Neural processing of words in the human extrastriate visual cortex.

Measurements of neuromagnetic fields were made for the responses to visually presented words comprised of Japanese characters (phonograms), and for comparison of responses to single characters and character symbols, while subjects performed, respectively, semantic category matching, rhyming, and character matching tasks. The magnetic field responses recorded from the occipital and occipitotemporal regions consisted of 2-3 major peak components, occurring between 150 and 300 ms after the onset of the visual forms. The localization of equivalent current dipole sources of these components within the brain structure of individual subjects indicated that the main regions of the neural activity occurring at 150-250 ms were located in the extrastriate visual cortices. They included the lateral area mostly at the occipital gyrus, medial area consisting of parieto-occipital and calcarine sulci and lingual gyrus, and ventral area which is continuous from the lingual gyrus (LG) to fusiform gyrus (FG). In the ventral LG/FG area the left side was activated primarily by words, while the right side was responsive in more or less equally to words, characters, and symbols. It is suggested that the left occipitotemporal LG/FG mediates the neural function that subserves the specific visual word processing and/or general analysis of complex graphical features of visual forms.