Corticocortical connections of area F3 (SMA-proper) and area F6 (pre-SMA) in the macaque monkey

Abstract

The monkey mesial area 6 comprises two distinct cytoarchitectonic areas: F3 [supplementary motor area properly defined (SMA-proper)], located caudally, and F6 (pre-SMA), located rostrally. The aim of the present study was to describe the corticocortical connections of these two areas. To this purpose restricted injections of neuronal tracers (wheat germ-agglutinin conjugated to horseradish peroxidase, fluorescent tracers) were made in different somatotopic fields of F3, F6, and F1 (area 4) and their transport plotted. The results showed that F3 and F6 differ markedly in their cortical connections. F3 is richly linked with F1 and the posterior premotor and cingulate areas (F2, F4, 24d). Connections 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 cortical areas. These connections are with areas PC, PE, and PEa in the superior parietal lobule, cingulate areas 23 and PEci, the opercular parietal areas (PFop, PGop, SII) and the granular insula. F6 receives a rich 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 are extremely meagre. They are with areas PG and PFG in the inferior parietal lobule, the disgranular insula, and the superior temporal sulcus. A further result was the demonstration of a differential connectivity pattern of the cingulate areas 24d and 24c. Area 24d is strongly linked 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) is responsible for the "SMA" so-called high level motor functions, whereas F3 (the caudal area) is more closely related to movement execution.