Object and spatial alternation tasks with minimal delays activate the right anterior hippocampus proper in humans

Substantial evidence indicates that the hippocampus plays a critical role i n long-term declarative memory. In contrast, the role of the human hippocam pus in working memory, particularly when information needs to be maintained only for a few seconds, remains controversial. Using PET, we show robust a ctivation of the right anterior hippocampus proper during the performance o f both object and spatial alternation tasks. Hippocampal activation emerged even though subjects only had to remember a single, simple stimulus over a minimum delay of I s. No hippocampal activation occurred when the delay wa s increased to 5 s. This suggests that the role of the hippocampus in worki ng memory is not to maintain information across a delay interval. Instead, its activity reflects a more transient function during encoding and/or retr ieval. These data are among the first observations to demonstrate human hip pocampal involvement in working memory. NeuroReport 11:2203-2207 (C) 2000 L ippincott Williams & Wilkins.