Neural substrates for verbal working memory in deaf signers: fMRI study and lesion case report.

The nature of the representations maintained in verbal working memory is a topic of debate. Some authors argue for a modality-dependent code, tied to particular sensory or motor systems. Others argue for a modality-neutral code. Sign language affords a unique perspective because it factors out the effects of modality. In an fMRI experiment, deaf participants viewed and covertly rehearsed strings of non-sense signs; analyses focused on regions responsive in both sensory and rehearsal phases. Compared with previous findings in hearing subjects, deaf subjects showed a significantly increased involvement of parietal regions. A lesion case study indicates that this network is left-dominant. The findings support the hypothesis that linguistic working memory is supported by modality-specific neural systems, but some modality-neutral systems may also be involved.