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Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

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Neuroscience. 2nd edition.

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Anatomical Differences between the Right and Left Hemispheres

The clear differences in language function between the left and right hemispheres have naturally inspired neurologists and neuropsychologists to find a structural correlate of this behavioral asymmetry. One hemispheric difference that has received much attention over the years was identified in the late 1960s by Norman Geschwind and his colleagues at Harvard Medical School, who found an asymmetry in the superior aspect of the temporal lobe known as the planum temporale (Figure 27.4). This area was significantly larger on the left side in about two-thirds of human subjects studied postmortem. A similar difference has been described in higher apes, but not in other primates.

Figure 27.4. Asymmetry of the right and left human temporal lobes.

Figure 27.4

Asymmetry of the right and left human temporal lobes. (A) The superior portion of the brain has been removed as indicated to reveal the dorsal surface of the temporal lobes in the right-hand diagram (which presents a dorsal view of the horizontal plane). (more...)

Because the planum temporale is near (although not congruent with) the regions of the temporal lobe that contain cortical areas essential to language, it has been widely assumed that this leftward asymmetry reflects the greater involvement of the left hemisphere in language. Nonetheless, these anatomical differences in the two hemispheres of the brain, which are recognizable at birth, have by no means been proven to be an anatomical correlate of the lateralization of language function. The fact that a detectable planum asymmetry is present in only 67% of human brains, whereas the preeminence of language in the left hemisphere is evident in 97% of the population, argues that this association should be regarded with caution. In fact, recent studies using noninvasive imaging have indicated that there is less variability in the planum temporale than originally described. The anatomical underpinning of left/right differences in hemispheric language abilities, if any, remains uncertain, as it does for the lateralized hemispheric functions described in Chapter 26.

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2001, Sinauer Associates, Inc.
Bookshelf ID: NBK10953

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