Cortical activity related to accuracy of letter recognition

Previous imaging and neurophysiological studies have suggested that the pos terior inferior temporal region participates in tasks requiring the recogni tion of objects, including faces, words, and letters; however, the relation ship between accuracy of recognition and activity in that region has not be en systematically investigated. In this study, positron emission tomography was used to estimate glucose metabolism in 60 normal adults performing a c omputer-generated letter-recognition task. Both a region of interest and a voxel-based method of analysis, with subject state and trait variables stat istically controlled, found task accuracy to be: (1) negatively related to metabolism in the left ventrolateral inferior temporal occipital cortex (Br odmann's area 37, or ventrolateral BA 37) and (2) positively related to met abolism in a region of the right ventrolateral frontal cortex (Brodmann's a reas 47 and 11, or right BA 47/11). Left ventrolateral BA 37 was significan tly related both to hits and to false alarms, whereas the right BA 47/11 fi nding was related only to false alarms. The results were taken as supportin g an automaticity mechanism for left ventrolateral BA 37, whereby task accu racy was associated with automatic letter recognition and in turn to reduce d metabolism in this extrastriate area. The right BA47/11 finding was inter preted as reflecting a separate component of task accuracy, associated with selectivity of attention broadly and with inhibition of erroneous respondi ng in particular. The findings are interpreted as supporting the need for c ontrol of variance due to subject and task variables, not only in correlati onal but also in subtraction designs. (C) 2000 Academic Press.