Many people are affected by unwelcome thoughts and the urge to do certain actions such as repeatedly checking if we locked the door. These are known as obsessive-compulsive behaviors. While much research has been devoted to their most severe occurrence during obsessive-compulsive disorder (OCD), even less severe ‘subclinical’ occurrences are widely prevalent and contribute to significant distress.
Research suggests that obsessive-compulsive behaviors arise when our decisions excessively rely on habits, with little direction from our goals. Habits reflect automatic responses triggered by the environment, particularly when responses lead to pleasant, rewarding outcomes. Individuals exhibiting obsessive-compulsive behavior show abnormalities in brain circuits that typically process information about rewards. Such circuits can be potential targets for novel interventions to change reward processing, which can affect habitual behavior and obsessive-compulsive behaviors.
Noninvasive neuromodulation techniques such as high-definition transcranial alternating current stimulation (HD-tACS) can alter dysfunctional brain circuits. HD-tACS is a safe method in which weak electrical currents are applied to the scalp in order to change brain activity. However, for such techniques to be effective, we need to know the frequency of rhythmic activity that facilitates information processing in these circuits. Human electro- and magnetoencephalography studies of learning and decision-making have identified rhythmic activity in the high beta-low gamma (20-35 Hz) range following receipt of unexpected rewards. This reward-specific high-frequency activity is thought to originate in the orbitofrontal cortex, a brain region involved in obsessive-compulsive behaviors also. Given the abnormalities in the reward processing circuitry in individuals exhibiting obsessive-compulsive behavior, we hypothesized that modulating reward-related orbitofrontal rhythms in the beta-gamma range may affect obsessive-compulsive behaviors as well.
In our study, we used HD-tACS to modulate orbitofrontal beta-gamma activity. We identified the specific beta-gamma frequency at which an individual exhibits reward-related activity allowing us to personalize HD-tACS for every individual. In the first experiment, healthy participants learned to make rewarding choices habitually. We found that beta-gamma neuromodulation reduced habitual decision-making by hampering learning from rewarding feedback. In the second experiment, we examined the effects of personalized orbitofrontal beta-gamma HD-tACS directly on obsessive-compulsive behaviors. Healthy participants exhibiting a wide range of obsessive-compulsive symptoms underwent beta-gamma neuromodulation for thirty minutes every day over five consecutive days. We observed a significant reduction in their obsessive-compulsive symptoms by the fifth day. We further noted that improvements in symptoms were sustained for at least three months following the intervention, and larger improvements were observed for individuals with more severe symptoms. Together, our observations suggest that personalized beta-gamma neuromodulation targeting the reward processing network may be an effective strategy for reducing obsessive-compulsive behaviors.
Noninvasive neuromodulation is an emerging intervention that may hold promise for managing obsessive-compulsive behaviors. Additional studies with even larger sample sizes and in different populations including individuals diagnosed with OCD, compulsive substance use and gambling disorders will help determine the robustness and clinical viability of such interventions.
Grover, S., Nguyen, J.A., Viswanathan, V. et al. High-frequency neuromodulation improves obsessive–compulsive behavior. Nat Med (2021). https://doi.org/10.1038/s41591-020-01173-w