How the Brain Makes the Simple Complicated
This blog post on how the brain makes the simple complicated was inspired by my podcast interview with neuroscientist Dr. Dawna Markova (see episode 14 at http://scienceofsuccess.libsyn.com/podcast). In the interview, Dr. Markova commented that we now have evidence to support a difference between the way a man’s brain is structured and the way a woman’s brain is structured. Dr. Markova also said that this topic is still considered taboo. So naturally I had to explore it further – “curiosity killed the cat” as they say! This blog post explores the differences between male and female brains, how these differences play out in the body, and how these differences play out in behavior.
Please note that the word “gender” is used in this blog post to refer to biological sex (male or female).
The first topic, the differences between male and female brains, is simple but controversial. Unfortunately, it is the controversial part that can distort the simple part. In the podcast interview, Dr. Markova explains that when she was in graduate school as a neuroscientist they only studied male brains because it was assumed that the male and female brains were the same (see episode 14 at http://scienceofsuccess.libsyn.com/podcast). In addition, the female brain had the added complexity of changing hormone levels which impacts brain functioning. Dr. Geert de Vries, Director of the Neuroscience Institute at Georgia State University, and Dr. Nancy Forger, a neuroscientist, explain that it is because we rely on our brains to understand who we are, how to behave, and what we can achieve that discussing gender differences in the brain is so controversial (see http://bsd.biomedcentral.com/articles). Dr. de Vries and Dr. Forger also point out that about a century ago, gender differences in the brain were manipulated in an attempt to legitimize a diminished role for women in society. Therefore, the reader needs to beware because unsubstantiated claims about the nature and function of gender differences in the brain continue to be made. This is because there is a large group of neuroscientists, both male and female, who believe, whether consciously or not, that studying the male brain will give better insights about humans because studying the female brain is hampered by variations in hormone levels. Fortunately, there is a small group of neuroscientists who believe that studying the male brain alone will hamper the advancement of neuroscience because the female brain functions differently and is impacted by level of hormones. These latter neuroscientists understand that taking on this added complexity advances the overall understanding of the brain and the implications for behavior. It is the work of these latter neuroscientists that is described here.
The reader needs to beware because unsubstantiated claims about the nature and function of gender differences in the brain continue to be made.
The simple part of male and female brains is that there are known morphological, functional, biochemical, and developmental differences (Zaidi, Z. F.; “Gender Differences in Human Brain: A Review,” The Open Anatomy Journal, 2010, 2, p. 37-55 and Andreano, J.M., and Cahill, L.; “Sex Influences on the Neurobiology of Learning and Memory,” Learning and Memory, 2009, 16, p. 248-266). The morphological differences include things like the larger brain volume of men compared to women, the higher ratio of white matter to gray matter in men compared to women, and different neuroanatomies (women have relative to total brain size larger hippocampus, caudate nucleus, anterior cingulate gyrus, and dorsolateral prefrontal cortex; while men have relative to total brain size larger amygdala and planum temporale). The functional differences include things like the different cognitive strategies that men and women use for mental rotation and navigation tasks. The biochemical differences include things like the availability of dopamine transporters which is higher in women than men and the expression of 5-HT2 receptors which is higher in men than in women. Finally, the developmental differences point to differences in how male and female brains develop and age over time. Dr. Larry Cahill, Professor of Neurobiology at University of California Irvine, points out that these gender-based brain differences suggest the need “to develop sex specific treatments for a host of conditions, including depression, addiction, schizophrenia and posttraumatic stress disorder” and “researchers exploring the structure and function of the brain must take into account the sex of their subjects when analyzing their data—and include both women and men in future studies or risk obtaining misleading results” (see http://www.scientificamerican.com/article).
The second topic is how these gender-based brain differences play out in the body which is a bit more complicated. The brain operates within a larger system, the human body, which also has gender differences. For example, a process that happens in all cells of the female body but in none of the cells of the male body is the inactivation of one X chromosome. In addition, the distribution of adipose tissue, or fat, is different between men and women. Men tend to accumulate fat in their abdomen while women tend to accumulate fat just below the skin and in their thighs and buttocks. Adipose tissue is part of the endocrine system which produces peptide and steroid hormones to regulate all sorts of bodily functions. Some of these hormones reach the brain and act on receptors there. An example of a gender difference with regard to fat is obese men were seen to have increased visceral fat compared to women which resulted in higher levels of inflammatory cytokines in men. The liver has gender differences too in how it metabolizes or breaks down medicines. For example, the sleep aid zolpidem (tradename Ambien) is broken down much more slowly by the liver in women than in men so women need a significantly lower dose then men. Gender differences in sensory systems like smell, touch, and taste cause men and women to experience different information about the world (see http://bsd.biomedcentral.com/articles). Thus, gender differences are not only in the brain but in the organs and systems throughout the body all of which have interactions with the brain.
Gender differences are not only in the brain but in the organs and systems throughout the body all of which have interactions with the brain.
The third topic is how the gender-based brain differences play out in our behaviors. There is less concrete information on this topic because valid scientific findings depend on taking into account both gender and female hormone levels. A few of what are believed to be the most scientifically valid findings will be presented here. Remember that if a study on the brain does not mention the impact of gender or menstruation cycle, then the study likely only applies to white males. For example, Dr. Larry Cahill points out that there is overwhelming evidence that emotionally arousing events are better retained by the brain than relatively neutral events (Cahill, L.; “Sex Influences on Brain and Emotional Memory: The Burden of Proof Has Shifted,” Progress in Brain Research, 2010, Vol. 186, p. 29-40). Dr. Cahill also points out the evidence that there is an interaction between stress hormones and the amygdala in the brain that is responsible for the enhanced memory of an event laden with emotion. Interestingly, Dr. Cahill found that the arousal of the amygdala is primarily left hemisphere in females and primarily right hemisphere in males. The left hemisphere of the amygdala preferentially processes local and finer details of a situation while the right hemisphere of the amygdala preferentially processes global and local aspects of a situation. Therefore, women tend to process memory for details while men tend to process memory for gist of an emotionally-laden event. Even more interestingly, while naturally-cycling women display memory for details of an emotional event, women taking oral contraception display memory for gist or the same brain pattern as men. This means that sex hormones play a critical role in the enhanced detail memory of emotional events in women. Dr. Cahill also points out that there is no difference between naturally cycling females and males in the overall activity of the amygdala, the difference is in how the amygdala connects with the rest of the brain: the right hemisphere of the amygdala connects differently with the rest of the brain then the left hemisphere amygdala.
Several studies suggest that men and women use different cognitive strategies in displaying similar performance on the same task. For example, Dr. Anna Abraham and colleagues found no difference in creative performance by men and women but the regions of the brain engaged during creative performance showed some similarities and differences (Abraham, A.; Thybusch, K., Pieritz, K.; and Hermann, C.; “Gender Differences in Creative Thinking: Behavioral and fMRI Findings,” Brain Imaging and Behavior, 2014, 8, p. 39-51). The similarities were regions of the brain associated with the core structures of the default mode in the brain. However, there were observable differences. Specifically, during a concept expansion task, men preferentially engaged brain areas (hippocampal formation, amygdala, inferior frontal gyrus, and retrosplenial cortex) related to semantic cognition, rule learning, and decision-making while women preferentially engaged brain areas (dorsal and ventral medial prefrontal cortices, the posterior cingulate, the temporoparietal junction, and temporal poles) related to speech processing and social perception. In another study, Dr. Margaret Semrud-Clikeman and colleagues did not find a difference in visual-spatial ability but did find both similarities and some differences in brain regions activated by male and female subjects (Semrud-Clikeman, M.; Fine J.G.; Bledsoe, J.; and Zhu, D.C.; “Gender Differences in Brain Activation on a Mental Rotation Task,” International Journal of Neuroscience, 2012, 122, p. 590-597). Specifically, both males and females activated the bilateral middle frontal gyrus, the bilateral intraparietal sulcus (IPS), and the left precuneus when solving a mental rotation task. However, increased activation in the right inferior frontal gyrus/middle frontal gyrus, the left precuneus/posterior cingulate cortex/cuneus region, and the left middle occipital gyrus was found for men compared to women. Better accuracy and shorter response times were correlated with an increased activation in the IPS regardless of gender. Finally, Andreano and Cahill point out that differences in performance on navigation tasks by men and women is due to differences in cognitive strategy (Andreano, J.M., and Cahill, L.; “Sex Influences on the Neurobiology of Learning and Memory,” Learning and Memory, 2009, 16, p. 248-266). In other words, accounting for the different cognitive strategies eliminates the difference in performance on navigation tasks by men and women. Specifically, evidence suggests that for navigation tasks, men prefer a more allocentric strategy while women prefer a more egocentric strategy. They describe an allocentric strategy as using “the absolute position of more general landmarks, which may be distant, and orients oneself in terms of absolute directions (north/south), using a mental spatial map.” In contrast, they describe an egocentric strategy as “focusing on local landmarks as directional cues, and orienting oneself in terms of personal directions (left/right), which are relative to one’s position within the environment.”
Psychologist Dr. Simon Baren-Cohen and colleagues propose the Empathizing-Systematizing Theory (E-S Theory) to describe psychological differences between men and women (Baren-Cohen, S.; Knickmeyer, R.C.; and Belmonte, M.K.; “Sex Differences in the Brain: Implications for Explaining Autism,” Science, 2005, Vol. 310, p. 819-823). The theory is based on brain studies in humans and animals and postulates that males display higher systematizing while females display higher systematizing. Dr. Baren-Cohen defines systematizing as “the drive to analyze a system in terms of the rules that govern the system, in order to predict the behavior of the system” and empathizing as “the drive to identify another’s mental states and to respond to these with an appropriate emotion, in order to predict and to respond to the behavior of another person.” Dr. Baren-Cohen defines three brain types of “S” when systematizing abilities are greater than empathizing abilities, “E” when empathizing abilities are greater than systematizing abilities, and “B” when systematizing and empathizing abilities are equal. Dr. Schulte-Ruether and colleagues provide neuroscience evidence supporting the gender difference on empathizing abilities (Schulte-Ruether, M.; Markowitsch, H.J.; Shah, N.J.; Fink, J.R.; and Piefke, M.; “Gender Differences in Brain Networks Supporting Empathy,” Neuro Image, 2008, 42, p. 393-403). In support of the E-S Theory, Dr. Zeenat Zaidi reports that the brains of males are hard-wired for understanding and building systems while the brains of females are hard-wired for empathy (Zaidi, Z. F.; “Gender Differences in Human Brain: A Review,” The Open Anatomy Journal, 2010, 2, p. 37-55).
In summary, there is simple and strong evidence of the neuroanatomical, neurochemical, and neurophysiological differences between male and female brains. What these gender-based brain differences mean in terms of body function and behaviors is more complex to ascertain. The impact of gender-based brain differences on body function is complex because organs and systems in the body also have gender-based differences and the brain interacts with every part of the body. The impact of gender-based brain differences on behavior is complicated by the impact of hormone types and levels on the brain which, in turn, are impacted by the reproductive and endocrine systems in the body as well as by emotions. There appears to be growing evidence to support the E-S Theory that the brain is hard-wired to be relational in most female brains and is hard-wired to understand and control systems in most male brains. In addition, the brain-based behavioral studies that take into account gender, emotions, and female hormone levels provide evidence for similar cognitive performance using different cognitive strategies. Because different cognitive strategies can produce different insights for a complex problem, it makes sense to put those different cognitive strategies to work together in organizations.
There is simple and strong evidence of the neuroanatomical, neurochemical, and neurophysiological differences between male and female brains.
The brain-based behavioral studies that take into account gender and female hormone levels provide evidence for similar cognitive performance using different cognitive strategies.
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