Hockenbury Discovering Psychology 5th txtbk

Specialization in the Cerebral Hemispheres75CRITICAL THINKING“His” and “Her” Brains?Do the brains of men and women differ?And if so, do those differences cause them to“think differently,” as headlines sometimesclaim?Media reports often refer to physiologicalsex differences as “innate,” “biological,” or“hard-wired.” But even differences that arebiological in origin are not necessarily fixed,permanent, or inevitable (Hyde, 2007). Forexample, brain development and function areaffected by the sex hormones both beforebirth and throughout life (Morris & others,2004). However, hormone levels themselvesare strongly influenced by environmental factors,ranging from the food we eat to thestressful circumstances we experience. Aswe’ve emphasized throughout this chapter, brain function andstructure are highly responsive to environmental influences(Fiavell & Greenberg, 2008).Neuroscientists have identified a number of differencesbetween male and female brains, such as structures that on theaverage tend to be slightly larger in one sex (Cahill, 2006). Thefollowing are the best-substantiated differences:1. Men’s brains tend to be larger than women’s brains. Evenat birth, the male newborn has a larger brain, primarily becausetheir skulls are also larger. (Gilmore & others, 2007).2. Women and men have different proportions of gray to whitematter. Adult men and women have roughly the same amountof gray matter. However, women have a much higher proportionof gray matter in their brains, and the neuron cell bodies anddendrites that make up gray matter are much more closelypacked (Gur & others, 1999, 2002). Women also display greatercortical complexity, meaning that they have more folds, fissures,and wrinkles in their cerebral cortex (Luders & others, 2004).Gray matter is also distributed differently in male and femalebrains. Males have a higher percentage of gray matter in their lefthemisphere than in their right hemisphere. But in females, the distributionof gray and white matter is roughly equivalent in the leftand right hemispheres. This observation leads to the next difference.3. In general, the male brain is more asymmetrical and functionsare more lateralized than in the female brain. For example,women tend to rely on brain structures in both hemispheres forlanguage tasks, while men are more reliant on one brain hemisphere,usually the left, for language tasks (Shaywitz & others,1995; Cahill, 2006). Some brain-imaging studies have foundthat when it comes to solving complex arithmetic problems, spatialtasks, or mental rotation problems, males are more likely torely on focused activation of specific brain regions in the righthemisphere. Females are more likely to draw upon multipleregions in both hemispheres to solve the same problems (Kucian& others, 2005; Grön & others, 2000).So what does this mean? After an extensive review of research,Diane Halpern and her colleagues (2007) summarized the majoranatomical and functional differences in this way: Male brainsappear to be optimized for network connections within eachhemisphere. Female brains appear to have better connectionsbetween the two hemispheres. The better communicationSex Differences and the Brain Subtle genderdifferences in brain function and structuremake headlines. This headline implies thatnew discoveries about the brain will explain“why men and women think differently.”How valid is this conclusion?between the left and right hemispheres givesfemales an advantage in language. Femalesalso have a greater ability to integrate the lefthemisphere’s verbal-analytical processing withthe right hemisphere’s spatial and holisticmode of information processing.However, not all structural differences leadto differences in measurable behaviors or abilities.In a series of studies, neuroscientist JillGoldstein found that for several brain regions,the average size is slightly different in men andwomen (Goldstein, 2007; Goldstein & others, 2005). For example,the female hippocampus tends to be larger than the malehippocampus. But, when tested, memory skills were the same. Asneuroscientist Geert J. De Vries (2004) points out, “Despitedecades of research, we still do not know the functional significanceof most sex differences in the brain.”Thinking Critically About Brain DifferencesSo do such findings support the belief that “men and womenthink differently"? Do they explain gender differences in cognitiveabilities or personality traits? All the findings we’ve discussedneed to be examined in the context of what is known—and,more importantly, what is not known—about the brain.First, brain studies are typically based on small samples. Thosesamples may or may not be representative of the wider populationof men and women. And while scientists are careful to qualifytheir conclusions and describe the limitations of theirresearch, media reports rarely mention these qualifications.Second, many sex differences amount to minor variations in aparticular brain region. When differences are found, they aretypically statistically significant differences in the amount or kindof tissue, such as the gender differences in gray matter distributionnoted earlier. Even so, the basic brain structures are still thesame in men and women.Third, every brain is different to some degree (Gernsbacher,2007a). Regardless of gender, no two brains are identical.Finally, every brain is a “work in progress.” Experience affectsthe brain, including the size of brain structures. Thus, sex differencesin structures or function might well be the result of the differentlife experiences of men and women, rather than the cause(Halpern & others, 2007).CRITICAL THINKING QUESTIONS Why are sweeping claims about fundamental sex differencesin the human brain misleading? What is wrong with the statement that certain behaviors orpersonality traits are “hard-wired” in the male or femalebrain? Why is the notion that sex differences might be due to braindifferences so appealing to many people?