4 - Classical connectionist models

Summary

The work of Paul Broca established the study of aphasia as an important part of clinical neurology and nineteenth-century neuroscience. The localization of language capacities in parts of the brain, and the surprising fact of cerebral dominance for language, paved the way for a “scientific phrenology”, the study of the relation between convolutions and other areas of the brain and “higher functions”. From 1861 on, the neurological literature was filled with case reports of aphasic patients, often followed by autopsies, and, more generally, with reports of patients with a variety of psychological, intellectual, and complex perceptual problems accompanied by autopsies of the brain. The most illustrious neurologists of the day published papers on the subject of aphasia.

Among other things, it was a major point of interest to confirm or disconfirm Broca's claim that the faculty of articulate language was located in the posterior portion of the left third frontal convolution. For about a decade, controversy raged about the correctness of this claim, as cases of aphasia were discovered which had lesions elsewhere in the left hemisphere, and cases came to light of patients whose autopsied brains showed lesions in Broca's area, but who had not had disorders of language in life. As Broca pointed out, the latter cases might be explained by the right hemisphere taking over speech (though the conditions under which this was possible were not completely known), but the former indicated that Broca's analysis could not be the whole story. No unified theory relating all the observations on the aphasias was available, however, and the field became “data rich and theory poor”, characterized by many interesting observations that could not be understood within any single framework.