Gender Differences in Cerebral Blood Flow as a Function of Cognitive State with PET

This study explored the role of cognitive states in gender-based differences in brain function. Methods: We used the ¹⁵O-water bolus method to measure cerebral blood flow (CBF) in 14 young normal volunteers with PET. Each subject was scanned six times, three during different neuropsychological tasks linked to the prefrontal cortex and three others during customized sensorimotor control tasks. The prefrontal tasks were the Wisconsin Card Sorting (WCS) Test, Delayed Alternation task (DA) and Spatial Delayed Response task (DR). Results: A significant main influence of sex on global CBF (ml/min/100g) was seen, with higher values in women, as viewed across all six conditions (means: 60.9 versus 53.2, ANOVA F = 9.35, p < 0.01). Post-hoc contrasts, however, showed that this finding was not uniform in all conditions. Differences between men and women were seen during performance of the frontal lobe tasks, but not during the sensorimotor control tasks. Even within the three frontal lobe tasks, results tended to vary: the differences between the sexes were most significant during the DA and just reached traditional levels of significance during the WCS. Therefore, if we had utilized a single task condition to determine whether men and women have different global CBFs, disparate conclusions would have been reached depending upon the task chosen. Conclusion: Although clear sex differences in global CBF can be demonstrated, the cognitive state of the subjects must be controlled and considered when interpreting the differences. Also, variations in the cognitive state might explain some of the discrepancies in gender studies in the rCBF and cerebral glucose metabolism literature.