Short-Latency Afferent Inhibition and Excitation of Primary Motor Cortex in Patients with Focal Hand Dystonia

Sensorimotor integration is abnormal in patients with writer's cramp (WC), and this may contribute to the movement disorder. The earliest somatosensory input to the primary motor cortex (M1) is the short latency afferent inhibition (SAI), a recently described inhibition of the motor evoked potential (MEP) amplitude when the magnetic stimulus is preceded by a conditioning electrical stimulus to the contralateral median nerve applied 20–26 ms earlier. SAI originates through activation of inhibitory interneurones in M1 and is mediated either via thalamo-cortical projections directly into M1 or through a fast relay…