Credit: Emilia Stasiak

Until fairly recently, human activity was not thought to follow a particular pattern. Human actions are subject to personal decisions, and these are presumed to be too complex to predict reliably. Yet studies from the past few years have shown that contrary to this assumption, human activity—ranging from general movement to the execution of specific tasks such as sending e-mail and browsing the web—fits a consistent organizational structure of bursts of activity followed by periods of inactivity. The distribution and duration of resting and active periods are highly conserved across individuals.

A new study by Yoshiharu Yamamoto (University of Tokyo, Japan) and colleagues shows that these behavioral patterns are not limited to humans but apply to mice, as well (PLoS ONE 3, e2050; 2008). This finding suggests the possibility of a single principle governing the behavior of mammalian species and may have meaningful implications for behavioral modeling.

Yamamoto and colleagues had previously collected data on the activity of human adults. In this study they recorded the movements of healthy adolescents who wore watch-like monitoring devices for several days. The researchers also monitored the activity of mice using pressure-sensing sheets that were placed under mouse cages.

The group showed first that activity patterns of adolescents were the same as those of adults, despite their markedly different lifestyles. When the researchers compared data from healthy humans with rescaled data from wild-type mice, they found that the organization of activity was identical between the species.

The researchers then explored a potential application of these findings. Reduction in locomotor activity and disruption of the circadian cycle are among the key signs of clinical depression. Yamamoto and colleagues had previously shown that the activity pattern of depressed adults deviated from that of healthy adults. In this study the researchers compared historical data from depressed humans with new activity data from knockout mice lacking the core clock gene Per2, a mutation that alters the normal rest-activity cycle. The behavioral patterns were identical.

It is too soon to conclude that the mutant mice can model depression, Yamamoto tells Lab Animal. Rather, the importance of this study lies in the “demonstration of 'universality' in how animals move.” The shared behavioral organization may offer an opportunity to “study objectively the relationship between a symptom of neurobehavioral disorders, major depression in this case, and a symptom associated with elimination of a specific gene.”