
  • Axon sprouting: Damage to the axon of a neuron can break its connections to neighbouring neurons. When this happens, the neighbouring intact neurons may grow (‘sprout’) extra nerve endings to reconnect with these damaged neurons.
AO3 evaluation points: Neuroplasticity




Ways of Studying the Brain

There are many ways psychologists and scientists study the brain. These methods are used to better understand how the brain works (e.g. where functions are localised) and diagnose and treat illness.


Functional magnetic resonance imaging (fMRI) is a form of brain scanning. It uses magnetic fields to measure blood flow and oxygenation in the brain.

When an area of the brain is highly active, that area needs more oxygen and greater blood flow to provide this oxygen. By measuring blood flow and oxygenation, fMRI scanners enable researchers to identify which areas of the brain are activated during certain tasks.

fMRI scan

The example fMRI scans above are from Ovaysikia et al (2011). In this study, the researchers measured brain activity during two tasks: Reading words and recognising facial expressions. As can be seen from the fMRI scan above, the different tasks increased brain activity in different areas.

AO3 evaluation points: fMRI
  • Dynamic: fMRI scans record brain activity as it happens, which enables researchers to see activity in the brain over time (unlike post-mortem). For example, when a person switches from working out a maths equation to thinking about a childhood memory, fMRI scanners can pick up the change in brain activity.
  • Expensive: fMRI scanners are expensive to buy and maintain (compared to EEGs). This limits their use as psychological research tools, with studies that do use fMRI scanners often consisting of small sample sizes in order to reduce costs.

Electroencephalogram and ERPs

Electroencephalogram (EEG)An electroencephalogram (EEG) is a scan of the brain’s electrical activity. An EEG scan is performed by attaching electrodes to the scalp or by using a hat with electrodes attached.

The electrodes detect electrical activity in the brain cells beneath them. So, the more electrodes that are used in an EEG, the more complete a picture of brain activity the EEG can provide.

Event-related potentials (ERPs) are closely related to EEG scans. They use the same equipment but use statistical techniques to measure changes in brain activity in response to a stimulus. For example, the EEG could initially provide a baseline picture of brain activity, then researchers could introduce a stimulus (e.g. giving a subject some food to eat) and use ERPs to determine how brain activity changed in response.

AO3 evaluation points: Electroencephalogram and ERPs
  • Incomplete picture: The electrodes of EEGs only measure general electrical activity and are unable to provide a detailed view of what is happening in the brain. For example, neurons associated with feeling in the hands may be next to neurons associated with hearing, but the EEG will not be able to differentiate between the two. However, some psychological conditions have distinctive electrical signals (e.g. epilepsy) and so EEGs are useful diagnostic tools for them.
  • Dynamic: Like fMRI, EEG and ERPs enable researchers to measure changes in brain activity as they happen.
  • Lower cost: EEG brain scans are much less expensive than fMRI brain scans.


brainA post-mortem is a physical examination of the brain after a person has died. By physically analysing a brain (for example, by weighing it, dissecting parts of it, and comparing it to neurotypical (‘normal’) brains) and cross-referencing this with the person’s behaviour in life (e.g. any psychological disorders the person had) the examiner can learn more about the causes of behaviours and psychological disorders.

An example of this is described above: From post-mortem analysis of the brains of patients with speaking difficulties, Pierre Paul Broca identified that the Broca’s area of the brain is important for speech production.

AO3 evaluation points: Post-mortem
  • No brain activity: As the person is dead, a post-mortem does not enable researchers to measure dynamic brain activity (unlike fMRI and EEG). As such, researchers may have to speculate about (rather than measure) connections between the person’s physical brain and their psychological character (e.g. psychological conditions) when they were alive.

Biological rhythms

Note: This topic is A level only, you don’t need to learn about biological rhythms if you are taking the AS exam only.

The activities of the mind and body follow various cycles, which are known as biological rhythms. These biological rhythms are categorised in the following ways:

Category Length Example
Circadian 24 hours Sleep and wake cycle
Infradian More than 24 hours Female menstrual cycle
Ultradian Less than 24 hours Stages of sleep

Biological rhythms are controlled by endogenous pacemakers, which are influenced by exogenous zeitgebers:

  • Endogenous pacemakers: Rhythms within the body that regulate biological rhythms (your ‘body clock’).
    • E.g. Release of hormones (such as melatonin)
  • Exogenous zeitgebers: Factors in the external environment that inform endogenous pacemakers to regulate biological rhythms.
    • E.g. Sunlight and darkness prompt the body to release hormones that control sleep and wake cycles


Circadian rhythms are biological cycles lasting approximately 24 hours. An example of a circadian rhythm is the sleep/wake cycle: You might cycle between sleeping for 8 hours when it gets dark and being awake for 16 hours during the day, for instance.

typical circadian rhythm

Examples of endogenous pacemakers that control circadian rhythm include systems that release hormones such as melatonin, systems that regulate body temperature, and systems that control metabolism and digestion. The main system that controls circadian rhythms is the suprachiasmatic nucleus (SCN).

These internal processes are influenced by exogenous zeitgebers – perhaps the most obvious of which is sunlight. For example, the darkness of night is thought to trigger melatonin release, which makes you feel tired and want to go to bed.

Endogenous pacemakers appear to be more important than exogenous zeitgebers in regulating circadian rhythms. There are many studies, for example, where circadian rhythms remain regular despite significant disturbances to exogenous zeitgebers:

  • Speleologist Michael Siffre conducted several case studies (using himself as a subject) on the effects of living in a cave without the exogenous zeitgeber of natural light. In 1962, he spent two months in a cave without any natural light and without a clock. Then, in 1975, he conducted a similar experiment but for six months. In both experiments, Siffre maintained a regular sleep/wake cycle and circadian rhythm of around 25 hours.
  • Aschoff and Wever (1976) conducted an experiment where participants were kept in a World War 2 bunker without any natural light for four weeks. All participants (except one) maintained a circadian rhythm very close to 24 hours, despite the absence of natural light.
  • Folkard et al (1985) conducted a similar experiment where participants were kept in a cave without sunlight for three weeks. The participants were supposed to go to bed when a clock said 11:45pm and wake when it said 7:45am, but unbeknown to them the researchers slowly increased the clock speed so that what seemed like a 24-hour day was actually only 22 hours. Despite these faster clocks, all but one participant maintained a consistent 24 hour circadian rhythm.
AO3 evaluation points: Circadian rhythms
  • A.


Infradian rhythms are biological cycles lasting more than 24 hours. An example of an infradian rhythm is the human menstrual cycle: Women typically ovulate once every 28 days.

menstrual cycle infradian rhythm

As with circadian rhythms, infradian rhythms are controlled by endogenous pacemakers. For example, hormones such as estrogen and progesterone are crucial to the menstrual cycle.

Infradian rhythms can also be influenced by exogenous zeitgebers. For example, Stern and McClintock (1998) demonstrated that women’s menstrual cycles change when exposed to pheromones from other women.


Ultradian rhythms are biological cycles lasting less than 24 hours. An example of an ultradian rhythm is the different stages of sleep: During the night, a sleeping person will typically cycle between five stages:

Stage Length Description
1 5-15 minutes Light sleep. Alpha waves increase and brain activity starts to reduce. Heart rate slows and muscles relax.
2 5-15 minutes Light sleep. Brain activity reduces but with occasional bursts of activity.
3 5-15 minutes Deep sleep. Delta brain waves increase and brain activity is greatly reduced.
4 ~40 minutes Deep sleep. Delta waves peak, lowest level of brain activity during the sleep cycle.
Rapid eye movement (REM) >15 minutes High level of brain activity. Dreams are likely to occur. Body is completely relaxed.

One complete sleep cycle through all these stages will typically take around 90 minutes. So, during a full night’s sleep, a person may repeat this cycle four or five times.

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