Discriminative and affective touch converge: Somatosensory cortex represents Aß input in a CT-like manner

Abstract

Current theory divides the human mechanical sense into discriminative and affective systems. A discriminative system supports tactile exploration and manipulation via fast A-beta signaling, whereas an affective system supports the pleasure of friendly interpersonal touch via slow CT signaling. To probe this system segregation, we recorded the electroencephalogram from participants being stroked and reporting stroke pleasantness. We observed a somatosensory negativity that was maximal for CT optimal as compared with sub-optimal velocities, that predicted subjective pleasantness, and showed only for stroking of hairy skin known to be CT innervated. Importantly, the latency of this negativity preceded C fiber input to the brain by several hundred milliseconds and is best explained by interactions between CT and A-beta processes in the spinal cord. Our data challenge the divide between discriminative and affective touch implying instead that both fast A-beta and slow CT signaling play an important role in tactile pleasure.

Aβ-CT affective touch: Touch pleasantness ratings for gentle stroking and deep pressure exhibit dependence on A-fibers

“…Finally, a study using electroencephalography (EEG) demonstrates modulation of primary somatosensory cortex by gentle stroking prior to arrival of the slower CT signal, correlated with subsequent touch pleasantness ratings. This suggests CT modulation of dorsal column (Aβ-associated) spinal projections [15]. These findings call into question the causal role of A versus CT inputs in the pleasantness of gentle stroking.…”