Imaging of Neurovascular Activity during Motor Responses Evoked by Displacement-guided Focused Ultrasound (DgFUS) Neuromodulation in Mice.

Focused ultrasound (FUS) shows great promise for precise and non-invasive neuromodulation, with applications from basic neuroscience investigation to the treatment of neurological disorders. Yet, mechanistic monitoring of FUS is challenging and a causal link between FUS-induced displacement and both neurovascular and behavioral responses evoked by FUS in mice remains poorly understood. Here we harness displacement-guided focused ultrasound (DgFUS) to induce target-specific and non-auditory motor responses in anesthetized mice, and functional ultrasound (fUS) to image neurovascular activity during the evoked responses. We show that DgFUS elicits ipsilateral neurovascular responses, in which the primary (i.e. focal-onset) activation localizes with in situ brain displacement, followed by mild contralateral responses. We demonstrate that switching the target hemisphere of DgFUS within the thalamus results in lateralized hindlimb responses concurrent with lateralized neurovascular activation. We show strong correlation between displacement and both cerebral blood volume (CBV) and electromyography (EMG) measurement (Disp. vs. CBV: Spearman r = 0.9091, p < 0.0001, Disp. vs. EMG: r = 0.7332, p = 0.0091, CBV vs. EMG: r = 0.9041, p = 0.0002), indicating displacement-driven mechanism by which DgFUS evokes neurovascular and motor responses. Lastly, we demonstrate anxiety-related behavioral improvement with transcranial fUS-guided FUS delivered to the bilateral hippocampus, consistent with increases in resting-state hippocampal connectivity assessed by transcranial fUS imaging. The findings presented herein will help refine our understanding of neurovascular responses to FUS and the consequential motor and cognitive outcomes.