Non-Invasive Electrical Brain Stimulation Reduces Obsessive-Compulsive Behaviours

Post by D. Chloe Chung

What's the science?

Obsessive-compulsive (OC) behaviours are characterized by excessive, unreasonable thoughts and repetitive behaviours. While the exact underlying mechanisms are unclear, OC behaviours may result from excessive habit learning. Habit learning involves the brain’s medial orbitofrontal cortex (OFC) which is connected to the brain’s reward network. This week in Nature Medicine, Grover and colleagues show that non-invasive OFC stimulation, using a high-frequency current to target the high-frequency neural activity associated with reward processing, can modulate OC behaviours.

How did they do it?

In the first experiment, the authors wanted to determine the role of high-frequency, beta-gamma rhythms in reward learning. To do this, they selected a monetary reinforcement learning task that included two trial types – “reward trials” in which the participants earn money (versus not earning any) upon making an optimal choice (choosing the correct image), and “punishment trials” in which the participants lose money (versus not losing any) upon making an incorrect choice (choosing the wrong image). Before the actual task, beta-gamma frequency band activity was measured for 60 participants using electroencephalography (EEG), while the participants learned how to associate visual stimuli with monetary gain and loss. Next, the participants randomly received either control (“passive” sham or “active” alpha frequency of ~10Hz) or personalized beta-gamma neuromodulation (~27Hz on average) and completed the reinforcement learning task for 30 minutes each before, during, and after the neuromodulation (90 minutes total). 

In the second experiment, the authors aimed to evaluate whether chronic beta-gamma neuromodulation of the OFC can impact OC behaviours. To test this, 64 participants first completed a self-assessment of their OC behaviours and then received either control, alpha frequency, or personalized beta-gamma frequency for 5 days (30 minutes per day). The participants self-assessed their OC behaviours right after the last neuromodulation, as well as 1, 2, and 3 months post-neuromodulation. After these two experiments, the authors analyzed the relationship between intrinsic beta-gamma rhythms and a) changes during the reward learning and b) OC behaviours caused by beta-gamma neuromodulation.

What did they find?

In the first experiment, the authors observed that the reward behaviour was altered upon personalized beta-gamma neuromodulation targeting the OFC. Participants made fewer optimal choices during the reward trials of the monetary reinforcement learning task, while no change was observed in either control condition. Importantly, beta-gamma neuromodulation changed behaviours during the reward trials but not during the punishment trials, indicating that beta-gamma frequency specifically modulates reward-related behaviours. These neuromodulation-induced changes in the reward behaviour were found to be reversible, as the participants showed a similar rate of making optimal choices both before and after the neuromodulation. 

In the second experiment, the authors found that the 5-day beta-gamma neuromodulation successfully reduced obsessive-compulsive behaviours for three months (based on self-assessment). Interestingly, participants with more severe OC symptoms displayed a more drastic reduction in their compulsive behaviours after neuromodulation. Lastly, by comparing the two experiments, the authors found that convergent mechanisms exist between both neuromodulation-regulated reward and OC behaviours.

What’s the impact?

This study demonstrates that high-frequency neuromodulation can effectively regulate reward learning. Further, this work supports the link between reward learning and OC behaviours by highlighting shared mechanisms between the two. Findings from this study strongly suggest potential clinical benefits of personalized neuromodulation for obsessive-compulsive disorder (OCD) patients. It will be interesting for future studies to use additional methodologies, such as neuroimaging, to discover how neural processes are altered by beta-gamma neuromodulation.

Grover et al. High-frequency neuromodulation improves obsessive-compulsive behavior. Nature Medicine (2021). Access the original scientific publication here.