The Touch of Sight: Inter-Subject Correlation unveils crossmodal convergence in the human brain
Poster No:
2037
Submission Type:
Late-Breaking Abstract Submission
Authors:
Nicolo Castellani1, Francesca Simonelli1, Davide Bottari1, Jordi Manuello2, Donato Liloia2, Sergio Duca3, Emiliano Ricciardi1, Giacomo Handjaras1, Francesca Garbarini2
Institutions:
1IMT School for advanced studies Lucca, Lucca (Italy), 2University of Turin, Turin (Italy), 3Ospedale Koelliker, Turin (Italy)
First Author:
Co-Author(s):
Late Breaking Reviewer(s):
Introduction:
Feeling a touch is different from observing a touch. However, previous observations suggest shared neural representations between the two sensory modalities1,2,3. To clarify this phenomenon, in this fMRI study, we employed inter-subject correlation (ISC) analysis4, a measure of brain synchronization across individuals. Crucially, this approach assumes that brain areas synchronized across individuals represent the same features. Specifically, ISC5 was performed between two groups of participants exposed either to a continuous passive tactile stimulation, or to a naturalistic visual movie of an identical tactile stimulation. Any evidence of synchronization across the two groups would indicate a shared representation of tactile perception (Real-Touch) and tactile observation (Visual-Touch).
Methods:
The experimental design consisted of two between-subject conditions. The Real-Touch group (N=19, 8M, mean age 28±1) underwent a continuous tactile stimulation of both hands' digits and dorsum, covered from view; the Visual-Touch group (N=20, 10M, mean age 25±2) was presented with a video showing hands being stimulated with a brush. Catch trials were included throughout the stimulation to ensure subjects' attention. fMRI responses were measured using a Philips 3T Ingenia scanner. fMRI data were preprocessed using AFNI6 and cleaned from motion parameters and signal trends. ISC analysis was performed computing Pearson's correlation coefficient between the BOLD activity elicited in the Real-Touch and in the Visual-Touch subjects. Statistical significance of the ISC values was assessed using a non-parametric permutation test (1,000 permutations). The statistical threshold was set at p<0.001 FWEc with NN=20 as the minimum cluster size. Subsequently, in the significant ROIs, we tested the correlation's drop when introducing mismatched information related to lateralization and digitotopy. Statistical significance was assessed through a permutation test and FDR correction for multiple comparisons.
Results:
ISC between individuals exposed to Real-Touch or Visual-Touch isolated brain regions responding to both visual and tactile stimuli: a significant synchronization was found in several brain areas (10 ROIs). Among them, significant results were found in S1 and S21,2 and in the middle temporal area (Fig.1). Subsequently, we found significant reduction in ISC while introducing mismatching information (i.e. digitotopy and lateralization) in the majority of the identified ROIs.
·Fig.1. Inter Subject Correlation between visual and tactile naturalistic stimulation. Colored areas represent brain regions showing significant synchronization. Significant results were mainly located
Conclusions:
Our results suggest the presence of shared neural representations between real and observed touch. Moving from previous literature, we directly measured the similarities in brain activity when the same information is presented through different senses, identifying a multimodal representation of the hands. Crucially, primary and secondary somatosensory cortices are directly involved in this shared representation. The synchronization in the posterior portions of the postcentral gyrus (BA2) is coherent with evidence supporting the integration of touch and vision in this region8. Besides, the activation in the middle temporal regions may relate to the representation of tactile and visual motion information9 or to multimodal body parts representation10. This multimodal representation is influenced by bodily information, such as hand lateralization and digit representations, as evidenced by the correlation's drop when introducing mismatched information. Through an innovative methodological approach, we demonstrated a direct contribution of the somatosensory cortices in building a shared neural representation between vision and touch. This would open the way for future investigations of heteromodal remapping of visual input in somatosensory cortices, following permanent sensory deprivations, as in upper limbs agenesis or amputation.
Perception, Attention and Motor Behavior:
Perception: Multisensory and Crossmodal 1
Perception: Tactile/Somatosensory 2
Keywords:
FUNCTIONAL MRI
Perception
Touch
Vision
1|2Indicates the priority used for review
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Provide references using APA citation style.
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