Transcranial Focused Ultrasound (tFUS) and Transcranial Unfocused Ultrasound (tUS) Neuromodulation: From Theoretical Principles to Stimulation Practices.
Authors: di Biase L, Falato E, Di Lazzaro V
Transcranial focused ultrasound is an emerging technique for non-invasive neurostimulation. Compared to magnetic or electric non-invasive brain stimulation, this technique has a higher spatial resolution and can reach deep structures. In addition, both animal and human studies suggest that, potentially, different sites of the central and peripheral nervous system can be targeted by this technique. Depending on stimulation parameters, transcranial focused ultrasound is able to determine a wide spectrum of effects, ranging from suppression or facilitation of neural activity to tissue ablation. The aim is to review the state of the art of the human transcranial focused ultrasound neuromodulation literature, including the theoretical principles which underlie the explanation of the bioeffects on neural tissues, and showing the stimulation techniques and parameters used and their outcomes in terms of clinical, neurophysiological or neuroimaging results and safety.
Introduction
Purpose
Transcranial ultrasound stimulation
Study Objective
To review the state of the art of human transcranial focused ultrasound neuromodulation literature, covering underlying mechanisms, stimulation techniques and parameters, outcomes, and safety.
Animal model / Human subject
Human (Homo sapiens), strain: N/A, age: not specified, sex: not specified
Disease model
Healthy
Outcomes and Safety
Summary of Outcomes
Transcranial focused ultrasound (tFUS) produced reversible neuromodulation in humans — suppressing or facilitating neural activity as shown by decreased somatosensory evoked potentials, altered EEG oscillations, induced tactile sensations and BOLD responses in cortical and subcortical areas, changes in motor excitability, improved sensory discrimination and reported mood/behavioral improvements (including a case report of emergence from a minimally conscious state). Effective parameters included low-intensity pulsed FUS (identified as most effective for neuromodulation); by contrast high-intensity continuous FUS produced lesioning, and differences were observed between focused (typically pulsed, often inhibitory effects on MEPs) and unfocused/continuous ultrasound (e.g., an 8 MHz unfocused tUS increased MEP amplitude).
Duration of biological effect
6 min
Safety-related matter
The paper reports that tUS/tFUS is generally safe and well-tolerated when stimulation parameters follow guidelines, with most studies reporting no severe adverse effects; however mild-to-moderate symptoms (neck pain, sleepiness, muscle twitches, itchiness, headache) have been observed in some subjects.
Brain Region
Ultrasound Parameters
Focal Characteristics
Focal depth: None; Focal length: None; Aperture size: None
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