Brain Damage
The consequences of brain damage: aphasia
Aphasia: language impairments that occur as a consequence of brain damage.
Receptive aphasia: Problems understanding speech.
Expressive aphasia: Problems producing speech.
Often seen in stroke patients.
From mid to late 19th century neuropsychologists suggested that some cases have comprehension problems, whilst others have production problems.
Broca and Wernicke established centres for comprehension and production aphasic symptoms that implicated specific neuroanatomical regions of the brain
Broca's aphasia: problems producing speech relating to damage of the left frontal area of the brain. Speech output is reduced in phrase length and grammatical complexity, generated speech requires significant effort. Speech comprehension tends to be relatively normal. Dorso-lateral frontal lobes = Broca's area.
Wernicke's aphasia: problems understanding speech. Speech appears to have a normal rate of production but contains 'neologisms' (non-words ie. GWOOL for 'stool). Superior temporal gyrus location = Wernicke's area.
Language is a lateralized cognitive function; it is usually left-hemisphere dominant.
Lichtheim(1885) reasoned that Broca's area implicated in speech output, and Wernicke's area in speech input.
Arcurate fasciculus: fibres which connect the Wernicke's area (input) to Broca's area (output). Damage to the fibres can result in severely impaired word repetition. This is called conduction aphasia, it is a disruption of flow of information between Wernicke and Broca's area.