Transcranial direct current stimulation induces polarity-specific changes of cortical blood perfusion in the rat.

Objective: Transcranial direct current stimulation (tDCS) induces changes in cortical excitability and improves hand-motor function in chronic stroke. These effects depend on polarity, duration of stimulation and current intensity applied. Towards evaluating the therapeutic potential of tDCS in acute stroke, we investigated tDCS-effects on cerebral blood flow (CBF) in a tDCS rat model adapted for this purpose.

Methods: In a randomised crossover design eight Sprague-Dawley rats received three single cathodal and anodal tDCS for 15 min every other day. At each polarity, current intensities of 25, 50 and 100 μA were applied. CBF was measured prior and after tDCS for at least 30 min with laser Doppler flowmetry (LDF).

Results: At higher intensities (50 and 100 μA) anodal tDCS increased CBF up to 30 min. At 100 μA CBF was increased by about 25%, at 50 μA by about 18%. In contrast, cathodal tDCS led to a decrease of CBF, likewise depending on the current intensity applied. At 100 μA the effects were about 25% of baseline levels and persisted for at least 30 min. At 25 and 50 μA, baseline-levels were mostly re-established within 30 min.

Conclusions: tDCS modulates CBF in a polarity specific way, the extent of modulation depending on the stimulation parameters applied. Because of its polarity-specificity, we assume that CBF-alterations are causally related to tDCS-induced alterations in cortical excitability via neuro-vascular coupling. tDCS may constitute a therapeutic option in acute stroke patients or in patients at risk for vasospasm-induced ischemia after subarachnoid hemorrhage.