Changes in peripheral sensory afference do not alter predictive motor planning: evidence from carpal tunnel syndrome
Anticipatory control organises motor output prior to predictable perturbations and is expressed in multi-digit tasks as anticipatory synergy adjustments (ASAs), which coordinate digit forces before movement onset. Whether such feedforward coordination depends on peripheral sensory input remains unclear. Carpal tunnel syndrome provides a model of altered median nerve afference with within-subject restoration following surgical decompression. We quantified ASA onset and amplitude in eleven individuals with carpal tunnel syndrome performing a multi-finger grasp-and-release task before and three weeks after decompression surgery. Postoperatively, sensory function improved, and total grip force decreased significantly across task phases, indicating more efficient force regulation. In contrast, ASA onset timing and amplitude were unchanged. Equivalence testing confirmed that pre- and post-operative ASA measures fell within predefined bounds of practical equivalence. These findings demonstrate a central-peripheral dissociation: feedback-mediated grip force scaling is sensory-dependent and rapidly recalibrates following afferent restoration, whereas feedforward synergy coordination remains stable despite months of degraded peripheral input. The preserved ASA suggests that central motor planning circuits maintain anticipatory coordination through efferent copy or cerebellar-mediated internal models that do not require continuous peripheral recalibration. This resilience may reflect the brains ability to maintain predictive motor planning despite chronic sensory degradation, with implications for understanding compensatory mechanisms in peripheral neuropathies and the limits of sensory-dependent motor adaptation.