THE PHENOMENON OF BRAIN PLASTICITY 31cence, or one that is imprinted by poverty into a recognizable phenotype, is
quite different from one that can be modified by the demands of its owner.
Social constructionists might believe this diversity delegitimizes any efforts
to theorize plasticity as a material reality, but as I explain further, I see this
variability instead as evidence of the entanglement of matter, measure, and
meaning.
Plasticity and Socialization
Any discussion of brain plasticity should recognize not only its partial and
stratified character but also its absence in some research programs. This
is nowhere more striking than in neuroscientific research on sex differ-
ence. Rather than a brain that constantly changes throughout life, many
researchers are claiming that there are male and female brains, which are
fixed as such before birth. The dominant sex difference theory, which dates
to animal research from the 1960s, is that during the prenatal development
of reproductive organs, brains, along with genitals, are differentiated by
sex via their exposure to reproductive hormones. This theory was initially
used to address the development of the amygdala and hypothalamus, ar-
eas of the subcortex that are believed to work with reproductive organs,
but was eventually applied to the so-^ called higher cortical regions and to
a wide range of functions and behaviors. It is used to explain findings of
cognitive and affective differences, for example, in performance on tests
measuring visual- spatial tasks, mathematical reasoning, perceptual speed,
language skills, and aspects of social intelligence, as well as gender identity
and sexual orientation (for a review, see Bao and Swabb 2011).^17 It is also
used to understand autism as a gender disorder, essentially as the product
of an extremely male brain (Baron- Cohen et al. 2005; Baron- Cohen 2009,
2010; for critique, see Gilles- Buck and Richardson 2014).
Brain imaging has reanimated sex difference research because it allows
(images of ) living, human brains to be compared structurally (using mri)
or functionally (using functional mri [fmri]). To take one example, Jessica
Wood, Heitmiller and colleagues (2008a) used mri scans to examine the
relative size of the straight gyrus, an area of the medial prefrontal cortex, in
a group of men and women. Based on lesion and fmri studies, they argue
that the straight gyrus is used in tasks related to “social intelligence.”^18 In
their study they found proportionally more gray matter on average in this