Cortical activity related to accuracy of letter recognition

Previous imaging and neurophysiological studies have suggested that the posterior inferior temporal region participates in tasks requiring the recognition of objects, including faces, words, and letters; however, the relationship between accuracy of recognition and activity in that region has not been systematically investigated. In this study, positron emission tomography was used to estimate glucose metabolism in 60 normal adults performing a computer-generated letter-recognition task. Both a region of interest and a voxel-based method of analysis, with subject state and trait variables statistically controlled, found task accuracy to be: (1) negatively related to metabolism in the left ventrolateral inferior temporal occipital cortex (Brodmann's area 37, or ventrolateral BA 37) and (2) positively related to metabolism in a region of the right ventrolateral frontal cortex (Brodmann's areas 47 and 11, or right BA 47/11). Left ventrolateral BA 37 was significantly related both to hits and to false alarms, whereas the right BA 47/11 finding was related only to false alarms. The results were taken as supporting an automaticity mechanism for left ventrolateral BA 37, whereby task accuracy was associated with automatic letter recognition and in turn to reduced metabolism in this extrastriate area. The right BA 47/11 finding was interpreted as reflecting a separate component of task accuracy, associated with selectivity of attention broadly and with inhibition of erroneous responding in particular. The findings are interpreted as supporting the need for control of variance due to subject and task variables, not only in correlational but also in subtraction designs.