At the beginning of neurodegenerative disease, the immune cells of the brain -- the 'microglia' -- take up glucose, a sugar molecule, to a much greater extent than hitherto assumed. These results are of great significance for the interpretation of brain scans depicting the distribution of glucose in the brain. Furthermore, such image-based data could potentially serve as a biomarker to non-invasively capture the response of microglia to therapeutic interventions in people with dementia.