Reducing Merkel cell activity in the whisker follicle disrupts cortical encoding of whisker movement amplitude and velocity

Merkel cells (MCs) and associated primary sensory afferents of the whisker follicle-sinus complex robustly code whisker self-movement, angle, and whisk phase during whisking. However, direct evidence of their roles in encoding whisker movement at cortical level is currently missing. To this end, spiking activity of primary somatosensory barrel cortex (wS1) neurons was measured in response to varying whisker deflection amplitude and velocity in transgenic mice with previously established reduced mechanoelectrical coupling at MC-associated afferents. Under reduced MC activity, wS1 neurons exhibited increased sensitivity to whisker deflection. This appeared to arise from a lack of variation in response magnitude to varying whisker deflection amplitude and velocity. This latter effect was further indicated by weaker variation in the temporal profile of the evoked spiking activity when whisker deflection amplitude and velocity varied. Nevertheless, under reduced MC activity, wS1 neurons retained the ability to discriminate stimulus features based on the timing of the first post-stimulus spike. Collectively, results from this study suggest that MCs contribute to both cortical encoding of whisker amplitude and velocity predominantly by tuning cortical response magnitude and by patterning evoked spiking activity, rather than in tuning cortical response latency.