Human 8- to 10-Hz pulsatile motor output during active exploration of textured surfaces reflects the textures' frictional properties.

Active sensing in biological system consists of emitting/receiving a periodic signal to explore the environment. The signal can be emitted toward distant objects, as in echolocation, or in direct contact with the object, for example, whisking in rodents. We explored the hypothesis that a similar mechanism exists in humans. Humans generate periodic signals at ~10 Hz during voluntary finger movements, which reflects a pulsatile motor command in the central nervous system. In the present study, we tested whether the ~10-Hz signal persists during the active exploration of textures and whether the textures' features can modulate the signal. Our results confirm our assumptions. The ~10-Hz signal persisted during active touch, and its amplitude increased with textures of higher friction. These findings support the idea that the ~10-Hz periodic signal generated during voluntary finger movements is part of an active sensing mechanism acting in a pulse-amplitude modulation fashion to convey relevant tactile information to the brain. For the first time, we show that pulsatile motor output during voluntary movement of a finger persists during active exploration of a surface. We propose that this is part of an active sensing system in humans, with generation of an ~10-Hz signal during active touch that reinforces extraction of information about features of the touched surface.