STEREOLOGICAL AND ALLOMETRIC STUDIES ON MAMMALIAN CEREBRAL-CORTEX WITH IMPLICATIONS FOR MEDICAL BRAIN IMAGING

Design-based stereological methods (the Cavalieri principle and vertic al sectioning) have been used to estimate the volumes, surface areas a nd thicknesses of the cerebral cortex. Cortices of individual hemisphe res were analysed in a selection of 31 adult domestic mammals (horses, oxen, pigs, goats, dogs, cats and rabbits). There were 13 females and 18 males. After correcting for fixation shrinkage effects, results we re tested for species, laterality and sex differences using linear reg ression and analysis of variance. Mean body weights of domestic mammal s varied from 4 kg to 460 kg and brain volumes from 11 cm(3) to 603 cm (3). Hemisphere dimensions varied between species but, except for volu me (which exhibited a species x sex interaction effect), no other diff erences were detected. It is concluded that these mammalian brains are , in terms of their gross anatomy, symmetric and not sexually dimorphi c. Apparent cortical thickness (measured directly on slices) proved to be a satisfactory estimate of true thickness (estimated by dividing c ortical volume by the mean of outer and inner cortical surfaces). This has implications for medical slice images on which mean cortical thic kness can be estimated only from apparent local thicknesses.