Neuropsychology. Theories relating mental processes to particular parts of the body go back to the Ancient Greeks – e.g. philosophers such as Empedocles and Aristotle located the mind in the heart, whereas Hippocrates located it in the brain. Modern neuropsychology examines how neurological processes affect behaviour. Essentially, the study of relationships between brain and behaviour. This involves the study of brain function, for example by examining the structure of the brain and the corresponding neural activity within it. Another approach is to examine damaged brains, looking at the consequences of the damage for behaviour, perception, language etc.. Although correlation between a particular cognitive or behavioural deficit and damage to a specific brain region cannot be taken as conclusive evidence that this part of the brain is the 'source' of this cognitive function, it clearly demonstrates that this region plays some kind of an essential role in relation to this function.
Examples of this in relation to language processing were discovered in early research performed by Broca and Wernicke, in the nineteenth century. However, it has sometimes proved remarkably difficult to localize certain mental processes, in particular memory, to specific regions of the brain. This has led to a shift of emphasis, from looking for particular locations (e.g. localisation of memory functions) towards examining brain processes involved in storage and retrieval of memories.\nIn addition to examining human brains, experiments upon animal brains are also carried out by neuropsychologists, in the hope of providing insight into human brain processes. For obvious ethical reasons, deliberate damage cannot be inflicted on human brains in order to study resulting psychological deficits from particular brain lesions, whereas current ethical/professional standards do allow this with animal studies (though not without strong disagreement from a number of quarters).
Other methods involve electrical stimulation of human brains during surgery, performed under local anaesthetic, with the patient therefore conscious and able to report any resulting sensations (it should be noted that such research is only carried out as a by-product of necessary clinical intervention). The rate of blood flow to different regions can also shed light on neuropsychological questions, as can electrical recordings of brain activity. These techniques are 'non-invasive', such as magnetic resonance imaging.