The hectic pace of modern life means that people are often eating at odd times of the day and night, and these shifted schedules could be taking a toll on memory, new research suggests.
A study in mice found that eating during times of day when one would normally be sleeping impaired the animals' memory for objects they had seen, even when the rats got the same amount of sleep as mice on a normal eating and sleeping schedule.
Humans, like many animals, have internal clocks aligned to the daily cycles of light and dark, called circadian rhythms. Yet in today's society, these rhythms are becoming more and more disrupted, study co-author Christopher Colwell, of the University of California, Los Angeles, told reporters last week at the 44th annual meeting of the Society for Neuroscience in Washington, D.C. [ Top 10 Spooky Sleep Disorders ]
"Since so many of us are showing disruption in our sleep-wake cycle, we're wondering if we could use the timing of food as a countermeasure," Colwell said.
Studies have shown that eating meals during the body's natural sleep phase may be bad for an animal's health, but could it also affect cognition?
To find out, Colwell and a team of researchers acclimatized mice to a normal sleep schedule, sleeping during the day. (Mice are nocturnal, so they are normally awake at night and asleep during the day.) Then, the researchers allowed some of the animals to eat only during the time they were typically asleep, while allowing others to eat when the animals would normally be awake.
"Mice, just like people, will quickly learn to get up and eat during their normal sleep time," Colwell said.
The mice on the misaligned eating schedule had shifted sleep times, but they still slept for the same total amount of time, ate the same amount of food and weighed the same as the mice that ate at normal times, Colwell said.
Next, the researchers tested the mice's memory. In one experiment, they put the mice in a box with two different objects, and allowed them to explore. Then, after putting the animals on different feeding schedules, the researchers placed them in the box with one of the familiar objects and one new object, and measured how long the mice spent exploring each one.
Compared with the mice on the aligned eating schedule, the misaligned mice showed a significant decline in memory. The animals on the altered feeding and sleep schedule spent more time exploring the familiar object, suggesting they didn't remember encountering the object before.
In a second experiment, the researchers conditioned both groups of mice to feel fear in a certain location, and later put them back in that location to see if they showed fear (which the animals typically show by freezing in place).
As predicted, the mice on the shifted eating schedule froze less often in the fearful situation than their normal-schedule peers, suggesting the odd eating and sleeping schedule affected the animals' memory of scary situations.
"Those animals that were misaligned show severe deficits in their recall of the training that they received," Colwell said. He and his colleagues previously found that jet lag has similar effects on memory in both human and mouse studies.
Finally, the researchers measured the strengthening of neural connections — a measure of learning in the brain. Again, they found that the mice that ate during normal sleeping periods learned less quickly than the mice that ate at normal times.
It's not clear how applicable the findings are to humans, but the results nevertheless raise concerns about the effect of shifted eating times on human cognitive performance, the researchers said.
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