Specificity in inhibitory systems associated with prefrontal pathways to temporal cortex in primates.

The prefrontal cortex selects relevant signals and suppresses irrelevant stimuli for a given task through mechanisms that are not understood. We addressed this issue using as a model system the pathways from the functionally distinct prefrontal areas 10 and 32 to auditory association cortex, and investigated their relationship to inhibitory neurons labeled for calbindin (CB) or parvalbumin (PV), which differ in mode of inhibition. Projection neurons in area 10 originated mostly in layers 2-3 and were intermingled with CB inhibitory neurons. In contrast, projections from area 32 originated predominantly in layers 5-6 among PV inhibitory neurons. Prefrontal axonal boutons terminating in layers 2-3 of auditory association cortex were larger than those terminating in layer 1. Most prefrontal axons synapsed on spines of excitatory neurons but a significant number targeted dendritic shafts of inhibitory neurons. Axons from area 10 targeted CB and PV inhibitory neurons, whereas axons from area 32 targeted PV inhibitory neurons. The preferential association of the 2 prefrontal pathways with distinct classes of inhibitory neurons at their origin and termination may reflect the specialization of area 10 in working memory functions and area 32 in emotional communication. These findings suggest diversity in inhibitory control by distinct prefrontal pathways.