Mixed-selective organization of reach and grasp in the primate fronto-parietal network

Reaching and grasping in primates require coordinated control of several parameters, such as grip type, wrist orientation, spatial position, and hand laterality. The anterior intraparietal (AIP) and rostral ventral premotor (F5) areas are key hubs in this process. This study used electrophysiological data to investigate how these parameters are co-represented in AIP and F5. The results indicate that neurons predominantly show mixed selectivity with stable temporal organization related to movement and pre-movement phases. This uncategorizable mixture of selectivity allows flexible decoding. Despite condition-dependent shifts, selectivity preferences were largely preserved across task conditions. Notably, object-related factors (orientation and position) remained more stable during grip type changes in AIP, whereas grip type was more stable in F5, suggesting a functional hierarchical organization of context-dependent coding in both areas. Together, despite the continuous range of mixed selectivity at the single-neuron level, neural ensembles exhibit a stable organization on the temporal and functional scales, enabling flexible readouts.