Structure & Function Differences in the Brain

• Adolescent brain development appears to be different in males and females. Males age 6-17 years have been shown to display more prominent age-related decreases in gray matter (the part of the brain that allows us to think) and increases in white matter (which transfers information between distant regions) than females. These changes in brain composition appear to be linked to developmental processes in which nerve cell connections are “pruned” in gray matter and made more efficient (myelinated) in white matter. The more dramatic changes seen in males may be related to the different effects of estrogen and testosterone on the brain. ¹
  
  
• Women have smaller brains than men, with women having more gray matter and men having more white matter. This finding may help explain why women are typically better than men at verbal tasks, while men are typically better than women at spatial tasks, as well as why the sexes perform equally well on intelligence tests in spite of males having larger brains. ²
  
  
• Several studies have evaluated sex differences in the histology of the cerebral cortex. One study in humans detected higher neuronal density in the female cortex compared to males. ³ In contrast, other studies have shown that the number of neurons in the cerebral cortex is greater in males than in females. Studies by Rabinowicz et al demonstrated that males have 15% more cortical neurons and 13% greater neuronal density than females. ⁴ Similarly, Pakkenberg et al showed a 16% higher neuronal number in males, but sex differences in neuronal density were not present. ⁵ Although women have fewer neocortical neurons, certain anatomical and histological characteristics of female brains may allow for more extensive dendritic arborization and more neuronal connections among nerve cells in women. ^{4, 6} Certain diseases that cause neuronal loss in the cerebral cortex may be more detrimental to women due to their lower number of cortical neurons compared to men. ^{6, 7} Animal studies have shown that the higher neuronal number in the binocular and monocular regions of the rat primary visual cortex results from a more prolonged period of neuronal cell death in females during postnatal development. ⁸ In addition, testosterone has been shown to protect neurons from apoptosis in the sexually dimorphic nucleus of the rat hypothalamus during embryonic development; therefore, it is possible that testosterone contributes to the higher number of neurons in the male cerebral cortex. ^{7, 9}
  
  
• Boys are more prone to mental retardation and learning disabilities than girls. This may be due to the fact that male fetuses require the maintenance of higher numbers of nerve cells in the cerebral cortex than female fetuses - early damage to the male developing brain could result in higher losses of needed neurons. ⁶
  
  
• The cerebellum, an area of the brain important for posture and balance, and the pons, a brain structure linked to the cerebellum that helps control consciousness, are larger in men than in women. ¹⁰
  
  
• As the brain ages, the amount of tissue mass declines and the amount of fluid increases. This effect is less severe in women than in men, suggesting that women are somewhat less vulnerable to age-related changes in mental abilities. ^11-14 However, women are more prone to dementia than men, perhaps because of the potential greater susceptibility to loss of neurons and neuronal connections in women. ⁶

Language Differences

• Although men and women have been shown to process some language tasks similarly, in other aspects of language processing there are significant sex differences. ¹⁵
  
  
• Imaging studies of the living brain indicate that in women neurons on both sides of the brain are activated when they are listening, while in men neurons on only one side of the brain are activated. ^{16, 17}
  
  
• Men and women appear to process single words similarly, but in the interpretation of whole sentences, women use both sides of the brain while men use one side. ¹⁵
  
  
• Boys have a higher incidence than girls of developmental language disorders, such as developmental dyslexia. Despite these differences during childhood, it is not clear whether adult women have better verbal skills than men. ¹⁵

Spatial Information Differences

• Men and women process spatial information differently. ¹⁸
  
  
• When negotiating a virtual reality maze, both men and women use the right hippocampus to figure out how to exit. However, men also use the left hippocampus for this task, while women do not, and women also use the right prefrontal cortex, while men do not. ¹⁹
  
  
• In an imaging study, men were found to activate a distributed system of different brain regions on both sides of the brain while performing a spatial task. Women, however, activated these regions on only the right side of the brain. ¹⁸
  
  
• Women appear to rely on landmarks to navigate their environments, whereas men tend to use compass directions. ²⁰

Memory Differences

• Some functions of memory appear to be different in males and females. ²¹
  
  
• Higher rates of blood flow in certain portions of the brain are associated with increased memory of verbal tasks in women, but not in men. ²²
  
  
• Compared to men, women have been shown to be better at remembering faces. ²³

For additional information about the brain, see the Mental Health section.

References

1. De Bellis, M.D., et al., Sex differences in brain maturation during childhood and adolescence. Cereb Cortex, 2001. 11(6): p. 552-7.

2. Gur, R.C., et al., Sex differences in brain gray and white matter in healthy young adults: correlations with cognitive performance. J Neurosci, 1999. 19(10): p. 4065-72.

3. Haug, H., Brain sizes, surfaces, and neuronal sizes of the cortex cerebri: a stereological investigation of man and his variability and a comparison with some mammals (primates, whales, marsupials, insectivores, and one elephant). Am J Anat, 1987. 180(2): p. 126-42.

4. Rabinowicz, T., et al., Gender differences in the human cerebral cortex: more neurons in males; more processes in females. J Child Neurol, 1999. 14(2): p. 98-107.

5. Pakkenberg, B. and H.J. Gundersen, Neocortical neuron number in humans: effect of sex and age. J Comp Neurol, 1997. 384(2): p. 312-20.

6. de Courten-Myers, G.M., The human cerebral cortex: gender differences in structure and function. J Neuropathol Exp Neurol, 1999. 58(3): p. 217-26.

7. Rabinowicz, T., et al., Structure of the cerebral cortex in men and women. J Neuropathol Exp Neurol, 2002. 61(1): p. 46-57.

8. Nunez, J.L., D.M. Lauschke, and J.M. Juraska, Cell death in the development of the posterior cortex in male and female rats. J Comp Neurol, 2001. 436(1): p. 32-41.

9. Davis, E.C., P. Popper, and R.A. Gorski, The role of apoptosis in sexual differentiation of the rat sexually dimorphic nucleus of the preoptic area. Brain Res, 1996. 734(1-2): p. 10-8.

10. Raz, N., et al., Age and sex differences in the cerebellum and the ventral pons: a prospective MR study of healthy adults. AJNR Am J Neuroradiol, 2001. 22(6): p. 1161-7.

11. Gur, R.C., et al., Gender differences in age effect on brain atrophy measured by magnetic resonance imaging. Proc Natl Acad Sci U S A, 1991. 88(7): p. 2845-9.

12. Meyer, J.S., et al., Risk factors accelerating cerebral degenerative changes, cognitive decline and dementia. Int J Geriatr Psychiatry, 1999. 14(12): p. 1050-61.

13. Coffey, C.E., et al., Sex differences in brain aging: a quantitative magnetic resonance imaging study. Arch Neurol, 1998. 55(2): p. 169-79.

14. Witelson, S.F., Sex differences in neuroanatomical changes with aging. N Engl J Med, 1991. 325(3): p. 211-2.

15. Kansaku, K. and S. Kitazawa, Imaging studies on sex differences in the lateralization of language. Neurosci Res, 2001. 41(4): p. 333-7.

16. Phillips, M.D., et al., Temporal lobe activation demonstrates sex-based differences during passive listening. Radiology, 2001. 220(1): p. 202-7.

17. Shaywitz, B.A., et al., Sex differences in the functional organization of the brain for language. Nature, 1995. 373(6515): p. 607-9.

18. Gur, R.C., et al., An fMRI study of sex differences in regional activation to a verbal and a spatial task. Brain Lang, 2000. 74(2): p. 157-70.

19. Gron, G., et al., Brain activation during human navigation: gender-different neural networks as substrate of performance. Nat Neurosci, 2000. 3(4): p. 404-8.

20. Saucier, D.M., et al., Are sex differences in navigation caused by sexually dimorphic strategies or by differences in the ability to use the strategies? Behav Neurosci, 2002. 116(3): p. 403-10.

21. Duff, S.J. and E. Hampson, A sex difference on a novel spatial working memory task in humans. Brain Cogn, 2001. 47(3): p. 470-93.

22. Ragland, J.D., et al., Sex differences in brain-behavior relationships between verbal episodic memory and resting regional cerebral blood flow. Neuropsychologia, 2000. 38(4): p. 451-61.

23. Gur, R.C., et al., Computerized neurocognitive scanning: I. Methodology and validation in healthy people. Neuropsychopharmacology, 2001. 25(5): p. 766-76.

Last updated: May 4, 2005