Mice are at their best at night. But a new analysis suggests researchers often test the nocturnal creatures during the day—which could alter results and create variability across studies—if they record time-of-day information at all.
Of the 200 papers examined in the new study, more than half either failed to report the timing of behavioral testing or did so ambiguously. Only 20 percent reported nighttime testing. The analysis was published in Neuroscience & Biobehavioral Reviews.
West Virginia University neuroscientist Randy Nelson, the study's lead author, says this is likely a matter of human convenience. “It is easier to get students and techs to work during the day than [at] night,” Nelson says. But that convenience comes at a cost.
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“Time of day not only impacts the intensity of many variables, including locomotor activity, aggressive behavior, and plasma hormone levels,” but changes in those variables can only be observed during certain parts of the diurnal cycle, says University of Wyoming behavioral neuroscientist William D. Todd. This means that “failing to report time of day of data collection and tests makes interpretation of results extremely difficult,” adds Beth Israel Deaconess Medical Center staff scientist Natalia Machado. Neither Todd nor Machado was involved in the new study.
The study researchers say it is critical that scientists report the timing of their work and consider the fact that animals' behavioral and physiological responses can vary with the hour. As a first step, Nelson says, “taking care of time-of-day considerations seems like low-hanging fruit in terms of increasing behavioral neuroscience research reliability, reproducibility and rigor.”
University of Calgary psychologist Michael Antle, who was also not involved in the analysis, says such differences in how studies are run contribute to a “replication crisis” in science, with other laboratories unable to re-create study results. “Running a study at the wrong time,” he says, “could lead to us completely missing a finding altogether.”
