Planum Temporale Cortical Asymmetry

The cortical minicolumns of the cortex of the planum temporale are uniquely asymmetric in humans. It has been reported that the cortex of the planum temporale in humans, which is often identified with Wernicke’s area, has greater spacing between minicolumns and more overall neuropil volume in the left hemisphere, whereas there is no such asymmetry in chimpanzees or macaque monkeys (Buxhoeveden et al., 2001). Studies from other regions of the human cortex, however, suggest that leftward dominance of neuropil space may be a more general feature of humans that is not restricted to language-related cortical regions (Seldon et al., 1981; Amunts et al., 1999, 2007). Neuropil asymmetries have not been shown to exist in chimpanzees and other great apes for BA44 and BA45 (Schenker et al., 2008) or primary motor cortex (Sherwood et al., 2007). Thus, the leftward asymmetry of minicolumn spacing and overall neuropil volume may characterize the cortex of the planum temporale (area Tpt) in humans, but because it is an architectural trait that is also found in many other areas, it is not likely to be a direct specialization for language function.