Specific Reading and Phonological Processing Deficits are Associated with Damage to the Left Frontal Operculum

Functional neuroimaging studies in normal subjects indicate that a region in the left frontal operculum (FO) is more active when subjects read pronounceable nonwords as compared to most word types. Here, we report convergent evidence on this finding using the lesion method. We tested the prediction that subjects with left FO damage would have impaired reading of pronounceable nonwords, but relatively intact reading of most word types. Eleven target subjects with circumscribed left FO lesions, and two comparison groups of either brain-damaged or normal subjects matched to the target subjects for age, sex, handedness, and education, were studied using reading tasks derived from previous neuroimaging work. As predicted, the FO group was significantly less accurate than the comparison groups at reading nonwords. By contrast, the FO subjects showed relatively intact word reading, a pattern consistent with the syndrome of “phonological dyslexia”. The FO subjects, however, did exhibit particular difficulty reading low frequency words with inconsistent grapheme-to-phoneme correspondences (e.g., PINT), which parallels the finding from functional imaging studies that reading such items produces more activation in left FO than reading high frequency words and low frequency words with consistent grapheme-to-phoneme correspondences (e.g., JADE) (Fiez et al., 1999). In several follow-up experiments, we found that the FO subjects were also impaired on other phonological tasks that have been associated with left frontal opercular activation in functional neuroimaging studies. The findings converge nicely with extant functional imaging work, and provide further evidence that regions within the left FO are part of a system that makes specific and critical contributions to some of the phonological processes that support reading.