How Do Similar Thalamocortical Circuits Produce Psychosis Versus Compulsivity?

The thalamus is now recognized as a dynamic regulator of cortical information flow, with the thalamic reticular nucleus (TRN) providing inhibitory control over the routing, gain, and timing of thalamocortical communication. Schizophrenia and obsessive-compulsive disorder (OCD) both involve thalamocortical abnormalities, yet produce distinct clinical phenotypes, psychosis versus compulsivity. This narrative review synthesizes evidence from neuroimaging, electrophysiology, postmortem studies, and animal models to compare thalamocortical gating mechanisms across these disorders. In schizophrenia, converging evidence supports weakened TRN-mediated inhibition as a core gating deficit. Postmortem reductions in GAD67 and parvalbumin within TRN neurons, optogenetic models reproducing sensory gating deficits through TRN parvalbumin (PV) suppression, and a ∼40% reduction in sleep spindle density collectively point to diminished inhibitory regulation of thalamic relay output. At the network level, this maps onto reduced thalamo-prefrontal connectivity with increased thalamo-sensorimotor coupling, consistent with deficient top-down filtering and excessive bottom-up sensory transmission. In OCD, no study has directly examined TRN structure or function. However, cortico-striato-thalamo-cortical (CSTC) models implicate thalamic relay disinhibition through basal ganglia pathways, and emerging evidence of increased spindle frequencies correlating with obsession severity suggests a pattern qualitatively distinct from schizophrenia. These preliminary observations raise the possibility that OCD involves temporally inflexible rather than weakened gating, though this hypothesis remains speculative. Together, these lines of evidence suggest that similar thalamocortical architectures may be disrupted through distinct regulatory mechanisms, insufficient inhibitory control versus loss of temporal flexibility, offering a framework for understanding how overlapping circuits produce divergent psychiatric phenotypes.