Former hand territory activity increases after amputation during intact hand movements, but is unaffected by illusory visual feedback

Abstract

Background: In healthy adults, hand movements are controlled largely by the contralateral primary motor cortex. Following amputation, however, movements of the intact hand are accompanied by increased activity in the sensorimotor cortices of both cerebral hemispheres.

Objective: The authors tested whether use of the intact hand reactivates the cortical territory formerly devoted to the now missing hand and whether these effects can be augmented by motor imagery (MI) and/or exposure to illusory visual "feedback" (VF) of the absent hand created with a mirror.

Methods: Functional magnetic resonance imaging (fMRI) was used to delineate the boundaries of normative sensorimotor hand representations in healthy controls. Brain activity from 11 unilateral hand amputees was recorded while they performed aurally paced thumb-finger sequencing movements with their intact hands under 4 conditions: (1) motor execution of the intact hand alone (ME), (2) ME with corresponding MI of the amputated hand, (3) ME with VF of the amputated hand, and (4) ME with MI and VF.

Results: Intact hand movements increased activity specifically within the former sensorimotor hand territory during all conditions, an effect that may be attributable to decreased levels of interhemispheric inhibition and/or use-dependent functional reorganization following amputation. This effect was not significantly increased by the addition of VF and/or MI of the amputated hand. However, in amputees, MI was associated with an expansion of this ipsilateral response into parietal, premotor, and presupplementary motor areas.

Conclusion: Active engagement of the intact hand may be critical for therapies seeking to stimulate the former hand territory.