Neural correlates of phoneme-to-grapheme conversion.

In writing to dictation, one mode of language processing is based on the knowledge of how to convert speech sounds to the corresponding letters, namely, phoneme-to-grapheme conversion (phonological mode). Little is known about the neural substrates of the phoneme-to-grapheme conversion. Our study aims to clarify the neural substrates of phoneme-to-grapheme conversion in writing to dictation using functional magnetic resonance imaging. We employed Japanese as the stimulus language because in Japanese, one phoneme is represented by one grapheme (kana) and vice versa. Functional magnetic resonance imaging revealed that the left premotor, extending into Broca's area was activated. The present results suggested that the frontal region is required for the conversion of phonemes to graphemes in writing to dictation.