Early deficit studies

Paul Broca (1824-1880) French physician, pioneered the clinical approach with human subjects. His (1861) case of ``Tan'' who had suffered massive damage to his left frontal lobe and consequently suffered loss of articulate speech, epilepsy and right hemiplegia (the central region of this lesion came to be known as Broca's area).

This was the first time that a complex mental function like language had been localised in a particular part of the cortex.

But there were found atypical cases too, in which aphasia developed after damage to the right frontal cortex, or lesions outside Broca's area affected speech, or damage to Broca's area did not affect speech. Even people who accepted correlation of damage with deficit function did not necessarily believe that the function was performed in that area (this led later to stimulation studies). Carl Wernicke in 1874 presented cases in whom damage to an area in the left temporal lobe (later, Wernicke's area) resulted in loss of comprehension while leaving speech intact. Broca's area was then popularly connected with speech production.

Though evidence connecting them to specific brain damage is not always clear-cut, broadly two types of aphasia exist (difference of detail between Broca's and motor aphasia and between Wernicke's and sensory aphasia is seen in the ability to repeat sentences which is impaired only in B and W and not in S and M (according to Norman Geschwind's classification - see Neuroscience by Purves et. al., p. 486):

• Motor aphasia (usually by lesions in 3rd frontal convolution of left hemisphere) - Patients can understand language and conversation, even complex abstract concepts, but cannot talk or write coherently. They can pronounce words with perfect intonation, so the motor aspects of word utterance are intact, but the words seem to be randomly emitted. Typical speech could go like: ``... house ran duck ink ink, resolve...''

• Sensory aphasia (usually by lesions of posterior part of the left temporal lobe, above left temporal auditory cortex) - Fluency is unaffected but understanding is impaired. Patients can understand simple requests and attend only when called by their names, but cannot understand a simple conversation. Talk is not incoherent as in Broca's aphasia; Wernicke aphasia is characterised by fluent but incongruent talk. (Syntactically correct ...)

Separation of comprehension and production areas was later challenged by Chomskian influence. See sec. .