EEG time-warping to study non-strictly-periodic EEG signals related to the production of rhythmic movements

Dynamic acoustic salience evokes motor responses

Audio-motor integration is currently viewed as a predictive process in which the brain simulates upcoming sounds based on voluntary actions. This perspective does not consider how our auditory environment may trigger involuntary action in the absence of prediction. We address this issue by examining the relationship between acoustic salience and involuntary motor responses. We investigate how acoustic features in music contribute to the perception of salience, and whether those features trigger involuntary peripheral motor responses. Participants with little-to-no musical training listened to musical excerpts once while remaining still during the recording of their muscle activity with surface electromyography (sEMG), and again while they continuously rated perceived salience within the music using a slider. We show cross-correlations between 1) salience ratings and acoustic features, 2) acoustic features and spontaneous muscle activity, and 3) salience ratings and spontaneous muscle activity. Amplitude, intensity, and spectral centroid were perceived as the most salient features in music, and fluctuations in these features evoked involuntary peripheral muscle responses. Our results suggest an involuntary mechanism for audio-motor integration, which may rely on brainstem-spinal or brainstem-cerebellar-spinal pathways. Based on these results, we argue that a new framework is needed to explain the full range of human sensorimotor capabilities. This goal can be achieved by considering how predictive and reactive audio-motor integration mechanisms could operate independently or interactively to optimize human behavior.

Dynamics of the perception and EEG signals triggered by tonic warm and cool stimulation

Thermosensation is crucial for humans to probe the environment and detect threats arising from noxious heat or cold. Over the last years, EEG frequency-tagging using long-lasting periodic radiant heat stimulation has been proposed as a means to study the cortical processes underlying tonic heat perception. This approach is based on the notion that periodic modulation of a sustained stimulus can elicit synchronized periodic activity in the neuronal populations responding to the stimulus, known as a steady-state response (SSR). In this paper, we extend this approach using a contact thermode to generate both heat- and cold-evoked SSRs. Furthermore, we characterize the temporal dynamics of the elicited responses, relate these dynamics to perception, and assess the effects of displacing the stimulated skin surface to gain insight on the heat- and cold-sensitive afferents conveying these responses. Two experiments were conducted in healthy volunteers. In both experiments, noxious heat and innocuous cool stimuli were applied during 75 seconds to the forearm using a Peltier-based contact thermode, with intensities varying sinusoidally at 0.2 Hz. Displacement of the thermal stimulation on the skin surface was achieved by independently controlling the Peltier elements of the thermal probe. Continuous intensity ratings to sustained heat and cold stimulation were obtained in the first experiment with 14 subjects, and the EEG was recorded in the second experiment on 15 subjects. Both contact heat and cool stimulation elicited periodic EEG responses and percepts. Compared to heat stimulation, the responses to cool stimulation had a lower magnitude and shorter latency. All responses tended to habituate along time, and this response attenuation was most pronounced for cool compared to warm stimulation, and for stimulation delivered using a fixed surface compared to a variable surface.