Abstract
Identifying biomarkers of developing mental disorder is crucial to improving early identification and treatment—a key strategy for reducing the burden of mental disorders. Cross-frequency coupling between two different frequencies of neural oscillations is one such promising measure, believed to reflect synchronization between local and global networks in the brain. Specifically, in adults phase–amplitude coupling (PAC) has been shown to be involved in a range of cognitive processes, including working and long-term memory, attention, language, and fluid intelligence. Evidence suggests that increased PAC mediates both temporary and lasting improvements in working memory elicited by transcranial direct-current stimulation and reductions in depressive symptoms after transcranial magnetic stimulation. Moreover, research has shown that abnormal patterns of PAC are associated with depression and schizophrenia in adults. PAC is believed to be closely related to cortico-cortico white matter (WM) microstructure, which is well established in the literature as a structural mechanism underlying mental health. Some cognitive findings have been replicated in adolescents and abnormal patterns of PAC have also been linked to ADHD in young people. However, currently most research has focused on cross-sectional adult samples. Whereas initial hypotheses suggested that PAC was a state-based measure due to an early focus on cognitive, task-based research, current evidence suggests that PAC has both state-based and stable components. Future longitudinal research focusing on PAC throughout adolescent development could further our understanding of the relationship between mental health and cognition and facilitate the development of new methods for the identification and treatment of youth mental health.
Highlights
In Australia, mental disorders were estimated to have a direct economic cost of up to $51 billion and a further $130 billion cost as a result of diminished well-being during the 2018–2019 period (Productivity Commission, 2019)
Noda et al (2017) analyzed resting-state phase–amplitude coupling (PAC) before and after a typical 2-week course (10 sessions) of repetitive transcranial magnetic stimulation (TMS) targeting the dorsolateral prefrontal cortex in adult patients with depression; rTMS was associated with improved scores on the Hamilton Rating Scale for Depression, Beck Depression Inventory and increased PAC at the C3 and T3 electrode site at rest. These findings suggest that decreased resting-state theta–gamma PAC may be a biomarker of poorer mental health and that lasting changes in PAC may be a mechanism underlying TMS treatment
PAC has been implicated in mental health as well, with a number of studies identifying abnormalities in PAC as features of psychotic disorders and ADHD
Summary
In Australia, mental disorders were estimated to have a direct economic cost of up to $51 billion and a further $130 billion cost as a result of diminished well-being during the 2018–2019 period (Productivity Commission, 2019). Noda et al (2017) analyzed resting-state PAC before and after a typical 2-week course (10 sessions) of repetitive TMS (rTMS) targeting the dorsolateral prefrontal cortex in adult patients with depression; rTMS was associated with improved scores on the Hamilton Rating Scale for Depression, Beck Depression Inventory and increased PAC at the C3 (left temporal) and T3 electrode site at rest These findings suggest that decreased resting-state theta–gamma PAC may be a biomarker of poorer mental health ( depression) and that lasting changes in PAC may be a mechanism underlying TMS treatment. Both studies identified increased theta–gamma PAC at rest within regions known to be associated with the default mode network (DMN) in patient groups compared to controls These results suggest people with psychosis have dysfunctional hyperactivation of resting-state theta–gamma PAC within DMN-related brain regions, which may be a result of compensatory reallocation of cognitive resources due to dysfunction in the prefrontal cortex. Longitudinal research to determine whether PAC demonstrates similar non-linear growth trajectories to AAC and how these are associated with adolescent cognitive development and mental health may be crucial to better understanding how PAC research can contribute to better understanding mental health
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