Structure and Localisation of Function in the Brain
Structure of the Brain
The brain is the most complex organ in the human body. Psychologists divide it into regions to understand which parts are responsible for which functions — a principle called localisation of function. The outer surface of the brain, the cerebral cortex, is divided into four main lobes, each with distinct roles.
The Four Lobes
The frontal lobe sits at the front of the brain. It contains the motor cortex, which controls voluntary movement, and the prefrontal cortex, which is involved in planning, decision-making and personality. Damage to the frontal lobe can change personality and affect self-control, as illustrated by the famous historical case of Phineas Gage.
The temporal lobe is located at the sides of the brain, roughly behind the ears. It processes sounds and contains Wernicke’s area, which is crucial for understanding spoken and written language. The temporal lobe is also involved in memory consolidation.
The parietal lobe lies behind the frontal lobe and above the temporal lobe. It contains the somatosensory cortex, which receives and processes information from the skin, muscles and joints — allowing you to feel touch, temperature and pain.
The occipital lobe is at the back of the brain. It is entirely dedicated to visual processing. The primary visual cortex receives signals from the eyes, and surrounding areas interpret colour, movement and shape.
The cerebellum is a cauliflower-like structure at the back and base of the brain. It coordinates smooth, precise movement and balance. Without the cerebellum, actions such as catching a ball or writing would become clumsy and uncoordinated. It also plays a role in procedural learning — acquiring motor skills through practice.
The four lobes: frontal (front, movement + planning), temporal (sides, hearing + language), parietal (top-back, touch + senses), occipital (back, vision). The cerebellum (base-back) coordinates movement and balance.
Localisation of Function
Within each lobe, specific areas have specific functions. The motor area (primary motor cortex) in the frontal lobe controls voluntary movement. The somatosensory area in the parietal lobe processes touch and body sensation. These two areas run as parallel strips separated by a groove called the central sulcus.
The visual area in the occipital lobe processes sight; the auditory area in the temporal lobe processes sound. Language is handled by two key areas: Broca’s area in the frontal lobe controls speech production, while Wernicke’s area in the temporal lobe is involved in language comprehension.
Aim: Wilder Penfield aimed to map the functions of the cortex in patients undergoing brain surgery for epilepsy, to understand which areas controlled movement, sensation and conscious experience.
Method: During surgery, Penfield applied a small electrical probe to specific areas of the cortex in patients who were kept awake under local anaesthetic. The patients could report what they experienced as each area was stimulated. Penfield carefully recorded which physical movement or sensation resulted from stimulating each point.
Results: Stimulating the motor cortex caused involuntary movements in specific body parts, producing a systematic map of the body across the cortex — now called the motor homunculus. Stimulating the temporal lobe caused patients to report vivid memories, sounds and experiences, suggesting this region has a role in conscious experience. Penfield called this region the “interpretive cortex.”
Conclusion: The cortex is systematically organised, with different areas responsible for different functions. The temporal lobe in particular appeared to be involved in interpreting and replaying past experiences, providing early evidence that specific functions are localised to specific brain areas.
Penfield mapped the cortex by electrically stimulating the brains of awake epilepsy patients during surgery. Stimulating the motor cortex caused body movements; stimulating the temporal lobe triggered vivid memories. His conclusion was that cortical functions are localised — different areas control different behaviours.
A strength of the localisation of function idea is that it is supported by consistent evidence from multiple sources: Penfield’s electrical stimulation, case studies of brain-damaged patients, and modern brain scanning studies all point to the same organisational principle.
However, localisation has limits. Many complex behaviours — language, emotion, memory — involve networks of brain areas rather than a single region. Brain plasticity research shows that after injury, healthy parts of the brain can sometimes take over functions previously performed by damaged areas, suggesting the brain is more flexible than a strict localisation view implies.