Consolidation of Reward Memory during Sleep Does Not Require Dopaminergic Activation

Abstract

Sleep enhances memories, especially if they are related to future rewards. Although dopamine has been shown to be a key determinant during reward learning, the role of dopaminergic neurotransmission for amplifying reward-related memories during sleep remains unclear. In this study, we scrutinize the idea that dopamine is needed for the preferential consolidation of rewarded information. We impaired dopaminergic neurotransmission, thereby aiming to wipe out preferential sleep-dependent consolidation of high- over low-rewarded memories during sleep. Following a double-blind, balanced, crossover design, 17 young healthy men received the dopamine d2-like receptor blocker sulpiride (800 mg) or placebo, after learning a motivated learning task. The task required participants to memorize 80 highly and 80 lowly rewarded pictures. Half of them were presented for a short (750 msec) and a long (1500 msec) duration, respectively, which permitted dissociation of the effects of reward on sleep-associated consolidation from those of mere encoding depth. Retrieval was tested after a retention interval of approximately 22 hr that included 8 hr of nocturnal sleep. As expected, at retrieval, highly rewarded memories were remembered better than lowly rewarded memories, under placebo. However, there was no evidence for an effect of reducing dopaminergic neurotransmission with sulpiride during sleep on this differential retention of rewarded information. This result indicates that dopaminergic activation likely is not required for the preferential consolidation of reward-associated memory. Rather, it appears that dopaminergic activation only tags such memories at encoding for intensified reprocessing during sleep.

Responsible remembering and forgetting as contributors to memory for important information

“…Specifically, rather than a hypothetical friend, a second participant or confederate (either trustworthy or untrustworthy) in a similar design could be responsible for remembering "friend" items to determine how offloading behavior differs in the presence of another person compared with an imaginary friend. Lastly, participants were tested immediately after encoding, but future work could institute a distractor task between study and recall to examine whether the observed effects are maintained after a delay (see Asfestani et al, 2020;Spaniol, Schain, & Bowen, 2014).…”

Does Sleep Selectively Strengthen Certain Memories Over Others Based on Emotion and Perceived Future Relevance?

“…Such an interaction between dopamine and reward was however not replicated in a study using a dopamine antagonist, with the re-test 22 hours after encoding. 4 Another study that included reward information, but additionally also emotional stimuli, 89 is discussed in the section "Studies with Multiple Cues of Future Relevance".…”

L-DOPA increases slow-wave sleep duration and selectively modulates memory persistence in older adults

“…Indeed, in similar paradigms to ours dopamine-like medication has been associated with changes in enhanced memory persistence in healthy elderly ( Grogan et al, 2015 ) in a dose-dependent fashion ( Chowdhury et al, 2012 ), supporting the inverted U-shape hypothesis. Yet, others have found no impact of a dopamine agonist on verbal memory persistence ( Feld et al, 2014 ), or a dopamine d2-like receptor blocker ( Asfestani et al, 2020 ) on overnight reward consolidation in young adults. These differences in findings may be due to different medications or due to age-related reductions in dopamine neurons ( Carlsson et al, 1980 ; Kish et al, 1992 ; MacDonald et al, 2012 ) and/or slow-wave sleep duration, spindle counts and amplitudes ( Nicolas et al, 2001 ).…”