Mammals acquire much of their sensory information by actively moving their sensory organs. Yet, the principles of encoding by active sensing are not known. Here we investigated the encoding principles of active touch by rat whiskers (vibrissae). We induced artificial whisking in anesthetized rats and recorded from first-order neurons in the trigeminal ganglion. During active touch, first-order trigeminal neurons presented a rich repertoire of responses, which could not be inferred from their responses to passive deflection stimuli. Individual neurons encoded four specific events: whisking, contact with object, pressure against object, and detachment from object. Whisking-responsive neurons fired at specific deflection angles, reporting the actual whiskers' position with high precision. Touch-responsive neurons encoded the horizontal coordinate of objects' position by spike timing. These findings suggest two specific encoding-decoding schemes for horizontal object position in the vibrissal system.
