A phenomological model for capturing cerebrovascular reactivity to anodal transcranial direct current stimulation

The paper presents a phenomological model to capture cerebrovascular reactivity (CVR) that represented the capacity of blood vessels to dilate during anodal transcranial direct current stimulation (tDCS). Anodal tDCS modulated cortical neural activity leading to CVR, where it can identify impaired cerebral microvessels functionality leading to impairments of cerebral blood flow that may cause impairments in the cerebral functions. In this study, CVR was probed with near infra-red spectroscopy (NIRS) where NIRS recorded changes in oxy-haemoglobin and deoxy-haemoglobin concentrations during anodal tDCS-induced activation of the cortical region located under the electrode and in-between the light sources and detectors. The regional CVR during anodal tDCS was captured by adapting an arteriolar compliance model of the cerebral blood flow response to neural stimuli, where a fourth-order discrete-time model represented the haemodynamic response to anodal tDCS. A case study showed detectable CVR response (0-60sec) to a 0.526A/m² square-pulse (0-30sec) of anodal tDCS where these alterations in the vascular system may result in secondary changes in the cortical excitability. This needs to be carefully studied in the future with multi-modal imaging in a larger patient group, for example, in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy.