Structural-Functional Brain Network Modulation using Transcranial Focused Ultrasound Stimulation: Implications on the Default Mode Network in Humans.

Transcranial focused ultrasound (tFUS) has emerged as a promising noninvasive technique for brain stimulation due to its precise focusing and deep penetration capabilities. However, its potential to modulate brain networks beyond the stimulation site and optimal sonication parameters required for such modulation remain unclear. In light of this knowledge gap, this study investigates the effects of tFUS targeted at the medial prefrontal cortex (mPFC), a key component of the default mode network (DMN), to determine whether varying the sonication parameters could specifically modulate the DMN. Specifically, in this study, 21 healthy participants were divided into groups that received excitatory, suppressive, or sham tFUS stimulation targeting the mPFC. To assess the effects, diffusion-weighted MRI and resting-state functional MRI were employed to assess the correspondence between structural and functional brain connectomes before and after tFUS. Subsequently, changes following tFUS were compared among the three groups. Our results showed that while tFUS generally increased coupling between structure and function near the stimulation site after both excitatory and suppressive stimulation, a significant enhancement in structure-function correspondence was specifically observed within the DMN connected to the stimulation site under excitatory stimulation. Based on these observations, the findings highlight the potential of specific tFUS protocols to effectively modulate the DMN, thereby offering insights into optimizing tFUS for brain network modulation and its potential as a non-invasive therapeutic intervention.