Cortical neuromodulation modifies cerebral vasomotor reactivity

Background and Purpose-: Cerebral vasomotor reactivity (VMR) is a capability of cerebral vessels to dilate in response to hypercapnia. Transcranial direct current stimulation (tDCS) effects on cerebral hemodynamics have been poorly studied. Methods and Results-: Ten healthy subjects underwent anodal/cathodal tDCS on the left motor cortex. Before and after tDCS, VMR assessment by transcranial Doppler and an electrocardiogram were performed. Normalized low-frequency band power of heart rate variability and its reactivity from basal to VMR condition (LFNreact) were estimated as relative markers of sympathetic activation. tDCS exerted a polarity-specific effect on both VMR (P=0.0001) and LFN_react (P=0.001). Anodal tDCS decreased VMR by 3.4%/mm Hg CO₂ bilaterally and increased LFN_react, whereas cathodal tDCS increased VMR by 0.8%/mm Hg CO2 bilaterally and reduced LFNreact. Conclusions-: Cerebral VMR is modified by tDCS. Based on the consensual changes with heart rate variability, we can hypothesize that the sympathetic nervous system could modulate the bihemispheric modification of VMR. Further studies are needed to confirm this hypothesis.