Anatomic Asymmetry in Temporal Speech Area in Developing Human Brains

Abstract

The observation of marked differences between the two cerebral hemispheres in the intellectual functions in man sparked a search for corresponding anatomic asymmetry. Numerous studies looked for left-right differences. However. no consistent anatomic differences between the left and right hemispheres were observed for gross measures of total length, weight or volume Within the last decade a revival of interest in an atomic asymmetry, particularly in certain portions of the brains, was ushered in by Geschwind and Levit sky (1968) . They examined the language areas in the temporal lobes and found that the left planum temporale (posterior portion of Heschl gyrus) was much larger than the right. This difference was confirmed by several subsequent studies (Witelson et aI. , 1973; Wada et aI. , 1975; Rubens et aI. , 1976). If the neuroanatomic asymmetry is present in aduIt s. OTIC obvious question that follows is whether it is present in the brains of human infants. And the av ailable studies(Witelson et aI. , 1973; LeMay and Cu lehras, 1972; Chi et aI. , 1977) with infants indicate that the left planum temporale is consistently larger than the right and to an extent comparable to that in adults The neuroanatomic asymmetry observed in neonates might indicate that there may be a preprogammed neural substrate for the left hemisphere to be specialized for linguistic functions , and the anatomic asymrnetry is not the result of ontogenetic environmental influences and learning This study was supported in part by the research grant of Seoul National University Hospital and China Medical Board research grant No 71-732- II •5 *junior med;';al student This study was aimed to observe the development of the temporal speech area in human fetuses , from its first appearance to its full establishment at terms.