Transcranial focused ultrasound-mediated neurochemical and functional connectivity changes in deep cortical regions in humans
Low-intensity transcranial ultrasound stimulation (TUS) is a non-invasive technique that has been gaining attention in the field of neuroscience and psychiatry. It has the ability to target both cortical and deep brain regions with high spatial specificity, making it a promising tool for a range of applications from basic research to therapeutic use in neurological and psychiatric diseases.
One of the main advantages of TUS over other non-invasive techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) is its ability to produce offline effects, which can last several minutes to hours after stimulation. These effects are of particular interest as they may reflect long-term neuroplasticity, lasting longer than transient neuronal adaption effects and having the potential to be used to modulate aberrant activity in brain regions or networks for therapeutic applications.
However, the mechanisms and neurochemical substrates underlying TUS neuromodulation in humans and how these relate to excitation and inhibition are still poorly understood. In a recent study, researchers aimed to investigate the effects of TUS on the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and functional connectivity in healthy controls.
The study used a theta-burst TUS protocol, which has been shown to increase corticospinal excitability. The participants were separately stimulated in two deep cortical regions, the dorsal anterior cingulate cortex (dACC) and the posterior cingulate cortex (PCC). The researchers used magnetic resonance spectroscopy (MRS) and resting-state functional magnetic resonance imaging (rsfMRI) to measure the effects of TUS.
The study found that TUS selectively reduces GABA levels in the PCC, but not the dACC, at around 20-30 minutes post-stimulation. This suggests that TUS changes overall excitability by reducing GABAergic inhibition. Additionally, the study also found that functional connectivity increased following TUS
Yaakub, S.N. et al. (2023) “Transcranial focused ultrasound-mediated neurochemical and functional connectivity changes in deep cortical regions in humans,” BIORXIV [Preprint]. Available at: https://doi.org/10.1101/2023.01.20.524869.