Lack of Sleep Influences Pleasure

Summary
Correct interpretation by your brain of happy experiences leads to beneficial decision-making, which ultimately impacts your survival. However, a poor interpretation may result in dangerous risk-taking (drug addiction) and emotional collapse (mood disorders). Sleep loss also makes one react irrationally to unhappy situations; although its puzzling effect is that it cheers up clinically depressed people. This study used functional magnetic resonance imaging (fMRI) showed that sleep deprivation increased reactivity in neural networks that were responsive to happy situations making experiences seem more pleasurable. A certain reward-based neural pathway that linked sleep deprivation to a fast-acting improvement of mood was noted. In a well-rested person, these neural networks were not significantly engaged at all.  This study shows that sleep deprivation makes one react strongly to negative, as well as positive stimuli.

Introduction
The brain has regions linked together to receive information, analyze it, motivate an action, and reward with a feeling. This “reward pathway” is also connected to areas controlling memory and behavior. Appropriate interpretation of beneficial experiences makes us happy, but an incorrect reading may lead to dangerous behavior, like drug abuse. The same pathway that regulates emotional responses to situations will also activate responses that may result in mood disorders. Sleep deprivation adversely affects this process, making people respond strongly to negative situations. Surprisingly, a lack of sleep briefly cheers up clinically depressed people but the effect disappears when the person has the required amount of sleep. In healthy individuals, sleep deprivation can cause misplaced cheerfulness. This study suggests that sleep deprivation changes the brain’s response to positive, as well as negative, stimuli.  This is done by increasing the reactivity of certain areas of the brain and altering connectivity to other areas.

Methods
* Twenty-seven healthy volunteers, between 18 and 30 years of age, were divided into control and experimental groups. The experimental group was deprived of sleep for an average of 31.9 hours.
* One-hundred picture slides were shown, and the participants marked each either as emotionally pleasant or neutral. They were scanned for fMRI during the task.
* The proportion of emotional responses, “neutral” and “pleasant,” were analyzed for each individual. Data from the fMRI was analyzed using standard techniques for brain activity and connectivity between different regions of the brain.
* The correlation between the behavioral and brain activity data was established.

Results
* Sleep-deprived participants found a significantly higher number of pictures pleasurable. The control group marked only about half the pictures as pleasurable. Sleep deprivation seemed to create a “positive bias.”
* Greater activity was recorded in common areas of the reward pathway (the left insula cortex and amygdala) in the sleep-deprived individuals as the pictures became more and more pleasurable.
* Connectivity of the reward pathway to the visual pathway was increased after sleep deprivation, but the connectivity with memory was lower.

Shortcomings/Next steps
Arousal was the response to the situations that combined to give either a positive or negative stimulus. This may have a separate effect on the reactivity of the brain. Future experiments are needed to try to distinguish between these effects. Individual biases, or early sensitization to certain experiences, may have affected some of the results. Additional studies of the regions of the brain that are connected to decision-making, along with the effects of sleep deprivation on those regions, are required.

Conclusions
Lack of sleep intensifies the reactivity of certain brain regions in response to pleasant experiences that involved a motivating action in response to rewarding situations. This causes a sleep-deprived individual to regard more experiences as pleasurable than he or she normally would. The bidirectional response of a sleep-deprived brain to both positive and negative situations may cause emotional instability. This can result in a lack of judgment when making decisions. A sleep-deprived brain can have a more intense reaction to a perceived happy situation. This may be the reason why sleep deprivation can act as an antidepressant. Study of sleep deprivation may be clinically useful in deciding treatments for people and also in understanding the pleasure centers in the brain.

For More Information:
Sleep Deprivation Amplifies Reactivity of Brain Reward Networks, Biasing the Appraisal of Positive Emotional Experiences
Publication Journal: The Journal of Neuroscience, March 2011
By Ninad Gujar; Seung-Schik Yoo; University of California, Berkeley, California, and the Harvard Medical School, Boston, Massachusetts

*FYI Living Lab Reports Are Summaries of the Original Research.


Tags from the story
, ,