The paper describes corticostriatal-thalamocortical (CSTC) circuits as central to the neurobiology of OCD. It notes that these circuit models link specific brain loops with obsessive thoughts and compulsive behaviors, and that OCD is widely conceptualized in terms of dysfunction in neural circuits rather than a single brain region.

The article states that research on OCD has increasingly focused on neural circuits, including circuits responsible for grooming and anxiety-like behaviors. It emphasizes that the next generation of OCD research needs to address neural circuitry, linking circuit function to symptoms and behavior.

This review summarizes evidence that OCD symptoms arise from dysfunction in brain circuits, especially cortico-striato-thalamo-cortical loops. It connects abnormal circuit activity with intrusive thoughts, repetitive behaviors, and impaired inhibition of actions.

The symptoms point to dysfunctions in inhibitory control, implicating the dorsal anterior cingulate cortex (dACC) as part of a wider cortico-striato-thalamo-cortical (CSTC) circuitry based on findings from resting-state and task-dependent paradigms. The approach helped to reveal a general network-based dysfunction at the core of OCD. Although both groups demonstrated increased activation of CSTC circuits with increased memory load, the OCD group exhibited hyperactivation of the parietal lobe, mid frontal gyrus, dorsal prefrontal cortex, and dACC at both low and high levels of memory load compared to healthy controls.

This review states that neuroimaging has identified both **structural and functional changes** in multiple brain regions and networks in patients with obsessive-compulsive disorder, including the cortico-striato-thalamo-cortical (CSTC) circuits, limbic regions, and default mode network. It notes that these neural alterations are linked to OCD symptom dimensions and that **treatment-related changes in these circuits** have been observed, suggesting a relationship between neural circuit changes and symptom improvement.

It also extends findings from previous studies that have reported hyperactivation or hyperconnectivity of regions in the CSTC circuits in OCD subjects during an “incentive flanker task” and at rest. Using a seed-based functional connectivity analysis method, Harrison et al. revealed increased resting-state ventral corticostriatal functional connectivity in OCD. Evidence from animal studies also confirms the involvement of this circuit in OCD: using an optogenetic technique, Ahmari et al. found increased grooming (OCD-like behaviors) in mice after repeated stimulation of the CSTC circuits.

Converging neuroimaging, neuropsychological, and neurophysiological evidence supports the involvement of fronto-striato-thalamo-cortical (FSTC) circuitry in the pathophysiology of OCD. Hyperactivity within orbitofrontal cortex, anterior cingulate cortex, and caudate nucleus has been consistently reported in patients with OCD. Importantly, successful treatment with either cognitive-behavioral therapy or pharmacotherapy is associated with reductions in this abnormal activity, suggesting that changes in these neural circuits are linked to changes in symptomatology and behavior.

The authors note that “several studies have provided evidence that CBT can affect the glucose metabolic rates, regional cerebral blood flow (rCBF) and blood oxygenation level dependence (BOLD) response of brain areas associated with the cortico–striato–thalamo‐cortical (CSTC) circuit in OCD patients.” They hypothesized that CBT would modulate the intrinsic whole‐brain network and that “these changes may be associated with improvements in clinical presentation.” In the results, they report that 12 weeks of CBT “decreased the degree centrality in the left dorsolateral prefrontal cortex (DLPFC) and normalized the higher resting‐state functional connectivity between the left DLPFC and the right orbitofrontal cortex in OCD patients,” and that connectivity changes correlated with symptom changes, suggesting that alterations in specific neural circuits are linked to changes in OCD symptoms and behavior.

This systematic review concludes that “evidence indicates that the connectivity within cerebral networks in OCD patients seems to change following CBT.” It summarizes findings that CBT is associated with altered activation and connectivity in the orbitofrontal cortex, anterior cingulate cortex, caudate nucleus, and other nodes of the cortico–striatal–thalamo–cortical circuit, and notes that “changes in these neural systems are often associated with clinical improvement and reductions in compulsive behaviors.” The authors state that the converging data “suggest that psychotherapeutic intervention can induce plastic changes in neural circuits underlying OCD, which in turn are related to changes in symptoms and maladaptive thought patterns.”

Anxiety disorders involve dysregulation in neural circuits that process threat, including the amygdala, hippocampus, medial prefrontal cortex, and their projections to brainstem and striatal regions. Altered connectivity and plasticity within these circuits can lead to pathological fear and anxiety, as seen in both animal models and human neuroimaging studies. Exposure-based treatments leverage plastic changes in these networks, demonstrating that modifying neural circuit function can reshape maladaptive fear responses and anxiety-related thoughts.

Converging lines of evidence from neuroimaging, neurosurgery, and pharmacology suggest that OCD is associated with abnormalities in cortico-striatal-thalamo-cortical (CSTC) circuits. Functional neuroimaging studies have revealed hypermetabolism in the orbitofrontal cortex, anterior cingulate cortex, and caudate nucleus in patients with OCD. Reductions in regional cerebral blood flow and metabolism in these regions following successful treatment parallel clinical improvement, indicating that modulation of these neural circuits can strongly influence obsessive-compulsive symptoms and associated thoughts.

NIMH explains that brain imaging studies of people with OCD show differences in the frontal cortex and subcortical structures of the brain. Research suggests that OCD involves problems in communication between the frontal cortex and deeper brain structures. Treatments that affect the serotonin system, as well as cognitive behavioral therapy, can help improve the symptoms of OCD, indicating that interventions that alter brain chemistry and circuit function can influence the intrusive thoughts and repetitive behaviors characteristic of the disorder.

According to NIMH, brain imaging studies of people with anxiety disorders have shown that the amygdala and hippocampus, brain regions that control fear and memory of emotional events, often show altered activity. Research indicates that heightened activity in the amygdala is associated with anxiety responses, and that treatments such as psychotherapy and medication can help normalize brain activity in these regions. This supports the idea that changes in neural circuits involved in fear and emotion regulation can significantly influence anxiety-related thoughts and behaviors.

This review describes anxiety as arising from dysfunction in distributed neural circuits, particularly networks involving the amygdala, hippocampus, and prefrontal cortex. It explains that alterations in connectivity and plasticity within these circuits can influence attention biases, threat appraisal, and avoidance behavior, and notes that both pharmacological and psychological treatments can induce plastic changes in these networks. The authors highlight evidence that successful treatment is often associated with “normalization of hyperactive amygdala responses and enhanced top-down regulation by prefrontal regions,” linking circuit-level changes to shifts in anxious thoughts and behaviors.

This review summarizes neuroimaging work demonstrating that anxiety disorders are associated with dysfunction in a network including the amygdala, insula, anterior cingulate cortex and prefrontal cortex. Hyperresponsivity of the amygdala to threat-related stimuli and altered prefrontal regulation are consistently reported. Pharmacological and psychological treatments have been shown to modify activity within these circuits, and such changes correlate with clinical improvement, indicating that alterations in neural circuits can causally influence anxious behavior and maladaptive thought patterns.

This paper reviews how deep brain stimulation (DBS) targeting **cortico-striatal circuits** (such as the ventral capsule/ventral striatum) can alleviate severe, treatment-resistant OCD. It notes that modulation of these specific pathways leads to **changes in obsessions and compulsive behaviors**, and emphasizes that OCD is increasingly conceptualized as a disorder of "dysregulated cortico-striato-thalamo-cortical circuitry" that can be **normalized through targeted circuit interventions**.

The review explains that OCD involves areas such as the orbitofrontal cortex, anterior cingulate cortex, caudate nucleus, and thalamus connected through established neuroanatomic circuitry. It concludes that OCD dysfunction is a byproduct of defective neural networks rather than a single brain region.

Deep brain stimulation (DBS) targeting the ventral capsule/ventral striatum in severe, treatment-resistant OCD produced robust clinical improvement in obsessive-compulsive symptoms. Functional imaging before and after DBS showed modulation of activity in orbitofrontal, anterior cingulate, and striatal regions within the cortico-striato-thalamo-cortical circuit. The degree of symptom improvement correlated with the extent of normalization in these circuit dynamics, indicating that altering neural circuit function can strongly influence OCD-related thoughts and behaviors.

This systematic review of neuroimaging studies states that “the altered activation in the prefrontal cortex and precuneus were key regions related to the effects of CBT.” Reviewing anxiety, OCD, and other conditions, it finds that CBT is consistently associated with changes in activity and connectivity in networks including the prefrontal cortex, anterior cingulate, and limbic regions such as the amygdala. The authors conclude that CBT “can lead to functional and structural changes in neural circuits implicated in emotion regulation and cognitive control,” and that these neural changes parallel improvements in clinical symptoms and maladaptive cognitions.

This neuroimaging study reports that patients with OCD exhibit “altered resting-state functional connectivity of fronto-striatal and default mode networks,” including abnormal coupling between the orbitofrontal cortex, striatum, and posterior cingulate cortex. The authors discuss how these circuit-level abnormalities may underlie characteristic OCD symptoms such as intrusive thoughts and repetitive behaviors by disrupting normal error monitoring and habit control. They also note that the degree of connectivity alteration in specific circuits correlates with symptom severity, supporting the idea that variations in neural circuitry are tightly linked to differences in behavior and thought patterns in OCD.

Penn Medicine reports that a specific pattern of brain activity in a frontal region is linked to compulsive behaviors in OCD. The article says abnormal brain-circuit activity between the basal ganglia and frontal cortex is thought to underlie motivation, learning, and habit formation.

Voxel-based morphometry revealed increased gray matter volumes in orbitofrontal cortex and anterior cingulate cortex and decreased volumes in other frontal and parietal regions in patients with OCD compared with healthy controls. These structural changes affect nodes of the cortico-striato-thalamo-cortical circuit and are associated with severity of obsessive-compulsive symptoms, supporting the link between circuit morphology and pathological thoughts and behaviors.

Results: We show how dysfunction in cortico-striato-thalamo-cortical (CSTC) circuits may underpin symptoms; and shed light on the putative neurochemistry within these loops such as the role of serotonin, dopamine, and glutamate systems. We also show how OCD is characterized by cognitive dysfunction including problems in cognitive flexibility, visuospatial memory, response inhibition, and goal-directed behavior, linked to aberrant activity within CSTC circuits. An imbalance between the direct and indirect pathways is thought to contribute to OCD pathology, with overactivity in the direct pathway creating a positive feedback loop resulting in CSTC circuit hyperactivity and compulsive behavior.

Summarizing a Baylor College of Medicine/Texas Children’s Hospital study of OCD patients undergoing deep brain stimulation, the release explains that the team identified "a specific neural activity pattern as a novel biomarker to accurately predict and monitor the clinical status" of individuals with OCD. The authors state that they have found "a neurophysiological biomarker that can serve as a reliable indicator of **improvements in mood and behaviors in OCD patients after DBS treatment**," linking changes in recorded circuit activity to changes in behavior.

UCLA psychiatrist Jeffrey Schwartz explains that "thanks to **neuroplasticity** — the brain’s ability to create and reorganize neural connections — people can find relief from anxiety, depression, substance abuse, obsessive-compulsive disorder and everyday mental health challenges." He describes a four-step cognitive method for OCD and notes that **repetition of these steps changes the brain over time**, implying that systematic changes in thought patterns drive **lasting changes in neural circuits and associated symptoms**.

Describing her study, Dr. Susanne Ahmari explains that "from human imaging studies we know that there's increased activity in certain brain regions in OCD patients" including cortical areas that control thoughts and the striatum, which is important for controlling movements. She reports that when mice received repeated stimulation of the cortico-striatal pathway for only 5 minutes a day over multiple days, there was a progressive evolution of repetitive grooming behavior that "stuck around even when the stimulation was stopped", indicating that a small intervention in a specific circuit led to persistent abnormal behavior.

Across anxiety disorders and OCD, convergent work from lesion studies, optogenetics, deep brain stimulation, and psychotherapy neuroimaging shows that targeted changes in fear and cortico-striatal circuits causally alter behavior and thought patterns. Lesions or inhibitory stimulation of amygdala–prefrontal pathways can reduce pathological fear, while chronic stress or experimental potentiation of these circuits can induce heightened anxiety and intrusive threat-related thinking in animals. Similarly, in OCD, both invasive (deep brain stimulation, lesions) and noninvasive (CBT-induced plasticity) interventions that modify activity in cortico-striato-thalamo-cortical loops reliably track with changes in compulsive behaviors and obsessions.