Obsessive-compulsive disorder (OCD) is marked by repetitive, anxiety-inducing thoughts, urges and compulsions, such as excessive cleaning, counting and checking. These behaviors are also prevalent in the general population: one study in a large sample of U.S. adults found more than a quarter had experienced obsessions or compulsions at some point in their life. Although most of these individuals do not develop full-blown OCD, such symptoms can still interfere with daily life. A new study, published on January 18 in Nature Medicine, hints that these behaviors may be alleviated by stimulating the brain with an electrical current—without the need to insert electrodes under the skull.
Robert Reinhart, a neuroscientist at Boston University, and his group drew on two parallel lines of research for this study. First, evidence suggests that obsessive-compulsive behaviors may arise as a result of overlearning habits—leading to their excessive repetition—and abnormalities in brain circuits involved in learning from rewards. Separately, studies point to the importance of high-frequency rhythms in the so-called high-beta/low-gamma range (also referred to as simply beta-gamma) in decision-making and learning from positive feedback.
Drawing on these prior observations, Shrey Grover, a doctoral student in Reinhart’s lab, hypothesized with others in the team that manipulating beta-gamma rhythms in the orbitofrontal cortex (OFC)—a key region in the reward network located in the front of the brain—might disrupt the ability to repetitively pursue rewarding choices. In doing so, the researchers thought, the intervention could reduce obsessive-compulsive behaviors associated with maladaptive habits.
To test this hypothesis, Grover and his colleagues carried out a two-part study. The first segment was aimed at identifying whether the high-frequency brain activity influenced how well people were able to learn from rewards. The team recruited 60 volunteers and first used electroencephalography to pinpoint the unique frequencies of beta-gamma rhythms in the OFC that were active in a given individual while that person took part in a task that involved associating symbols with monetary wins or losses. Previous work had shown that applying stimulation based on the particular patterns of rhythms in a person’s brain may enhance the effectiveness of the procedure.
The participants were then split into three groups, all of whom received a noninvasive form of brain stimulation known as transcranial alternating current stimulation (tACS), which was applied to the OFC for 30 minutes over five consecutive days. Each group had a different type of stimulation: One received personalized currents tuned to an individual’s beta-gamma frequencies. Another was exposed to an “active” placebo, consisting of stimulations at a lower frequency. And the third was a “passive” placebo group in which no significant current was applied to the brain. Those who received the personalized beta-gamma stimulation became less able to make optimal choices on the reward-based learning tasks—changes not observed in the two placebo groups.
Further assessment of the participants’ behavior using computational models of reward-based learning suggested that the personalized tACS disrupted the learning process by making people more likely to try out different options rather than sticking with only one—even if they were less likely to result in a reward.
These findings set the stage for the second part of the study, in which the team set out to examine whether manipulating the beta-gamma rhythms typically engaged during reward-based learning would influence obsessive-compulsive behaviors. The researchers carried out a similar set of experiments on another set of volunteers: 64 people who did not have a formal OCD diagnosis but who exhibited symptoms such as checking, hoarding and obsessing. Participants received either personalized beta-gamma stimulation or an active placebo. Those in the personalized beta-gamma group experienced a reduction in compulsive behaviors that persisted for up to three months. And those with more of those obsessive-compulsive characteristics prior to stimulation exhibited the biggest changes.
According to Grover, the team decided to study people with symptoms of OCD but no diagnosis of the disorder because researchers have increasingly been viewing obsessive-compulsive behaviors on a mild-to-severe spectrum. And even in the absence of clinically diagnosed OCD, such symptoms can cause significant distress. “By examining a nonclinical population exhibiting a range of obsessive-compulsive behaviors, we were able to examine the effectiveness of [an intervention] that may be helpful to a larger pool of individuals,” Grover says. Yet the researchers’ findings also suggest “that if we were to extend such an intervention to individuals diagnosed with obsessive-compulsive disorder or to other conditions of compulsivity—gambling disorder, addiction, some forms of eating disorders—-we might be able to observe strong effects.”
The long-lasting effects on obsessive-compulsive behaviors is “quite impressive,” says Trevor Robbins, a professor of cognitive neuroscience at the University of Cambridge, who was not involved in this research. “[Neuromodulation] is certainly a treatment that should be investigated rigorously for conditions like OCD.”
Carolyn Rodriguez, a psychiatrist and neuroscientist at Stanford University, who was also not involved in the study, says that because it was carried out in a nonclinical population without a formal diagnosis, the implications of these findings remain to be seen. “The neurobiology of people who are nonclinical but have these kinds of behaviors may be different than individuals who are diagnosed with OCD,” she adds. “These findings are an interesting start, [but] we need to understand how it's relevant to people who have OCD.” Rodriguez also points out that there are already several treatments available for the condition, including medication, therapy and a Food and Drug Administration–approved device that utilizes transcranial magnetic stimulation (TMS), a noninvasive method that uses magnetic fields to stimulate the brain. (Rodriguez is currently leading a clinical trial of TMS for OCD.)
The potential therapeutic effects of tACS on memory, food craving and other neural processes have been tested in dozens of studies in the past. Questions have been raised about whether this method actually exerts any meaningful changes in the brain, however. In the new study, what, exactly, the high-frequency tACS did to the brain remains unknown. But Grover notes that the researchers’ two placebo conditions—particularly the one that involves stimulating at a different frequency—provide strong evidence that the high-frequency stimulation was responsible for the behavioral effects the team observed.
Grover and his colleagues are currently working on further experiments to pinpoint the mechanisms underlying their intervention. And they hope to conduct studies with clinical populations diagnosed with OCD in the near future. “[The recent paper] is just a preliminary step toward further understanding why this high-frequency activity is so important for obsessive-compulsive behavior,” Grover says. “The fact that we can observe changes in these symptoms even now suggests there may actually be clinical benefit to this—and gives us all the more reason to try to extend the findings of this research.”