Effect of hemisphere-selective repetitive magnetic brain stimulation on middle cerebral artery blood flow velocity.

The changes of cerebral hemodynamics following repetitive hemisphere-selective magnetic stimulation over the motor cortex were investigated in 8 healthy volunteers. Bilateral simultaneous monitoring of middle cerebral artery blood flow velocity was done using transcranial Doppler ultrasonography during magnetic stimulation with single, double and triple stimuli with interstimulus intervals of 100 msec. Magnetic cortex stimulation was followed by a significant increase of ipsilateral flow velocity ranging from 5.3% +/- 2.7% for single stimuli up to 8.5% +/- 4.1% for triple stimuli and by a smaller increase of contralateral flow velocity. The ipsilateral increases are comparable to those measured previously during voluntary finger movements and indicate a physiological cortex stimulation. In parallel, the average sum of the baseline to peak hand motor response amplitudes increased from 1.5 +/- 0.7 mV (single stimuli) to 4.5 +/- 3.2 mV (triple stimuli). The increase of flow velocity in the non-stimulated hemisphere occurred during the absence of motor responses and might reflect a transcallosal activation of inhibitory neuronal structures. The occurrence of maximum velocity responses within 2-3 heartbeats following the first cortex stimulus points to a fast adjustment of cerebral perfusion in response to transcranial brain stimulation. No significant change of flow velocity was observed following motor responses evoked by unilateral magnetic stimulation of the brachial plexus or following acoustic artifacts of the coil discharge.