Revisiting Geschwind's hypothesis on brain lateralisation: A functional MRI study of digit ratio (2D:4D) and sex interaction effects on spatial working memory

Abstract

The Geschwind-Behan-Galaburda (GBG) hypothesis links cerebral lateralisation with prenatal testosterone exposure. Digit ratio measures in adults have been established as potential markers of foetal sex hormonal milieu. The aim of the study was to evaluate the sex-dependent interaction of digit ratio measures and cerebral lateralization as well as their neurohemodynamic correlates using functional MRI (fMRI). Digit ratio measures-ratio of index finger (2D) length to ring finger (4D) length (2D:4D) and difference between 2D:4D of two hands, i.e., right minus left (DR-L)-were calculated using high resolution digital images in 70 right-handed participants (42 men) based on reliable and valid method. fMRI was acquired during the performance of a spatial working memory task in a subset of 25 individuals (14 men), and analysed using Statistical Parametric Mapping 8 (SPM8) and the Laterality Index toolbox for SPM8. Men had significantly less bilateral 2D:4D than women. There was a significant negative correlation between right 2D:4D and 2-Back task accuracy (2BACC) in women. A significant sex-by-right 2D:4D interaction was observed in left parahippocampal gyrus activation. Additionally, sex-by-DR-L interaction was observed in left IPL activation. DR-L showed a significant positive correlation with the whole brain Laterality Index (LI), and LI, in turn, demonstrated a significant negative correlation with 2BACC. Our study observations suggest several novel sex-differential relationships between 2D:4D measures and fMRI activation during spatial working memory task performance. Given the pre-existing background data supporting digit ratio measures as putative indicator of prenatal sex hormonal milieu, our study findings add support to the Geschwind-Behan-Galaburda (GBG) hypothesis.

Implicit motives show sex-dimorphic associations with digit ratio.

“…Because handedness emerges as a stable trait early in life (e.g., Hepper, Wells, & Lynch, 2005), this observation suggests that DR-L is a marker of fundamental variations in lateralized brain function. Consistent with this, Kalmady et al (2013) found in a brain-imaging study that lower (i.e., more negative) DR-L was associated with more right-hemispheric activation. These observations are also generally consistent with findings documenting that high testosterone prenatally is associated with asymmetric brain development in favor of the right hemisphere (Geschwind & Galaburda, 1987).…”

Sex differences in visual-spatial working memory: A meta-analysis

“…Therefore, this task was coded as a distinct category under the label Btoken.^The n-back task also is a well-known measure of working memory, although it might be more readily associated with verbal working memory. In an example of a visual-spatial working memory version of the n-back task, Kalmady et al (2013) asked participants to identify the location of the dot that changed color immediately after it was presented (0 back) or two trials before (2 back). Considering that the direction of sex differences can vary as a function of task, specific task is a potentially important moderator of sex differences in visual-spatial working memory that was coded in the present analysis.…”

Differences in salivary testosterone, digit ratio and empathy between intellectually gifted and control boys

“…These speculations have no empirical support within gifted boys and cannot be considered plausible explanations. Although, Kalmady et al (2013) evaluated the sex-dependent interaction of digit ratio measures and cerebral lateralization and they reported that men had significantly less bilateral 2D:4D than women, and their findings support the concept of higher prenatal testosterone linked with higher laterality (Kalmady et al, 2013).…”