Decrease of middle cerebral artery blood flow velocity after low-frequency repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex.

Objectives: Repetitive transcranial magnetic stimulation (rTMS) has been tried therapeutically in a variety of neuropsychiatric disorders. Both, inhibition and activation of cortical areas may be achieved using different stimulation parameters. Using low-frequency rTMS (0.9 Hz), inhibition of cortical areas can be observed.

Methods: In the present study, 38 right-handed, healthy, normotensive subjects (aged 21-50 years, mean 30.2 years, SD=4.9; 17 women) were enrolled. Twenty-five participants received active rTMS (5 min of 0.9 Hz rTMS, stimulus intensity 90% of motor threshold) of the right dorsolateral prefrontal cortex. Sham stimulation (n=13 subjects) occurred in the same manner as active rTMS, except that the angle of the coil was at 45 degrees off the skull. Simultaneously, ipsilateral and contralateral maximal middle cerebral artery (MCA) flow velocity (and pulsatility index, PI) was monitored using transcranial Doppler sonography.

Results: In the group with active rTMS, maximal MCA flow velocity decreased from a baseline (before rTMS) of 101.6 cm/s (SD=26.0) to a mean of 92.6 cm/s (SD=23.7) immediately after rTMS, T=5.06, P<0.001. This equals a mean decrease of 9.0 cm/s (SD=8.3) or approximately 8.9% of baseline flow. Five and 10 min after rTMS, there was a return to baseline. PI significantly decreased 10 min after rTMS (mean difference -0.05, SD=0.05, T=2.29, P<0.05). In the contralateral MCA, maximal flow velocity tended to increase 10 min after rTMS (mean difference +7.4 cm/s, SD=17.5; T=-2.03, P=0.054). With sham rTMS, no significant changes occurred.

Conclusions: The results from our study support the hypothesis that low-frequency rTMS may influence cerebral blood flow (CBF) over short periods of time, inducing a temporary decrease of maximal CBF in the ipsilateral MCA followed by an increase in the contralateral MCA.