OCD Brains Recruit More Neural Regions During Sequencing Tasks - Including Areas Not Previously Linked to the Disorder

Obsessive-compulsive disorder is defined by repetitive thoughts and compulsive actions that patients recognize as excessive but feel unable to stop. One way to describe what happens neurologically is that patients become stuck - looping through the same mental or behavioral sequences rather than moving forward through them cleanly. That description is imprecise, but it raises a specific research question: do people with OCD actually process sequences differently in the brain, even when performing tasks unrelated to their particular compulsions?

A study from Brown University's Carney Institute for Brain Science, published in Imaging Neuroscience, examined this question directly. The research team, working in the laboratory of Theresa Desrochers, an associate professor of brain science and psychiatry at Brown, asked participants with OCD and healthy controls to perform a sequential cognitive task inside an MRI scanner while their brain activity was recorded.

Same Performance, Different Brain Patterns

The task required participants to name either the color or the shape of a series of objects in a specific order - for example, color, color, shape, shape - while keeping track of where they were in the sequence. This design requires multiple cognitive systems to work together simultaneously: working memory to track sequence position, categorization to identify object properties, and control processes to switch between task dimensions on cue.

Participants with OCD completed the task as accurately as the control group. There was no behavioral deficit. But the MRI data told a different story. Individuals with OCD showed greater activation across more brain regions than controls, with differences concentrated in areas connected to motor and cognitive task control, working memory, and object recognition.

"Their behavior looked similar, but the brains of the participants with OCD recruited more brain regions than the people in the control group," said lead study author Hannah Doyle, a postdoctoral research associate in Desrochers' lab.

Regions Not Previously Associated With OCD

Two of the differentially active regions had not previously been linked to OCD in the literature. The middle temporal gyrus - an area involved in working memory, semantic memory retrieval, and language processing - showed elevated activity in the OCD group. So did a region spanning part of the occipital gyrus and the temporo-occipital junction, involved in lower-level visual processing and object recognition.

Previous OCD research has focused heavily on frontostriatal circuits - the connections between the prefrontal cortex and the striatum - and more recently on orbitofrontal and cingulate regions. The discovery that visual and semantic processing areas also show anomalous activity during a sequencing task extends the neural map of OCD and may explain aspects of the disorder that frontostriatal-centric frameworks do not fully account for.

Potential Implications for TMS Therapy

Transcranial magnetic stimulation, which uses focused magnetic pulses to stimulate specific brain regions, was approved by the FDA as an OCD treatment in 2018. Current TMS protocols for OCD target previously identified regions; the treatment produces meaningful symptom improvement in approximately 30-40% of patients - better than nothing, but leaving the majority without adequate benefit.

Nicole McLaughlin, associate professor of psychiatry at Brown and a neuropsychologist at Butler Hospital, suggested the newly identified regions could offer better targets. "If we reposition coils during TMS treatments to be near these brain regions, we might end up seeing a greater improvement in symptoms," she said. This is a hypothesis, not yet a tested clinical advance - repositioning coils based on these findings and measuring symptom outcomes would require dedicated clinical trials.

The team is exploring whether the sequencing task itself could serve as an assessment tool, tracking how patients' neural patterns change over the course of TMS treatment. If successful treatment causes the OCD brain patterns to shift toward those seen in controls, that shift could serve as a biomarker for therapeutic response - potentially identifying which patients are responding to treatment before symptoms visibly improve.

The study's sample was limited in size, which is common in neuroimaging research due to the cost and logistical demands of MRI scanning. Replication in larger, independent samples will be necessary before the findings can inform clinical practice, and the sequencing task's utility as a treatment-tracking tool remains to be demonstrated prospectively.