Tonic somatosensory responses and deficits of tactile awareness converge in the parietal operculum

Although clinical neuroscience and the neuroscience of consciousness have long sought mechanistic explanations
of tactile-awareness disorders, mechanistic insights are rare, mainly because of the difficulty of depicting the fine-
grained neural dynamics underlying somatosensory processes.
Here, we combined the stereo-EEG responses to somatosensory stimulation with the lesion mapping of patients
with a tactile-awareness disorder, namely tactile extinction.
Whereas stereo-EEG responses present different temporal patterns, including early/phasic and long-lasting/tonic
activities, tactile-extinction lesion mapping co-localizes only with the latter. Overlaps are limited to the posterior
part of the perisylvian regions, suggesting that tonic activities may play a role in sustaining tactile awareness. To
assess this hypothesis further, we correlated the prevalence of tonic responses with the tactile-extinction lesion
mapping, showing that they follow the same topographical gradient. Finally, in parallel with the notion that visuo-
tactile stimulation improves detection in tactile-extinction patients, we demonstrated an enhancement of tonic
responses to visuotactile stimuli, with a strong voxel-wise correlation with the lesion mapping.
The combination of these results establishes tonic responses in the parietal operculum as the ideal neural correl-
ate of tactile awareness.