Architectonics and cortical connections of the ventral premotor area F5 of the macaque

Abstract

The rostral part of the macaque ventral premotor cortex (PMv), corresponding to the histochemical area F5, is a functionally heterogeneous cortical sector. Two main populations of visuomotor neurons were electrophysiologically identified in this premotor sector : “Mirror neurons” and “Canonical neurons”. “Mirror neurons” were mostly found in the F5 sector extending on the lateral convexity while “Canonical neurons” were found in the F5 sector located in the posterior bank of the inferior arcuate sulcus (IAS). In the present study, we aimed to verify whether there is an anatomical counterpart underlying this differential distribution of F5 visuomotor neurons using both, architectonic and hodological approaches. The results showed that the rostral PMv hosts three architectonically distinct areas, which occupy different parts of F5. One area, referred to as “convexity” (F5c) F5, extends on most of the postarcuate convexity cortex adjacent to the IAS. The other two areas, referred to as “posterior” (F5p) and “anterior” (F5a) F5, lie within the postarcuate bank at different antero-posterior levels. This subdivision was strongly supported by our hodological data showing that the three architectonically defined PMv areas are characterized by different connectional patterns. F5p was strongly connected with the hand field of F1, with the arm-related premotor fields of F4, F2vr, F6 and F3 and with the cingulate areas 24d and 24c. Parietal afferents originated from areas PF, PFG, AIP, PEip and SII region. Weak connections with the prefrontal cortex involved the caudal sector of area 46v. Finally, F5p was a source of corticospinal projections. F5c was strongly connected with face/mouth fields of F4 and F3 and weakly with F1. Cingulate connections involved areas 24c and 24a. Strong connections were observed with caudal frontal opercular areas. Parietal afferents mostly originated from PF, SII and PV (mostly face/mouth representations), but also from AIP and PFG. Connections with the prefrontal cortex involved a more rostral sector of area 46v and area 12r. F5a lacked connections with F1 and displayed connections with F4, F6 and cingulate areas, 24c, 24d and 24a. Strong connections were observed with rostral frontal opercular areas. Parietal afferents originated mostly from PF, PFG, AIP and from the hand representations of PV and SII. Relatively robust prefrontal connections were observed with rostral area 46v and areas 12r and 12l. The present data, together with functional data available in the literature, suggest that the three rostral PMv areas F5p, F5a and F5c correspond to functionally distinct cortical entities. Thus, the current study provides a new anatomical frame of reference of the macaque PMv that appears to be very promising for gaining new insight into the possible role of this premotor sector in different aspects of motor control and cognitive motor functions.