RAPID COMMUNICATION Rapid Plasticity of Human Cortical Movement Representation Induced by Practice

Classen, Joseph, Joachim Liepert, Steven P. Wise, Mark HalTo address these questions, we examined whether the dilett, and Leonardo G. Cohen. Rapid plasticity of human cortical rection of transcranial magnetic stimulation (TMS)-evoked movement representation induced by practice. J. Neurophysiol. 79: thumb movements can be modulated by repetition of simple 1117–1123, 1998. The process of acquiring motor skills through thumb movements during a short period of time. TMS at the sustained performance of complex movements is associated weak stimulus intensities predominantly activates pyramidal with neural plasticity. However, it is unknown whether even simple tract cells indirectly via their afferent input (Rothwell et al. movements, repeated over a short period of time, are effective in 1991) and thus reflects properties of the stimulated neuronal inducing cortical representational changes. Whether the motor cornetwork. When delivered to the optimal scalp position for tex can retain specific kinematic aspects of a recently practiced stimulation of the motor cortex (Cohen et al. 1990; Wassermovement is also unknown. We used focal transcranial magnetic stimulation (TMS) of the motor cortex to evoke isolated and direcmann et al. 1996), TMS can elicit isolated and reproducible tionally consistent thumb movements. Thumb movements then thumb movements in most individuals. The hypothesis of were practiced in a different direction. Subsequently, TMS came these experiments was that performance of simple, unskilled to evoke movements in or near the recently practiced direction for repetitive thumb movements can trigger plasticity and that several minutes before returning to the original direction. To initithese plastic changes encode kinematic details of the pracate a change of the TMS-evoked movement direction, 15 or 30 ticed movement. min of continuous training were required in most of the subjects and, on two occasions, as little as 5 or 10 min. Substantially smaller M E T H O D S effects followed more direct stimulation of corticofugal axons with transcranial electrical stimulation, pointing to cortex as the site of Procedure and subjects plasticity. These findings suggest that the training rapidly, and transiently, established a change in the cortical network representSubjects were seated comfortably in a chair firmly connected to ing the thumb, which encoded kinematic details of the practiced a custom-built aluminum frame designed to immobilize the head movement. This phenomenon may be regarded as a short-term and keep the stimulation coil in a constant position with reference memory for movement and be the first step of skill acquisition. to the head. The subject’s right forearm was immobilized in a semipronated position in a molded arm rest. The thumb was left entirely free to move and the other fingers were supported at their