In previous studies, it was discovered that rewarding participants during a visual perceptual task can lead to improved performance. In this new research, however, it is suggested that these performance gains will only occur if the participants will follow up on the task with sleep.
According to Yuka Sasaki, a professor of cognitive, linguistic, and psychological sciences at Brown University and a corresponding author to the study, these new findings may have a particular implication towards students who sleep in late (sometimes never sleep at all) in favor of studying or cramming. She said that since college students work hard, they sometimes shorten their sleep. However, sleep is crucial in order for them to retain what they have learned in the classroom.
The study which was published in the Proceedings of the National Academy of Sciences describes how the scientists conducted the experiment. The researchers asked young adults to identify a letter and the orientation of a set of lines on a busy background. One group was even asked to not eat hours before the task and were given a few drops of water for every correct answer. Meanwhile, another group was not given any reward at all. When comparing results, the researchers discovered that the rewarded participants were able to exhibit significant performance gains but only after they slept. Through this study, it is proven that rewards do not necessarily improve visual perceptual learning until they get much-needed sleep.
According to the researchers, rewards -- or the anticipation of it -- reinforces the circuits between the reward and visual areas of the brain. These circuits are likely to be reactivated during sleep to facilitate task learning. During the post-training sleep of the rewarded participants, the electroencephalogram (EEG) recordings were able to detect an increased activation in the prefrontal lobe (also known as the reward-processing area of the brain) and a decreased activation in the untrained visual areas.
Previous studies were able to explain these patterns of activation. What happens is that the reward-processing area of the brain sends signals to inhibit some of the neurons in the visual processing area of the brain resulting in preserving the most efficient connections and the irrelevant connections are trimmed, hence, improving the task performance of a participant. Sasaki and her team also examined when exactly do these patterns of activation occur especially since untrained visual areas of the brain would exhibit reduced activation during REM and non-REM sleep. However, the reward processing areas are active when an individual reaches their REM sleep.
Researchers explain that REM sleep is important for task learning and this is likely because the connections are reorganized and optimized during this stage and it may be linked to the reward processing area of the brain. In line with this, the study participants who were rewarded exhibited long periods of REM sleep compared to those who did not receive any reward. Sasaki added that physical-based rewards such as food or water may have a stronger impact compared to other rewards like money. She says water deprivations could be fundamental. "When you're really thirsty and you were rewarded with water, the impact of that may be more prevailing to the brain." She said.
With these results, Sasaki and her team hope to encourage collaborations between sleep researchers and scientists in studying reinforcement
