The when and where of spatial storage in memory-guided saccades.

The memory-guided saccade paradigm is an ideal experimental model for studying spatial working memory. Both the posterior parietal cortex and frontal cortex are known to play a role in working memory; however, there is much debate about the degree of their involvement in the retention of information. We used event-related potentials and electromagnetic tomography to clarify the precise time course and location of the neural correlates of spatial working memory during a memory-guided saccade task in humans. We observed sustained activity in the inferior parietal lobe and extrastriate areas that persisted for the entire duration of the sensory- and memory-phases. This time course reveals that these regions participate in both initial sensory processing of visual cues and in the short-term maintenance of spatial location memory. Similar sustained activation was also observed in the anterior cingulate cortex, probably reflecting attentive control during the task. Differential activity between conditions was also recorded in the dorsolateral prefrontal cortex and in the frontal eye fields, but only during the initial part of the memory-phase. This finding suggests that these areas are not involved in the storage of spatial information, but rather in response selection and in transformation of spatial information into a motor coordinate framework, respectively. By exploiting techniques that provide exquisite temporal resolution and reasonably precise anatomical localization, this study provides evidence supporting the key role of inferior parietal lobe in the storage of spatial information during a working memory guided saccade.