PLANUM TEMPORALE ASYMMETRIES IN GREAT APES AS REVEALED BY MAGNETIC-RESONANCE-IMAGING (MRI)

THE planum temporale (PT), a portion of Wernicke's area, is important for linguistic functions in humans and is larger in the left compared to the right hemisphere. In this study, we assessed the presence and s ize of the PT in a sample of non-human primates including 21 great ape s, four lesser apes, 11 Old World monkeys and eight New World monkeys using magnetic resonance imaging. The PT was measured in both the sagi ttal and coronal planes by use of multiplanar reformatting software. T he PT could only be identified in the sample of great apes and not in the remaining non-human primate species. Within the great ape sample, the PT was larger in the left hemisphere than in the right in a statis tical majority of the subjects. These results are consistent with the notion that the PT evolved as a definable structure about 15 million y ears ago and may have arisen as a result for selection for greater cor tical folding which in turn led to greater gyrification in larger brai ns. (C) 1998 Lippncott Williams & Wilkins.