Spatiotemporal Dynamics of the Cortical Responses Induced by a Prolonged Tactile Stimulation of the Human Fingertips
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The sense of touch is fundamental for daily behavior. The aim of this work is to understand the neural network responsible for touch processing during a prolonged tactile stimulation, delivered by means of a mechatronic platform by passively sliding a ridged surface under the subject’s fingertip while recording the electroencephalogram (EEG). We then analyzed: (i) the temporal features of the Somatosensory Evoked Potentials and their topographical distribution bilaterally across the cortex; (ii) the associated temporal modulation of the EEG frequency bands. Long-latency SEP were identified with the following physiological sequence P100—N140—P240. P100 and N140 were bilateral potentials with higher amplitude in the contralateral hemisphere and with delayed latency in the ipsilateral side. Moreover, we found a late potential elicited around 200 ms after the stimulation was stopped, which likely encoded the end of tactile input. The analysis of cortical oscillations indicated an initial increase in the power of theta band (4–7 Hz) for 500 ms after the stimulus onset followed a decrease in the power of the alpha band (8–15 Hz) that lasted for the remainder of stimulation. This decrease was prominent in the somatosensory cortex and equally distributed in both contralateral and ipsilateral hemispheres. This study shows that prolonged stimulation of the human fingertip engages the cortex in widespread bilateral processing of tactile information, with different modulations of the theta and alpha bands across time.
KeywordsTouch Somatosensory cortex EEG Bilateral processing SEPs
We thank Alessio Tommasetti for the graphic design of Fig. 1. This work was supported by the Ministry of Education, Universities and Research (Italy) and the Swedish Research Council via the Italy-Sweden bilateral research project J52I15000030005 SensBrain (Brain network mechanisms for integration of natural tactile input patterns), by the EU Grant FET 611687 NEBIAS Project (NEurocontrolled BIdirectional Artificial upper limb and hand prosthesiS) and by the Ronda project, Robotica indossabile personalizzata per la riabilitazione motoria dell’arto superiore in pazienti neurologici. Regione Toscana, Bando FAS Salute 2014 PAR FAS 2007-2013.
CG designed the study, developed the experimental set up, performed the experiments, analyzed the data, discussed the results and wrote the paper. FA designed the study, co-supervised the experiments, analyzed the data, discussed the results and wrote the paper. CMO co-designed the study, developed the tactile stimulation platform and supervised its experimentation, discussed the results and wrote the paper. CF performed the experiments. CC and HJ provided neurophysiological background and discussed the results. SM co-supervised the experiments, co-designed the study, discussed the results and wrote the paper. All authors reviewed and approved the final manuscript.
Compliance with Ethical Standards
All procedures performed in this study involving healthy subjects were in accordance with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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