State-dependent neurovascular modulation induced by transcranial ultrasound stimulation.

Previous studies reported baseline state-dependent effects on neural and hemodynamic responses to transcranial ultrasound stimulation. However, due to neurovascular coupling, neither neural nor hemodynamic baseline alone can fully explain the ultrasound-induced responses. In this study, using a general linear model, we aimed to investigate the roles of both neural and hemodynamic baseline status as well as their interactions in ultrasound-induced responses. Thirty Sprague-Dawley rats were randomly assigned to Hypoxia, Hyperoxia, and Normoxia groups. The baseline states were altered by changing the oxygen concentrations. Micro-electrode and laser speckle contrast imaging were used to record local field potentials and cerebral blood flow during resting, before, and after ultrasound stimulation, respectively. We found that baseline neural activity played a positive role in neural response (Coefficient = 0.634, t = 1.748, p = 0.096, ${\eta }_p^2$ = 0.133), but a negative role in hemodynamic response (Coefficient = $-$ 0.060, t = $-$ 1.996, p = 0.060, ${\eta }_p^2$ = 0.166). Baseline hemodynamic activity also had a significantly negative correlation with the hemodynamic response (Coefficient = $-$ 0.760, t = $-$ 3.947, p $<$ 0.001, ${\eta }_p^2$ = 0.438). This study enriched our understanding of state-dependent effects underlying the neurovascular activation by ultrasound stimulation.