Behavioural tagging effects emerge after a delay with or without sleep

Introduction: Learning that a particular category of images (e.g., animals) is associated with high reward not only strengthens memory for those images, but also enhances the consolidation of semantically related items encoded shortly before (Patil et al., 2017) – a phenomenon known as behavioural tagging. Considering that sleep facilitates the consolidation of high-reward memories (Sterpenich et al., 2021), we investigated whether behavioural tagging is enhanced by sleep.

Methods: In a pre-registered experiment, participants completed two in-lab sessions separated by a 12-hour delay of either overnight sleep (n=30, age: 20.57±0.58 years) or daytime wakefulness (n=29, age: 22.21±0.88 years; figure 1A). In Session 1, participants incidentally encoded images of animals and tools in two separate learning phases: a pre-conditioning phase, where neither category was associated with a reward (figure 1B), and a conditioning phase, where one category was associated with a high reward (£10) and the other with a low reward (£1; figure 1C). In Session 2, recognition memory was tested for all the images.

Results: Recognition performance for images encoded in the pre-conditioning phase was better for images from the high-reward category (F=5.96, p=.018; figure 2A), replicating the behavioural tagging effect. This effect was absent in a separate control experiment in which memory was tested immediately after learning (F=0.27, p=.61; figure 2B), suggesting that behavioural tagging depends on post-encoding consolidation processes. Inconsistent with the hypothesis that sleep enhances behavioural tagging, the benefit of reward on memory was not enhanced by sleep (vs wakefulness; F=1.02, p=.32).

Discussion: Our findings replicate the behavioural tagging effect, whereby reward retroactively enhances memory for semantically related items. This effect depended on a post-encoding consolidation process that was not sleep-specific, suggesting that salient memories can be stabilised during wakefulness.