Metabolic brain imaging studies.

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 In fact,  experimental neuropsychological investigation of inferred brain organization of cognitive sex differences is an inexpensive prelude to the more expensive and more reliable techniques of metabolic brain imaging.  Positron emission tomography (PET) studies comparing normal men’s and women’s brain activities during sexually “segregated” verbal or visuospatial tasks  have nicely corroborated the general finding of the psychologist precursors.   The men are always more “lateralized” on these tasks.  They use one hemisphere, the right for visuospatial, left for verbal, relatively more than the women who more typically use both hemispheres.    In fact,  metabolic brain imaging studies are revolutionizing our knowledge of sex differences in brain function.    A number of surprising results have recently emerged from this type of research.  First,  it turns out that on most cognitive tasks that have been investigated,  women develop a higher overall brain metabolism,  especially in the anterior part of the brain,  the frontal lobes.  Several studies have even found a higher metabolic base rate of the brain in women,  -even when they are not expending any mental effort at all.   No study, of over a dozen, has ever found higher brain metabolism in men than in women.  Secondly,  when one side of the brain is relatively more activated metabolically during a task,  the effect is more marked in men than women,  especially in the frontal lobe area.   Third,  these differences in brain metabolism during effort-demanding tasks are generally unrelated to actual performance levels on these tasks,   most tasks failing to produce a sex difference in actual behavioral competence.  It is still not clear whether women consent greater effort on these tasks thus explaining their higher metabolic rates.  A recent study used functional magnetic resonance imaging to study 38 right-handed subjects (19 males and 19 females) during orthographic (letter recognition), phonological (rhyme) and semantic (semantic category) tasks. During phonological tasks, brain activation in men was lateralized to the left inferior frontal gyrus regions.   In women the pattern of activation was very different, engaging more diffuse neural systems that involved both the left and right inferior frontal gyrus.

One well designed studied investigated sex differences in normal men and women on verbal and visuospatial tasks using electroencephalography.   Electroencephalography (EEG) is a technique consisting of recording electrical brain waves from surface electrodes placed on the scalp.   This  particular investigation carried out by the husband and wife team Ruben and Raquel Gur found that women had a higher baseline and task-related brain activation overall,  as in the PET studies.  However,  they found,  using this particular technique,  that it was the women who manifested more asymmetric hemispheric activation as a function of the type of task,   contradicting the PET results described above.