Centrally generated movement-related signals engage ipsilateral S1 finger representations after tetraplegia

Ipsilateral primary somatosensory cortex (S1) exhibits somatotopically organized activity during unilateral hand movements, but whether this activity depends on peripheral input remains debated. We addressed this question using functional magnetic resonance imaging (fMRI) in 14 individuals with tetraplegia and 18 able-bodied controls. Participants performed or attempted individual finger movements during 3T fMRI. We quantified movement-related univariate activity and multivariate representational structure within ipsilateral S1. Univariate activity within the anatomically defined ipsilateral S1 hand area did not differ significantly between groups, whereas a continuous spatial analysis identified greater movement-related activity in individuals with tetraplegia in S1 bands lateral to the hand representation. Multivariate analyses revealed reliable separation of finger-specific activity patterns in both groups, with no significant group difference in mean inter-finger distance. The typicality of the overall representational geometry also did not differ significantly between groups. Finally, a person with complete hand paralysis and no measurable feeling or movement still showed clear, finger-specific brain activity patterns and a typical representation of the affected hand. Together, these findings indicate that centrally generated movement-related signals can engage finger-specific representations in ipsilateral S1 without overt movement or measurable hand-related peripheral input. Ipsilateral somatotopic activity therefore cannot be explained solely by sensory reafference from the moving hand.