Martin, Sarah; Valdés Hernández, Maria. (2017). Data extraction and analysis of the systematic search on gender differences on brain MRI structures and connectivity, 2000-2017 [dataset]. University of Edinburgh, Centre for Clinical Brain Sciences, Department of Neuroimaging Sciences. http://dx.doi.org/10.7488/ds/2053.
Magnetic resonance imaging (MRI) is an invaluable imaging technique used in medicine, generating images of structures inside the body. The images produced are used to examine almost any part of the body and are essential in diagnosing conditions, planning treatments and assessing treatment effectivity. The development of MRI has allowed for great advancements in health and biomedical research. In particular, it has granted us better opportunities to expand our knowledge of the intricate workings of the human brain, relating to its structure and function. Of particular interest both in neuroscience and society, is how structures and connectivity within the brain might differ between men and women, and whether these differences contribute to the differences demonstrated by men and women in their personality traits, behaviors and emotions.
Previous MRI-based studies consistently report sex differences in overall brain size. Indeed, it is widely acknowledged that male brains are approximately 9-12% larger compared to female brains. However, published literature addressing whether differences exist in more defined sub-regions of the brain is highly inconclusive and recent research efforts by Joel et al. (2015) have challenged the broadly conceived idea that human brains are distinctly ‘male’ or ‘female’.
Many factors can contribute to the reporting of inconsistent findings across studies, including variations in study design, duplicate reporting of results in more than one publication and selective reporting of favorable findings.
The goal of a systematic review is to address a specific research question and provide a thorough summary of the existing literature, through the collection and integration of multiple research studies. The selection of these studies for the review is based upon a structured methodological search, thereby preventing any bias in study selection. This review aimed to identify whether structural and connectivity differences exist between the brains of men and women based upon magnetic resonance imaging (MRI) data from existing literature, and in which regions these differences exist. After collating the data from 171 publications that were selected for inclusion, this review found that men and women demonstrate significant structural differences in the regions of the Broca area, cerebellum and in features related with disease throughout the brain. However, several factors including the number and age of subjects in each individual study as well as the MRI-imaging techniques and processing carried out heavily influence these findings. These results highlight the need for future neuroscientific research to account for the differences between men and women in regional brain areas. In addition, studies comprising large numbers of individuals at different stages across the lifespan and in which imaging methods are consistent and reproducible are required to allow more precise conclusions regarding specific sex differences that exist in the brain, where they exist and how they develop over time. Grasping a better understanding of how sex influences the brain will aid in efforts to identify the underlying mechanisms of the differences in the behavior of men and women, as well as in the differences between men and women in vulnerability to certain brain-related disorders.