Right parietal contributions to verbal working memory: spatial or executive?

The left inferior parietal cortex has been claimed to be the site of the verbal short-term store, yet imaging studies report activity of a homologous right-hemisphere region in verbal working memory tasks as well. In spite of its prevalent activity, right parietal contributions to verbal working memory are poorly understood. To clarify its role in verbal working memory performance, we tested a patient with a lesion in the right parietal lobe on verbal and spatial versions of the N-back task. The patient was impaired in all the spatial conditions regardless of load (0-, 1-, and 2-back), whereas in the verbal N-back he was impaired only in the conditions with a memory demand (1- and 2-back). Given that we had presented stimuli at multiple locations in the verbal N-back, however, it remained possible that the lesion impaired spatial representation rather than verbal working memory per se. With central stimulus presentation, his performance dramatically improved indicating that his difficulty with the N-back task was largely due to his poor visuospatial abilities.