Sex and Psychology - General Differences in Physical Brain Parameters

General Differences in Physical Brain Parameters

See also: Sex differences in humans#Brain and nervous system and Neuroscience and intelligence

Studies have found many similarities but also differences in brain structure, neurotransmitters, and function. However, some argue that innate differences in the neurobiology of men and women have not been conclusively identified. The relationship between sex differences in the brain and human behavior is a subject of controversy in psychology and society at large.

A 2004 review in Nature Reviews Neuroscience stated that the brain's sexual dimorphism is probably determined by genes on the sex chromosomes. They likely do so by genes in cells in the gonads causing the gonads to produce sex hormones that travel to the brain which affect brain cells and also by genes in brain cells directly affecting these brain cells. In the human brain, a difference between sexes has been observed in regarding the PCDH11X/Y gene pair which is unique to Homo sapiens.

In adults, men's brains are an average of 11–12% heavier than women's brains. However, men's bodies are also larger and heavier than women's bodies. In the United States, for example, adult men are an average of 18% heavier than adult women. Some researchers propose that the brain-to-body mass ratio does not differ between the sexes. However, some argue that the brain-to-body mass ratio tends to decrease as body size increases, and a sex difference in brain size still exists between men and women of the same size. A 1992 study of 6,325 Army personnel found that men's brains had an average volume of 1442 cm3, while the women averaged 1332 cm3. These differences were shown to be smaller but to persist even when adjusted for body size measured as body height or body surface, such that women averaged 100g less brain mass than men of equal size.

Though statistically there are sex differences in white matter and gray matter percentage, this ratio is directly related to brain size, and some argue these sex differences in gray and white matter percentage are caused by the average size difference between men and women. Others argue that these differences remain after controlling for brain volume.

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