Neural and behavioral correlates of declarative memory are associated with temporal discounting in older adults

When facing intertemporal choices, or decisions involving trade-offs between smaller, sooner and larger, delayed rewards, people tend to discount the value of future rewards. There are substantial individual differences in this tendency toward temporal discounting, however. The neurocognitive mechanisms underlying these individual differences remain unclear. One possibility is that individual differences in declarative memory ability underlie individual differences in temporal discounting. Here we tested this hypothesis in older adults (both cognitively normal and with mild cognitive impairment), given that declarative memory declines with age, at rates that vary across individuals. We related temporal discounting to performance on neuropsychological measures of declarative memory, as well as to structural measures of medial temporal lobe regions that are critical for memory. Performance on episodic and semantic memory retrieval tasks was associated with temporal discounting, such that people with better declarative memory discounted delayed rewards less. This relationship held even when controlling for executive function abilities that might influence memory retrieval. Underlining the specificity of this association, performance on measures of executive function (Trail Making Test, Digit Span Backwards, lexical fluency) was unrelated to temporal discounting, and declarative memory ability was unrelated to risk preferences. Finally, cortical thickness in the entorhinal cortex was associated with reduced temporal discounting, with declarative memory ability partially mediating this association. These findings suggest that individual differences in temporal discounting are primarily driven by memory ability, and not executive function, and that a decline in medial temporal lobe structural integrity with aging may impact time preferences.nnSignificance statementDespite the large body of literature supporting the role of both declarative memory and executive function in choices between immediate and delayed rewards (intertemporal choices), no study has examined which of these neurocognitive mechanisms underlies individual differences in the tendency to discount future rewards (temporal discounting). This has been challenging given the limited variability in, and high correlation between, these abilities in young adults. Here we show that older adults with better declarative memory discount delayed rewards less, even when controlling for executive function. Moreover, cortical thickness in entorhinal cortex, a region integral to memory processes, is also associated with temporal discounting. This knowledge will aid in the development of interventions to increase patience, especially as memory declines with aging.