Brodmann (1909) area 9

Brodmann area 9, or BA9, refers to a cytoarchitecturally defined portion of the frontal cortex in the brain of humans and other primates. It contributes to the dorsolateral and medial prefrontal cortex and plays a role in executive functions such as working memory, planning, inhibition, decision-making, and reasoning. Its cytoarchitecture is referred to as granular due to the concentration of granule cells in layer IV. Its internal pyramidal layer (V) is divisible into two sublayers, an outer layer 5a of densely distributed medium-size ganglion cells that partially merges with layer IV, and an inner, clearer, cell-poor layer 5b; the pyramidal cells of sublayer 3b of the external pyramidal layer (III) are smaller and sparser in distribution; the external granular layer (II) is narrow, with small numbers of sparsely distributed granule cells.