CORTICOCORTICAL CONNECTIONS OF AREA-F3 (SMA-PROPER) AND AREA F6 (PRE-SMA) IN THE MACAQUE MONKEY

The monkey mesial area 6 comprises two distinct cytoarchitectonic area s: F3 [supplementary motor area properly defined (SMA-proper)], locate d caudally, and F6 (pre-SMA), located rostrally. The aim of the presen t study was to describe the corticocortical connections of these two a reas. To this purpose restricted injections of neuronal tracers (wheat germ-agglutinin conjugated to horseradish peroxidase, fluorescent tra cers) were made in different somatotopic fields of F3, F6, and F1 (are a 4) and their transport plotted. The results showed that F3 and F6 di ffer markedly in their cortical connections. F3 is richly linked with F1 and the posterior premotor and cingulate areas (F2, F4, 24d). Conne ctions with the anterior premotor and cingulate areas (F6, F7, F5, 24c ) although present, are relatively modest. There is no input from the prefrontal lobe. F3 is also connected with several postrolandic cortic al areas. These connections are with areas PC, PE, and PEa in the supe rior parietal lobule, cingulate areas 23 and PEci, the opercular parie tal areas (PFop, PGop, SII) and the granular insula. F6 receives a ric h input from the anterior premotor areas (especially F5) and cingulate area 24c, whereas its input from the posterior premotor and cingulate areas is very weak. A strong input originates from area 46. There are no connections with F1. The connections with the postrolandic areas a re extremely meagre. They are with areas PG and PFG in the inferior pa rietal lobule, the disgranular insula, and the superior temporal sulcu s. A further result was the demonstration of a differential connectivi ty pattern of the cingulate areas 24d and 24c. Area 24d is strongly li nked with F1 and F3, whereas area 24c is connected mostly with F6. The present data support the notion that the classical SMA comprises two functionally distinct areas. They suggest that F6 (the rostral area) i s responsible for the ''SMA'' so-called high level motor functions, wh ereas F3 (the caudal area) is more closely related to movement executi on. (C) 1993 Wiley-Liss, Inc.