Neuropsychology: Language and Brain

Paul Broca (1861), a French surgeon, found that injuries to the third left frontal convolution results aphasia. This is called Motor aphasia or Broca’s aphasia. Its localization in one hemisphere of the brain indicated that the brain did not behave equipotentially. Carl Wernicke (1848-1904) presented cases in which patients had lesions of the superior posterior part of the left hemisphere and had trouble comprehending language (Wernicke’s aphasia). This resulted in the idea that component processes of language were localized. On the basis of Wernicke's observations, the modern doctrine of component process localization and disconnection syndromes was begun. This doctrine states that complex mental functions, such as language, represent the combined processing of a number of subcomponent processes represented in widely different areas of the brain.
Jean Baptiste Bouilland highlighted the importance of the frontal lobes to speech and argued that since, writing, drawing and painting are performed by the right hand, then the left hemisphere controls these functions. In 1870, Gustave Theodore Fritsch and Eduard Hitzig (German Physicians) discovered that the neo-cortex was not only exitable by electrical stimulation but also selectively excitable. They found that selective stimulation of the anterior part of the brain in dogs elicited movement of particular body parts. Goltz argued, if these areas are important, then their removal would abolish the behaviour. He decorticated (removed the outer part of the brain) the dogs. But the functions were not abolished, but reduced.
On the basis of Goltz’s findings, John Hughlings Jackson, a British Neurologist, suggested that nervous system consisted of a series of layers organized in functional hierarchy, with higher level layers (the cerebral cortex) controlling more complex aspects of behaviour, and lower structure (spinal cord, medulla and pons) allowing lower-level functions. Jackson’s work in the field of focal epilepsy also localized sensory and motor function to particular brain region.