Aphasia

Peri-sylvian aphasias

Structures around the sylvian fissure mediate auditory language repetition. Auditory signals are processed by Heschl's gyrus (primary auditory cortex), and phonemic analysis probably takes place in the adjacent auditory association cortex (Wernicke's area). Speech is encoded by more anterior regions (among them, Broca's area, in front of the motor cortex), and these regions direct the adjacent motor cortex to produce the appropriate movements. Damage to any of these regions impairs language repetition, the hallmark of the perisylvian aphasias. Language comprehension requires that the phonetically analyzed information be communicated to regions outside the perisylvian region (among them, the angular gyrus).

Broca's aphasia

Characterized by non-fluent speech, poor repetition and relatively spared comprehension. Lesions are in Broca's area and adjacent cortex.

Wernicke's aphasia

Fluent, but nonsensical speech with phonemic paraphasias (substitution of incorrect sounds), and impaired repetition and comprehension. Lesions are in Wernicke's area.

Conduction aphasia

Fluent speech, spared comprehension, and poor repetition. Lesions may disconnect Wernicke's from Broca's area.

Global aphasia

Non-fluent speech, poor repetition and poor comprehension. The entire perisylvian cortex is involved.

Transcortical aphasias

Transcortical aphasias can be characterized by intact repetition. Lesions are more varied than with perisylvian aphasias. Transcortical aphasias may also result from subcortical damage.

Transcortical motor aphasia

Speech is non-fluent, but repetition and comprehension are spared. Lesions are frontal, but Broca's area is not affected.

Transcortical sensory aphasia

Speech is fluent, yet empty and often includes substitutions of incorrect words. Comprehension is poor, yet repetition is normal. Lesions are posterior, but Wernicke's area is not affected.

Anomic aphasia

This is like a mild transcortical sensory aphasia, where comprehension is not affected, yet naming is impaired. Speech is fluent, with circumlocution, when the person cannot find the right word. Repetition is normal.

Mixed transcortical aphasia

Speech is non-fluent, with poor comprehension, but with normal repetition. People may echo fragments of other people's speech. Lesions usually include those of both transcortical motor and transcortical sensory aphasias.

See also