Non-Invasive Transcranial Ultrasound Stimulation (TUS) Modulates Reward Sensitivity via Nucleus Accumbens (NAcc) Neuromodulation
- 3 days ago
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For decades, precisely modulating deep brain regions in humans has been a critical goal in neuroscience, promising transformative advancements in both fundamental research and clinical treatment. Until recently, achieving this required invasive surgical procedures, most notably deep brain stimulation (DBS). However, pioneering new research led by the University of Plymouth demonstrates that Transcranial Ultrasound Stimulation (TUS)—a non-invasive method harnessing focused ultrasound beams through the skull—can selectively modulate deep brain activity and affect human learning and decision making, achieving results comparable to DBS.
The study, published in Nature Communications, focused specifically on manipulating the Nucleus Accumbens (NAcc), a deep subcortical region within the ventral striatum. The NAcc is often referred to as the hub where dopamine signals and limbic inputs converge to shape how strongly rewards influence our choices, sitting at the center of theories regarding motivation and reinforcement learning.
Researchers recruited 26 healthy adults for a within-subject experiment utilizing a probabilistic reversal learning task performed during fMRI scanning. Participants attended sessions receiving TUS targeted at the NAcc (TUS-NAcc), TUS targeted at a control region, the dorsal anterior cingulate cortex (TUS-dACC), or a Sham condition. The TUS intervention involved applying repetitive TUS for just 80 seconds, patterned at 5 Hz. Neural activity recordings began approximately 10–15 minutes post-TUS, when any potential auditory effects had dissipated.
The results demonstrated that TUS-NAcc causally influenced neural and behavioural responses. Behaviorally, TUS-NAcc altered features linked to Reward Sensitivity, including an increased tendency toward "win–stay" strategy use and higher learning rates following reward feedback. This indicates that participants became more likely to repeat a choice that had previously paid off. The TUS-NAcc induced changes in reward-related behavior were most prominent approximately 28 to 35 minutes after the stimulation.
Neurally, TUS-NAcc altered the BOLD responses related to reward signals in the NAcc and surrounding areas. Specifically, the researchers observed an enhancement of the parametric BOLD representation of reward expectation in the NAcc after TUS-NAcc compared to both Sham and TUS-dACC conditions.
To confirm the efficacy and target engagement of the TUS, the researchers cross-checked their findings against three patients who had undergone DBS electrode implantation in the bilateral NAcc for treatment-resistant anorexia nervosa. The study confirmed that DBS-NAcc perturbed the same behavioral indices related to positive outcome-related behavior as TUS-NAcc.
It is important to note that the behavioral effects of TUS were excitatory, resulting in increased Reward Sensitivity, whereas high-frequency DBS is generally considered functionally inhibitory or normalizing, which lowered patient reward sensitivity towards healthy levels in this cohort.
Professor Elsa Fouragnan, who led the research, highlighted the significance of the findings, noting that the ability to modulate this deep structure non-invasively opens "extraordinary possibilities for clinical translation". These results establish TUS as a viable and powerful approach for non-invasive deep-brain neuromodulation, suggesting its potential as a targeted, nonpharmacological intervention for neurological and psychiatric disorders, including addictions, depression, and eating disorders.
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Keywords: Transcranial Ultrasound Stimulation
Transcranial Ultrasound Stimulation
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