Sensory and premotor connections of the orbital and medial prefrontal cortex of macaque monkeys

Sensory and premotor inputs to the orbital and medial prefrontal cortex (OMPFC) were studied with retrograde axonal tracers. Restricted areas of the lateral and posterior orbital cortex had specific connections with visual-, somatosensory-, olfactory-, gustatory-, and visceral-related structures. More medial areas received few direct sensory inputs. Within the lateral and posterior orbital cortex, area 12l received a substantial projection from visual areas in the inferior temporal cortex (TE). Area 12m received somatosensory input from face, digit, or forelimb regions in the opercular part of area 1-2, in area 7b, in the second somatosensory area (SII), and in the anterior infraparietal area (AIP). Areas 13m and 13l also received a projection from the opercular part of areas 1-2 and 3b. The posteromedial and lateral agranular insular areas (Iapm and Ial, respectively) received fibers from the ventral part of the parvicellular division of the ventroposterior medial nucleus of the thalamus (VPMpc) that may represent a visceral afferent system. The dorsal part of VPMpc projected to the adjacent gustatory cortex. These restricted inputs from several sensory modalities and the convergent corticocortical connections to orbital areas 13l and 13m suggest a network related to feeding. The OMPFC was also connected to premotor cortex in ventral area 6 (areas 6va and 6vb), in cingulate area 24c, and probably in the supplementary eye field. Area 6va projected to area 12m, whereas a region of area 6vb projected to area 13l. The region of the supplementary eye field projected to areas 12l, 12o, and 12r. Area Ial received fibers from area 24c. Lighter and more diffuse projections also reached wider areas of the OMPFC. For example, injections in several orbital areas labeled a few cells scattered through the anterior part of area TE and the superior temporal gyrus. There was also a projection to the intermediate agranular insular area (Iai) and to areas 13a and 12o from the apparently multimodal areas in the superior temporal sulcus and gyrus.