Week 3 Reading: The Origin of Language and the Brain Norman Geschwind Brain Lesions in Man · Information on the organization of language and the brain has come from many areas: - Cases of brain tumours, though these are of limited value since the tumours distort brain tissue - Cases of penetrating brain wounds are not the best source - Stimulation duriing surgery - The Wada Test, in which sodium amytal is injected into one carotid artery, has been a major source of knowledge concerning the lateralization of language functions in the brain · The majority of the knowledge we have concerning the relationship of the brain to language has been derived from the study of adults whose brains have been damaged due to the occlusion of blood vessels (through post-mortem examination) Aphasic Disorder . The term aphasia describes disorders of language resulting from damage to the brain · Before, the distinction between language and speech was stressed . In speech disorders, the verbal output was impaired because of weakness or incoordination of the muscles of articulation · In language disorders, the criterion was that the verbal output had to be linguistically incorrect · In aphasic disorders of comprehension, the patient may lost the ability to comprehend spoken/written language yet may have normal hearing or vision when tested non-verbally - These disorders can occur without the impairment of other disabilities · Aphasias were the first demonstration of the fact that selective damage to the brain could affect one class of learned behaviour while sparing other classes · Paul Broca made two major contributions to this area: · 1) He was the first to prove that aphasia was linked to specific lesions · 2) he was also the first to show that these lesions were predominantly in the left hemisphere of the brain · However, it was Carl Wernicke who was responsible for initiating modern study of this area - He established that there were linguistic differences between the aphasias produced by damage in the left temporal lobe (Wernicke's Area) and those produced by lesions in the left frontal lobe (Broca's Area)
Linguistic Changes in Aphasia Broca's Aphasia · Broca's Aphasia patients typically produce little speech, which is emitted slowly, with great effort and with poor articulation - However, it's not just at the phonemic level that the speech of these patients is abnormal, since the patient cannot produce correct English sentences - Small grammatical words and endings are typically omitted - Patients have the capacity to find single words (i.e when asked about the weather, they may say "overcast") - Patients show a comparable disorder in written output as well, but they comprehend spoken and written language normally · In contrast to these deficiencies, the patient retains musical capacities; they can sing melodies correctly and elegantly · Because Broca's area is so close to the motor cortex, the motor cortex is often also damaged, so patients often suffer from paralysis of the right side of the body Wernicke's Aphasia ·