Background and Purpose--It is still a matter of debate whether the ipsilateral voluntary hand activation has a facilitatory or inhibitory effect on the nondominant or affected hemisphere. To give an answer to this question is of great importance for the rehabilitation of stroke patients, because they often use the unaffected hand for compensation.

Methods--Ten healthy volunteers and 11 stroke patients were investigated using transcranial magnetic stimulation (TMS). TMS was applied to the dominant/unaffected hemisphere during performance of different tasks (simple index finger abduction, pinch grip, and power grip) at various force levels (5%, 10%, 50%, and 100% maximal voluntary contraction) with the ipsilateral hand. Peak-to-peak amplitudes of motor-evoked potentials were used as measure for motor cortex excitability.

Results--Both simple and complex tasks led to a facilitation of the contralateral corticospinal system at all levels of applied force. Not only the facilitatory effect in general but also the slope of the relationship between force level and MEP amplitude were significantly lower in stroke patients indicating that both the general activation level of the impaired motor system and the bandwidth of possible activation levels are diminished.

Conclusion--Voluntary activation of the hand does not exert an inhibitory effect on the excitability of the ipsilateral hemisphere in healthy volunteers or in stroke patients.