The hippocampus and semantic memory over time.

We previously reported impoverished semantic memory in patients with hippocampal amnesia (Klooster & Duff, 2015). Here, we test whether this disruption results from the patients not updating semantic representations since the onset of their amnesia. We extend previous work by comparing performance of hippocampal patients and their current age (CA) comparisons (M = 58.5 years) to a new comparison group matched to the patients' age of onset (AoO) of hippocampal damage (M = 36.8). Participants completed feature and senses-listing tasks and the Word Associates Test. Both comparison groups performed significantly better than the patients with amnesia. A key new finding was that the older CA group performed significantly better than the younger AoO group. Semantic memory may become richer over time as additional information is added to existing representations. We conclude that a failure to update semantic memory may explain (at least some of) the previously observed deficits in amnesia and that the hippocampus may support semantic memory across the lifespan. Longitudinal data from patients with hippocampal pathology would provide a critical test of our conclusion.