Subdivision of frontal cortex mechanisms for language production in aphasia.

Ventrolateral prefrontal cortex (VLPFC) has long been linked to language production, but the precise mechanisms are still being elucidated. Using neuropsychological case studies, we explored possible sub-specialization within this region for different linguistic and executive functions. Frontal patients with different lesion profiles completed two sequencing tasks, which were hypothesized to engage partially overlapping components. The multi-word priming task tested the sequencing of co-activated representations and the overriding of primed word orders. The sequence reproduction task tested the sequencing of co-activated representations, but did not employ a priming manipulation. We compared patients' performance on the two tasks to that of healthy, age-matched controls. Results are partially consistent with an anterior-posterior gradient of cognitive control within lateral prefrontal cortex (Koechlin & Summerfield, 2007). However, we also found a stimulus-specific pattern, which suggests that sub-specialization might be contingent on type of representation as well as type of control signal. Isolating such components functionally and anatomically might lead to a better understanding of language production deficits in aphasia.