Article Figures & Data
Figures
- Figure 1.
A, Experimental setup. The participant's hands are kept comfortably on the table, covered from view by a wooden box. With an ad hoc built brush, the experimenter stimulated the participant's fingers (e.g., the right thumb). B, Data processing and performed model. The figure summarizes the analysis pipeline. After data collection, slow activity in both EEG signal and auditory information associated with continuous touch was extracted. An encoding model was used to obtain the TRFs. C, Power spectrum (0.5–8 Hz) of the audio envelope of touch for each experimental condition. D, Tactile TRF results of right thumb stimulation. The grand average TRF (N = 27) is depicted in purple, with single participants in light gray. The topographies show the spatial distribution of the grand-averaged TRFs of the first positive (∼140 ms) and negative (∼245 ms) responses in two 45 ms time windows centered on each peak.
- Figure 2.
Tactile TRFs versus null TRFs. Top panel, The TRF corresponding to each experimental condition (colored lines) and the null TRF (in light gray). The null TRF is obtained by fitting the model on randomly mismatched pairs of stimulations (sound envelope of touch) and EEG responses. The TRFs and the null TRFs represent here the average across central contralateral electrodes with respect to the finger stimulated. For all finger stimulations, the topographies reveal a first positive central contralateral activity (∼140 ms) followed by a second negative bilateral response (∼245 ms). Lower panel, Results of the cluster-based permutation tests between the experimental TRF and null TRF, across 0–400 ms time lags and all sensors. For each experimental condition, a first positive response (pclust < 0.05) and a second negative response (pclust < 0.05) emerged.
- Figure 3.
Tactile TRFs versus control TRFs. Top panel, The TRF corresponding to each experimental condition (colored lines, same TRFs reported in Fig. 2) and the control TRF (in black). The control TRF is obtained by keeping visual and auditory spurious activity constant but without the somatosensory component of the stimulation (i.e., the experimenter's left thumb is stimulated and not the participant's). The tactile TRFs and the control TRFs represent here the average across central contralateral electrodes with respect to the finger stimulated. The topographies reveal a first positive contralateral peak (∼140 ms) followed by a second negative bilateral response (∼245 ms). Lower panel, Results of the cluster-based permutation tests between the experimental TRF and control TRF, across 0–400 ms time lags and all sensors. For each experimental condition, a positive response (pclust < 0.05) and a second negative response (pclust < 0.05) emerged.
- Figure 4.
Contrasts between hands and between fingers. Results of the cluster-based permutation paired tests between the normalized TRFs for digit lateralization (left thumb vs right thumb and left pinkie vs right pinkie) and, for digit representation (left thumb vs left pinkie and right thumb vs right pinkie), across 50–400 ms time lags and all sensors. Regarding the digit lateralization (left panel), for the left thumb versus right thumb contrast and for the left pinkie versus right pinkie contrast, results highlighted topographical differences between the TRFs associated with fingers across hands (all pclust < 0.05). Regarding digit representation, contrasting the left thumb versus left pinkie and the right thumb versus left thumb showed topographies differences across the TRFs associated with the fingers of each hand (all pclust < 0.05). Results suggest that the tactile entrainment can be used to successfully measure the somatotopy of finger representation.
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