GlossaryCSTC circuit

CSTC circuit

Cortico-striato-thalamo-cortical circuit — a neural feedback loop connecting the orbitofrontal cortex, caudate nucleus, thalamus, and anterior cingulate cortex. Chronically hyperactive and "locked" in OCD, generating intrusive thoughts and compulsive responses. Psilocybin's proposed mechanism in OCD is normalisation of fronto-striatal connectivity within this loop — distinct from its default mode network disruption mechanism in depression.

Full Explanation

The CSTC (cortico-striato-thalamo-cortical) circuit is a neural feedback loop connecting the orbitofrontal cortex, caudate nucleus, thalamus, and anterior cingulate cortex. Chronically hyperactive and "locked" in OCD, it generates intrusive thoughts and compulsive responses. Psilocybin's proposed mechanism in OCD is normalisation of fronto-striatal connectivity within this loop — distinct from its default mode network disruption mechanism in depression.

See: OCD (/conditions/ocd).

Why It Matters

The CSTC circuit explains why OCD may respond to psilocybin through a different pathway than depression — fronto-striatal normalisation rather than DMN disruption.

Related Terms

Default Mode Network (DMN)

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Default Mode Network (DMN)

A brain network associated with self-referential thinking, rumination, and the sense of ego; psilocybin temporarily reduces its activity.

CYP enzyme (CYP2D6 / CYP1A2)

Cytochrome P450 enzymes responsible for metabolising psilocin and many psychiatric medications in the liver. CYP2D6 is strongly inhibited by fluoxetine (Prozac) and paroxetine (Paxil), slowing their own clearance and potentially affecting psilocybin metabolism. CYP1A2 is strongly inhibited by fluvoxamine (Luvox), which may unpredictably increase psilocin blood levels — making that combination pharmacokinetically risky. Relevant when combining psilocybin with any psychiatric medication.

Fronto-striatal connectivity

Functional connectivity between the prefrontal cortex and the striatum. Abnormally elevated in OCD, contributing to the locked feedback loop of intrusive thoughts and compulsive behaviours. The Yale Phase 2 OCD trial (NCT05546658) uses fMRI to measure whether psilocybin normalises fronto-striatal connectivity at 48 hours post-dosing — providing the first neural biomarker evidence for psilocybin's mechanism in OCD.

Afterglow

The period of heightened mood, openness, and mental flexibility that commonly follows a full-dose psilocybin session — typically lasting 24 hours to several weeks. During the afterglow, neuroplasticity is elevated, default mode network activity is altered, and emotional and cognitive patterns are unusually open to change. Considered the critical integration window: therapeutic insights translate into lasting behavior change most effectively during this period. (Majić et al., 2015)

Spores

Reproductive cells produced by mushrooms, used to start new cultures and legal to possess in most US states.

Set and Setting

The combination of mindset (set) and environment (setting) that shapes a psychedelic experience.