From three-dimensional space vision to prehensile hand movements: The lateral intraparietal area links the area V3A and the anterior intraparietal area in macaques

The posterior parietal cortex is included in the dorsal cortical visual pathway underlying the three-dimensional (3-D) visual recognition of space and objects. The neurons in the lateral intraparietal area (LIP) respond visually to the three-dimensional objects, whereas those in the anterior intraparietal area (AIP) respond to hand movements to grasp them. LIP receives visual inputs from V3A, whereas AIP projects to the premotor areas; however, it is not known whether the neurons in LIP project to AIP. We herein investigated the connectional substrates that underlie the transformation of three-dimensional vision to prehensile hand movements in the Japanese monkey (Macaca fuscata). After identifying the three-dimensional visually responsive region in the posterior part of LIP by the unit recordings, we injected a bidirectional tracer, wheat germ agglutinin conjugated to horseradish peroxidase, into one of the recording sites. We found that LIP receives neuronal projections from V3A and sends axons to AIP. To confirm our findings, we injected several orthograde tracers into V3A and retrograde tracers into AIP in the same hemispheres. We found that the V3A neurons projecting to LIP terminate in the vicinity of the LIP neurons projecting to AIP. The results suggest that the cortical connections of V3A-LIP-AIP in the lateral bank of the intraparietal sulcus play an important role in the visuomotor transformation for prehensile hand movements.