Increased thalamocortical connectivity in schizophrenia correlates with sleep spindle deficits: evidence for a common pathophysiology

Abstract Background Converging evidence implicates abnormal thalamocortical interactions in the pathophysiology of schizophrenia. This evidence includes consistent findings of increased resting-state functional connectivity MRI of the thalamus with somatosensory and motor cortex during wake and reduced spindle activity during sleep. We hypothesized that these abnormalities would be correlated, reflecting a common mechanism: reduced inhibition of thalamocortical neurons by the thalamic reticular nucleus (TRN), which is the major inhibitory nucleus of the thalamus and is abnormal in schizophrenia. Reduced TRN inhibition would be expected to lead to increased and less filtered thalamic relay of sensory and motor information to the cortex during wake and reduced burst firing necessary for spindle initiation during sleep. Methods Twenty-six schizophrenia outpatients and 30 demographically matched healthy individuals had overnight polysomnography and resting-state functional connectivity MRI scans. We examined the relations of sleep spindle density during stage 2 non-rapid eye movement sleep with connectivity of the thalamus with the cortex during wakeful rest. Results As in prior studies, schizophrenia patients exhibited increased functional connectivity of the thalamus with bilateral somatosensory and motor cortex, and reduced sleep spindle density. Spindle density inversely correlated with thalamocortical connectivity, including in somotosensory and motor cortex, regardless of diagnosis. Conclusions These findings link two biomarkers of schizophrenia – the sleep spindle density deficit and abnormally increased thalamocortical functional connectivity – and point to deficient TRN inhibition as a plausible mechanism. If TRN-mediated thalamocortical dysfunction increases risk for schizophrenia and contributes to its manifestations, understanding its mechanism could guide the development of targeted interventions.