Greater dependence on working memory and restricted familiarity in orangutans compared with rhesus monkeys

• Type of Material: Article
• Authors: Ryan J Brady, Emory University; Jennifer M Mickelberg, Zoo Atlanta; Robert Hampton, Emory University
• Language: English
• Date: 2021-09-01
• Publisher: Emory University Libraries
• Publication Version: Final Published Version
• Copyright Statement: © 2021 Brady et al.; Published by Cold Spring Harbor Laboratory Press
• License: Creative Commons Attribution-NonCommercial 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1101/LM.053422.121
• Title of Journal or Parent Work: Learning and Memory
• Volume: 28
• Issue: 8
• Start Page: 260
• End Page: 269
• Grant/Funding Information: This work was supported by National Science Foundation grants BCS-1632477 and BCS-1946767, and by Office of Research Infrastructure Program/OD P51OD011132.
• Keywords: Animals; Prefrontal Cortex; Macaca mulatta; Recognition, Psychology; Memory, Short-Term; Pongo
• Research Categories: Biology, Zoology

Abstract

The prefrontal cortex is larger than would be predicted by body size or visual cortex volume in great apes compared with monkeys. Because prefrontal cortex is critical for working memory, we hypothesized that recognition memory tests would engage working memory in orangutans more robustly than in rhesus monkeys. In contrast to working memory, the familiarity response that results from repetition of an image is less cognitively taxing and has been associated with nonfrontal brain regions. Across three experiments, we observed a striking species difference in the control of behavior by these two types of memory. First, we found that recognition memory performance in orangutans was controlled by working memory under conditions in which this memory system plays little role in rhesus monkeys. Second, we found that unlike the case in monkeys, familiarity was not involved in recognition memory performance in orangutans, shown by differences with monkeys across three different measures. Memory in orangutans was not improved by use of novel images, was always impaired by a concurrent cognitive load, and orangutans did not accurately identify images seen minutes ago. These results are surprising and puzzling, but do support the view that prefrontal expansion in great apes favored working memory. At least in orangutans, increased dependence on working memory may come at a cost in terms of the availability of familiarity.