No convincing evidence the hippocampus is associated with working memory

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• Previous analysis of 26 working memory fMRI studies found no convincing hippocampal activity during the critical delay phase.
• Six commentaries were received, prompting further consideration of hippocampal involvement in working memory.

Purpose of the Study:

• To evaluate existing evidence for hippocampal involvement in working memory maintenance.
• To assess electrophysiological, neuropsychological, and neuroimaging data concerning the hippocampus and working memory.

Main Methods:

• Systematic review and analysis of published functional magnetic resonance imaging (fMRI) studies.
• Consideration of depth-electrode recordings, activity-silent working memory mechanisms, and hippocampal lesion evidence.
• Critical evaluation of commentaries on a prior discussion paper.

Main Results:

• No convincing evidence of sustained hippocampal activity during the working memory delay period was found via electrophysiology or neuropsychology.
• Activity-silent working memory mechanisms in the hippocampus remain speculative.
• Only approximately 5% of working memory fMRI studies report hippocampal activity, and lesion data suggest it's not essential.

Conclusions:

• The current evidence does not convincingly associate the hippocampus with working memory maintenance.
• The burden of proof lies with those proposing a significant role for the hippocampus in working memory.
• From the author's perspective, compelling evidence for hippocampal involvement in working memory is currently lacking.