What's New in Neurofeedback

• FDA Approves Brain Stem Cell Transplant
• Your Brain Remembers What You Forget
• Memory loss link to early stress
• Study Suggests Fish Is Good for Brain
• Brain Dysfunction May Link Suicide, Epilepsy
• Some Minds Appear Wired to Lie
• Science chips away at ALD

  All links at: news.yahoo.com/fc/Science/Brain_Research

Beyond nominal differences biological predispositions for each sex do exist. Genetically, one's physical sex is determined by chromosomes, gender less so. Our species' chromosomes code for various forms of sexually dimorphism, the most obvious being physical size. Human males generally outweigh females, 170 lb to 135 lbs. (But we often forget how much larger girls were than boys prior to puberty.) Chromosomes also code for slightly larger male brains, 1350 g to 1190 g (Klekamp et al 1989, Zilles, 1972; Wessely, 1970; & Witelson, 1985), to control the additional body mass. The size of the corpus callosum, a major axonal bundles between left and right cortices, reveals sex differences but more importantly handedness differences. So often gender differences are conflated with handedness and hormonal differences. As it turns out, right-handed individuals exhibit less callosal area than non-right-handers, regardless of gender, 20 % less in males, 7 % less in females. Bermudez & Zatorre (2001) reported relatively a larger splenium (posterior section) in females compared to males; this part of the corpus callosum is most involved in perceptual processes and may explain perceptual processing differences (below).

In terms of relative brain area sizes, women have larger language areas (Harasty et al, 1997), lateral frontal areas (Schlaepfer et al, 1995) and more densely packed neurons in temporal (Witelson et al 1995) and prefrontal areas (Witleson et al., 2001). Men show larger medial frontal areas (Goldstein et al, 2001), larger cingulate (Paus et al 1996), amygdala and hypothalamus (Swaab et al, 1985), more white matter volume (Gur et al, 1999), and more neurons overall (Pakkenberg & Gunderson, 1997). Anatomy can only take one so far. To find out how each gender tends to utilize their 3-lb universe differently, how each gender builds up a different mental and behavior repertoire, we need to examine behavior.

In the current century most of us will see four times as many days than our prehistoric ancestors, and women will see more than men (below). Here are median age lifespans by era:

Prehistoric Times     18
Ancient Greece	      20
Middle Ages, England  33
1620, Massachusetts   35
1850, England         41
1900, USA             47
1915, USA             54
1954, USA             70
1992, USA             75

Millions at 65 years of age or older
        1900  1940  1980  2040	
Male      4     5    10    30	
Female    5     6    18    36	

In terms of performance, men throw and catch better (Hall & Kimura, 1995), women are better at fine motor skills (Nicholson & Kimura, 1996). Men surpass women in mental rotation (Collins & Kimura, 1997), navigation (Astur et al, 2002), and geographical knowledge (Beatty & Troster, 1987), which is why we hate to ask directions, but females excel at spatial memory (McBurney et al, 1997), so they can remember the directions better once asked. Girls have an early advantage over boys in math and continue to show excellence at computation (Hyde et al, 1990) whereas men excel at mathematical reasoning (Benbow, 1988). Women excel at sensory sensitivity (Velle, 1987), perceptual speed (Majeres, 1983), facial and body expression (Hall 1984), as well as visual recognition memory (McGivern et al, 1998) and women are better at associational aspects of verbal ability such as fluency tasks (Hines, 1991) and rote word list learning (Kramer et al., 1988), although inherently organized verbal information (e.g., stories) show no consistent sex differences (Baxter & Seidenberg, 1997). Finally, men excel at aggression (any newspaper). Viva la difference.

Females may or may not have greater bihemispheric representation of language than males: aphasia is nearly 4 times as common in males after left hemisphere damage (48% in males vs. 13% in females) but no sex differences occur with right brain damage (2% males, 1% females). Brain organization differences may be more intrahemispheric than interhemispheric as aphasia occurs commonly in women with left hemisphere anterior damage (80 % of cases) but no lesion location association is seen for male aphasics. Similarly, apraxia, or difficulty in selecting hand movements, is associated with left frontal damage in women and with left posterior damage in men. In terms of functional neuroimaging differences, men typically show greater cerebral asymmetries (EEG, Corsi-Cabrera et al, 1997; MEG ,Reite et al, 1995, fMRI, Rossell et al., 2002). During language tasks men activate left inferior frontal and fusiform gyri while women showed a symmetrical pattern, with greater right-frontal and right-middle-temporal activity (Rossell et al., 2002).

Overall, sex differences exist, and cultural influences often magnify these differences and underestimate commonalities. Possible mechanisms responsible for these differences include