How the brain adapts to nature's rhythms: a year of neuroimaging in a seasonal mammal

At temperate and polar latitudes, animals and humans experience seasonal changes that impact physiology and behavior. In these habitats, the prevalence and severity of certain psychiatric disorders fluctuate seasonally. Such patterns imply that an adaptive system fine-tunes brain physiology in response to annual environmental changes, and alterations to this system may adversely affect mental health. To date, the core neuronal circuitry of the seasonal control of brain functioning is still largely unknown. To address this question, we identified brain regions sensitive to seasonal changes, using neuroimaging in the domestic sheep (Ovis aries), an animal model commonly used to study seasonality. Here, we developed MRI neuroinformatics resources (templates and atlas) dedicated to the analysis of the sheep brain and revealed that seasons broadly modify grey matter organization and volume of both cortical and subcortical regions involved in the control of homeostasis, sensory processing, learning, memory, behavior control, and social cognition. Many of these regions were not previously known to be affected by seasonal variations, highlighting that the seasonal control of brain function involves plasticity mechanisms across multiple brain sites.