Extraction of intended palpation times from facial EMGs in a mouse model of active sensing

The rodent whisker system is a common model for somatosensory neuroscience and sensorimotor integration. In support of ongoing efforts to assess neural stimulation approaches for future sensory prostheses, in which we deliver optogenetic stimulation to the somatosensory cortex of behaving mice, we must coordinate feedback in real time with active sensing whisker motions. Here we describe methods for extracting the times of whisker palpations from bilateral bipolar facial electromyograms (EMG). In particular, we show onset times extracted offline from EMG envelopes lead whisker motion onsets extracted from high speed video (HSV) by ≈ 16 ms. While HSV provides ground truth for sensing motions, it is not a feasible source of real time information suitable for neurofeedback experiments. As an alternative, we find the temporal derivative of the EMG envelope reliably predicts whisker motion onsets with short latency. Thus EMG, although providing noisy and partial information, can serve well as an input to control algorithms for testing neural processing of active sensing information, and providing stimulation for artificial touch experiments.