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17 September 2014
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  • Studying people with brain damage
  • The effects of stroke on behaviour
  • Localization of brain function
  • Images of the brain: positron emission tomography:

Studying people with brain damage

Neuropsychology is concerned with the relationship between the human brain and behaviour. The classic way of investigating brain functions is to examine individuals with various forms of brain damage, like head injuries, tumours, or neurological disease. Any changes in behaviour are assumed to be due to this brain tissue damage.

The effects of stroke on behaviour

Strokes are a very common form of brain damage, caused by a reduction in blood flow to particular parts of the brain. Common effects of stroke include loss of muscle control on one side of the body, facial droop, and temporary paralysis due to lack of motor control. The effects of a stroke depend on the particular area of the brain where blood flow has been disrupted. For example, strokes that damage tissue at the back of the brain often cause visual difficulties, even if the eyes are perfectly intact. In contrast, stroke damage to the frontal lobes of the brain can cause problems with memory and attention.

Localization of brain function

Studies of stroke and other brain-damaged patients have shown a localization of brain function. That is, particular brain areas are dedicated to particular behaviours. For example, in most people, areas of the left hand side of the cortex known as Broca's area and Wernicke's area are used in producing and understanding language.

Images of the brain: positron emission tomography:

Recently, studies of brain-damaged individuals have been supplemented with imaging techniques like positron emission tomography (PET). In a PET scan, water containing a radioactive form of oxygen is injected into the bloodstream. The radioactive water emits subatomic particles called positrons, which quickly degrade and give off gamma rays, detected by sensors placed around the head.

Blood vessels enlarge during periods of activity, so those areas that are especially active will emit higher levels of gamma rays. Different densities of gamma rays can then be converted into different colours on a map of the brain, allowing researchers to see which brain areas are involved in particular activities.

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