Distinct spatial patterns of brain activity associated with memory storage and search.

The time it takes for a human participant to decide whether a given stimulus is an element of a remembered set increases approximately linearly with the number of elements in the set. Here we tested for and detected a spatial pattern of brain activity whose magnitude of expression during this memory search process correlates with set size. We then tested the idea that memory search simply involves a re-activation of neurons involved in remembering the set by statistically comparing the patterns of brain activity corresponding to memory search and set size dependent working memory maintenance. These patterns were significantly different, suggesting that memory search and working memory maintenance are mediated by distinct neural mechanisms.