AQA Psychology for A Level Year 2 - Student Bk

The specification says… Localisation of function in the brain Localisation of function in the brain: motor, somatosensory, visual, auditory and language centres; Broca’s and Wernicke’s areas. The human brain is surely one of the most complex and fascinating of all biological systems. On this spread, we discuss the idea that different functions of the brain are localised in specific areas as well as taking a whistle-stop tour through some of the key parts of the brain. Key terms Localisation of function – The theory that different areas of the brain are responsible for different behaviours, processes or activities. Motor area – A region of the frontal lobe involved in regulating movement. Somatosensory area – An area of the parietal lobe that processes sensory information such as touch. Visual area – A part of the occipital lobe that receives and processes visual information. Auditory area – Located in the temporal lobe and concerned with the analysis of speech-based information. Broca’s area – An area of the frontal lobe of the brain in the left hemisphere (in most people) responsible for speech production. Wernicke’s area – An area of the temporal lobe (encircling the auditory cortex) in the left hemisphere (in most people) responsible for language comprehension. Localisation of function in the brain Localisation versus holistic theory During the 19th century, scientists such as Paul Broca and Karl Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions. Before these investigations (and before the case of Phineas Gage – see facing page), scientists generally supported the holistic theory of the brain – that all parts of the brain were involved in the processing of thought and action. In contrast, Broca and Wernicke argued for localisation of function (sometimes referred to as cortical specialisation ). This is the idea that different parts of the brain perform different tasks and are involved with different parts of the body. It follows then, that if a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected. Hemispheres of the brain and the cerebral cortex The brain is divided into two symmetrical halves called left and right hemispheres. Some of our physical and psychological functions are controlled or dominated by a particular hemisphere – this is called lateralisation (see next spread). As a general rule, activity on the left-hand side of the body is controlled by the right hemisphere and activity on the right-hand side of the body by the left hemisphere. The outer layer of both hemispheres is the cerebral cortex (or ‘cortex’) like a tea cosy covering the inner parts of the brain. This ‘tea-cosy’ is about 3 mm thick and is what separates us from other animals because the human cortex is much more developed. The cortex appears grey due to the location of cell bodies (hence the phrase ‘grey matter’ to describe the surface appearance of the brain). The motor, somatosensory, visual and auditory centres The cortex of both hemispheres is sub-divided into four lobes which are named after the bones beneath which they lie: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe (see diagram on facing page). Each lobe is associated with different functions. At the back of the frontal lobe (in both hemispheres) is the motor area which controls voluntary movement in the opposite side of the body. Damage to this area of the brain may result in a loss of control over fine movements. At the front of both parietal lobes is the somatosensory area which is separated from the motor area by a ‘valley’ called the central sulcus . The somatosensory area is where sensory information from the skin (e.g. related to touch, heat, pressure,etc.) is represented. The amount of somatosensory area devoted to a particular body part denotes its sensitivity, for instance, receptors for our face and hands occupy over half of the somatosensory area. In the occipital lobe at the back of the brain is the visual area (or visual cortex). Each eye sends information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex. This means that damage to the left hemisphere, for example, can produce blindness in part of the right visual field of both eyes. Finally, the temporal lobes house the auditory area , which analyses speech-based information. Damage may produce partial hearing loss; the more extensive the damage, the more extensive the loss. In addition, damage to a specific area of the temporal lobe – Wernicke’s area (discussed below) – may affect the ability to comprehend language. The language area of the brain Unlike the areas above which are found in both hemispheres, language is restricted to the left side of the brain in most people. In the 1880s, Paul Broca, a surgeon, identified a small area in the left frontal lobe responsible for speech production. Damage to Broca’s area causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency (as seen in a number of Broca’s patients like ‘Tan’ – so-called because that was the only word he could say). Around the same time as Broca, Karl Wernicke was describing patients who had no problem producing language but severe difficulties understanding it, such that the speech they produced was fluent but meaningless. Wernicke identified a region ( Wernicke’s area ) in the left temporal lobe as being responsible for language comprehension which would result in Wernicke’s aphasia when damaged. Patients who have Wernicke’s aphasia will often produce nonsense words ( neologisms ) as part of the content of their speech. The brain – like the Earth – is divided into two distinct hemispheres. Chapter 2 Biopsychology 38 •