Tuesday, March 8, 2011
Deboleena Roy and Kim Wallen
CLICK HERE FOR LINK TO PODCAST
This past Tuesday, the CMBC hosted a lunch discussion titled “What does the brain have to do with sex and gender?” The discussion was led by Dr. Deboleena Roy (Women’s studies and Neuroscience) and Dr. Kim Wallen (Psychology).
The topic of sex and gender differences is of great interest to many. From my own experience as a student in the psychology department, the question of whether sex or gender differences exists in particular behaviors or traits is probably one of the most commonly asked questions both in the classroom and at research presentations. It was thus no surprise to me that Tuesday’s lunch meeting was filled to its capacity with student and faculty attendees.
Both Dr. Roy and Dr. Wallen gave brief opening remarks leading up to an open group dialogue. Unfortunately, this blog space isn’t large enough for me to report all the interesting information I learned from the lunch. So, I’ll try and highlight just some of the issues our discussion leaders raised as well as give some snippets of the directions the group discussion took.
Language and Metaphor in Science: A Feminist Scientist’s Perspective
In her opening comments, Dr. Roy provided a brief overview of some of the feminist engagements in research on gender and sex differences specifically, and in scientific research more broadly. She discussed, among other things, how feminist scholars over the years have pushed for a critical analysis on the types of language and metaphors scientists use in understanding particular biological phenomena. An example she gave was how early neuroendocrinologists would portray the workings of the Hypothalamic-Pituitary-Gonadal (HPG) axis. Early on, Dr. Roy described, many scientists explained the axis hierarchically, implying that the hypothalamus regulates the activity of the pituitary and gonad glands. A different metaphor, however, also seemed to fit the data. Namely, the axis could be thought of as a set of feedback loops between the hypothalamus, pituitary and gonad glands. In fact, some of Dr. Roy’s own research revealed that estrogen receptors exist on Gonadotropin Releasing Hormone (GnRH) neurons within the hypothalamus, suggesting that there may indeed be a feedback regulatory system from the ovaries to the hypothalamus. Dr. Roy further discussed how the metaphors scientists use not only affect the types of interpretations at which we arrive, but also the types of follow-up experiments and future directions scientists choose to make, as well as how the results are disseminated by the media.
A Recent Finding of Sex Differences in the Brain
Dr. Wallen began his opening comments with a summary of a recent finding from his lab. The goal was for the lunch attendees to work together to figure out what these findings might mean for the topic of sex and gender differences in the brain. The basic finding was that men and women subjects show differential patterns of brain activation, specifically amygdala activation, in response to viewing erotic compared to non-erotic images. Specifically, men showed greater amygdala activation to erotic images (compared to non-erotic images) than did women. Further, it doesn’t appear that this pattern can be explained simply by the fact that men found the pictures more arousing (ratings of the images revealed that men and women found the images equally arousing).
Dr. Wallen’s team didn’t look only at men and women, but also a third group of subjects, women with Complete Androgen Insensitivity Syndrome (from here on, CAIS women). According to Dr. Wallen, these women have a Y chromosome but lack typical androgen receptors. As a result, phenotypically these individuals are like women, except for the fact that they have a Y chromosome. Of interest for this study was the pattern of amygdala activation in CAIS women. As it turns out, Dr. Wallen and his students found that their amygdala activation was comparable to the women. That is, men also showed greater amygdala activation in response to the stimuli compared to CAIS women. Further, women and CAIS women did not show a differential heightened pattern of amygdala activation to the sexual images.
The ensuing discussion about what these findings mean was fascinating. One topic discussed was that in order to know what these findings mean for sex differences in the brain, we first must figure out how to best characterize CAIS women in relation to the other two groups. From a strict chromosomal standpoint, CAIS women can be thought of as genetically male. But what does it mean to be genetically male? As Dr. Wallen points out, if you consider the fact that genetic traits are only expressed in the context of an environment, and that CAIS women lack androgen receptors (which would provide the typical hormonal environment in which male traits develop), then CAIS women wouldn’t count as genetically male.
Sex vs. Gender Differences
Dr. Roy suggests that the difficulty in characterizing the CAIS women highlights the struggle we have in trying to answer a question that seems simple: what makes a male a male. She suggests that this difficulty is due to a deep bias we have in perceiving the world as strictly consisting of men and women. That is, that we have intuitions that biologically we all start out with male and female bodies. These bodies then go through a process of socialization that turns those male and female bodies into men and women.
The separation between the biological and the socio-cultural underpinnings of the differences between the sexes maps onto what are traditionally considered “sex differences” (ones due to biological factors) and “gender differences” (one due to socio-cultural factors). Dr. Roy pointed out that there is a changing trend in the object of study in feminist science scholarship. Whereas early feminist scholars focused primarily on understanding gender differences, more recent feminist scientists have begun to focus on questions related to sex differences themselves, including whether the construct of sex itself might not be as rigid as once believed.
Structural vs. Functional Differences
Dr. Roy brought up yet another issue related to the findings, which is the distinction between structural and functional sex differences. That is, although the study revealed “structural” differences across participants in the patterns of Amygdala activation, all participants reported similar arousal ratings to the erotic images. Dr. Roy suggested that when the neuro-imaging and behavioral results are considered together, they might reflect a more general fact that multiple structures may lead to the same functional outcome. Dr. Wallen agreed, suggesting that the processing of sexual imagery might go through the amygdala in men and through a different circuit in women.
A number of follow-up analyses might be informative in this respect. For example, are there correlations between ratings of arousal and heightened amygdala activation? Further, are these correlations different across the different populations? I found this issue of “multiple roads leading to the same end point” interesting as it raises the possibility that there may be important differences even within both the male and female populations.
Other possible explanations of the findings were also discussed, highlighting the difficulty of figuring out what exactly the brain has to do with sex and gender differences. For example at one point, Dr. Wallen pointed out that we don’t know if the men and women in the study are even “seeing” the same thing within the images. To further complicate the matter, Dr. Wallen also reminded us that the study only looked at a single region of the brain, a particular class of images, and using a specific experimental design. Whether the types of explanations that are currently on the table will remain viable once more data come in remains to be seen.