A Review Zeenat F. Why do men and women think differently? Why do they behave differently in stressed situations? Why do women act more emotionally as compared to men? Why do men and women excel at different types of tasks? Why do boys like to play with cars and trucks and superman?
These are the common questions which arise commonly in minds. The human brain is a highly complex organ.
Studies of perception, cognition, memory and neural functions have found apparent gender differences. These differences may be attributed to various genetic, hormonal, and environmental factors and do not reflect any overall superiority advantage to either sex.
Both sexes are equal in intelligence, but tend to operate differently. Men and women appear to use different parts of the brain to encode memories, sense emotions, recognize faces, solve certain problems and make decisions.
Indeed, when men and women of similar intelligence and aptitude perform equally well, their brains appear to go about it differently, as if nature had separate blueprints. Sex differences in the brain may play a role in learning processes, language development, and progression of neurologically- based diseases.
Sex differences need to be considered in studying brain structure and function and may raise the possibility of sex-specific treatments for neurological diseases. In this article it is reviewed that how does the brain of a male look and function differently from a female's brain, and what accounts for these differences? Human brain, gender differences, brain aging, neurological disorders, learning. The adult human brain weighs on average about 3lb 1. This is due to the larger physical stature of men.
The brain weight is related to the body weight partly because it increases with increasing height . This difference is also present at birth. However, when the size of the brain is compared to body weight at this age, there is almost no difference between boys and girls. So, a girl baby and a boy baby who weigh the same will have similar brain sizes. Box , Riyadh , Saudi Arabia; Tel: Men had larger volumes, relative to cerebrum size, in frontomedial cortex, the amygdala and hypothalamus.
There was greater sexual dimorphism in brain areas that are homologous with those identified in animal studies showing greater levels of sex steroid receptors during critical periods of brain development. These findings have implications for developmental studies that would directly test hypotheses about mechanisms relating sex steroid hormones to sexual dimorphisms in humans .
Grey Matter vs White Matter Ratios of grey to white matter also differ significantly between the sexes in diverse regions of the human cortex . Variations in the amount of white and grey matter in the brain remain significant . Men have approximately 6. At the age of 20, a man has around , km and a woman, about , km of myelinated axons in their brains . Men appear to have more gray matter, made up of active neurons, and women more of the white matter responsible for communication between different areas of the brain .
In women's brains, the neurons are packed in tightly, so that they're closer together. Some women even have as many as 12 percent more neurons than men do . These neurons are densely crowded on certain layers of the cortex, namely the ones responsible for signals coming in and out of the brain, and these differences were present from birth .
When controlling for total cerebral volume, women had a higher percentage of grey matter than men, and men had a higher percentage of white matter [6, 8] and both gray and white matter volumes correlated with cognitive performance across sex groups.
Sex and age were the main determinants of the total number of neurons in the human neocortex, whereas body size, per se, had no influence on neuron number . Gender differences in precentral, cingulate, and anterior temporal white matter areas were also found, suggesting that microstructural white matter organization in these regions may have a sexual dimorphism . Hypothalamus Hypothalamus, where most of the basic functions of life are controlled, including hormonal activity via the pituitary gland also shows gender differences.
The volume of a specific nucleus in the hypothalamus third cell group of the interstitial nuclei of the anterior hypothalamus is twice as large in heterosexual men as in women and homosexual men . The preoptic area, involved in mating behavior, is about 2. This enlargement is dependent on the amount of male sex hormones or androgens.
Apparently, the difference in this area is only apparent after a person is 4 years old. At 4 years of age, there is a decrease in the number of cells in this nucleus in girls.
The neuropil of the preoptic area is sexually dimorphic . Gender-related differences were found in 2 cell groups in the preoptic-anterior hypothalamic area PO-AHA in human brain. Both nuclei were larger in male and appeared to be related in women to circulating steroid hormone levels .
The suprachiasmatic nucleus of the hypothalamus, involved with circadian rhythms and reproduction cycles, is different in shape in these two sexes. In males, this nucleus is shaped like a sphere whereas in females it is more elongated.
However, the number of cells and volume of this nucleus are not different in men and women. It is possible that the shape of the suprachiasmatic nucleus influences the connections that this area makes with other areas of the brain, especially the other areas of the hypothalamus.
In most hypothalamic areas that stain positively for androgen receptor AR , nuclear staining in particular is less intense in young adult women than in men. The strongest sex difference is found in the lateral and medial mamillary nucleus . The mamillary body complex is known to receive input from the hippocampus by the fornix and to be involved in cognition. In addition, a sex difference in AR staining is present in the horizontal diagonal band of Broca, the sexually dimorphic nucleus of the preoptic area, the medial preoptic area, th e dorsal and ventral zone of the periventricular nucleus, the paraventricular nucleus, the supraoptic nucleus, the ventromedial hypothalamic nucleus and the infundibular nucleus.
No sex differences were observed in AR staining in the bed nucleus of the stria terminalis, the nucleus basalis of Meynert and the island of Calleja . Among subjects with a massa intermedia, the structure was an average of Anatomical sex differences in structures that connect the two cerebral hemispheres may, in part, underlie functional sex differences in cognitive function and cerebral lateralization .
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 . According to the majority of studies, men possess larger cerebra th an women of the same age and health status, even if the body size differences are controlled statistically.
Male brains were larger than female brains in all locations, though male enlargement was most prominent in the frontal and occipital poles, bilaterally . The male differentiated brain has a thicker right hemisphere. This may be the reason males tend to be more spatial, and mathematical. The left hemisphere, which is important to communication, is thicker in female orien ted brains. Women have a more developed neuropil, or the space between cell bodies, which contains synapses, dendrites and axons.
This may explain why women are more prone to dementia such as Alzheimer's disease than men, because although both may lose the same number of neurons due to the disease, in males, the functional reserve may be greater as a larger number of nerve cells are present, which could prevent some of the functional losses . In the temporal neocortex, a key part which is involved in both social and emotional processes and memory, men had a one third higher density than women of synapses, and had more brain cells, though the excess was slight compared with the excess in the number of synapses.
Sexual dimorphism has been reported in the cortical volume of the Wernicke and Broca areas , as well as in the frontal and medial paralimbic cortices [5, 19, 22, 23]. Differences have been reported in the thickness and density of the grey matter in the parietal lobes  in the density of neurons [10, 11, 20, 24] and in the complexity of the dendritic arbors as well as in the density of dendritic spines in several cortical areas .
In female brains, the cortex is constructed differently, with neurons packed more closely together in layers 2 and 4 which form the hard wiring for signals coming into the brain of the temporal lobe, and in layers 3, 5 and 6 which carry the wiring for outbound signals of the prefrontal cortex . Widespread areas of the cortical mantle are significantly thicker in women than in men . Studies have shown greater cortical thickness in posterior temporal and inferior parietal regions in females relative to males, independent of differences in brain or body size.
Age-by-sex interactions were no t significant in the temporoparietal region, suggesting that sex differences in these regions are present from at least late childhood and then are maintained throughout .
In a study it is shown that men have a significantly higher synaptic density than Gender Differences in Human Brain: Differences in brain anatomy have included the length of the left temporal plane, which is usually longer than the right.
Orbitofrontal to Amygdala Ratio OAR The ratio between the orbitofrontal cortex, a region involved in regulating emotions, and the size of the amygdala, involved in producing emotional reactions, was significan tly larger in women than men. One can speculate from these findings that women might on average prove more capable of controlling their emotional reactions.
Women have larger orbital frontal cortices than men, resulting in highly significant difference in the ratio o f orbital grey to amygdala volume. This may relate to behavioral evidence for sex differen ces in emotio n processing . Females have a more acute sense of smell, and on average, have a larger deep limbic system including hippocampus  and anterior commissure, a bundle of fibers which acts to interconnect the two amygdales , than males.
Due to the larger deep limbic brain women are more in touch with their feelings, they are generally better able to express their feelings than men. They have an increased ability to bond and are connected to others. On the other hand larger deep limbic system leaves a female somewhat more susceptible to depression, especially at times of significant hormonal changes such as the onset of puberty, before menses, after the birth of a child and at menopause.
Women attempt suicide three times more than men . Corpus Callosum A large tract of neural fibers that allows the free flow of communication between both hemispheres of the brain is larger in women, compared to men [8, 30]. The larger corpus callosum allows more transmissions between the two hemispheres. Thus women use both hemispheres creating more synapses between the two sides of the brain.
Although this discovery has been challenged in a volumetric study of the corpus callosum in Korean people in their 20s and 40s. It was shown that Korean men have larger corpus callosum as compared to women. There was no significant difference in corpus callosum volume between 20s and 40s.
There was a positive relationship between body weight and corpus callosum for 20s, but not for 40s . In another study a dramatic difference in the shape of corpus callosum was observed but there was no conclusive evidence of sexual dimorphism in the area of the corpus callosum or its subdivisions. The caudal portion of corpus callosum, the splenium was more of bulbous shaped in females and more tubular shaped in males. The maximum width of splenium was significantly greater in females than in males .
It has been reported that there is significant rightward asymmetries of callosal thickness predominantly in the an terior body and anterior third of the callosum, suggesting a more diffuse functional organization of callosal projections in the right hemisphere. Asymmetries were increased in men, supporting the assumption of a sexually dimorphic organization of male and female brains that involves hemispheric relations and is reflected in the organization and distribution of callosal fibers .
In Magnetic resonance imaging study, callosal measurements showed no significant effects of sex or handedness, although subtle differences in callosal shape were observed in anterior and posterior regions between males and females and surface variability was increased in males . It was found that in men the size of corpus callosum is related to handedness.
The more left-handed a person was, the bigger the corpus callosum he had.