Routing of task-relevant information in mouse PPC during continuous visuomotor control

Posterior Parietal Cortex (PPC) exhibits tuning to many variables, including strong representations of visual information, movement, and behavioral biases. Whether PPC communicates all these variables to other areas is less clear. We examined PPC activity in mice performing a novel, closed-loop, 2D visuomotor joystick task that required animals to act exclusively on a task-relevant axis of visual motion. To determine what components of PPC's representation were sent to M1, we performed two-photon calcium imaging of layer 2/3 neurons in contralateral PPC of expert mice with PPC-M1 projection neurons identified via retrograde tracing. Consistent with previous results, PPC neurons exhibited random mixed selectivity and were typically most strongly modulated by joystick movement. Most of the visually responsive neurons were more strongly modulated by task-relevant than task-irrelevant visual motion. Encoding in labeled PPC-M1 neurons was similar to encoding in unlabeled neurons, with one major exception: unlike the task-relevant visual enrichment in unlabeled PPC neurons, task-relevant and task-irrelevant visual motion were encoded at similarly weak levels in PPC-M1 neurons. This argues that although PPC encodes a mix of visual, movement and other information, the PPC-M1 pathway is dominated by movement information and does not propagate PPC's learned enrichment of task-relevant visual signals.