Given the overall lack of treatment adherence/efficacy, side effects of drugs, and the substantial burden of anxiety disorders on the individual and on the national healthcare system, there is a critical need for mechanistic research into the CNS mechanisms that underlie these disorders. Accordingly, the objective of this grant is to use noninvasive neuromodulation to causally identify the key neural mechanisms that mediate the cognitive symptoms of anxiety. This project is relevant to public health because it has the potential to lead to novel repetitive transcranial magnetic stimulation treatments for pathological anxiety.
Although extensive research has explored the involvement of subcortical structures in arousal, arousal symptoms are only one facet of the symptom profile shared across anxiety disorders. Much less is known about the cognitive symptoms (i.e. difficulty concentrating) experienced by anxiety patients. Accordingly, there is a critical need for mechanistic research into the CNS mechanisms that mediate the cognitive symptoms experienced by anxiety patients. Without such research, treatment development for these disorders will continue to make slow progress. The objective of this application is to determine the key neural mechanisms that mediate the cognitive symptoms of anxiety. The central hypothesis is that the right dorsolateral prefrontal cortex (dlPFC) regulates emotion through top-down inhibition of emotion-related regions. The approach will be to use repetitive transcranial magnetic stimulation (rTMS) to study the effect of right dlPFC activity on objective and subjective measures of induced anxiety, anxiety-related working memory deficits (WM), and TMS-evoked blood oxygenation-level dependent (BOLD) responses during simultaneous TMS/fMRI (i.e. target engagement). The rationale for this approach is that by experimentally manipulating right dlPFC activity using rTMS, this research will be able to causally demonstrate involvement of this region in anxiety regulation, which could translate to future targeted rTMS treatments for anxiety. The first aim will be to determine the effect of a 1-week course of rTMS treatment (1 Hz vs. 10 Hz; right dlPFC target) on anxiety using the threat of unpredictable shock paradigm. The second aim will be to determine the effect of a 1-week course of rTMS treatment (1 Hz vs. 10 Hz; right dlPFC target) on anxiety-related WM-deficits using the Sternberg WM paradigm during threat of shock. The third aim will be to demonstrate target engagement by measuring BOLD responses evoked by TMS pulses to the right dlPFC during threat of shock. The work is innovative because it will combine advanced neuromodulatory techniques (fMRI guidance, electric-field modelling, neuronavigation, active-sham control) with a translational threat of shock paradigm. PUBLIC HEALTH RELEVANCE: Once completed, this research should yield direct evidence for a causal role of the right dlPFC in anxiety regulation, complete with evidence of target engagement, and a novel application to anxiety.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
TRIPLE
Enrollment
68
A Magventure MagPro 100X stimulator with a B65 active/placebo figure-8 coil will be used. The TMS coil will be placed on the head over the target. rTMS intensity will be 100% of the motor threshold (MT), adjusted for field strength difference at motor cortex and target cortex using the individual E-field model. Subjects will receive 3000 pulses/session.
University of Pennsylvania
Philadelphia, Pennsylvania, United States
Anxiety Potentiated Startle
Electromyography Facial electromyography (EMG) startle responses were recorded from the left orbicularis oculi muscle at 2000 Hz using a Biopac MP160 unit (Biopac; Goleta, CA) via 15 × 20 mm hydrogel coated vinyl electrodes (Rhythmlink #DECUS10026; Columbia, SC). Startle EMG was bandpass filtered from 30 to 300 Hz, rectified, and smoothed using a 20-ms sliding window. Startle responses were scored as the peak (max during the 20 ms to 120 ms post-noise window) - the baseline (50 ms pre-noise window), and converted to t-scores with a mean of 50 and a standard deviation of 10 (tx = \[Zx × 10\] + 50). Greater t-scores mean larger blinks, which could be associated with greater anxiety, however there is no clinically relevent threshold. Noisy trials (baseline SD \> 2x run SD) were excluded, and "no blink" (peak \< baseline range) trials were coded as 0. To calculate APS, we subtracted the response during the neutral ITI from the response during the unpredictable ITI.
Time frame: Pre and 24-hours post stimulation
Fear Potentiated Startle
Electromyography Facial electromyography (EMG) startle responses were recorded from the left orbicularis oculi muscle at 2000 Hz using a Biopac MP160 unit (Biopac; Goleta, CA) via 15 × 20 mm hydrogel coated vinyl electrodes (Rhythmlink #DECUS10026; Columbia, SC). Startle EMG was bandpass filtered from 30 to 300 Hz, rectified, and smoothed using a 20-ms sliding window. Startle responses were scored as the peak (max during the 20 ms to 120 ms post-noise window) - the baseline (50 ms pre-noise window), and converted to t-scores with a mean of 50 and a standard deviation of 10 (tx = \[Zx × 10\] + 50). Greater t-scores mean larger blinks, which could be associated with greater fear, however there is no clinically relevent threshold. Noisy trials (baseline SD \> 2x run SD) were excluded, and "no blink" (peak \< baseline range) trials were coded as 0. To calculate FPS, we subtracted the response during the predictable ITI from the response during the predictable Cue.
Time frame: Pre and 24 hours post stimulation
Sternberg WM Accuracy
Sternberg task: On each WM trial, subjects will see a series of 4 letters presented singularly (encoding period) that will be followed by a brief interval where subjects are required to maintain these letters (maintenance period). At the end of the maintenance period, subjects will be prompted to make a response based on the task instructions (response period). The response prompt will consist of a letter and a number. The letter will be chosen from the study series, and the number will correspond to a position in the series. The subjects will indicate whether the position of the letter in the series matches the number.
Time frame: Pre and 24 hours post stimulation
TMS-evoked BOLD Responses
As with Experiment 1, subjects will have Neutral, Predictable, and Unpredictable periods. During the neutral periods, they will be safe from shocks. During the predictable periods, they can receive shocks but only when there is a cue present. During the unpredictable periods, they are at risk for shock during the entire duration of the block. Rather than probing their ongoing anxiety with the startle probes, we replaced the startle probes with single TMS pulses to the right dlPFC. This allowed us to causally examine the effect of right dlPFC activity (induced by the TMS pulse) on the neural activity. BOLD responses are collapsed across regions and conditions to examine right dlPFC BOLD down regulation.
Time frame: Responses are measured within the TMS/fMRI session in response to each TMS pulse and collapsed across trials. There is no sham condition. This session was typically conducted during the washout period, but varied depending upon participant schedule.
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