The Impact of Sex Hormones on the Brain

Amber Badgerow

October 16, 2011

PSY 213

John Olmsted

The Impact of Sex Hormones on the Brain

Question:

There are distinct differences between male and female brains, but numerous things can influence the brain’s structure. How do sex hormones contribute to the difference in the structure of the male and female brain?

Prediction:

Sex hormones may be involved with the difference of gray and white matter volume in the male and female brain. Therefore, they could also contribute to the difference in regional volume in various parts of the male or female brain.

Article 1: “Regional sex differences in grey matter volume are associated with sex hormones in the young adult human brain”

This article was written by A. Veronica Witte, Markus Savli, Alexander Holik, Siegfried Kasper, and Rupert Lanzenberger (most of whom are on the Functional Neuroimaging Group- PET & fMRI from the Medical University of Vienna) to describe their study that was conducted to clarify the function of sex hormones in the sex differences of gray matter volume in the brain. They used MRI scans to obtain voxel-based morphometry (VBM) from 34 participants (17 males and 17 females). Previous studies had shown that males exhibit greater cerebral spinal fluid volume and white matter volume, but women have greater cortical grey matter volume. Specific regions of the brain also tend to be distinctly different between the sexes. The results of their study revealed that there was a relation between 17ß-estradiol levels and cluster mean gray matter volumes in the left superior parietal gyrus. The circulating 17ß-estradiol levels explained 12.6% of the variance in gray matter volumes. Cluster mean gray matter volumes in the right middle temporal pole were correlated with progesterone levels, which explained 13% of the variance. Progesterone was associated with larger temporal gray matter volume in men. Testosterone levels were related to greater cluster mean gray matter volumes in the opercular part of the left inferior frontal gyrus. Circulating testosterone levels explained 2.2% of the variance. These findings indicate that sex hormones organizationally influence regional gray matter volumes.

Article 2: “Sex steroids and brain structure in pubertal boys and girls”

Jiska S. Peper, Rachel M. Brouwer, Hugo G. Schnack, G. Caroline van Baal, Marieke van Leeuwen, Ste´phanie M. van den Berg, Henrie¨tte A. Delemarre-Van de Waal, Dorret I. Boomsma, Rene´ S. Kahn, and Hilleke E. Hulshoff Pol conducted a study on the association between brain structure and pubertal rises in testosterone and estradiol levels. There were 37 boys and 41 girls who participated in the study. Volumetric-MRI was used to measure global brain volumes. Higher estradiol levels in girls were associated with smaller global gray matter volume. In boys, higher testosterone levels were related to greater global gray matter volume. VBM was used to measure regional gray and white matter volumes. A correlation was found between higher estradiol levels in girls and lower gray matter volume in the parietal (supramarginal gyrus and angular gyrus), middle temporal, and prefrontal (superior gyrus, inferior gyrus, and orbitofrontal gyrus) areas. However, greater gray matter volume in parts of the middle frontal gyrus, inferior temporal gyrus, and middle occipital gyrus was also related to higher estradiol levels. Although testosterone levels had no indicative correlations with gray or white matter volume in boys or girls, a trend was seen between higher testosterone levels in girls and decreased gray matter volume in the left inferior frontal gyrus, left middle temporal gyrus, and right fusiform gyrus. The absence of a relationship between sex steroid levels and regional brain structures in boys could be explained by the possibility of the male and female brain reacting differently to sex steroids' effects. Yet, the results still indicate that sex steroid hormones have an effect on the brain structure of males and females, with estradiol levels in females having an observable effect.

Source Validity:

Despite the fact that both sources were reliably authored and used appropriate and dependable techniques, they each had some limitations. The sample size could be larger, especially regarding the first study, to ensure more accurate results. In article one, it could be noted that the methods used were unable to reveal causal dependencies and other factors could have caused differences in brain structure independent of sex hormones. However, the narrow age range, the education similarity, and the fact that there was no variance in the menstrual cycle phase in women positively affected validity. Article two also had some limitations, namely that the girls were older than boys and that the method used may not have been able to detect more subtle brain changes from hormones. However, this source also ensured similarity between the participants. Bias is possible, but not likely since both sources used previous impartial research on which to base their own studies.

Reflection on Hypothesis:

My hypothesis was supported by these findings. However, there is still research that needs to be conducted to further elucidate the relationship between sex hormones and brain structure differences between men and women.

Works Cited:

Witte A. Veronica, Savli Markus, Holik Alexander, Kasper Siegfried, Lanzenberger Rupert.

“Regional sex differences in grey matter volume are associated with sex hormones in the

young adult human brain.” NeuroImage 49. 2 (2010): 1205-1212. Elsevier Inc. ScienceDirect.

Web. Oct. 14, 2011.

< http://0-www.sciencedirect.com.library.pcc.edu/science/article/pii/S1053811909010258>

Peper Jiska S. et al. “Sex steroids and brain structure in pubertal boys and girls.”

Psychoneuroendocrinology 34.3 (2009): 332-342. Elsevier Ltd. ScienceDirect. Web. Oct.

14, 2011.

< http://0-www.sciencedirect.com.library.pcc.edu/science/article/pii/S0306453008002539>