No convincing evidence the hippocampus is associated with working memory

Abstract

In a previous discussion paper, twenty-six working memory fMRI studies that reported activity in the hippocampus were systematically analyzed. None of these studies provided convincing evidence that the hippocampus was active during the late delay phase, the only period in which working memory can be isolated from long-term memory processes. Based on these results, it was concluded that working memory does not activate the hippocampus. Six commentaries on the discussion paper were received from Courtney (2022), Kessels and Bergmann (2022), Peters and Reithler (2022), Rose and Chao (2022), Stern and Hasselmo (2022), and Wood et al. (2022). Based on these commentaries, the present response paper considered whether there is evidence of sustained hippocampal activity during the working memory delay period based on depth-electrode recording, whether there are activity-silent working memory mechanisms in the hippocampus, and whether there is hippocampal lesion evidence indicating this region is important for working memory. There was no convincing electrophysiological or neuropsychological evidence that the hippocampus is associated with working memory maintenance, and activity-silent mechanisms were arguably speculative. Given that only a small fraction (approximately 5%) of working memory fMRI studies have reported hippocampal activity and lesion evidence indicates the hippocampus is not necessary for working memory, the burden of proof is on proponents of the view that the hippocampus is important for working memory to provide compelling evidence to support their position. To date, from my perspective, there is no convincing evidence that the hippocampus is associated with working memory.