Spatial cortical patterns of metabolic activity in monkeys performing a visually guided reaching task with one forelimb.

The 2-[14C]deoxyglucose method was used to map the metabolic activity in the neocortex of monkeys (Macaca nemestrina) performing a visually guided reaching task with one forelimb. Monkeys received liquid reward for correct, single directional reaching movements, which were required at a rate of about 10 per minute. We estimated the weighted average of local glucose consumption within several neocortical areas, and we reconstructed quantitative, high-resolution, two-dimensional maps of the detailed spatiointensive patterns of activity. Our findings demonstrate the involvement of the striate and prestriate cortices, the inferior intraparietal and superior temporal visual association areas, the frontal eye field and the caudal periprincipal cortex, the primary somatosensory and the related superior intraparietal area, the primary and association auditory cortices, the superior temporal multimodal region, and the premotor, primary, supplementary, and cingulate motor areas. The visual cortex in the superior temporal and the intraparietal sulci, which is concerned with "where", was activated during visually guided reaching. In contrast, the inferior temporal visual association cortex, which is concerned with "what", was not involved in our study. We suggest that the activated direction-selective layer four of V1 and the thick stripes of V2 convey visuomotor information to the activated cortex in the posterior bank and the floor of the superior temporal sulcus, which may encode the constantly updated position of the moving forelimb. In parallel, the activated cortex in the ventral part and the lateral bank of the intraparietal sulcus may encode visuospatial information related to the localization of the visual target in the extrapersonal space. Furthermore, the dorsal part of the medial bank of the intraparietal sulcus may be involved in proprioceptive guidance of movement, based on the parallel metabolic effects shown only contralateral to the moving forelimb within this region and the forelimb representations in the primary somatosensory and motor cortices. Finally, the bilaterally activated network including the inferior postarcuate skeletomotor and prearcuate oculomotor cortical fields and the caudal periprincipal region 46 may participate in sensory and oculomotor to motor transformations, in parallel with the medial and lateral intraparietal cortices with which this network is reciprocally interconnected.