TOPOGRAPHY OF PYRAMIDAL NEURON INTRINSIC CONNECTIONS IN MACAQUE MONKEY PREFRONTAL CORTEX (AREA-9 AND AREA-46)

An understanding of the normal organization of prefrontal cortex is es sential to the recognition of pathology underlying human behavioral di sorders believed to depend on this region. We have therefore studied t he pattern of intrinsic intra- and interlaminar pyramidal neuron conne ctivity in prefrontal areas 9 and 46 (of Walker) in macaque monkey cer ebral cortex (anterior to the arcuate sulcus between the principal sul cus and midline). We made focal (200-400 mum) injections of biocytin a nd mapped the pattern of orthogradely transported label. Injections ma de into the superficial layers label wide-ranging lateral projections within the same areas of prefrontal cortex. Projections local to such small injections form a narrow band of terminals in layers 1-3 (200-40 0 mum wide, 2-4 mm long) centered on the injection site. Collateral fi bers spread orthogonal to this terminal band, making frequent bifurcat ions, to establish a series of parallel bands of terminals with uninne rvated bands between, spaced regularly across the cortex (center to ce nter 500-600 mum). The entire pattern of terminal label is stripelike, with occasional narrower interbands and crosslinks between the bands, and can extend over 7-8 mm across the cortex. These projections arise from pyramidal neurons in layers 2, 3, and 5 and terminate in layers 1-3. The stripelike pattern contrasts with patchlike patterns in other cortical regions (V1, V2, V4, motor, somatosensory) and is smaller in scale than stripelike zones of corticocortical afferent terminals to this region, reported to be 300-750 mum wide and spaced 1.0-1.5 mm cen ter to center. (C) 1993 Wiley-Liss, Inc.