We’re all maybe a little bit surly the day after a sleepless night, but a new study suggests selfishness can be directly related to how well rested we are. The robust research offered evidence, from both an individual and a societal level, to demonstrate sleep loss can correspond with how generous we are to one another.
"Over the past 20 years, we have discovered a very intimate link between our sleep health and our mental health,” explained Matthew Walker, co-author on the new study and director of the Center for Human Sleep Science at UC Berkeley. “Indeed, we've not been able to discover a single major psychiatric condition in which sleep is normal.”
In 2018 Walker and colleagues published a fascinating study revealing poor sleep can make people withdraw from social interactions. Even more compelling, the study found this sense of sleep-induced loneliness can be transmitted like a social contagion, influencing anti-social feelings in others.
The findings led Walker and his team to wonder how deeply sleep loss can influence social behaviors. In particular, the researchers set out to investigate whether sleep loss makes people less inclined to help out others. Essentially, are we more selfish when we are tired?
To explore this question, the researchers conducted three novel experiments. First, they enrolled 24 healthy subjects for a two-night sleep lab study.
One night the volunteers were allowed to sleep normally, and the other night they were forced to stay awake. The day after each intervention the volunteers completed a questionnaire designed to evaluate empathy and altruism, and an MRI measuring brain activity in regions linked to social cognition was performed.
This first experiment showed a distinct correlation between sleep loss, impaired empathy with others, and decreased brain activity in specific neural networks known to be associated with social-emotional functioning.
"When we think about other people, this network engages and allows us to comprehend what other person's needs are: What are they thinking about? Are they in pain? Do they need help?" said study co-author Eti Ben Simon. "However, this network was markedly impaired when individuals were sleep deprived. It's as though these parts of the brain fail to respond when we are trying to interact with other people after not getting enough sleep."
The second part of the research set out to explore how sleep conditions in the real-world can influence a person’s desire to help others. More than 100 people were recruited for a four-day project. Instead of artificially having their sleep disrupted, this cohort was simply tasked with monitoring their sleep patterns and quality each night, and then asked to complete a questionnaire the next day measuring their altruistic desires.
The researchers saw a distinct correlation between sleep efficiency and a person's desire to help others the following day. The link was not present when tracking overall sleep quantity, but instead it was specifically related to the quality of a person’s sleep.
So if you spend eight hours in bed but only actually sleep for six of those hours you may be more selfish the next day than if you only had six hours in bed but slept the whole time. In this case what matters is quality, not quantity.
The final part of the study, and perhaps the most compelling, was an investigation into the potential societal implications of this kind of sleep/selfishness relationship. The researchers looked at a database of several million donations to charity across a five-year period.
The hypothesis was that if people were generally more selfish after poor sleep then overall donations to charities should decline during periods such as the annual shift to daylight-savings time in spring, a stretch known to disrupt many people’s sleep patterns.
Here, the researchers saw a 10% drop in charitable donations across the week following the switch to daylight-savings time, compared to the week prior and the general averages. This significant change was not seen in parts of the United States that don’t observe daylight-savings.
Importantly, the researchers suggest this broader societal finding relating to charitable donations indicates the sense of selfishness brought on by sleep disruption is not reliant on social contact.
“Findings from Study 3 additionally establish that the withdrawal of helping associated with sleep loss does not depend on direct personal interaction with those in need of help, since such donation gifts of money were absent of interpersonal or in-person contact,” the researchers explained in the study. “Instead, data from Study 3 suggests a broader and more intrinsically determined phenotype of impaired socioemotional functioning, one that is not reliant on actual social interaction.”
A recent study from the National Sleep Foundation revealed more than half of all Americans feel they do not regularly sleep well and are excessively tired for several days each week. And in light of these novel findings, Walker said there are societal implications to be faced when the majority of people in a given community may be acting more selfishly due to sleeplessness.
"The realization that the quantity and quality of sleep affects an entire society, caused by an impairment in prosocial behavior, may provide insights into our societal state of affairs in the present day," Walker said. “Sleep, it turns out, is an incredible lubricant to prosocial, connected, empathic, kind and generous human behavior. In these divisive times, if there was ever a need for a strong, prosocial lubricant to enable the very best version of ourselves within society, now seems to be it.”
The new study was published in PLOS Biology.
Source: UC Berkeley