The researchers decided to look into areas of the brain they knew were related to decision making and reward. So they took powerful pictures - using functional magnetic resonance imaging (fMRI) - to reveal activity in:
- The frontal lobe - governs decision making
- Deep-brain reward centres - involved in response to food.
The authors say their findings offer a brain-activity explanation for how problems with sleep could play a part in developing obesity or remaining overweight.
They say sleeplessness reduces the so-called higher order powers of our brain, and creates an excessive response in more primitive parts of the brain. This combination of brain activities may be leading to poor food choices.
As the authors put it: "Diminished activity in higher-order cortical evaluation regions, combined with excess subcortical limbic responsivity [results] in the selection of foods most capable of triggering weight-gain."
Brain scans and food tests after sleep
Using fMRI, the neuroscientists and psychologists scanned the brains of 23 healthy young adults the morning after different sleeping conditions.
The participants got a normal night's sleep in the lab for one session and then about a week later came back for a sleep-deprived night. Both times they were connected to sleep monitoring equipment in order to check the levels of sleep they got.
The pictures below show the brain activity observed on the morning after a lack of sleep.
- Scan 1: Sleep deprivation caused more brain activity (shown in yellow/orange) in the amygdala, an area associated with motivation to eat.
- Scan 2: Sleep deprivation also produced less activity (shown in blue) in regions of the frontal cortex and insular cortex, both associated with the evaluation and choice of food items.
Brain scan pictures courtesy of Matthew Walker and colleagues
The brain scan pictures, taken by the scientists from UC Berkeley, were generated as the participants were asked to rate pictures of 80 different foods presented to them.
The sleep-deprived people were asked: "How much do you rate this food right now?" They had to answer on a scale of one to four:
- Strongly do not want
- Somewhat do not want
- Somewhat want
- Strongly want.
To make sure the desires expressed would be genuine during what the researchers called the "food desire task trial," they told the participants they would be given a serving of each of the two food items they rated most highly. The dishes were then actually served up after the scanning had been completed.
The morning after poor sleep, the researchers were able to correlate the types of food chosen and the way the brain scans looked.
The study is published in the Nature Communications journal.
"High-calorie foods became significantly more desirable when participants were sleep-deprived," Matthew Walker told the press. The UC Berkeley professor of psychology and neuroscience added:
"This combination of altered brain activity and decision-making may help explain why people who sleep less also tend to be overweight or obese."
Prof. Matthew Walker, who was the senior author of the research, said that our power over food is "blunted by a lack of sleep."
Stephanie Greer, from the Walker's Sleep and Neuroimaging Laboratory at Berkeley, also an author in the research, added: "These results shed light on how the brain becomes impaired by sleep deprivation, leading to the selection of more unhealthy foods and, ultimately, higher rates of obesity."