Phase-to-rate transformations encode touch in cortical neurons of a scanning sensorimotor system

Active somatosensory perception requires the integration of signals arising from both external stimuli and motor activity. The authors found a population of neurons in rat somatosensory cortex that responded to touch only when contact occurred at a specific phase in the whisk cycle, providing information about the position of the object relative to the rat's face. Sensory perception involves the dual challenge of encoding external stimuli and managing the influence of changes in body position that alter the sensory field. To examine mechanisms used to integrate sensory signals elicited by both external stimuli and motor activity, we recorded from rats trained to rhythmically sweep their vibrissa in search of a target. We found a select population of neurons in primary somatosensory cortex that are transiently excited by the confluence of touch by a single vibrissa and the phase of vibrissa motion in the whisk cycle; different units have different preferred phases. This conditional response enables the rodent to estimate object position in a coordinate frame that is normalized to the trajectory of the motor output, as defined by phase in the whisk cycle, rather than angle of the vibrissa relative to the face. The underlying computation is consistent with gating by an inhibitory shunt.