Neuroanatomy
In General
The average human adult brain weighs about three pounds. Male brains are about 10 percent larger than female brains. Men’s heads are also about 2 percent bigger than women’s, but this is a function of men being physically larger on the average. Brain weight increases with increases in height. This difference is present at birth. A boy’s brain is between 12 to 20 percent larger than that of a girl, but there is almost no difference between boys and girls at this age when the size of the brain is compared. So, a girl baby and a boy baby who weigh the same will have similar brain sizes. The logic is that having a larger body with more muscle mass necessitates more neural power to control it. A male’s larger muscle mass and larger body size supposedly requires more neurons (Zaidi, 2010).
Yet this is not quite accurate. Other studies show no differences in brain size and, if there is one, the neural processing power is equalized by differences in the “dense wiring” of the female brain versus the “loose wiring” of the male. Yet there area size differences. This was first discovered by the phrenologists in the nineteenth-century who found the skulls of European males to be larger than those of females and non-Europeans. Some might say this is “racism,” but it is not. Quantitative measurements do not lie, but how the results are interpreted can lead to a pernicious biological determinism or, as we call it today, “racist.” The bottom line, however is that most studies show that there is an association between brain structure and distinctive behavior tendencies although it is a weak one at best (Van Eijk et al., 2021). The key, as will be shown, isn’t in the design differences of the brain but in the functional differences.
Brain Area Volume, Tissue Density, and Connectivity
Variations in the amount of white and grey matter in the brain remain significant. Men have approximately 6.5 times more gray matter in their brains than do women who have about ten times more of white matter responsible for communication between different areas of the brain. The neurons are packed in tightly in the female brain. Some women have as many as 12 percent more neurons than men do. These neurons are densely packed into different cortical layers responsible for signals coming in and out of the brain. Women average about 19 billion neurons versus the average of 23 billion in male brains. A difference of 16 percent (Zaidi, 2010).
Neural densities vary in the male brain with some areas being more condensed than others. Men on average have larger volumes and higher tissue densities in the left amygdala, hippocampus, insular cortex, and putamen. The right lobe of the cerebellum and the left claustrum are denser. They have larger bilateral anterior parahippocampal gyri, posterior cingulate gyri, precuneus, temporal poles, and cerebellum, left posterior and anterior cingulate gyri, right amygdala, hippocampus, and putamen (Ruigrok et al., 2014). The male hypothalamus has 2.5 times more tissue devoted to sexual drive than the female hypothalamus. The muscular control centers in the male brain are larger than those of the female and much more directed toward aggression. This makes the male brain much more for territory defense and mate protection as compared to the female brain which is more hardwired for the protection of offspring. This idea of territory, defense, and dominance relates to the male affinity for hierarchy and status (Brizendine, 2010).
A meta-analysis of brain research between 1990 and 2013 revealed that there were overall brain volume differences from infants to the elderly (subjects over 80-years-old). On the average, male brains were larger in these areas:
- total brain volume (11 percent)
- cerebellum (9 percent)
- cerebrospinal fluid (11.5 percent)
- cerebrum (10 percent)
- intracranial volume (12 percent)
- gray matter (9 percent)
- white matter (13 percent)
Females, on the other hand, have on average have higher density in various other brain areas including the left frontal lobe and a slightly larger right frontal lobe, inferior and middle frontal gyri, pars triangularis, planum temporo-parietal operculum, anterior cingulate gyrus, insular cortex, Heschl’s gyrus, bilateral thalami and precuneus, left para-hippocampal gyrus and lateral occipital cortex.
There is a marked difference in the female cortical density and connectivity in the limbic and limbic and language areas would account for their greater abilities in emotional processing and language ability. Volume size in males is mostly in bilateral limbic areas and left posterior cingulate gyrus while higher densities are mostly limited to the left side of the limbic system. On the other hand, larger volumes in females are more present in the right hemisphere related to language in addition to the right insular cortex and anterior cingulate gyrus in the limbic system (Ruigrok et al., 2014).
A study 336 women and 225 men using magnetic resonance imaging found a gender difference in the functional areas of the brain. It was uniformly found across five brain areas that women had 14 percent greater functional connectivity density than men and up to five percent thicker gray matter. This means that the male brain activity is less integrated and more spread out while the female brain is more densely connected in certain areas. This finding has been offered as one possible cause for men having more neuropsychiatric diseases such as autism spectrum disorder (Tomasi & Volkow, 2012).
The male brain may be somewhat larger, but the female brain may be more powerful in its efficiency.
Cerebral Hemispheres
Men possess larger cerebrums than women of the same age and health status even when for statistically controlling for body size differences. Male brains were larger than female brains in all locations with the frontal and occipital lobes being the most prominent. The male brain also has a thicker right hemisphere. This may explain why men typically have better spatial and mathematical abilities. The left hemisphere with its language and communication centers is thicker in female brains making them notably better at language and verbal self-expression (Zaidi, 2010).
Corpus Callosum
The corpus collosum is the large band of cross-fiber tracts linking the two cerebral hemispheres. Past studies have found that the female corpus callosum is thicker which means the female brain is more tightly integrated although this finding has been disputed by other studies (Zaidi, 2010). Yet, the evidence consistently points to the male corpus callosum being generally somewhat smaller. A 2014 study at the University of Pennsylvania imaged the brains of 428 young adult males and 521 young adult females—an extraordinarily large sample—and found that the females’ brains consistently showed more strongly coordinated activity between hemispheres while the males’ brain activity was more active in local areas. This finding, which confirms the results of previous studies, concludes that the corpus callosum is bigger in women than in men and that women’s brains tend to be more bilaterally symmetrical than those of men (Goldman, 2017). This difference has been characterized as the “spotlight mind” of the male and the “floodlight mind” of the female. A difference that makes a difference, but how significant would depend on the situation.
Differences Between Male and Female Body Awareness
Interoceptive Ability
Body awareness is a combination of experience from outside and inside of the body boundary. Exteroception is the consciousness of the stimuli at the exterior of the body boundary and encompasses most of what we consider everyday, externally-oriented, sensory awareness. Interoception is the perception of sensations and feelings within the body. It is composed of two parts. Proprioception is the perception of body sensations related to movement, musculature, posture, movement, and balance. Visceroception is the internal perception of sensations emanating from the soft organs.
In general, men and women differ in their body awareness. Women hold significantly more negative attitudes toward their bodies and are more likely to focus on specific body parts and functions rather than the body as a whole. Men, for the most part, tend to have more positive attitudes and global somatic experiences. Their positivity stems from they feel about their bodies and their beliefs about the cultural standards of male physical attractiveness (Franzoi, Kessenich, & Sugrue, 1989; Franzoi, 1995). (See my blog-lecture “Are You The Rock or the River?” for further discussion.)
Compared to men, women have historically exhibited more awareness of their internal bodily states (Garfinkel et al., 2015). One recent study of 34 females of the mean age of 44.2 and 33 males with the mean age of 37.2 used functional MRI imaging and self-questionnaire forms to measure their levels of interoceptive awareness. It found a female advantage in the fronto-temporo-parietal brain region. These results support the idea of a female advantage in sensitivity toward internal body sensations. Women also have stronger functional connectivity in the frontal cortex and cingulate cortex which would imply greater emotional awareness (Alfano et al., 2023). But, on the other hand, other studies have historically shown that females have far less interoceptive accuracy in local body areas and body functions pertaining to:
- blood glucose levels;
- blood pressure;
- cardiac and respiratory activity
- gastric activity;
- nicotine use;
- the relationship between sexual arousal and actual physiological response (Prentice et al., 2022).
(For a broader review, see Prentice and Murphy, 2022. Also see my blog-lecture on the subjective and objective views of body awareness).
On the face of it, that men are more body sensitive is counter-intuitive to the notion that internal perceptual sensitivity and emotional experience must be related. One possible explanation for this difference is the finding that men use more body sensation cues to help understand their body experience while women use more external cues based on their immediate situation. The difference diminishes when men and women are placed in more natural, outdoor settings; i.e., non-laboratory environments (Pennebaker & Roberts, 1992).
Emotional Processing
While men may outperform women in interoceptive sensibility, they fall far short in the realm of emotional experience. In this area, they are comparatively simplistic creatures compared to the complexity of women’s experience and their superior ability at verbalizing their experience (Barrett et al., 2000). Here women outperform men in their abilities to recognize and process emotions in themselves and others. Women are generally better than men in (a) analyzing non-verbal body language, (b) identifying the emotional state of different facial expressions, and (c) discerning emotional tones in the human voice. Women are also more engaged with their own emotions and consistently score higher in emotional self-awareness as well as in emotional intelligence (Prentice et al., 2022). Yet even though women are better than men in recognizing non-verbal emotions, the difference, while noticeable, is not that great (Thompson & Voyer, 2014).
Women are generally more sensitive to disturbing negative stimuli and so are more vulnerable to emotional upset. Yet, in studies of emotional response and physiological arousal, women experience more arousal to negative stimuli than do men, but generally, there is very little difference in physiological response and emotional experienced (Bianchin & Angrilli, 2012; Poláčková Šolcová & Lačev 2017; Šolcová & Lačev, 2017). Both sexes experience emotions intensely, but are different in how they process and express that experience. (Male emotional patterns will be discussed in a later part in this series.)
Neurohormones
The male adult brain is affected by a variety of hormones including vasopressin, Mullerian inhibiting substance, oxytocin, prolactin, cortisol, androstenedione, dopamine, and (!) estrogen, but the giant of them all due to its reputation and exclusivity is testosterone (Brizendine, 2010).
Testosterone
The adolescent male body experiences a 20 to 30-fold increase in testosterone and many assumptions are made about accompanying changes in mood and behavior; much of the same is done when girls reach menarche. But correlation is not causation. A meta-analysis of 27 studies of testosterone on male adolescent behaviors found only a weak link between testosterone and aggression (Geniole et al., 2020). What this means is that at present there is little evidence to confirm what effects changing testosterone levels have on adolescent male aggression (Duke, Balzer, & Steinbeck, 2014). Yet, testosterone is related to aggression. One experiment injected testosterone into young males and females and found neural and behavioral changes. Then there is the well-known statistic of higher violence rates found in younger men and male criminals. The problem is that there is a causal link between testosterone and aggression in animals, but in humans the relationship is muddied by other complex mediating variables such as social forces and personality. The way out of this box comes from looking at competition in human activities along with other situational factors. Adult men with higher testosterone levels tend to be more aggressive if they have dominant personalities and higher levels of impulsivity; meaning lower levels of self-control (Carré & Archer, 2018; Carré, et. al., 2016).
Lastly, one interesting detail of note is that the width of the male face positively correlates with testosterone level (Lefevre et al., 2013; Mitteroecker et al., 2015).
Male Brain Development Over Time
Fetal Period
Circulating hormones in the womb are crucial in the sexual differentiation of the brain. Brains with male or female characteristics are determined by these hormones. The presence of androgens in early life produces a “male” brain. In contrast, lack of androgens causes feminization; without androgens, a fetus develops into a female automatically by default (Zaidi, 2010).
Infancy
Gender similarities are the norm for both sexes during infancy specifically in the temperamental factors of sociability, shyness, difficulty, soothability, emotionality, and adaptability. Differences appear in levels of physical activity, self-control, and perceptual sensitivity. Boys are more active, less attentive, and less inhibited (Else-Quest & Shibley-Hyde, 2018; Swain, 2004).
Toddlerhood
Gender identity begins in the toddler years. Children discover gender-specific social norms exhibited by parental behaviors. Boys are to be tough, competitive, stoic, and athletic. These influences are internalized and then further refined as children grow up. Boys, beginning at about age 10, identify being masculine with physical action in sports and games. Boys are socialized to be active, aggressive, competitive, and physically expressive. Differences appear in levels of physical activity, self-control, and perceptual sensitivity. Boys are more active, less attentive, and less inhibited (Swain, 2004).
Childhood
This is the stage where children enter peer groups and become subject to interpersonal social forces. Children are gender-segregated in their play with gender-specific toys. Boys display more educational and behavioral difficulties early on. Attention-Deficit Hyperactivity Disorder appears at this time (Else-Quest & Shibbley-Hyde, 2016).
Adolescence
Boys semi-consciously use the somatic ideals of maleness to construct their masculinity to establish a place within the peer group. The best way is to be physically competent and athletic, but there are also the banal theatrics of acting tough or dressing fashionably (Swain, 2004). The prefrontal cortex which controls planning, decision-making, and self-restraint is not fully connected yet and this is indicated by the often poor and impulsive behavioral choices made by adolescent boys.
Adulthood
The prefontal cortext now becomes fully “wired up” in adulthood. The adult brain has more cognitive control than the adolescent brain which is more driven by emotions, rewards, and social acceptance. Intelligence also peaks during early to middle adulthood, roughly ages 25 to 60. However, intelligence involves many different cognitive abilities each of which appears in its own time. Fluid intelligence, which includes abilities like solving problems and identifying patterns, peaks around age 30. By contrast, crystallized intelligence, which deals with vocabulary and knowledge of facts, increases until about age 50 (Brizendine, 2010.)
Late Adulthood
A brain scan study of 53 healthy men and 50 age-matched females showed that males lost gray matter volume at a faster rate than females and such changes have been linked to Parkinson’s disease, attention-deficit hyperactivity disorder, and dementia (Király et al., 2015). While the brain tends to shrink with age, the male brain deteriorates at a faster pace than does a woman’s. Brain metabolism slows as people grow older, and this too differs between men and women (Goyal et al., 2019).
Closing Thoughts
Yes, there are a lot of interesting differences between the male and female brain and, obviously, they function somewhat differently from one another.
Now all of this may sound like an advantage depending on whose side you’re on, but it’s only an advantage up to a certain point. It’s just a noticeable a difference and probably–In The Grand Scheme of Things–many differences often don’t make a whole lot of difference. A person should always keep a guiding question in the back of their minds when looking at this data: Is this a difference that really makes a difference? For example, the male brain size percentages are relatively higher than a female brain, but still relatively low. Yet, given the differences in cortical structures some differences between the sexes become more evident and understandable.
So, what are we dealing with here overall?
There are currently two opposed currents of thought in the neurosciences regarding gender differences in brain anatomy. The first group, which has already collected a substantial amount of data, asserts that the male and female brain are essentially different. A newer group of researchers argues that there are no overall anatomical differences between the male and female brain (Alfano et al., 2023).
The human brain is an incredibly complex organ with a mind-boggling, Byzantine design. Past research confirms there are apparent differences between men and women in thinking, memory recall, perception, emotional processing, and interoceptive sensitivity. These differences may all be influenced by genes, hormones, and environmental conditioning. Differences between men and men, for the most part, are small, but large enough to be noticed and measured, but they do not imply value differences of better or worse. The sexes are equal in intelligence but tend to think somewhat differently. They use different parts of the brain to process memories, emotions, problems, decisions, and faces with some differences in tissue volume and neural connectivity—women being more tightly wired and men more loosely wired, as it were—along with major differences in neurohormone profiles (Zaidi, 2010).
The truth, as far as I can see based on the evidence, is somewhere in the middle. Given that it is commonly evident that there are differences in male and female thinking, perception, feeling, and behavior then there must be corresponding brain and hormonal activity guiding these differences; meaning the differences are more functional due to internal structural differences than having entirely differing brains. And then there are the issues of personality, environment, and culture which must also be taken into consideration as moderating factors.
Is the male brain different from the female brain? Yes. There I said it. But is it so different that it is completely alienated from the female? No, of course not. In fact, I think they are designed to support one another in their similarities while complementing one another in their differences because both have their own strengths and weaknesses.
Paul Shane, Ph.D., LMT
Director, Academic Content
References
Alfano, V., Cavaliere, C., Di Cecca, A., Ciccarelli, G., Salvatore, M., Aiello, M., & Federico, G. (2023). Sex differences in functional brain networks involved in interoception: An fMRI study. Frontiers of Neuroscience, doi:10.3389/fnins.2023.1130025.
Barrett, L., Lane, R., Sechrest, L., & Schwartz, G. (2000). Sex differences in emotional awareness. Personality and Social Psychology Bulletin 26(9), p. 1027-1035.
Bianchin, M. & Angrilli, A. (2012). Gender differences in emotional responses: A psychophysiological study. Physiology & Behavior 105, p. 925-932.
Brizendine, L. (2010). The Male Brain. New York, NY: Broadway Books.
Carré, J. & Archer, J. (2018). Testosterone and human behavior: The role of individual and contextual variables. Current Opinion in Psychology 19, p. 149-153.
Carré, J., Geniole, S., Ortiz, T., Bird, B., Videto, A., & Bonin, P. (2016). Exogenous testosterone rapidly increases aggressive behavior in dominant and impulsive men. Biological Psychiatry 82, p. 249-256.
Duke, S., Balzer, B., & Steinbeck, K. (2014). Testosterone and its effects on human male adolescent mood and behavior: A systematic review. Journal of Adolescent Health 55, p. 315-322.
Else-Quest, N. & Shibley-Hyde, J. (2018). The Psychology of Women and Gender: Half the Human Experience+, Ninth Edition. Los Angeles, CA: SAGE Publications.
Franzoi, S. (1995). The body-as-object versus the body-as-process: Gender differences and gender considerations. Sex Roles 33(5/6), p. 417-437.
Franzoi, S., Kessenich, J., & Sugrue, P. (1989). Gender differences in the experience of body awareness: An experiential sampling study. Sex Roles 21(7/8), p. 499-515.
Garfinkel, S., Seth, A., Barrett, A., Suzuki, K., & Critchley, H. (2015). Knowing your own heart: Distinguishing interoceptive accuracy from interoceptive awareness. Biological Psychology 104, p. 65–74.
Geniole, S., Bird, B., McVittie, J., Purcell, R., Archer, J., & Carré, J. (2020). Is testosterone linked to human aggression? A meta-analytic examination of the relationship between baseline, dynamic, and manipulated testosterone on human aggression. Hormones and Behavior 123, 104644, https://doi.org/10.1016/j.yhbeh.2019.104644
Goldman, B. (2017, May 22). Two minds: The cognitive differences between men and women. Stanford Medicine. https://stanmed.stanford.edu/how-mens-and-womens-brains-are-different/.
Goyal, M., Blazey, T., Su, Y., Couture, L., Durbin, T., Bateman, R., Benzinger, T., Morris, JC, Raichle, M., & Vlassenko, A. (2019). Persistent metabolic youth in the aging female brain. Proceedings of the National Academy of Sciences 116(8), p. 3251-3255.
Jäncke, L., Mérillat, S., Liem, F., & Hänggi, J. (2014). Brain sex, sex, and the aging brain. Human Brain Mapping 36, p. 150-169.
Király, A., Szabo, N., Tóth, E., Csete, G., Faragó, P., Kocsis, K., Must, A., Vécsei, L., & Kincses, Z. (2015). Male brain ages faster: The age and gender dependence of subcortical volumes. Brain Imaging and Behavior 10, p. 901-910.
Lefevre, C., Lewis, G., Perrett, D., & Penke, L. (2013). Telling facial metrics: Facial width is associated with testosterone levels in men. Evolution and Human Behavior 34(4), p. 273-279.
Mitteroecker, P., Windhager, S., & Mueller, G., & Schaefer, K. (2015). The morphometrics of “masculinity” in human faces. PLoS ONE 10(2), doi:10.1371/jounral.pone.0118374.
Pennebaker, J. & Roberts, T. (1992). Toward a his and hers theory of emotion: gender differences in visceral perception. Journal of Social & Clinical Psychology 11 (3), p. 199–212.
Poláčková Šolcová, I. & Lačev, A. (2017). Differences in male and female subjective experience and physiological reactions to emotional stimuli. International Journal of Psychophysiology 117, p. 75-82.
Prentice, F., Hobson, H., Spooner, R., & Murphy, J. (2022). Gender differences in interoceptive accuracy and emotional ability: An explanation for incompatible findings. Neuroscience and Biobehavioral Reviews 141, https://doi.org/10.1016/j.neubiorev.2022.104808
Prentice, F., Murphy, J., 2022. Sex differences in interoceptive accuracy: a meta-analysis. Neuroscience & Biobehavioral Review 132, p. 497–518.
Ruigrok, A., Salimi-Khorshidi, G., Lai, M., Baron-Cohen, S., Lombardo, M., Tait, R., & Suckling, J. (2014). A meta-analysis of sex differences in human brain structure. Neuroscience and Biobehavioral Reviews 39, p. 34-50.
Swain, J. (2004). The resources and strategies that 10-11-year-old boys use to construct masculinities in the school setting. British Educational Research Journal 30(1), p. 167-185.
Šolcová, I. & Lačev, A. (2017). Differences in male and female subjective experience and physiological reactions to emotional stimuli. International Journal of Psychophysiology 117, p. 75-82.
Thompson, A. & Voyer, D. (2014). Sex differences in the ability to recognize non-verbal displays of emotion: A meta-analysis. Cognition and Emotion 28(7), p. 1164-1195.
Tomasi, D. & Volkow, N. (2012). Gender differences in brain functional connectivity density. Human Brain Mapping 33, p. 849-860.
Van Eijk, L., Zhu, D., Couvy-Duchesne, B., Strike, L., Lee A., Hansell, N., Thompson, P., de Zubicaray, G., McMahon, K., Wright, M., & Zietsch, B. (2021). Are sex differences in human brain structure associated with sex differences in behavior? Psychological Science 32(8), p. 1183-1197.
Wnuk, A. (2018). BrainFacts, 8th Edition, Washington, DC: Society for Neuroscience, chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.brainfacts.org/-/media/Brainfacts2/BrainFacts-Book/Brain-Facts-PDF-with-links.pdf
Zaidi, Z. (2010). Gender differences in the human brain: A review. The Open Anatomy Journal 6, p. 37-55.