Planum Temporale Cerebral Asymmetry
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The planum temporale (PT) is the tissue that lies posterior to Heschl's gyrus and encompasses Werncike's area. It was one of the first systematic cerebral asymmetries described in humans by Geschwind in 1965. Since that time, the leftward asymmetry in the PT has been replicated in many studies including in post-mortem specimens and in vivo.
There is really no difference in PT asymmetry between humans and great apes. Studies by Gannon and colleagues in post-mortem specimens and from in vivo scans by Cantalupo and Hopkins have shown that the leftward PT asymmetry is present in all great apes though no systematic study has been done between ape species. More recently, Hopkins and Nir (2010) reported significant leftward asymmetries in the PT region for grey matter volumes and the magnitude of asymmetry was comparable to reports in human subjects. For both chimpanzees and humans, approimately 70% of the sample showed a significant leftward asymmetry. In fossils, the PT cannot be quantified directly but indirectly, some have measured the length of the sylvian fissure and it is longer in the left compared to right hemisphere. Direct measures of sylvian fissure length have also been done in apes and they also show a leftward asymmetry.
Indirect measures of the planum temporale PT have been attempted in many other species by measuring the length of the sylvian fissure. The data are inconsistent and appear to be influenced by methodological differences.
Planum temporale surface area and grey matter asymmetries in chimpanzees (Pan troglodytes): the effect of handedness and comparison with findings in humans., , Behav Brain Res, 04/2010, Volume 208, Issue 2, p.436-43, (2010)
Wernicke's area homologue in chimpanzees (Pan troglodytes) and its relation to the appearance of modern human language, , Proceedings of the Royal Society of London B: Biological Sciences, 06/2010, Volume 277, Issue 1691, p.2165 - 2174, (2010)