PATTERNS OF INTRINSIC AND ASSOCIATIONAL CIRCUITRY IN MONKEY PREFRONTAL CORTEX

Both local and long-range connections are critical mediators of inform ation processing in the cerebral cortex, but little is known about the relationships among these types of connections, especially in higher- order cortical regions. We used quantitative reconstructions of the la bel arising from discrete (approximately 350 mu m diameter) injections of biotinylated dextran amine and cholera toxin B to determine the sp atial organization of the axon collaterals and principal axon projecti ons furnished by pyramidal neurons in the supragranular layers of monk ey prefrontal cortex (areas 9 and 46). Both terminals and cell bodies labeled by transport along axon collaterals in the gray matter formed intrinsic clusters which were arrayed as a series of discontinuous str ipes of similar size and shape. The co-registration of anterograde and retrograde transport confirmed that these convergent and divergent in trinsic connections also were reciprocal. Transport from the same inje ction sites along principal axons through the white matter formed asso ciational clusters which were also arrayed as a series of discontinuou s stripes. The dimensions of the anterogradely- and retrogradely-label ed associational stripes were very similar to each other and to the in trinsic stripes. These findings demonstrate that divergence, convergen ce, and reciprocity characterize both the intrinsic and associational excitatory connections in the prefrontal cortex. These patterns of con nections provide an anatomical substrate by which activation of a disc rete group of neurons would lead to the recruitment of a specific neur onal network comprised of both local and distant groups of cells. Furt hermore, the consistent size of the intrinsic and associational stripe s (approximately 275 by 1,800 mu m) suggests that they may represent b asic functional units in the primate prefrontal cortex. (C) 1996 Wiley -Liss, Inc.