Rapid retinotopic reactivation during spatial memory.

Memories are thought to be constructed from features processed in different cortical regions. However, it is unknown how the retrieval process unfolds over time. The present investigation aimed to address this issue by combining evidence from event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI). During study, abstract shapes were presented to the left or right of fixation and participants were instructed to remember each shape and its spatial location. At test, studied (old) and new shapes were presented at fixation and participants classified each shape as old and on the "left", old and on the "right", or "new". Accurate memory for items previously presented on the left or right produced fMRI activity in the right or left extrastriate cortex (BA18), respectively. ERP results revealed these retinotopic memory effects occurred within 100-250 ms after stimulus onset indicating memory construction can occur very rapidly.