Chronotype, Longitudinal Volumetric Brain Variations Throughout Adolescence, and Depressive Symptom Development.

OBJECTIVE: Adolescence is a critical period for circadian rhythm, with a strong shift toward eveningness around age 14. Also, eveningness in adolescence has been found to predict later onset of depressive symptoms. However, no previous study has investigated structural variations associated with chronotype in early adolescence and how this adds to the development of depressive symptoms. METHOD: Assessment of 128 community-based adolescents (51% girls) at age 14 and 19 years was performed. Using whole-brain voxel-based morphometry, baseline (at age 14) regional gray matter volumes (GMVs), follow-up (at age 19) regional GMVs, and longitudinal changes (between 14 and 19) associated with Morningness/Eveningness Scale in Children score and sleep habits at baseline were measured. The association of GMV with depressive symptoms at 19 years was studied, and the role of potential clinical and genetic factors as mediators and moderators was assessed. RESULTS: Higher eveningness was associated with larger GMV in the right medial prefrontal cortex at ages 14 and 19 in the whole sample. GMV in this region related to depressive symptoms at age 19 in catechol-O-methyltransferase (COMT) Val/Val, but not in Met COMT, carriers. Larger GMV also was observed in the right fusiform gyrus at age 14, which was explained by later wake-up time during weekends. CONCLUSION: In adolescence, eveningness and its related sleep habits correlated with distinct developmental patterns. Eveningness was specifically associated with GMV changes in the medial prefrontal cortex; this could serve as a brain vulnerability factor for later self-reported depressive symptoms in COMT Val/Val carriers.

Normal aging modulates prefrontoparietal networks underlying multiple memory processes.

A functional decline of brain regions underlying memory processing represents a hallmark of cognitive aging. Although a rich literature documents age-related differences in several memory domains, the effect of aging on networks that underlie multiple memory processes has been relatively unexplored. Here we used functional magnetic resonance imaging during working memory and incidental episodic encoding memory to investigate patterns of age-related differences in activity and functional covariance patterns common across multiple memory domains. Relative to younger subjects, older subjects showed increased activation in left dorso-lateral prefrontal cortex along with decreased deactivation in the posterior cingulate. Older subjects showed greater functional covariance during both memory tasks in a set of regions that included a positive prefronto-parietal-occipital network as well as a negative network that spanned the default mode regions. These findings suggest that the memory process-invariant recruitment of brain regions within prefronto-parietal-occipital network increases with aging. Our results are in line with the dedifferentiation hypothesis of neurocognitive aging, thereby suggesting a decreased specialization of the brain networks supporting different memory networks.