The research, published in Nature Communications, used functional magnetic resonance imaging (fMRI) to scan the brains of 23 healthy young adults, first after a normal night's sleep and then after a sleepless night.
Led by researchers from the University of California, Berkeley, the scientists behind the study found that sleep deprivation impaired functioning in the brain’s frontal lobe – which governs complex decision making – but increased deeper brain reward centres.
These alterations in brain functioning were accompanied by changes in food preference, said the team.
"What we have discovered is that high-level brain regions required for complex judgments and decisions become blunted by a lack of sleep, while more primal brain structures that control motivation and desire are amplified," said Professor Matthew Walker, senior author – who noted that this combination made high-calorie foods ‘more desirable’.
While several previous studies have linked poor sleep to greater appetites, particularly for sweet and salty foods, the new findings provide a specific brain mechanism explaining why food choices change for the worse following a sleepless night, said Walker.
“This combination of altered brain activity and decision-making may help explain why people who sleep less also tend to be overweight or obese,” he suggested.
In the new study, researchers measured brain activity as the 23 participants viewed a series of 80 food images that ranged from high-to low-calorie and healthy and unhealthy, and rated their desire for each of the items.
As an incentive, they were given the food they most craved after the fMRI scan.
Food choices presented in the experiment ranged from fruits and vegetables, such as strawberries, apples and carrots, to high-calorie burgers, pizza and doughnuts.
Br tracking brain activity in reaction to the food stimuli, Walker and his colleagues were able to map out alterations in brain functioning that may be linked to food choices and sleep deprevation.
Their analysis revealed impaired activity in the sleep-deprived brain's frontal lobe, which governs complex decision-making, but increased activity in deeper brain centres that respond to rewards.
“Sleep deprivation significantly decreases activity in appetitive evaluation regions within the human frontal cortex and insular cortex during food desirability choices, combined with a converse amplification of activity within the amygdala [reward region],” explained the researchers.
The team said that the reduced activity in frontal areas, coupled with increased reward processes in the amygdala are associated with a significant increase in the desire for weight-gain promoting high-calorie foods following sleep deprivation – adding that the extent to which brain activity alters, and high-calorie food desire increases can be predicted by the subjective severity of sleep loss.
On a positive note, Walker added that the findings indicate that "getting enough sleep is one factor that can help promote weight control by priming the brain mechanisms governing appropriate food choices."