People with Tourette syndrome often describe a rising, uncomfortable sensation just before a tic fires, a feeling they cannot ignore until the movement happens. People with obsessive-compulsive disorder describe something strikingly similar: an internal pressure that builds until a compulsion is carried out. Clinicians have long noticed the overlap. Roughly 50% of people diagnosed with Tourette syndrome also meet criteria for OCD, according to the Tourette Association of America. Now, a study published in Cell Reports identifies a specific brain circuit that may explain why.
A research team at Kobe University traced a pathway in mice that runs from the motor cortex through a deep-brain relay station called the intralaminar thalamus and into the insular cortex, a region involved in body awareness and emotional processing. When the researchers chemically silenced that relay, tic-like behaviors in the mice dropped significantly. The finding offers the most direct evidence to date that a single circuit could generate the premonitory urges behind both tics and compulsions.
A circuit that bridges movement and feeling
The basal ganglia, a cluster of structures deep in the brain, help govern voluntary movement. In Tourette syndrome, abnormal signaling in these structures is thought to produce involuntary tics. But tics are not purely motor events. Most people with the condition report a sensory buildup beforehand, a premonitory urge, that feels more like an itch demanding to be scratched than a random muscle spasm.
The Kobe University team wanted to know how motor signals reach the insular cortex, the brain region most consistently linked to that urge sensation. Using viral tracing techniques in mice, they mapped a route: output from the basal ganglia travels to the intralaminar thalamic nuclei, which then project to the insula. When they used chemogenetics, a method that lets researchers switch specific neurons on or off with a designer drug, to quiet the thalamic relay, tic intensity fell.
A related preprint posted on bioRxiv described supporting experiments, including fiber photometry recordings that tracked real-time neural activity in both the insula and the primary motor cortex during tic events. Because preprints have not completed peer review, those results carry less formal weight, but they align closely with the published findings.
Human brain imaging points to the same regions
The mouse data do not stand alone. Several peer-reviewed human neuroimaging studies have independently flagged the same brain areas.
A functional MRI study published in Neurology found that connectivity between the right dorsal anterior insula and the supplementary motor area correlated with how severe patients rated their urge to tic. Structural MRI work published in Brain and Behavior showed that premonitory urge severity tracked with thinner grey matter in the insula and sensorimotor cortex among young people with Tourette syndrome. And a resting-state fMRI study in the Journal of Psychiatric Research went a step further, distinguishing separate network-level signatures for tic severity, OCD symptom severity, and premonitory urge severity within the same group of Tourette patients.
A broader analysis published in late 2024 in Nature Communications frames Tourette syndrome as a disorder involving multiple overlapping networks, with the insula, dorsal anterior cingulate cortex, and supplementary motor area all playing roles in urge and tic generation. That framework helps explain why the thalamo-insular pathway identified at Kobe matters: it sits where motor planning and emotional awareness intersect, precisely the territory where tics and compulsions overlap.
A possible explanation for deep brain stimulation results
The circuit also offers a mechanistic explanation for something neurosurgeons have observed in the clinic. Deep brain stimulation (DBS) targeting the centromedian-parafascicular complex of the thalamus, part of the intralaminar group, has reduced tics in patients with severe, treatment-resistant Tourette syndrome. A review article in Neurosurgical Review summarized results across multiple studies and meta-analyses, reporting consistent tic reductions in small patient cohorts, though sample sizes have generally remained in the single digits to low double digits per study and designs have varied.
What has been less clear is why stimulating that particular thalamic region helps. The Kobe University findings suggest an answer: DBS may be dampening the relay that carries aberrant motor signals to the insula, reducing the urge that drives the tic. If that interpretation holds, it could also explain anecdotal reports of OCD symptom improvement in some DBS patients, though that connection has not been rigorously tested.
What the study cannot yet tell us
The most important caveat is species. Mouse brains are not human brains. The thalamo-insular pathway mapped in this study has clear anatomical parallels in people, and the human imaging data point to the same regions, but no single study has yet confirmed the full three-node relay operating in humans with comorbid Tourette syndrome and OCD.
Clinical translation raises its own questions. Existing DBS data focus primarily on tic reduction; longitudinal trials specifically measuring OCD symptom changes in Tourette patients receiving thalamic stimulation are scarce. Whether non-invasive approaches like transcranial magnetic stimulation or focused ultrasound could modulate this pathway precisely enough to help with both tics and compulsions remains untested.
Self-report also introduces complexity. Neuroimaging can show that insular activity spikes before a tic or that connectivity patterns track with reported urges, but it cannot directly capture the internal experience of a premonitory urge or a compulsive drive. Clinician ratings, behavioral observations, and patient-reported scales remain essential for linking brain activity to lived experience, and each introduces its own variability.
Why the thalamo-insular pathway changes the research landscape
For the estimated 1 in 160 children worldwide who develop Tourette syndrome, according to the CDC, and the millions more who live with OCD, the practical significance is this: researchers now have a specific anatomical target. The intralaminar thalamus and its connections to the insula and motor cortex appear to sit at a junction between movement control and urge awareness. That does not immediately produce a new pill or a new device, but it sharpens the aim of ongoing work in neuromodulation and pharmacology.
The next critical step, according to the Kobe University team’s press release distributed through EurekAlert, is human imaging work that tracks the full relay chain in patients who have both conditions. Clinical trials that measure tic severity and obsessive-compulsive symptoms simultaneously, while incorporating imaging of the thalamo-insular pathway, would test whether this shared circuit can be safely and effectively modulated. Until those trials report results, the mouse-to-human bridge remains incomplete, but the blueprint is now considerably more detailed than it was before.
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*This article was researched with the help of AI, with human editors creating the final content.
