After a left-hemisphere stroke, which neural regions' damage is most often linked to apraxia of speech (AOS)?

• A. Wernicke's area only
• B. Insula and left inferior frontal gyrus (Broca's area) and supplementary motor area
• C. Primary motor cortex
• D. Cerebellum

Answer: (B)

Apraxia of speech results from disruption of the brain’s motor planning for speech. The regions most often linked to AOS when the left hemisphere is damaged are the insula, the left inferior frontal gyrus (Broca’s area), and the supplementary motor area. These areas form a network that plans, sequences, and initiates the articulatory movements needed for fluent speech. When this fronto-insular–motor planning network is damaged, speech becomes slow, effortful, and distorted, with inconsistent errors and visible attempts to correct them, even when the person knows what they want to say and their muscles aren’t weak.

Damage to the primary motor cortex tends to produce weakness and motor execution problems—dysarthria—rather than the planning difficulties characteristic of AOS. The cerebellum, when affected, leads to ataxic dysarthria with timing and coordination problems. Wernicke’s area is mainly tied to language comprehension, so its injury more often yields aphasia rather than the motor planning deficits seen in AOS. Therefore, injury to the insula, left inferior frontal gyrus, and supplementary motor area best accounts for apraxia of speech after a left-hemisphere stroke.