The default mode network (DMN), a set of brain regions more active at rest than during demanding tasks, shows abnormal hyperactivation and hyperconnectivity in schizophrenia and depression. In schizophrenia, this may contribute to excessive self-reference and problems with attention and working memory. In depression, DMN hyperactivity may underlie negative rumination. Greater DMN suppression in healthy brains is linked to better performance on attention-focused tasks. The review considers these findings in relation to the DMN's psychological functions and its alteration across various neuropsychiatric disorders.
Resting-state brain networks may help explain hallucinations across different sensory modalities and populations. This report from the International Consortium on Hallucination Research reviews evidence linking resting-state alterations to auditory hallucinations, finding connectivity differences in left-hemisphere auditory and language regions, plus atypical interactions of the default mode network with networks for cognitive control and salience. Similar patterns appear in visual hallucinations, suggesting both domain-general and modality-specific network changes. However, high methodological heterogeneity across studies limits direct comparisons. The authors offer recommendations for future research on resting-state connectivity and hallucinations.
Abnormalities in the 40-Hz auditory steady-state response (ASSR), a measure of gamma-band brain activity, appear in schizophrenia and in animal models with reduced NMDA receptor function. This study compared 40-Hz ASSR deficits in schizophrenia patients to those induced by ketamine (an NMDA receptor antagonist) in healthy participants. Schizophrenia patients showed increased prestimulus broadband gamma power and reduced evoked power, total power, and phase-locking factor, replicating prior work, but no phase delay. Ketamine similarly increased prestimulus gamma power and reduced evoked power, total power, and phase-locking factor, while also advancing the ASSR phase. Direct comparison revealed significant differences only in phase, suggesting NMDA receptor hypofunction contributes to gamma oscillation abnormalities in schizophrenia.