Describe the localisation of function in the cerebral cortex and explain how lesion, split-brain and neuroimaging evidence links specific brain regions to cognition

What this dot point is asking

QCAA wants you to explain how the cerebral cortex is organised into regions with specialised functions, and to evaluate the evidence (lesion studies, split-brain research and neuroimaging) that supports the idea that particular brain areas underpin particular kinds of thinking. You need named studies and named structures, not vague claims that the brain controls behaviour.

The answer

Localisation of function is the principle that specific psychological functions are controlled by specific, identifiable regions of the brain. The opposing idea, the equipotentiality or distributed view, holds that complex functions draw on networks spread across the cortex. The truth lies between the two: simple sensory and motor functions are tightly localised, while complex cognition is distributed.

The four lobes

The cerebral cortex, the outer wrinkled layer of the cerebrum, is divided into four lobes in each hemisphere.

• Frontal lobe. Higher-order thinking, planning, decision-making, voluntary movement (the motor cortex sits along its rear strip) and personality. It contains Broca's area (usually left hemisphere), which controls speech production.
• Parietal lobe. Processes somatosensory information (touch, temperature, pain, body position). The somatosensory cortex runs along its front strip, directly behind the motor cortex.
• Temporal lobe. Auditory processing, memory and language comprehension. It contains Wernicke's area (usually left hemisphere), which handles understanding speech.
• Occipital lobe. Almost entirely devoted to visual processing; the primary visual cortex sits here.

Hemispheric specialisation

The cortex is split into left and right hemispheres connected by the corpus callosum, a thick band of around 200 million nerve fibres. Each hemisphere controls the opposite (contralateral) side of the body. In most people the left hemisphere is dominant for language and logical, sequential processing, while the right is more involved in spatial reasoning, faces and holistic processing. This specialisation is a tendency, not an absolute.

Evidence from lesion studies

Lesion studies examine people whose brain damage produces predictable changes in behaviour, allowing inferences about what the damaged region normally does.

• Phineas Gage (1848). A railway worker whose frontal lobe was pierced by an iron rod. He survived but reportedly underwent dramatic personality change, becoming impulsive and unreliable. The case provided early evidence that the frontal lobe governs personality and self-control.
• Paul Broca (1861). Studied a patient (known as Tan, because that was almost the only word he could say) who could understand language but not produce fluent speech. Post-mortem revealed damage to the left frontal lobe, now called Broca's area. This was strong evidence for the localisation of speech production.
• Carl Wernicke (1874). Identified patients who produced fluent but meaningless speech and could not comprehend language. Damage was in the left temporal lobe, now Wernicke's area, evidence for the localisation of language comprehension.

Split-brain studies

Roger Sperry and Michael Gazzaniga studied patients whose corpus callosum had been surgically cut to control severe epilepsy. With the hemispheres disconnected, the researchers could present information to one hemisphere at a time. When an object was shown only to the right hemisphere (left visual field), patients could not name it (because language sits in the left hemisphere) but could select it by touch with the left hand. This demonstrated that the two hemispheres can process information independently and that language is lateralised. Sperry shared the 1981 Nobel Prize for this work.

Neuroimaging evidence

Modern techniques map function in living, healthy brains.

• fMRI tracks blood oxygenation to show which regions are active during a task in near real time, with good spatial resolution.
• PET uses a radioactive tracer to show metabolic activity and is useful for studying neurotransmitter systems.
• EEG records electrical activity at the scalp with excellent temporal resolution but poor spatial precision.

Neuroimaging confirms localised activity (the occipital lobe lighting up during vision) while also revealing that complex tasks recruit distributed networks across multiple regions.

Putting it together for an exam

A strong answer names the lobe, states its function, then supports it with a named study and method. For example: "The frontal lobe governs personality and executive function, as shown by the Phineas Gage lesion case, in which frontal damage produced marked personality change." Linking structure, function and evidence is what separates a high-level response from a list of facts.