Circadian-Related Hypothalamic Structure Differs by Chronotype in Bipolar Disorder.

Area of Science:

• Neuroscience
• Psychiatry
• Chronobiology

Background:

• Circadian rhythm disturbances are a core feature of bipolar disorder (BD).
• Evening chronotype in BD is associated with poorer outcomes.
• Hypothesized link between BD psychopathology, evening chronotype, and structural brain alterations in circadian-related hypothalamic regions, particularly the suprachiasmatic nucleus (SCN).

Purpose of the Study:

• To investigate structural neuroimaging differences in circadian-related hypothalamic regions in bipolar disorder (BD) patients with varying chronotypes.
• To determine if BD psychopathology combined with evening chronotype is associated with specific structural alterations in the SCN.
• To examine the specificity of these alterations relative to other psychiatric disorders.

Main Methods:

• Utilized structural neuroimaging data from the UK Biobank, including participants with BD, major depressive disorder, psychotic disorders, and healthy controls.
• Segmented the SCN-containing anterior-inferior hypothalamic subunit, a key region for circadian functional neuroanatomy.
• Performed analysis of variance to test for diagnosis × chronotype interactions on subunit volume, controlling for covariates like age, sex, and medication use.

Main Results:

• A significant diagnosis × chronotype interaction was observed in the volume of the SCN-containing anterior-inferior hypothalamic subunit (p = .010).
• This interaction was driven by larger volumes in BD individuals with evening chronotype compared to those with morning chronotype (p_FWER = .004).
• No similar associations were found in other hypothalamic regions or across other diagnostic groups.

Conclusions:

• Hypothalamic structure in BD varies with chronotype, with associations localized to an anterior-inferior region involved in circadian regulation.
• Chronotype represents a biologically meaningful dimension of variation in BD, supported by neuroanatomical evidence.
• Further research, including longitudinal and interventional studies, is needed to clarify the clinical significance and mechanisms of these findings.