Adaptation in somatosensory afferents improves rate and temporal coding of vibrotactile stimulus features.

Most neurons reduce their firing rate during sustained stimulation. We tested if adaptation in primary low-threshold mechanoreceptors (LTMRs) improves their ability to encode vibrotactile stimulation of the rat hind paw. If adaptation were to help disambiguate the neural representation of different stimuli, stimulus features could be more accurately discriminated from adapted LTMR responses than from initial LTMR responses. Therefore, we applied decoders to the initial and late (adapted) phases of LTMR ensemble responses to assess discrimination of stimulus features. Rate coding of stimulus intensity was improved when firing rate was differentially modulated depending on stimulus features because this altered tuning non-uniformly across neurons. Temporal coding of stimulus frequency (based on interspike intervals, ISIs) was improved via reduction of spike-timing jitter. These results show that adaptation in LTMRs acts via different mechanisms - tuning curve alterations and jitter reduction - to improve rate-based coding of stimulus intensity and ISI-based coding of stimulus frequency.