Anterior-posterior gradient in the integrated processing of forelimb movement direction and distance in macaque parietal cortex

A major issue of modern Neuroscience is to understand how the activity of cells and populations represents multiple spatial and motor features during goal-directed movements. The direction and distance (depth) of arm movements often appear to be controlled independently at the behavioral level, but it is unknown whether they share neural resources or not. We addressed this issue in parietal cortex that is known to integrate multiple signals. Using information theory, singular value decomposition and dimensionality reduction methods we compared direction and depth effect magnitude and measured their convergence across three parietal areas during an instructed delay 3D arm movement task. All methods showed a stronger direction effect during early movement preparation, whereas depth signals prevailed during movement execution. Going from anterior to posterior sectors, we found an increase in the number of cells that processed both signals and a stronger influence of depth information. These findings suggest a serial direction and depth processing that supports behavioral evidence. In addition, they reveal a gradient of joint versus independent control of these features in parietal cortex that could be framed in the context of its functional heterogeneity and its role in sensorimotor transformations.