Although the posterior parietal cortex has been found to play a key role in linking sensation and action, it is still unclear whether its neurons encode higher perception or motor intention. Since most studies in sensorimotor neurophysiology have utilized reactive movements to stationary goals pre-defined by sensory cues, this approach is fundamentally incapable of determining whether the observed neural activity reflects current sensory stimuli or predicts future movements.  

To overcome this barrier, the researchers elaborated an experimental framework that utilizes a flexible manual interception task in which movement is directed by predicted sensory consequences, rather than by perceived stimuli. The primary innovation of the proposed project is the disentanglement of neuronal activity related to decoupled sensory and motor variables. In such a flexible sensory-motor contingency, time-course and decoding analyses of spiking activity provides sufficient spatiotemporal resolution to clearly distinguish neuronal activity co-varying with the sensory inflow from that co-varying with the motor outflow. 

The researchers recorded the single-unit activities from area 7a and area 5d in PPC in two rhesus monkeys while they were performing the flexible manual interception task. Both neuronal tuning and population decoding analyses demonstrated that that area 7a, but not area 5d, encodes upcoming hand movement directions rather than instantaneous target location, implying a proactive role of PPC in motor preparation.