Brain Volumes of the Lamb, Rat and Bird Do Not Show Hemispheric Asymmetry: a Stereological Study

It is well known that there are functional differences between right and left brain hemispheres. However, it is not clear whether these functional differences are reflected in morphometric differences. This study was carried out to investigate the right-left asymmetry, and sex and species differences of the brains using the Cavalieri principle for volume estimation. Seventeen lambs, 10 rats and 12 avian brains were used to estimate brain volumes. A transparent point grid was superimposed on the slices of lamb brains directly and the slices of the rat and avian brains were projected onto a screen at 10x magnification. Surface areas of the cut slice faces were estimated by simply counting the points that hit the slices. Mean brain volumes were 37.74 cm, 598.95 mm and 730.38 mm and the coefficients of variations were 0.08, 0.05 and 0.05 for lamb, rat and avian brains respectively. The differences between left and right hemispheres did not show statistical significance (P > 0.05). However, the male brain volumes were larger than the females for the lamb and bird (P < 0.05). In light of such findings, it will be necessary to evaluate neuron number of the brain hemispheres to provide more useful data regarding inter-hemispheric brain asymmetry.