Neural correlates of vibrissa resonance; band-pass and somatotopic representation of high-frequency stimuli.

The array of vibrissae on a rat's face is the first stage of a high-resolution tactile sensing system. Recently, it was discovered that vibrissae (whiskers) resonate when stimulated at specific frequencies, generating several-fold increases in motion amplitude. We investigated the neural correlates of vibrissa resonance in trigeminal ganglion and primary somatosensory cortex (SI) neurons (regular and fast spiking units) by presenting low-amplitude, high-frequency vibrissa stimulation. We found that somatosensory neurons showed band-pass tuning and enhanced sensitivity to small amplitude stimuli, reflecting the resonance amplification of vibrissa motion. Further, a putative somatotopic map of frequency selectivity was observed in SI, with isofrequency columns extending along the representations of arcs of vibrissae, in agreement with the gradient in vibrissa resonance across the vibrissa pad. These findings suggest several parallels between frequency processing in the vibrissa system and the auditory system and have important implications for detection and discrimination of tactile information.