FRONTAL GRANULAR CORTEX INPUT TO THE CINGULATE (M3), SUPPLEMENTARY (M2) AND PRIMARY (M1) MOTOR CORTICES IN THE RHESUS-MONKEY

Although frontal lobe interconnections of the primary (area 4 or Ml) a nd supplementary (area 6m or M2) motor cortices are well understood, h ow frontal granular (or prefrontal) cortex influences these and other motor cortices is not. Using fluorescent dyes in rhesus monkeys, we in vestigated the distribution of frontal lobe inputs to M1, M2, and the cingulate motor cortex (area 24c or M3, and area 23c). M1 received inp ut from M2, lateral area 6, areas 4C and PrCO, and granular area 12. M 2 received input from these same areas as well as M1; granular areas 4 5, 8, 9, and 46; and the lateral part of the orbitofrontal cortex. Inp ut from the ventral part of lateral area 6, area PrCO, and frontal gra nular cortex targeted only the ventral portion of M1, and primarily th e rostral portion of M2. In contrast, M3 and area 23c received input f rom M1, M2; lateral area 6 and area 4C; granular areas 8, 12, 9, 46, 1 0, and 32; as well as orbitofrontal cortex. Only M3 received input fro m the ventral part of lateral area 6 and areas PrCO, 45, 12vl, and the posterior part of the orbitofrontal cortex. This diversity of frontal lobe inputs, and the heavy component of prefrontal input to the cingu late motor cortex, suggests a hierarchy among the motor cortices studi ed. M1 receives the least diverse frontal lobe input, and its origin i s largely from other agranular motor areas. M2 receives more diverse i nput, arising primarily from agranular motor and prefrontal associatio n cortices. M3 and area 23c receive both diverse and widespread fronta l lobe input, which includes agranular motor, prefrontal association, and frontal limbic cortices. These connectivity patterns suggest that frontal association and frontal limbic areas have direct and preferent ial access to that part of the corticospinal projection which arises f rom the cingulate motor cortex. (C) 1993 Wiley-Liss, Inc.