Abstract
Transcranial focused ultrasound (tFUS) is an emerging non-invasive brain stimulation tool for safely and reversibly modulating brain circuits. The effectiveness of tFUS on human brain has been demonstrated, but how tFUS influences the human voluntary motor processing in the brain remains unclear. We apply low-intensity tFUS to modulate the movement-related cortical potential (MRCP) originating from human subjects practicing a voluntary foot tapping task. 64-channel electroencephalograph (EEG) is recorded concurrently and further used to reconstruct the brain source activity specifically at the primary leg motor cortical area using the electrophysiological source imaging (ESI). The ESI illustrates the ultrasound modulated MRCP source dynamics with high spatiotemporal resolutions. The MRCP source is imaged and its source profile is further evaluated for assessing the tFUS neuromodulatory effects on the voluntary MRCP. Moreover, the effect of ultrasound pulse repetition frequency (UPRF) is further assessed in modulating the MRCP. The ESI results show that tFUS significantly increases the MRCP source profile amplitude (MSPA) comparing to a sham ultrasound condition, and further, a high UPRF enhances the MSPA more than a low UPRF does. The present results demonstrate the neuromodulatory effects of the low-intensity tFUS on enhancing the human voluntary movement-related cortical activities evidenced through the ESI. This work provides the first evidence of tFUS enhancing the human endogenous motor cortical activities through excitatory modulation.
Highlights
A S AN emerging non-invasive neuromodulation tool, the low-intensity transcranial focused ultrasound delivers highly controllable mechanical energy from transducers, penetrating the skull with relatively low tissue attenuation and modulates the targeted brain circuits with high spatial selectivity. tFUS is featured with a vast parametric space, and by tuning its parameters, the ultrasound wave can be steered and be used to produce excitatory or inhibitory neural effects
To further illustrate the movement-related cortical potential (MRCP) change due to the tFUS conditions, the sequential evolution of electrophysiological source imaging (ESI) source distributions was included to show the spatiotemporal change of MRCP source activities in Supplementary Figs
We have demonstrated in humans that lowintensity transcranial focused ultrasound (i.e., ISPPA = 5.90 W/cm2 before skull) can modulate and enhance the voluntary movement-related cortical activity evidenced through the scalp-EEG based source imaging with improved spatiotemporal specificities
Summary
A S AN emerging non-invasive neuromodulation tool, the low-intensity transcranial focused ultrasound (tFUS) delivers highly controllable mechanical energy from transducers, penetrating the skull with relatively low tissue attenuation and modulates the targeted brain circuits with high spatial selectivity. tFUS is featured with a vast parametric space, and by tuning its parameters, the ultrasound wave can be steered and be used to produce excitatory or inhibitory neural effects. Among accumulating experimental demonstrations on healthy humans, a pioneer study using low-frequency and lowintensity tFUS was able to achieve robust neuromodulation effects at the primary somatosensory cortex (S1), evidenced through the ultrasound-modulated sensory-evoked brain activity recorded at electroencephalogram (EEG) sensors and the enhancement of sensory discrimination abilities [8]. Another pilot study on tFUS modulating the S1 circuits reported direct evoked limb sensations and the ultrasound stimulation event-related potentials (ERPs) at C3 and P3 EEG electrodes [11]. Extensive tactile sensations were elicited and reported by the human subjects [10]
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