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Abstract. Expanding previous studies of human cerebral cortical sexual dimorphism showing higher neuronal densities in males, we investigated whether gender differences also exist in the extent of neuropil, size of neuronal somata, and volumes of astrocytes. This histo-morphometric study includes select autopsy brains of 6 males and 5 females, 12 to 24 yr old. In each brain, 86 defined loci were analyzed for cortical thickness, neuronal and astrocytic (8 loci) density (stereological counts), and neuronal and astrocytic (8 loci) soma size, enabling calculations of neuropil and astrocytic volumes. The female group showed significantly larger neuropil volumes than males, whereas neuronal soma size and astrocytic volumes did not differ. The expanded data confirmed higher neuronal densities in males than in females without a gender difference in cortical thickness. These findings indicate that fundamental gender differences exist in the structure of the human cerebral cortex, with more numerous, smaller neuronal units in men and fewer, larger ones in women; they may underlie gender-specific abilities and susceptibilities to disease affecting the neocortex. Laterality differences between the sexes were restricted to neuronal soma size showing significantly larger values in the female group in the left hemisphere. This gender difference may support female's right-handedness, language advantage, and tendency for bilateral activation patterns.
Key Words: Astrocytes; Cerebral cortex; Gender; Laterality; Neuronal density; Neuronal soma size; Neuropil.
INTRODUCTION
Until recently, the physical bases underlying functional differences in the cerebral cortex of men and women have been elusive. Complementing a growing number of studies using a wide range of approaches, the present morphometric studies of the human cerebral cortex seek to contribute to the understanding of structural differences that may underlie the readily perceived and psychometrically demonstrable functional differences exhibited by men and women. One of the most firmly established differences between their brains is the larger size and weight of that of males, from birth onwards, with an adult male to female (M:F) weight ratio of 1.098 (1). Because the brain size of mammals increases with body size, the human M:F gender ratio in adult stature of 1.079 (1) accounts for at least part of this difference. Based on the difference in height (stature) alone, the extrapolated M:F brain volume ratio is 1.257 (= 1.079^sup 3^), which exceeds the...