Although the brain cannot store glucose, it relies on glucose as its primary energy source. The basal metabolic demand of the brain is estimated to be 30% of whole-brain glucose use, providing the fuel required for functions such as resting state connections. Seventy percent of brain glucose use is for spontaneous functional processes, including the production of action potentials, postsynaptic potentials, and the maintenance of ion gradients. The level of cerebral glucose metabolism is considered a reliable measure of neuronal activity. [F-18] fluorodeoxyglucose ([18F]-FDG or FDG) positron emission tomography (PET) is the most commonly used neuroimaging technique for directly evaluating brain glucose metabolism in vivo. In recent systematic reviews and meta-analyses of FDG-PET studies in ageing, we found older adults have lower frontal and temporal cerebral metabolic rates of glucose (CMRGLC) than younger adults (Deery et al., 2022). This pattern was found when effect size meta-analyses were performed at the lobular levels and activation likelihood estimates meta-analyses were undertaken at a regional level. The age effects were reduced after adjustments were made for grey matter and/or partial volume effects. The action of insulin in the brain has received attention recently because significant disturbances are not only observed in obesity and diabetes, but also in ageing and dementia. Although there is a large body of epidemiological evidence linking metabolic health, including insulin sensitivity, to ageing and disease, the relationship to CMRGLC in ageing has not been studied. The current study will assess the relationships between peripheral insulin sensitivity, as measured by Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), age, CMRGLC at the regional level using Statistical Parameter Mapping, and cognitive function.