Cortical thickness in perirhinal area BA35 predicts adaptive episodic memory-guided decision making in older adults

To make adaptive decisions, it is often necessary to retrieve episodic memories, for example, about whether an item was previously associated with reward. Compared to young adults, older adults are impaired at making adaptive episodic memory-based choices. There are substantial individual differences across older adults, however. In this study, we examined whether hippocampal volume or extrahippocampal cortical thickness in the medial temporal lobe (MTL) is associated with better episodic memory-based decision making in cognitively unimpaired older adults.

Older adults (n = 87; aged 61-88) completed a decision making task and a T1-weighted anatomical MRI scan. In the task, they studied images of houses paired with arbitrary reward values ($5 or $0). Later, they made incentivized approach/avoid decisions about these items. Finally, their memory for the items and their values was assessed. MTL structural data were segmented with the ASHS-T1 pipeline to obtain volume measures for anterior and posterior hippocampus, and cortical thickness measures in entorhinal cortex, parahippocampal cortex, and perirhinal cortex Brodmann areas (BAs) 35 and 36.

BA35 cortical thickness was associated with better performance in the decision making task. This effect persisted after adjusting for memory performance, suggesting that BA35 thickness is specifically linked to the retrieval and use of episodic memories at the time of choice.

Although this study is cross-sectional, it suggests that atrophy in BA35 may contribute to subtle changes in the ability to use memory to make reward-maximizing choices, even in individuals who do not yet show evident cognitive impairment.