Functional and structural cortical specializations for human language revealed by functional magnetic resonance imaging

The ability to acquire and utilize languages is a fundamental and essential human capacity. However, apart from the relatively coarse anatomical identification of language areas, little is currently known about the cerebral structures involved in language production and comprehension. The first goal of my thesis was to identify the cortical representation during expressive language tasks (production). Bilingual subjects were imaged during language tasks performed in multiple languages to isolate brain systems specialized for speech production. The question asked was whether the spatial representation of a second language is the same as a native language. The results suggested that the representation of the two languages was separated in the dominant inferior frontal gyrus if the second language was acquired in early adulthood, whereas the representation for both languages was the same if the two languages were acquired simultaneously in infancy. Since the content of the spoken passages was equivalent in both languages, it was hypothesized that regions of the language system representing "comprehension" would be in common. This prediction was confirmed in the temporal-lobe language-sensitive regions and led to the next part of the thesis. The second goal was to characterize the cortical representation of the two aspects of comprehension, reception and expression. The results suggested that a single cortical region within the dominant superior temporal gyrus was active during both comprehension tasks. Furthermore, a functional complex composed of the common region and adjacent specialized regions selective for either comprehension of spoken sentences or meaningful speech production was discovered. Findings from these studies are consistent with distinct roles for the anterior (inferior frontal gyrus) and posterior (superior temporal gyrus) language areas with respect to language production and comprehension. Furthermore, these results advance our understanding of the complex organizations within each of the specific regions that serve language functions.