From Scanner to Sound Bite:Issues in Interpreting and Reporting Sex Differences in the Brain by Cordelia Fine - HTML preview
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Current Directions in Psychological
From Scanner to Sound Bite : Issues in Interpreting and Reporting Sex Differences in the Brain Cordelia Fine
2010 19: 280
Current Directions in Psychological Science
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From Scanner to Sound Bite: Issues in
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Interpreting and Reporting Sex
Reprints and permission:
Differences in the Brain
Centre for Agency, Values and Ethics, Macquarie University, and Department of Psychological Sciences, University of Melbourne
Neuroimaging research is yielding reports of sex differences in the brain. Yet the likelihood of spurious findings of sex differences, the teething problems of new technology, the obscurity of the relation between brain structure and psychological function, and difficulties inferring mental states from neuroimaging data all require us to be considerably cautious in interpreting such results.
Unfortunately, these issues are often overlooked in popular accounts. Together with a tendency for people to regard neuroscientific information as more scientific than behavioral data, and as indicative of male and female ‘‘nature,’’ these issues point to the worrisome possibility of public misunderstanding of what contemporary neuroscience tells us about gender.
neuroimaging, gender, science communication, neuroethics
For as long as there has been brain science there has been both
and, in keeping with the female brain’s supposedly more
scientific and popular interest in male–female differences and
interhemispheric functioning, are claimed to have a relatively
their psychological consequences. For example, 19th-century
larger corpus callosum (the bundle of neurons that connects the
scientific opinion held that women’s intellectual inferiority
two hemispheres). In both academic and especially popular
could be attributed to their smaller and lighter brains—a fact
work, these structural differences are proposed to have
that was widely known among the Victorian public as the
‘‘missing five ounces’’ of female brain (see Russett, 1989).
Today, the weighing scales and other crude methodologies of
the Victorian brain scientists have been supplanted by sophis-
Production: The Problem of
ticated neuroimaging techniques that give unprecedented
access to structural details of the brain and patterns of neural
When neuroscientists, in a single experiment, establish a ‘‘sig-
activity. Yet there remains cause for skepticism regarding
nificant difference’’ between the sexes, does this reflect a real
neuroscientific claims about sex differences and concern over
and reliable sex difference? Because sex is a primary and
the way such information is reported to, and interpreted by, the
ubiquitous social category, classifying participants by sex is
public. In this article, I lay out four scientific issues arising
obvious, easy, and may be done by default (Kaiser, Haller,
from the production and interpretation of ‘‘facts’’ about sex
Schmitz, & Nitsch, 2009). However, since by convention
differences in the brain, then discuss how these issues are
researchers declare a difference to be ‘‘significant’’ if there is overlooked and exacerbated when neuroscience findings are
no more than a one in 20 probability that it occurred by chance,
disseminated in the popular media and digested by the public.
if 20 researchers routinely test for sex differences, then even if To illustrate these points, I use as an example a long-there is no real difference between the populations, one
standing and influential claim about male–female brain
difference. The greater male lateralization (GML) hypothesis
proposes that males, compared with females, are more strongly
left hemisphere dominant for language processing and right
Cordelia Fine, Department of Psychological Sciences, University of Melbourne, hemisphere dominant for visuospatial processing. Females,
Victoria 3010, Australia
by contrast, tend to engage both hemispheres for these tasks
Sex Differences in the Brain
researcher will find a statistically significant difference. The
Interpretation: The Obscurity of
concern is that, given that the publication process is geared
toward emphasizing difference rather than similarity, this
1-in-20 finding of difference will be reported while the 19 fail-
Further difficulties arise when it comes to understanding what,
ures to find a difference will not. Indeed, Kaiser et al. provide
if anything, brain differences might imply for psychological
examples of how, in language research, even marginal sex
function. Despite the extraordinary progress made in neu-
differences in the brain are given prominence in the published
roscience, we still have minimal understanding of how neural
structures contribute to complex psychological phenomena.
The problem of spurious results for all sex-differences
Again, the GML hypothesis is an instructive example: There
research has been long-noted. However, the inevitable teething
is no a priori reason to think that a more lateralized brain would problems of the new neuroimaging technologies may exacer-be advantageous for visuospatial processing but disadvanta-
bate the situation. Nuisance variables like breathing rate and
geous for language function. (Nor, to my knowledge, have any
caffeine intake can influence the imaging signal and give rise
such relations been demonstrated.) Bishop and Wahlsten
to spurious results; this is particularly the case when sample
(1997) questioned the assumption that a modest size difference
sizes are small, as they often are in the studies that have
in a structure as complex and massively interconnected as the
reported sex differences (Wallentin, 2009). Researchers have
corpus callosum would have tangible implications for a spe-
found that sex differences in language lateralization fail to
cific psychological construct.
generalize to a distinct but similar task within a second group
Nonetheless, functional speculations arising from the GML
of men and women and that identical analyses of the same par-
hypothesis have recently taken new form in suggestions that a
ticipants can also ‘‘discover’’ brain-activation differences
male brain skewed toward more lateralized, intrahemispheric
between randomly created groups matched on sex, perfor-
processing may be advantageous for scientific disciplines that
mance, and obvious demographic characteristics (Ihnen,
supposedly require focused scrutiny of details rather than
Church, Petersen, & Schlaggar, 2009). As controversies over
integration of information (Baron-Cohen, Knickmeyer, &
statistical procedures are resolved, researchers may turn out
Belmonte, 2005; Gur & Gur, 2007), and that a female brain
to have used inadequate or inappropriate techniques: It has
skewed toward more long-range processing may be advanta-
recently been argued that some reported sex differences in
geous for empathizing (Baron-Cohen et al., 2005).
language lateralization have not been put to adequate
While speculation is an important part of the scientific pro-
statistical test or that they can come and go depending on how
cess, as Fausto-Sterling (2000, p. 118) has observed, the prob-
the analysis is done (Kaiser et al., 2009). There is also an
lem is that ‘‘despite the many recent insights of brain research,
this organ remains a vast unknown, a perfect medium on which
whether—neuroscientists should control for the sex difference
to project, even unwittingly, assumptions about gender.’’ As
in average brain size when attempting to establish whether the
noted earlier, it was once readily assumed that brain weight
sexes differ in the volumes of particular brain regions (see, for
correlated with intelligence, thus explaining women’s sup-
example, Fausto-Sterling, 2000). A change in methodology can
posed intellectual inferiority. With that history in mind, we
transform what appears to be a sex difference into a difference
should be wary of suggestions that the typical female brain is
between people with smaller and larger brains (e.g., Im et al.,
suboptimally designed for currently male-dominated pursuits
like science—suggestions made in the absence of adequate
These difficulties point to the importance of not placing too
knowledge of how the brain enables scientific thinking and
much confidence in any single functional or structural neuro-
practice. There is no neuroscientific reason, for example, to
imaging study that seems to demonstrate a sex difference. The
think that the shorter circuits of an intrahemispheric brain will
wisdom of such caution is demonstrated by meta-analyses of
enable narrower focus in the mind.
tests of the GML hypothesis. A recent meta-analysis of 26 func-
Inferring a mental process from significant activation in a par-
tional neuroimaging studies of language lateralization found no
ticular brain region (for example, inferring that the amygdala was significant sex difference (Sommer, Aleman, Somers, Boks, &
activated, therefore participants were anxious) is known as
Kahn, 2008). Similarly, a meta-analysis of 49 postmortem and
reverse inference and is also fraught with difficulty. The statisti-structural neuroimaging studies of the corpus callosum found
cal procedures of functional neuroimaging identify regions that
no support for the hypothesis that this structure is larger in
are differentially activated by the experimental task, compared
females, even allowing for their relatively smaller brains
with a control task. However, while brain function involves spe-
(Bishop & Wahlsten, 1997).
cialization—the entire brain is not involved in all of its func-
The failure of meta-analyses to support predictions of the
tions—there is no simple one-to-one mapping between brain
GML hypothesis, to which much research attention has been
regions and psychological processes. Mental processes arise from
devoted, highlights the importance of remaining skeptical
the complex interaction of multiple areas, and any one region will about other reported sex differences. Clearly, isolated reports
be involved in any number of mental processes. The anterior cin-
of sex differences in brain activation or regional brain volume
gulate, for example, is activated by so many tasks that one cogni-
require replication and generalization before they can be
tive neuroscientist known to the author refers to this region as
assumed to be reliable.
‘‘the on button’’ (Geoffrey Boynton, personal communication).
Moreover, the psychological implications of significant
(as much as 25%) larger in females, furnishing them not just
differences in the amount of brain activity in particular regions
with superior language skills but also greater multitasking abil-
are ambiguous. ‘‘More’’ activity does not necessarily imply
ity, a more intuitive leadership style, better emotion processing, psychologically ‘‘more’’ or ‘better,’’ or even that that region
and even greater capacity to remember to buy milk (see Fine,
is critically involved in that particular task (Poldrack, 2008).
Furthermore, data acquisition in functional magnetic resonance
Even books written by apparently authoritative and well-
imaging (fMRI) is slow: At its most sensitive, it averages over a
credentialed authors are rife with invalid structure–function
few seconds the activity of millions of neurons that can fire up
claims and reverse inferences, as well as factual errors, that
to one hundred impulses a second. (Positron emission tomogra-
go well beyond the GML hypothesis. To cite just a few exam-
phy, PET, is even slower.) This massively limits the interpreta-
ples from a multitude, functional neuroimaging findings may
tions that can be made about brief psychological events.
be used as evidence of sex differences in intrinsic interest in
Thus it becomes clear that observing, say, significantly
mathematics, in ‘‘hard-wired’’ ability to talk about feelings,
greater female anterior cingulate activity over the time course
or in capacity to empathize with the feelings of others. As
of the performance of a complex task is unlikely to indicate
I have discussed elsewhere (Fine, 2010), these particular claims
what mental process, if any, differs between males or females,
were made in part on the basis of studies that, respectively,
or in what direction that difference lies. It has been argued that didn’t involve mathematics, didn’t involve talking about feel-reverse inferences can be valuable when the underlying pro-
ings, and didn’t involve male participants. Furthermore, it
cesses involved in the participants’ task are well known, and
should by now be clear that currently no neuroimaging data
when they are used to generate hypotheses that drive further
could be cited as compelling support for such claims.
experimental work rather than to interpret neuroimaging results
(Poldrack, 2008). However, so far these conditions are rarely, if
ever, met in neuroimaging studies of sex differences. These
obstacles to valid reverse inference severely constrain the pos-
In addition to overinterpretation, misinterpretation, and misrep-
sibilities for making inferences about psychological differences
resentation, a number of characteristics of neuroscientific
between males and females from brain activation differences,
information and the way it is often communicated may further
even supposing these differences reported in studies are statis-
contribute to public misunderstanding. With its expensive,
tically valid and reliable.
complex machinery, the data yielded by neuroscience may
seem somehow more scientific and real than data collected in
less high-tech fashion. A consequence of this ‘‘neuro-realism’’
(Racine, Bar-Ilan, & Illes, 2005) is that substantial behavioral While neuroscientists may routinely test for sex differences in
evidence of gender similarity may be overshadowed by a single
the brain and emphasize those they find, or engage in post hoc
finding of a sex difference in the brain. There may also be a ten-
speculations about such differences’ functional implications,
dency to equate ‘‘in the brain’’ with ‘‘innate.’’ Although the
they are presumably aware of the issues outlined previously
effects of gender socialization must manifest in the brain
and are engaging with peers who share this knowledge. The
(where else?), some popular authors promote the idea that brain
public, however, rarely gain its knowledge from neuroscientists
differences constitute evidence that the sexes are ‘‘hard-wired’’
or the neuroscientific literature. Instead, information is pre-
to be different. Lastly, neuroscientific data have been shown to
sented to the public by popular writers. That such writers are
have a ‘‘seductive allure’’: For instance, people find circular
either not aware of the critical issues of production and inter-
explanations of psychological phenomena more satisfying
pretation I have outlined or think them unimportant may be
when accompanied by information about brain responses
inferred from the fact that their books confidently purport to
(Weisberg, Keil, Goodstein, Rawson, & Gray, 2008). Thus,
offer practical applications for life, love, and learning on the
popular neuroscience is well placed to entice people to over-
basis of sex differences in the brain.
look psychological and sociological data showing that gender
Consider, for example, how the GML is presented in the
difference is contingent on historical period, ethnicity, socio-
popular literature. It is not only regularly asserted as fact rather economic group, and social context and to instead conclude
than a hypothesis (a poorly supported one, as noted) but is used
that gender differences are immutable, inevitable, and the prod-
as a springboard for scientifically unwarranted claims about
uct of fixed differences between the ‘‘male brain’’ and the
men’s and women’s different psychological abilities. Thus one
author (working from an implicit metaphor of the brain as pin-
ball machine) explains how men’s language lateralization
impairs their ability to talk about their feelings, describing how the ‘‘signal’’ of an emotional feeling, having made it to the
While neuroimaging has potential to contribute in novel ways
right hemisphere, ‘‘may well get stopped, disappearing into
to our understanding of gender, scientists, popular commenta-
neural oblivion because the signal found no access to a receptor
tors, and the public need to be alert to the problem of premature
in a language center in the left side of the brain’’ (Gurian, 2004, speculation
p. 88). Similarly, the corpus callosum is regularly claimed to be
neuroimaging ‘‘facts’’ about male and female brains—that may
Sex Differences in the Brain
be spurious, overinterpreted, misinterpreted, or even fabri-
cated—influencing public attitudes about gender raises ethical
Baron-Cohen, S., Knickmeyer, R.C., & Belmonte, M.K. (2005). Sex concerns. The imaginative reader will not have too much
differences in the brain: Implications for explaining autism. Sci-
difficulty envisaging how, by reinforcing stereotypes, such
ence, 310, 819–823.
claims may affect people’s social attitudes in ways that oppose
Bishop, K.M., & Wahlsten, D. (1997). Sex differences in the human progress toward greater gender equality, just as such claims did
corpus callosum: Myth or reality? Neuroscience and Biobehav-
in the past. The task now is to open a dialogue between the pro-
ioral Reviews, 21, 581–601.
ducers, communicators, and consumers of knowledge about
Fausto-Sterling, A. (2000). Sexing the body: Gender politics and the sex differences in the brain and to take seriously the issues that construction of sexuality. New York, NY: Basic Books.
arise from scanner to sound bite.
Fine, C. (2010). Delusions of gender: How our minds, society, and
neurosexism create difference. New York, NY: W.W. Norton.
Gur, R.C., & Gur, R.E. (2007). Neural substrates for sex differences in Recommended Reading
cognition. In S.J. Ceci and W.M. Williams (Eds.), Why aren’t
Fine, C. (2010). (See References). An accessible book that covers all more women in science? Top researchers debate the evidence.
the issues in more detail than the current article.
Lehrer, J. (2008, August 17). Of course I love you, and I have the brain Association.
scan to prove it – We’re looking for too much in brain scans. Bos-
Gurian, M. (2004). What could he be thinking? A guide to the mys-
ton Globe, K1. An accessible account of general interpretative
teries of a man’s mind. London, England: Element.
issues in fMRI research.
Ihnen, S.K.Z., Church, J.A., Petersen, S.E., & Schlaggar, B.L. (2009).
Miller, G. (2008). Growing Pains for fMRI. Science, 320, 1412–1414.
Lack of generalizability of sex differences in the fMRI BOLD
A useful and accessible overview of issues, controversies, and
activity associated with language processing in adults. Neuro-
potential solutions in the interpretation of fMRI data that provides Image, 45, 1020–1032.
Im, K., Lee, J., Lyttelton, O., Kim, S.H., Evans, A.C., & Kim, S.I.
Russett, C. E. (1989). (See References). A historical account of Victor-
(2008). Brain size and cortical structure in the adult human brain.
ian brain science and its reactionary role in social attitudes toward Cerebral Cortex, 18, 2181–2191.
female suffrage and higher education—surprisingly helpful for illu-Kaiser, A., Haller, S., Schmitz, S., & Nitsch, C. (2009). On sex/gender minating current biases in neuroscientific interpretation.
related similarities and differences in fMRI language research.
Weisberg, D. S. (2008). Caveat lector: The presentation of neu-
Brain Research Reviews, 61, 49–59.
roscience information in the popular media. The Scientific Review
of Mental Health Practice, 6, 51–56. A readable overview outlin-
neuroscience: Where do we stand? Current Opinion in Neurobiol-
ing the limited insight into psychological processes offered by
ogy, 18, 223–227.
fMRI, the potential danger of the overinterpretation of neuroima-
Racine, E., Bar-Ilan, O., & Illes, J. (2005). fMRI in the public eye.
ging data in popular media, and the role of scientists in alleviating Nature Reviews Neuroscience, 6, 159–164.
Russett, C. E. (1989). Sexual science: The Victorian construction of womanhood. Cambridge, MA: Harvard University Press.
Declaration of Conflicting Interests
Sommer, I.E., Aleman, A., Somers, M., Boks, M.P., & Kahn, R.S.
(2008). Sex differences in handedness, asymmetry of the Planum
The authors declared that they had no conflicts of interest with respect Temporale and functional language lateralization. Brain Research,
to their authorship or the publication of this article.
Wallentin, M. (2009). Putative sex differences in verbal abilities and lan-Acknowledgments
guage cortex: A critical review. Brain and Language, 108, 175–183.
Weisberg, D.S., Keil, F.C., Goodstein, J., Rawson, E., & Gray, J.R.
I am grateful to Carsten Murawski and two anonymous reviewers for
their valuable feedback on earlier drafts of this article.
(2008). The seductive allure of neuroscience explanations. Journal of Cognitive Neuroscience, 20, 470–477.
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