Sleep spindles and slow waves in schizophrenia and related disorders: main findings, challenges and future perspectives

Sleep abnormalities have recently gained renewed attention in patients diagnosed with schizophrenia. Disrupted thalamocortical brain oscillations hold promise as putative biomarkers or endophenotypes of the disorder. Despite an increase in studies related to sleep spindle and slow‐wave activity, findings remain in part contradictory. Although sleep spindle deficits have been confirmed in several groups of patients with chronic, medicated schizophrenia, data on the early stages of the disorder and in unmedicated subjects are still insufficient. Findings on slow‐wave abnormalities are largely inconclusive, possibly due to the different criteria employed to define the phenomenon and to the influence of atypical antipsychotics. In this review, we aim to address the methodological and practical issues that may have limited the consistency of findings across research groups and different patient populations. Given the neurobiological relevance of these oscillations, which reflect the integrity of thalamocortical and cortico‐cortical function, research in this domain should be encouraged. To promote widespread consensus over the scientific and clinical implications of these sleep‐related phenomena, we advocate uniform and sound methodological approaches. These should encompass electroencephalographic recording and analysis techniques but also selection criteria and characterization of clinical populations. We review recent evidence that disrupted brain oscillations during sleep are putative endophenotypes of Schizophrenia. Whereas sleep spindle deficits have been confirmed in several groups of patients with chronic, medicated Schizophrenia, findings on slow‐wave abnormalities are largely inconclusive, possibly due to the influence of atypical antipsychotics. Uniformity of EEG recording and analysis techniques but also selection criteria and characterization of clinical populations is necessary to advance knowledge in this fast‐growing field.