By Goi Khia Eng, PhD
This article describes the results of a 2022 Michael Jenike Young Investigator Award, an IOCDF-funded research project.
Obsessive compulsive disorder (OCD) is a chronic condition with diverse symptom presentations. OCD is often thought of as driven by fears, such as fear of germs leading to washing, or worries about safety driving checking. However, many people with OCD also experience sensory phenomena, which are uncomfortable and aversive sensory experiences, including sensory-based physical urges. Consider someone who experiences a compelling need to tap both sides of the body the same number of times until it feels “even”, not out of fear that something bad might happen if they do not, but because of an intense urge like a persistent itch demanding relief. Sensory phenomena affect as many as 60% of individuals with OCD (Miguel et al., 2000; Shavitt et al., 2014) and can drive compulsive behaviors such as touching, tapping, repeating, evening-up or arranging objects that are performed until they feel “just right” (Ferrão et al., 2012; Katz et al., 2022).
The Science Behind Sensory Urges
Sensory-based urges in OCD (and the urges before tics in Tourette disorder) are similar to everyday urges-for-action, such as the urge to blink or scratch an itch, both in how they feel and in the brain processes involved. Like everyday urges, sensory urges are internally generated and tend to intensify when they are suppressed or delayed (Berman et al., 2012; Neuner et al., 2014). Brain imaging studies in people without mental health diagnoses show that everyday urges-for-action activate a network of brain areas involved in movement preparation, as well as physical sensations and sensations arising from within the body. This brain network involves the insula and sensorimotor regions (including the postcentral gyrus, precentral gyrus, supplementary motor area, and cingulate cortex) (Jackson et al., 2011; Zouki et al., 2024). Most work examining brain regions related to pathological urges has been conducted in Tourette disorder, where studies found increased activation in a similar network of brain regions a few seconds prior to the onset of tics (Bohlhalter et al., 2006; Neuner et al., 2014). Our previous work examining the urge to blink in people with OCD also found activation in similar regions when participants were told to suppress blinking (Stern et al., 2020).
Current Treatments for Sensory Phenomena Are Lacking
Although they are common and distressing, sensory phenomena are not well addressed by first-line OCD treatments, behavioral therapies like cognitive behavioral therapy (CBT) and exposure and response prevention (ERP), and serotonin reuptake inhibitor (SRI) medication (Abramowitz et al., 2003; Stein et al., 2007). Although these treatments help many people with OCD, symptoms like sensory phenomena without a fear component may be more challenging to treat, as behavioral therapies may not be as readily applicable and medications may be less effective (Foa et al., 1999; Stein et al., 2007). Even when sensory phenomena do respond to these treatments, only about half of patients achieve full recovery, underscoring the need to develop new approaches to targeting sensory symptoms in OCD.
Transcranial Magnetic Stimulation (TMS)
TMS is a non-invasive neuromodulation technique that involves placing a specialized coil against the scalp, which generates a magnetic field that induces small electrical currents in the brain (Hallett, 2007). Depending on the stimulation parameters, TMS can either increase or reduce brain activity in the targeted region.
TMS offers several research and clinical advantages. It requires no surgical intervention, no needles, and no substances entering the body beyond the magnetic field itself. Individuals remain seated while the coil is positioned against the scalp using anatomical landmarks or a neuronavigation system. Aside from clicking sounds and mild scalp sensations, TMS is generally well-tolerated with minimal side effects. TMS received FDA approval for treatment-resistant depression in 2008 and for OCD in 2018; it is typically delivered in multiple sessions over several days or weeks, and has an established safety profile across multiple psychiatric applications (Cotovio et al., 2023; Rossi et al., 2021).
From Eyeblinks to Clinically Relevant Sensory Urges
Our research began by studying eyeblink suppression as a model for investigating sensory-based urges (Bragdon et al., 2023; Eng et al., 2024; Stern et al., 2020). People with OCD failed to suppress eyeblinks more than control participants when instructed to do so (Stern et al., 2020). These failures were associated with more severe sensory phenomena (Eng et al., 2024), measured using the gold-standard University of São Paulo-Sensory Phenomena Scale (USP-SPS) (Rosario et al., 2009). Importantly, greater activation in several brain regions, including the postcentral gyrus (involved in processing sensory information), was associated with both eyeblink suppression failures and more severe sensory phenomena in OCD (Eng et al., 2025).
Building on these findings, we tested whether reducing activity in the postcentral gyrus could modulate sensory urges and brain activation. In an initial pilot sample of four participants with OCD, we delivered single-session inhibitory TMS to an individualized target in the postcentral gyrus on one day (active TMS) and sham (inactive) TMS on another (Eng et al., 2025). Active TMS, compared to sham, was generally associated with reduced activity in this brain region during eyeblink suppression and lower self-reported urge to perform compulsions.
Through funding from the Michael Jenike Young Investigator Award, we expanded data collection to include 12 additional participants, for a total sample of 16. Each participant completed i) one baseline brain-imaging session, during which they performed the eyeblink suppression task while their brains were scanned using magnetic resonance imaging (MRI), and ii) two single-session TMS visits on different days, at least 5 days apart. Of these two TMS visits, one visit delivered active inhibitory TMS to an individualized target in the postcentral gyrus, and the other delivered sham TMS, which followed the same procedures but without actual brain stimulation. Participants were not told which condition they received. Immediately before and after each TMS session, participants rated the strength of their urge to perform compulsions using visual analogue scales (VAS). Changes in this rating served as the primary outcome, reflecting acute changes of clinically relevant OCD urges. Immediately after TMS and completing the VAS ratings, participants performed the eyeblink suppression task in the MRI scanner.
The Innovation
To our knowledge, this is the first study to use neuromodulation to specifically target sensory-based urges and the postcentral gyrus in individuals with OCD. Our selection of the postcentral gyrus as a target region is novel and supported by evidence linking higher activation there to more eyeblink suppression failures and more severe sensory phenomena. To tailor stimulation for each participant, we did not target the exact same brain location in everyone. Instead, we used each participant’s own brain scan to identify the specific “hotspot” within the postcentral gyrus that was most active during eyeblink suppression. To lessen discomfort, we delivered TMS in quick bursts rather than using traditional repetitive protocols, so that stimulation can be completed in under a minute. Neuronavigation technology, which is essentially a GPS system for the brain, was used throughout the session to track the TMS coil’s position in real time relative to the participant’s brain to ensure precise and consistent targeting. These approaches acknowledge individual differences in brain anatomy and apply principles of personalized medicine to neuromodulation.
Study Findings
Our study results, while preliminary given the small sample size, showed encouraging patterns across multiple measures. Most importantly from a clinical perspective, participants reported greater reductions in the strength of their urge to perform OCD-related compulsions following active TMS compared to sham, suggesting that modulating activity in the postcentral gyrus may have clinical relevance. In terms of brain activation, regions of the urge network including the postcentral gyrus, precentral gyrus, and insula showed less activation during eyeblink suppression following active TMS compared to sham.
Notably, there was individual variability in response. Some participants showed substantial decreases in the strength of their urge to perform compulsions following active TMS compared to sham, while others showed smaller decreases or minimal change. We found that participants who reported greater reduction in their urge to perform compulsions after active TMS (compared to sham) showed greater decreases in brain activity in regions associated with urges-for-action (including the postcentral gyrus, precentral gyrus, supplementary motor area, and insula), as well as regions involved in cognition and emotional processing, and reduced connectivity between the postcentral gyrus TMS target and these regions.
Conclusion and study implications
This proof-of-concept investigation represents an important step toward addressing a significant unmet clinical need. By demonstrating that modulating activity in the postcentral gyrus was associated with changes in both the urge to perform compulsions and underlying brain circuitry (with notable individual variability), we established a foundation for developing targeted neuromodulation approaches for sensory-based urges in OCD. These findings are promising and worthy of replication in a larger sample.
Although this study examined only short-term effects, these mechanistic findings will inform future clinical trials employing repeated (multi-week) sessions of individualized TMS to achieve longer-term modulation of sensory phenomena in OCD. Beyond TMS, the insights gained from this work are also guiding our exploration of other cutting-edge non-invasive brain stimulation techniques, such as low-intensity focused ultrasound, which can reach deeper brain structures and may ultimately expand treatment options for individuals with sensory phenomena.
About the Author
Goi Khia Eng, PhD, is a Research Scientist at Nathan Kline Institute for Psychiatric Research. Her current research involves understanding the neural underpinnings of sensory phenomena in OCD and she aims to utilize non-invasive stimulation methods to elucidate the pathophysiology of these processes.
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