Background: We recently found marked deficits in sleep spindles, non-rapid eye movement (NREM) sleep oscillations that are generated within the thalamus and then amplified and sustained in the cortex, in patients with schizophrenia compared to both healthy and psychiatric controls. Here, we investigated the thalamic and cortical contributions to these sleep spindle deficits.
Methods: Anatomical volume of interest analysis (i.e., thalamic volumes) and electroencephalogram (EEG) source modeling (i.e., spindle-related cortical currents) were performed in patients with schizophrenia and healthy comparison subjects.
Findings: Schizophrenia patients had reduced mediodorsal (MD) thalamic volumes, especially on the left side, compared to healthy controls, whereas whole thalami and lateral geniculate nuclei did not differ between groups. Furthermore, left MD volumes were strongly correlated with the number of scalp-recorded spindles in an anterior frontal region, and cortical currents underlying these anterior frontal spindles were localized in the prefrontal cortex, in Brodmann area (BA) 10. Finally, prefrontal currents at the peak of spindle activity were significantly reduced in schizophrenia patients and correlated with their performance in an abstraction/working memory task.
Conclusion: Altogether, these findings point to deficits in a specific thalamo-cortical circuitry in schizophrenia, which is associated with some cognitive deficits commonly reported in those patients.
Keywords: MRI; Prefrontal cortex; Schizophrenia; Sleep spindles; Thalamus; hd-EEG.
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