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° 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.