Neuromodulation for Obsessive-Compulsive Behaviour

Shrey Grover

Department of Psychological & Brain Sciences, Brain, Behavior & Cognition Programme, Boston University

Shrey is a graduate student at Boston University. He previously studied in the mechanical engineering field in India. After that, he switched over and worked in a neuroscience lab for a couple of years and became interested in this line of work and subsequently applied to graduate programs at Boston University. He is currently working with Professor Robert Reinhart in the department of psychological and brain sciences. Reinhart lab focuses on various aspects related to cognition, how they relate to characteristic rhythmic activity partners in the brain and how they can change those activity patterns in a non-invasive manner. That forms the focus of his work right now and, in many ways, will form the foundation for the future work that he would like to pursue in this field, subsequently deeper into how these rhythmic activity patterns relate to cognition.

Is Obsessive-Compulsive Disease Just the Tip of the Iceberg?

Obsessive-Compulsive Disease falls onto a spectrum, where different individuals may experience symptoms at differing levels of severity. In their most severe form, these symptoms contribute to a diagnosis of Obsessive-Compulsive Disorder (OCD) when the individuals experience the most distress. According to various estimates, it’s among the most disabling diagnoses. But instead of focusing solely on OCD, we are now recognising that there are also subclinical forms of Obsessive-Compulsive Behaviour. That is, individuals that may not meet the official diagnosis of OCD, but still experience these behaviours to some degree, contributing to some distress in their lives.

Various epidemiological studies have estimated that anywhere between 10% to even as high as 28% of people may experience some distress due to these behaviours. These behaviours are highly heterogeneous, different people may experience different clusters of symptoms. So there’s a wide heterogeneity and prevalence of such behaviours in the population.

How Should We Conceptualise

Function vs Dysfunction

in Psychiatric Disease?

Broadly in the field of psychiatry, we have begun appreciating the contribution of cognitive neuroscience. We now try to understand how psychiatric classification and symptom classification relates to basic cognitive processes. We call this the transdiagnostic perspective of Obsessive-Compulsive Behavior, in which instead of looking solely at OCD, we identify that there are compulsive behaviours which are common across many different clinical conditions, including OCD, Gambling Disorders, Substance-Use Disorder, Compulsive Eating, Tourette’s Syndrome. 

There are so many other conditions that share specific symptom dimensions, and these symptom dimensions can be related to basic brain and cognitive function. Along with that, Obsessive-Compulsive Behavior has been associated with abnormalities in how we form and regulate our habits. Habit formation is a process that relies on how we process rewarding information.  If we do an action and we get a reward for it, it is quite likely that we will become habituated, we will rather execute those actions more habitually to maximise our rewards. That’s what we generally try to do, we try to maximise our state of rewards. 

Within the field of obsessive-compulsive research, people have realised that there are these basic abnormalities and the degree to which we rely on our habits to our day-to-day business and how those abnormalities and habits, are related to deficiencies and how we process rewarding information.

The Role of Beta-Gamma Oscillations

in Obsessive-Compulsive Disorder

Over the last decade, there have been many studies in human electroencephalography (EEG) and magnetoencephalography (MEG), in which we can examine patterns of electrical activity while someone is performing some tasks. Many studies were looking at the patterns of activity that are related to reward processing. In these studies, people have identified that when someone is presented with a rewarding feedback, let’s say they were making a selection between two choices, and their selection was awarded, then after receiving the rewarding feedback, there is a burst of rhythmic activity that we measure in the frontal electrodes, channels placed on the front part of the scalp. 

These rhythmic activity patterns fall in this high-beta low-gamma range, so when we examined the rhythmic activity patterns, we became interested in this line of work, because this suggests that these rhythmic activity patterns related to reward processing, may also be associated with Obsessive-Compulsive Behavior. This is because it is hypothesised that these rhythmic activity patterns originate from the orbitofrontal cortex, and the orbitofrontal cortex is also a brain region highly implicated in Obsessive-Compulsive Behaviors. Therefore, this was the critical neural signal which became the focus of our study, because if this neural signal is associated with reward processing and reward processing is associated with  Obsessive-Compulsive Behaviors and if both of these behaviours are rooted in the orbitofrontal cortex, then these beta-gamma rhythms really might be the key to change the activity patterns in the orbitofrontal cortex and consequently improve obsessive-compulsive symptoms.

Can Reward-Based Learning Be “Lesioned”

While Sparing Punishment-Based Learning?

Our neuromodulation was focused on beta-gamma rhythms rather than a blanket lesion of the orbitofrontal cortex. I think that’s the critical aspect here because beta-gamma rhythms are associated primarily with reward processing. Processing of punishing feedback is typically associated with a different frequency pattern in a different structure. So it’s this functional specialisation of our neuromodulation design that we suspect contributes to this valence specific effect in which changes happen only in the reward condition and not in the punishment condition.

Do People With the Severest Obsessive-Compulsive Symptoms Receive the Greatest Benefit From Neuromodulation?

We observe a reduction of approximately 28% on average across individuals, which we think it is a significant contribution and something which can potentially form the basis of even more robust and sustainable designs. In our analysis, we observed that individuals who had higher symptom severity showed greater benefits following neuromodulation. So it’s something that forms a foundation for subsequent research, in which we would like to examine what is the precise mechanism through which these effects arise and how they can be made even more robust and sustainable.

Career Advice to Aspiring Neuroscientists

Neuroscience is an extremely broad area, it’s an area that welcomes individuals from many different backgrounds and skillsets, ranging from psychology, to electrical engineering, to computer science. So my recommendation would be to capitalise on your skills, your interests, your background, and find a research question that you’re motivated for and neuroscience is broad enough that you will definitely find some people who are working on the kinds of questions you’re interested in. There’s definitely a lot of scope here and a lot of research happening every day we are learning lots and lots of things about the brain, and it’s an exciting time to be in neuroscience.

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