Essential role of the right superior parietal cortex in Japanese kana mirror reading - An fMRI study

Functional magnetic resonance imaging (fMRI) was used to investigate the ne ural substrates responsible for Japanese kana mirror reading. Japanese kana words, arranged vertically from top to bottom, were used in the mirror rea ding task in 10 normal right-handed Japanese adults. Since both mirror-reve rsed and normally oriented kana items are read in the same (top to bottom) direction, it was possible to minimize the oculomotor effects which often o ccur in the process of mirror reading of alphabetical language. By using th e SPM96 random effect analysis method, a significant increase in the blood oxygen level-dependent signal during mirror reading relative to normal read ing was detected in multiple brain regions, including the bilateral superio r occipital gyri, bilateral middle occipital gyri corresponding to Brodmann area (BA) 18/19, bilateral lingual gyri (BA 19), left inferior occipital g yrus (BA 18), left inferior temporal cortex (BA 37), bilateral fusiform gyr i (BA 19), right superior parietal cortex (SPC) (BA 7), left inferior front al gyrus (BA 44/45) and an inferior part of the left BA 6, In addition to t hese cortical regions, the right caudate nucleus and right cerebellum were also activated. The activation found in the right SPC and the left inferior temporal region is consistent with the hypothesis that mirror reading invo lves both the dorsal visuospatial and ventral object recognition pathways. In particular, a significant correlation was found between the fMRI signal change in the right SPC and the behavioural performance (error index) in th e task. This may reflect increased demand on the right SPC for the spatial transformation which is required for the accurate recognition of mirror-rev ersed kana items. This relationship between the haemodynamic response in a specific brain area and the behavioural data provides new evidence for the essential role of the right SPC in Japanese kana mirror reading.