Mysteries abound when it comes to the brain and sex hormones.
Now, the first direct glimpses of sex hormones' effects on the functioning human brain have researchers stumped. For unlike the older 2-D PET methodology used in the current study, which only yielded averaged data about brain activation of subjects as a group, the newer techniques can provide pictures of a person's unique neural signature during an experimental task. If subjects shared fewer patterns of activation in common, clues to their individualized, alternative patterns might have been washed out, because the older PET technique showed only the group averages. This task, which engages the brain's working memory and reasoning circuitry, has consistently been accompanied by increased activation of the prefrontal cortex and related areas in several previous brain imaging studies. Yet, absent the hormones, this circuitry appeared almost dormant in the current study.