SEX-DIFFERENCES IN HUMAN BRAIN MORPHOMETRY AND METABOLISM - AN IN-VIVO QUANTITATIVE MAGNETIC-RESONANCE-IMAGING AND POSITRON EMISSION TOMOGRAPHY STUDY ON THE EFFECT OF AGING

Background: There are significant age and sex effects in cognitive abi lity and brain disease. However, sex differences in aging of human bra in areas associated with nonreproductive behavior have not been extens ively studied. We hypothesized that there would be significant sex dif ferences in aging of brain areas that subserve speech, visuospatial, a nd memory function. Methods: We investigated sex differences in the ef fect of aging on human brain morphometry by means of volumetric magnet ic resonance imaging and on regional cerebral metabolism for glucose b y positron emission tomography. In the magnetic resonance imaging stud y, we examined 69 healthy right-handed subjects (34 women and 35 men), divided into young (age range, 20 to 35 years) and old (60 to 85 year s) groups. In the positron emission tomography study, we investigated 120 healthy right-handed subjects (65 women and 55 men) aged 21 to 91 years.Results: In the magnetic resonance imaging study, age-related vo lume loss was significantly greater in men than women in whole brain a nd frontal and temporal lobes, whereas it was greater in women than me n in hippocampus and parietal lobes. In the positron emission tomograp hy study, significant sex differences existed in the effect of age on regional brain metabolism, and asymmetry of metabolism, in the tempora l and parietal lobes, Broca's area, thalamus, and hippocampus. Conclus ions: We found significant sex differences in aging of brain areas tha t are essential to higher cognitive functioning. Thus, our findings ma y explain some of the age-sex differences in human cognition and respo nse to brain injury and disease.