The process of acquiring motor skills through the sustained performance of complex movements is associated with neural plasticity. However, it is unknown whether even simple movements, repeated over a short period of time, are effective in inducing cortical representational changes. Whether the motor cortex can retain specific kinematic aspects of a recently practiced movement is also unknown. We used focal transcranial magnetic stimulation (TMS) of the motor cortex to evoke isolated and directionally consistent thumb movements. Thumb movements then were practiced in a different direction. Subsequently, TMS came to evoke movements in or near the recently practiced direction for several minutes before returning to the original direction. To initiate a change of the TMS-evoked movement direction, 15 or 30 min of continuous training were required in most of the subjects and, on two occasions, as little as 5 or 10 min. Substantially smaller effects followed more direct stimulation of corticofugal axons with transcranial electrical stimulation, pointing to cortex as the site of plasticity. These findings suggest that the training rapidly, and transiently, established a change in the cortical network representing the thumb, which encoded kinematic details of the practiced movement. This phenomenon may be regarded as a short-term memory for movement and be the first step of skill acquisition.

Background and Purpose-Injury-induced cortical reorganization is a widely recognized phenomenon. In contrast, there is almost no information on treatment-induced plastic changes in the human brain. The aim of the present study was to evaluate reorganization in the motor cortex of stroke patients that was induced with an efficacious rehabilitation treatment. Methods-We used focal transcranial magnetic stimulation to map the cortical motor output area of a hand muscle on both sides in 13 stroke patients in the chronic stage of their illness before and after a 12-day-period of constraint-induced movement therapy. Results-Before treatment, the cortical representation area of the affected hand muscle was significantly smaller than the contralateral side. After treatment, the muscle output area size in the affected hemisphere was significantly enlarged, corresponding to a greatly improved motor performance of the paretic limb. Shifts of the center of the output map in the affected hemisphere suggested the recruitment of adjacent brain areas. In follow-up examinations up to 6 months after treatment, motor performance remained at a high level, whereas the cortical area sizes in the 2 hemispheres became almost identical, representing a return of the balance of excitability between the 2 hemispheres toward a normal condition. Conclusions-This is the first demonstration in humans of a long-term alteration in brain function associated with a therapy-induced improvement in the rehabilitation of movement after neurological injury. Key Words: plasticity, neuronal Ⅲ transcranial magnetic stimulation Ⅲ reorganization Ⅲ physical therapy Ⅲ stroke R esearch with animals has led to the discovery that cortical reorganization occurs after injury to the nervous system. 1-3 Spontaneously occurring cortical reorganization phenomena that result from nervous system damage or conditions that involve abnormal sensory input have been shown to be associated with pathological states in humans; these include phantom limb pain, 4 tinnitus, 5 and focal hand dystonia. 6 After motor stroke, a complex pattern of reorganization has been described. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] In the subacute stage after a stroke, a reduction in motor cortex excitability and a decrease in the cortical representation area of paretic muscles have been found to occur. 17,19 This may represent a disadvantageous reorganization associated with an impaired motor function and could be due to the damage of neuronal structures or could reflect the disuse of the affected limb. 21,22 In addition to injury-related cortical reorganization, there is a second kind of process, use-dependent cortical reorganization, that results from the increased use of body parts in behaviorally relevant tasks and leads to an enhancement of the representation of those body parts in the cerebral cortex. 21,[23][24][25][26] It is possible that this process could be used to remediate pathological symptoms through the reversal or elimination of disadvantageous cortical reorganizat...