Transcranial direct current stimulation impairs updating of avoidance-based associative learning.

Introduction: Exposure-based psychotherapies for the treatment of anxiety- and fear-based disorders rely on "corrective" associative learning. Namely the repeated confrontation with feared stimuli in the absence of negative outcomes allows the formation of new, corrected associations of safety, indicating that such stimuli no longer need to be avoided. Unfortunately, exposure-facilitated corrective learning tends to be bound by context and often poorly generalizes. One brain structure, the prefrontal cortex, is implicated in context-guided behavior and may be a relevant target for improving generalization of safety learning. Here, we tested whether inhibition of the left prefrontal cortex causally impaired updating of context-bound associations specifically or, alternatively, impaired updating of learned associations irrespective of contextual changes. Additionally, we tested whether prefrontal inhibition during corrective learning influenced subsequent generalization of associations to a novel context. Methods: In two separate experiments, participants received either 10 min of 2 mA cathodal transcranial direct current stimulation (tDCS) over EEG coordinate F3 (Experiment 1 n = 9, Experiment 2 n = 22) or sham stimulation (Experiment 1 n = 10, Experiment 2 n = 22) while previously learned associations were reversed in the same or a different context from initial learning. Next, to assess generalization of learning, participants were asked to indicate which of the previously seen images they preferred in a novel, never seen before context. Results: Results indicate that tDCS significantly impaired reversal irrespective of context in Experiment 2 only. When taking learning rate across trials into account, both experiments suggest that participants who received sham had the greatest learning rate when reversal occurred in a different context, as expected, whereas participants who received active tDCS in this condition had the lowest learning rate. However, active tDCS was associated with preferring the originally disadvantageous, but then neural stimulus after stimulus after reversal occurred in a different context in Experiment 1 only. Discussion: These results support a causal role for the left prefrontal cortex in the updating of avoidance-based associations and encourage further inquiry investigating the use of non-invasive brain stimulation on flexible updating of learned associations.

Low Intensity Focused Ultrasound for Non-invasive and Reversible Deep Brain Neuromodulation-A Paradigm Shift in Psychiatric Research.

This article describes an emerging non-invasive neuromodulatory technology, called low intensity focused ultrasound (LIFU). This technology is potentially paradigm shifting as it can deliver non-invasive and reversible deep brain neuromodulation through acoustic sonication, at millimeter precision. Low intensity focused ultrasound's spatial precision, yet non-invasive nature sets it apart from current technologies, such as transcranial magnetic or electrical stimulation and deep brain stimulation. Additionally, its reversible effects allow for the causal study of deep brain regions implicated in psychiatric illness. Studies to date have demonstrated that LIFU can safely modulate human brain activity at cortical and subcortical levels. Due to its novelty, most researchers and clinicians are not aware of the potential applications and promise of this technique, underscoring the need for foundational papers to introduce the community to LIFU. This mini-review and synthesis of recent advances examines several key papers on LIFU administered to humans, describes the population under study, parameters used, and relevant findings that may guide future research. We conclude with a concise overview of some of the more pressing questions to date, considerations when interpreting new data from an emerging field, and highlight the opportunities and challenges in this exciting new area of study.

A Secondary Analysis on Effects of Theta Burst Transcranial Magnetic Stimulation to Reduce Anger in Veterans With Posttraumatic Stress Disorder.

INTRODUCTION: Anger is an important clinical feature of posttraumatic stress disorder (PTSD) that can hamper recovery. We recently reported that intermittent theta burst stimulation (iTBS) demonstrated preliminary efficacy to reduce symptoms of posttraumatic stress disorder and major depression; here, we performed a secondary analysis testing whether iTBS reduced symptoms of anger over the course of iTBS treatment and compared to sham stimulation. MATERIALS AND METHODS: Fifty veterans with chronic PTSD received ten daily sessions of sham-controlled, double-blind iTBS (1800 pulses/session, once per weekday) targeting the right dorsolateral prefrontal cortex (intent-to-treat = 25 per group). Participants who completed the double-blind phase were offered another ten sessions of unblinded iTBS. Participants completed the Dimensions of Anger Reactions scale at pre-iTBS baseline, treatment midpoints, and endpoints of the blinded and unblinded phases, and at one-month after the last stimulation session. Correlations between anger, PTSD, depression, and sleep were also explored. RESULTS: After the first week, during the double-blind phase, participants randomized to active stimulation reported significantly reduced anger compared to sham stimulation (p = 0.04). Participants initially randomized to sham appeared to catch-up to the point they no longer differed from those initially randomized to active iTBS when they received iTBS during the unblinded phase (p = 0.14). Anger reduction was maintained at one-month after iTBS in participants initially randomized to active stimulation (i.e., total of four weeks of iTBS). CONCLUSIONS: This secondary analysis suggests that iTBS might reduce anger in veterans with PTSD. Future studies focused on more granular level anger outcomes and effects of number of stimulation sessions are needed.