Event Title

The influence of social and methodological values on functional neuroimaging research on sex differences

Presenter Information

Robyn Bluhm

Start Date

26-6-2010 10:45 AM

End Date

26-6-2010 11:45 AM

Description

This presentation is part of the Researching Sex Differences: Feminist Critiques and their Antecedents track.

The search for sex differences in the brain is not new. With the development of functional neuroimaging, however, research is shifting from the identification of sex differences in brain structures to differences in brain function. Although biological differences have always been interpreted in terms of sex-specific behavioural differences, anatomical (structural) research presents difficulties because it relies on tenuous links between an area of the brain and its purported function. Functional neuroimaging permits the detection of brain areas active during the performance of a behavioural task, so it should be expected to permit a much greater understanding of the neural basis of sex differences in behaviour. In this paper, I examine current functional neuroimaging research on sex differences in emotional experiences or responses and argue that, in reality, these studies still share many of the problematic methods and assumptions that characterize earlier research examining sex differences in the brain.

In making this case, I begin by examining feminist criticism of anatomical studies

purporting to show behaviourally-relevant sex differences in the brain. These criticisms include: the ad hoc nature of brain-based explanations of sex differences in behaviour, the difficulty of determining the meaning of sex differences observed in the lab, and the tendency to regard all biological differences as innate differences between the sexes. For example, Carol Tavris has described 19th century scientists’ attempts to explain women’s natural intellectual inferiority in terms of their smaller brain size, which were not thwarted by the discovery that, when differences in body size are taken into account, women have relatively larger brains than men. Instead, the focus switched to the relative size of specific areas of the brain associated with intelligence. Similarly, Anne Fausto-Sterling has analyzed the large body of research investigating possible sex differences in the corpus callosum (CC), the large fibre tract connecting the two cerebral hemispheres. This research assumes that differences in connectivity, rather than brain size, underlie sex differences in behaviour. Fausto-Sterling shows that these studies use a variety of methods to subdivide the CC, measure different areas, and use different techniques All of the studies, however, interpreted their results as indicating differences in the intact, three-dimensional CC, thus drawing conclusions well beyond those warranted by their data.

In showing that similar criticisms apply to current research on sex differences and emotion, I focus on several issues. First, functional neuroimaging studies may not provide as close a link between brain areas and behaviour as might be expected. Because these studies require that brain activity is examined during the performance of a standardized task, finding sex differences in brain function depends on the construction of a task that elicits these differences. Scientists start from the belief, supposedly supported by psychological studies, that men and women differ in their emotional experiences or behaviours, but developing a more explicit hypothesis that can be tested using neuroimaging is not straightforward. A number of aspects of emotion have been examined, including the cognitive control of emotion, response to emotion-laden pictures, “processing” of emotional words, memory for emotional words, and response to increased emotion-processing demands. I argue, however, that the interpretation of differences elicited during these tasks is unclear.

Second, as with the research Tavris surveyed, gender stereotypes pervade the interpretation of functional imaging studies. For example, one representative study examined neural responses to pictures showing disgusting and fear-inducing scenes, hypothesizing that women would have greater self-reported and neural responses than men to these pictures. Although women did report that the pictures were more emotionally arousing, the expected differences in brain activity were not observed. In fact, for the fear-inducing pictures, men actually showed greater activation in several areas associated with emotion processing. In discussing these unexpected results, the authors suggest that this difference may have occurred because the fear-inducing pictures all depicted attacks by humans and animals; the men’s greater neural response might reflect “greater attention from males to cues of aggression in their environment” (Schienle et al., 2005, p. 277).

Finally, the research on the CC criticized by Fausto-Sterling examined small sections of this structure rather than trying to understand the whole CC. A similar problem is created by current methodological practices in neuroimaging research, which encourage scientists to look for activation differences in a small group of brain structures, rather than develop more complex models of brain function. Briefly, concerns about “false positive” results – the detection of statistically-significant differences where no real difference exists – have changed both the way in which statistical models are employed to analyze data and the thresholds accepted for statistical significance. These changes have been particularly important for studies examining sex differences in brain activity, because they minimize the impact of variability in brain activity within each group. In response, researchers tend to focus on specific brain structures of interest, rather than examine the entire brain, because “corrected” thresholds for statistical significance are more likely to be reached when smaller brain areas are tested. In fact, Schienle et al. found no significant sex differences in neural response to emotion-inducing pictures until they conducted region of interest analyses. These simplistic models therefore make it easier to find functional differences, but also make it difficult to interpret any differences that are found, because they do not provide much information about how the brain actually processes emotional stimuli. In summary, both social and methodological values influencing functional neuroimaging research on sex differences encourage the design of studies that search for differences in brain activation in a small number of neural structures and then interpret those results in terms of simplistic, often stereotypical notions of sex differences in behaviour.

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Jun 26th, 10:45 AM Jun 26th, 11:45 AM

The influence of social and methodological values on functional neuroimaging research on sex differences

This presentation is part of the Researching Sex Differences: Feminist Critiques and their Antecedents track.

The search for sex differences in the brain is not new. With the development of functional neuroimaging, however, research is shifting from the identification of sex differences in brain structures to differences in brain function. Although biological differences have always been interpreted in terms of sex-specific behavioural differences, anatomical (structural) research presents difficulties because it relies on tenuous links between an area of the brain and its purported function. Functional neuroimaging permits the detection of brain areas active during the performance of a behavioural task, so it should be expected to permit a much greater understanding of the neural basis of sex differences in behaviour. In this paper, I examine current functional neuroimaging research on sex differences in emotional experiences or responses and argue that, in reality, these studies still share many of the problematic methods and assumptions that characterize earlier research examining sex differences in the brain.

In making this case, I begin by examining feminist criticism of anatomical studies

purporting to show behaviourally-relevant sex differences in the brain. These criticisms include: the ad hoc nature of brain-based explanations of sex differences in behaviour, the difficulty of determining the meaning of sex differences observed in the lab, and the tendency to regard all biological differences as innate differences between the sexes. For example, Carol Tavris has described 19th century scientists’ attempts to explain women’s natural intellectual inferiority in terms of their smaller brain size, which were not thwarted by the discovery that, when differences in body size are taken into account, women have relatively larger brains than men. Instead, the focus switched to the relative size of specific areas of the brain associated with intelligence. Similarly, Anne Fausto-Sterling has analyzed the large body of research investigating possible sex differences in the corpus callosum (CC), the large fibre tract connecting the two cerebral hemispheres. This research assumes that differences in connectivity, rather than brain size, underlie sex differences in behaviour. Fausto-Sterling shows that these studies use a variety of methods to subdivide the CC, measure different areas, and use different techniques All of the studies, however, interpreted their results as indicating differences in the intact, three-dimensional CC, thus drawing conclusions well beyond those warranted by their data.

In showing that similar criticisms apply to current research on sex differences and emotion, I focus on several issues. First, functional neuroimaging studies may not provide as close a link between brain areas and behaviour as might be expected. Because these studies require that brain activity is examined during the performance of a standardized task, finding sex differences in brain function depends on the construction of a task that elicits these differences. Scientists start from the belief, supposedly supported by psychological studies, that men and women differ in their emotional experiences or behaviours, but developing a more explicit hypothesis that can be tested using neuroimaging is not straightforward. A number of aspects of emotion have been examined, including the cognitive control of emotion, response to emotion-laden pictures, “processing” of emotional words, memory for emotional words, and response to increased emotion-processing demands. I argue, however, that the interpretation of differences elicited during these tasks is unclear.

Second, as with the research Tavris surveyed, gender stereotypes pervade the interpretation of functional imaging studies. For example, one representative study examined neural responses to pictures showing disgusting and fear-inducing scenes, hypothesizing that women would have greater self-reported and neural responses than men to these pictures. Although women did report that the pictures were more emotionally arousing, the expected differences in brain activity were not observed. In fact, for the fear-inducing pictures, men actually showed greater activation in several areas associated with emotion processing. In discussing these unexpected results, the authors suggest that this difference may have occurred because the fear-inducing pictures all depicted attacks by humans and animals; the men’s greater neural response might reflect “greater attention from males to cues of aggression in their environment” (Schienle et al., 2005, p. 277).

Finally, the research on the CC criticized by Fausto-Sterling examined small sections of this structure rather than trying to understand the whole CC. A similar problem is created by current methodological practices in neuroimaging research, which encourage scientists to look for activation differences in a small group of brain structures, rather than develop more complex models of brain function. Briefly, concerns about “false positive” results – the detection of statistically-significant differences where no real difference exists – have changed both the way in which statistical models are employed to analyze data and the thresholds accepted for statistical significance. These changes have been particularly important for studies examining sex differences in brain activity, because they minimize the impact of variability in brain activity within each group. In response, researchers tend to focus on specific brain structures of interest, rather than examine the entire brain, because “corrected” thresholds for statistical significance are more likely to be reached when smaller brain areas are tested. In fact, Schienle et al. found no significant sex differences in neural response to emotion-inducing pictures until they conducted region of interest analyses. These simplistic models therefore make it easier to find functional differences, but also make it difficult to interpret any differences that are found, because they do not provide much information about how the brain actually processes emotional stimuli. In summary, both social and methodological values influencing functional neuroimaging research on sex differences encourage the design of studies that search for differences in brain activation in a small number of neural structures and then interpret those results in terms of simplistic, often stereotypical notions of sex differences in behaviour.