Acute deprivation of unilateral sensory input rapidly enhances contralateral hand motor function, but the underlying mechanisms remain poorly understood. We herein used functional MRI to evaluate, in 14 healthy individuals, motor cortical activation for right finger motion before, during, and after sensory deprivation of left forearm induced by reversible, noninvasive ischemic nerve block (INB). Before INB, the motor task activated the left primary sensorimotor cortex (SM1) as expected. During INB, the volume of the left SM1 activation significantly increased, and, after INB, it returned to the pre-INB, baseline level. The effectiveness of the INB of the left forearm was ensured by confirming disappearance of the activation in right primary sensory cortex that is normally caused by tactile stimulation of the left index finger. These findings demonstrate that acute deafferentation of unilateral forearm causes rapid and reversible changes in the neural substrates for contralateral finger motion, mediated possibly by attenuation of transcallosal interhemispheric inhibition.