Brain asymmetries from midlife to old adulthood and hemispheric brain age

Motivation: The human brain demonstrates structural and functional asymmetries which have implications for ageing and the development of mental and neurological diseases. Age-relationships of these asymmetries are largely unknown. Goal(s): We aimed to map brain asymmetries from midlife to older ages and develop hemispheric brain age (HBA) models, which consider apparent hemispheric differences. Approach: We used structural and diffusion magnetic resonance imaging metrics (N=48,040, UK Biobank) to evaluate the age-relationship of brain asymmetry. Results: Most metrics indicated asymmetry, which appears lower at higher age in white matter and higher in grey matter. HBA reflects other brain ages and unique information of each hemisphere. Impact: We present for the first time comprehensive analyses of brain asymmetries throughout midlife and older ages and establish a new conceptualisation of BrainAge. This ”hemispheric” BrainAge can serve as a marker of asymmetry by comparing left to right hemisphere-derived BrainAges.