Temporal evolution of both premotor and motor cortical tuning

42 A prevailing theory in the cortical control of limb movement posits that premotor cortex initiates a 43 high-level motor plan that is transformed by the primary motor cortex (MI) into a low-level motor 44 command to be executed. This theory implies that the premotor cortex is shielded from the 45 motor periphery and therefore its activity should not represent the low-level features of 46 movement. Contrary to this theory, we show that both dorsal (PMd) and ventral premotor (PMv) 47 cortices exhibit population-level tuning properties that reflect the biomechanical properties of the 48 periphery similar to those observed in M1. We recorded single-unit activity from M1, PMd, and 49 PMv and characterized their tuning properties while six rhesus macaques performed a reaching 50 task in the horizontal plane. Each area exhibited a bimodal distribution of preferred directions 51 during execution consistent with the known biomechanical anisotropies of the muscles and limb 52 segments. Moreover, these distributions varied in orientation or shape from planning to 53 execution. A network model shows that such population dynamics are linked to a change in 54 biomechanics of the limb as the monkey begins to move, specifically to the state-dependent 55 properties of muscles. We suggest that, like M1, neural populations in PMd and PMv are more 56 directly linked with the motor periphery than previously thought. 57