Unterschiede im Gehirn von Männern und Frauen: Struktur

Die Gehirne von Männern und Frauen variieren, wie in dem Beitrag „Unterschiede im Gehirn von Mann und Frau“ kurz angerissen, auch in der Struktur, insbesondere in der Verteilung von weißer und grauer Masse.

Aus dem Abstract einer Studie (via Pelle Billing):

We examined the relationship between structural brain variation and general intelligence using voxel-based morphometric analysis of MRI data in men and women with equivalent IQ scores. Compared to men, women show more white matter and fewer gray matter areas related to intelligence. In men IQ/gray matter correlations are strongest in frontal and parietal lobes (BA 8, 9, 39, 40), whereas the strongest correlations in women are in the frontal lobe (BA10) along with Broca’s area. Men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance.

Quelle: The neuroanatomy of general intelligence: sex matters (Volltext, PDF)

Aus der Studie :

Here, we have systematically sought to explore sex differences in the structural brain organization underlying general intelligence. Of the major areas identified in our earlier analysis combining men and women, the sex-specific analyses show that some of the previous significant areas are found more in men and others are found more in the women; the relative roles of GM and WM also differ between the men and women. These present results highlight an important dissociation of brain morphology related to intellectual functioning in normal adult brains, as the pattern of voxel types and voxel locations linked with intellectual functioning differed substantially between the sexes. With respect to voxel types, men had roughly 6.5 times the number of GM voxels identified as related to intellectual functioning as did women, and women had roughly nine times more WM voxels than did men. With respect to regional effects, in women, 84% of the identified GM voxels correlated to IQ were in the frontal region, as compared to 45% in men. Even greater sex differences were observed in WM, where for women 86% of the identified voxels were frontal, as compared to 0% in men. More left hemisphere voxels (GM plus WM) were identified in both men and women (64.6% and 65.3%, respectively), consistent with previous reports of left lateralization of both anatomic and higher brain functions (Geschwind, 1972). It is well established that men have a larger cerebrum than women by about 8–10% (Filipek et al., 1994; Nopoulos et al., 2000; Passe et al., 1997a,b; Rabinowicz et al., 1999; Witelson et al., 1995). Thus, for the current study, we created separate templates for males and females to facilitate comparisons between the sexes, as opposed to bstretchingQ one gender’s brain to fit the size of another. Many studies have now confirmed a consistent sex difference in human brains: the GM/WM ratio is slightly higher in women than men (Allen et al., 2003; Goldstein et al., 2001; Gur et al., 1999; Passe et al., 1997a,b; Peters et al., 1998; Schlaepfer et al., 1995). In our sample, using the voxel classifications obtained with VBM, women showed a slightly higher GM/WM matter ratio (1.47) than did men (1.41), consistent with these previous reports. More specific regional analyses of GM volume differences (Goldstein et al., 2001) have shown that women have greater GM volume than men in regions including the precentral gyrus (BA 6, 4), fronto-orbital cortex (BA 47), superior frontal (BA 6, 8, 9), and lingual gyri (BA 17, 18), while men had larger volumes in frontomedial cortex (BA 11, 12), hypothalamus, amygdala, and angular gyrus (BA 39).

Das Ganze noch mal als Bild:

Die Autoren drücken sich wissenschaftlich-vorsichtig aus, verweisen aber auch auf die hohe Vererbbarkeit von Unterschieden bei der Verteilung von grauer und weißer Masse:

Although GM and WM volumes are highly hereditable in many areas (Posthuma et al., 2002; Thompson et al., 2001), there is evidence that GM volume in humans can increase with motor learning (Draganski et al., 2004) or the acquisition of a second language (Mechelli et al., 2004) and the nature of genetic determinism in general is now controversial (Silverman, 2004).

Die verschiedenen Funktionen der weißen und der grauen Substanz:

Aus dem Wikipediaartikel zur weißen Substanz:

White matter is the tissue through which messages pass between different areas of gray matter within the nervous system. Using a computer network as an analogy, the gray matter can be thought of as the actual computers themselves, whereas the white matter represents the network cables connecting the computers together.

Also noch mal die Zusammenfassung:

Von den Zellen, die den eigentlichen Computer darstellen, haben Männer 6 mal mehr, von den Zellen, die Verbindungen zwischen den einzelnen Teilen darstellen, haben Frauen 9 mal mehr.

Die Forscher betonen selbst, dass die generelle Intelligenz dennoch gleich ist. Und die Unterschiede zeigen sich auch in anderen Gehirnbereichen.

Die Unterschiede sind also gewaltig. Eine vollkommen andere Struktur spricht zudem dafür, dass diese evolutionär bedingt ist. Was aufgrund der Arbeitsteilung, die betrieben wurde, ja auch sinnvoll ist. Die Differenzierung von Männern und Frauen ermöglicht eben gerade eine Optimierung, die bestimmte Arbeiten effektiver macht und dadurch wiederum die Arbeitsteilung noch weiter verschärft. Wohl der Grund, warum man Arbeitsteilung zwischen Mann und Frau überall auf der Welt und mit gleicher Verteilung findet.

Dass Gehirne, die eine so deutlich andere Struktur haben, dennoch nicht zu verschiedenen Ausprägungen von Fähigkeiten führen (unabhängig von der Frage, ob die Struktur gesellschaftlich oder biologisch bedingt ist) wäre meiner Meinung nach sehr sehr unwahrscheinlich.

Männer und Frauen sind eben nicht gleich.