MORGANTOWN, W.Va. – Imagine waking up at 3 a.m. to take a test. That’s what lab animals do when their day and night cycles are not considered during scientific studies.  

All living things have what is called a circadian rhythm, which is the body’s natural cycle that tells you when it’s time to go to bed or eat. For humans, our circadian rhythm is almost 24 hours, and we are diurnal, which means we are naturally more active during the day. Animals that are commonly used in experiments, however, are nocturnal, and they are most active during the night.  

Courtesy: NIGMS

“There may be a 15 to 20% difference from daytime to nighttime, but because of convenience or whatever reason, when we do the experiments, we tend to do them during the day or during their rest period,” explained  Dr. Randy Nelson, chair of the West Virginia University School of Medicine’s Department of Neuroscience.

Nelson saw this problem and did an analysis of the 25 most cited papers in several behavioral areas, like learning and memory. He found that about 80 percent of the papers they surveyed either reported daytime testing or were unclear about what time of day the testing occurred.

There are several ways that scientists can take the circadian rhythm into account. They can opt to only test nocturnal animals at night, or they can attempt to flip their light dark cycle by keeping them in a dark room during the day or using dim, red lights. But, according to Nelson, not recording what method you used or not using any method at all can make it hard for another scientist to replicate the study.  

“It can happen to anybody, so you might just be busy. It may be inconvenient to flip your light dark cycle in your mouse rooms for a variety of reasons. You can’t do good care sometimes when you have the lights off during the day, so there’s lots of reasons for it,” explained Neslon. 

Nelson said it’s something scientists have to be reminded of. He recalled that he even made the mistake once. When day/night cycles were disregarded, his study indicted no effect on the nocturnal animals.

“We were so busy at the time that we tested them during the day, right? And later on, my student sort of said, ‘Hey, we’re all about timing and clocks and let’s test them during the night period when they’re active,’ and when we did that, we saw a whopping effect,” Nelson recalled. 

Nelson’s findings appear in Science Direct’s Neuroscience and Biobehavioral Reviews journal.