The role of left posterior inferior temporal cortex in spelling.

OBJECTIVE: To determine whether damage to left posterior inferior temporal cortex (PITC) is associated with agraphia and to characterize the nature of the spelling impairment.

BACKGROUND: Left angular gyrus may play a critical role in spelling. However, this traditional view is challenged by reports of agraphia after left temporo-occipital lesions and by functional imaging studies demonstrating activation of left PITC during writing in normal individuals.

METHODS: Patients with focal damage to the left temporo-occipital cortex and normal control subjects were administered a comprehensive spelling battery that included regular words, irregular words, and nonwords as stimuli.

RESULTS: Although patients performed worse than control subjects in all experimental conditions, the spelling deficit was particularly severe for irregular words, whereas regular word and nonword spelling were less impaired. Additional analyses indicated that orthographic regularity and word frequency had a much more pronounced effect on spelling accuracy in patients compared with control subjects. Most errors on irregular words were phonologically plausible, consistent with reliance on a sublexical phonologic spelling strategy (i.e., phoneme-grapheme conversion). Overall, the spelling impairment of the patients showed the characteristic profile of lexical agraphia. Lesion analyses indicated that the damage in the majority of patients encompassed an area within the left PITC (BA 37/20) where the authors previously obtained evidence of activation in a functional imaging study of writing in normal participants.

CONCLUSIONS: The behavioral and neuroanatomic observations in the patients are consistent with functional imaging studies of writing in neurologically intact individuals and provide converging evidence for the role of left PITC in spelling. Together, these findings implicate left PITC as a possible neural substrate of the putative orthographic lexicon that contains stored memory representations for the written forms of familiar words.