Of Mice and Men — Universality and Breakdown of Behavioral Organization

Toru Nakamura,Naoko Aoyagi,Toru Takumi,Kazuhiro Yoshiuchi,Yoshiharu Yamamoto,Zbigniew R Struzik,Atsuko Takano,Tim Bussey

doi:10.1371/journal.pone.0002050

Abstract

Mental or cognitive brain functions, and the effect on them of abnormal psychiatric diseases, are difficult to approach through molecular biological techniques due to the lack of appropriate assay systems with objective measures. We therefore study laws of behavioral organization, specifically how resting and active periods are interwoven throughout daily life, using objective criteria, and first discover that identical laws hold both for healthy humans subject to the full complexity of daily life, and wild-type mice subject to maximum environmental constraints. We find that active period durations with physical activity counts successively above a predefined threshold, when rescaled with individual means, follow a universal stretched exponential (gamma-type) cumulative distribution, while resting period durations below the threshold obey a universal power-law cumulative distribution with identical parameter values for both of the mammalian species. Further, by analyzing the behavioral organization of mice with a circadian clock gene (Period2) eliminated, and humans suffering from major depressive disorders, we find significantly lower parameter values (power-law scaling exponents) for the resting period durations in both these cases. Such a universality and breakdown of the behavioral organization of mice and humans, revealed through objective measures, is expected to facilitate the understanding of the molecular basis of the pathophysiology of neurobehavioral diseases, including depression, and lay the foundations for formulating a range of neuropsychiatric behavioral disorder models.

Highlights

The quest for a principle underlying human behavior is considered to be a difficult task, since actions are subject to the individual’s constant conscious deliberation and psyche, resulting in a continuously changing type and level of activity, arising from interaction with dynamically changing environmental demands
Nakamura et al [3] studied the nature of human behavioral organization, how resting and active periods are interwoven throughout daily life, and found that the duration statistics exhibit universal behavior, which can be generalized across individuals
When the overall average of non-zero counts is used as the threshold, the averaged cumulative distribution of resting period durations for 26 healthy human adolescents over on average 7 consecutive days take a power law form P(x$a),a2c over about 2 min to 100 min with the mean scaling exponent c = 0.9760.09 (Fig. 2a)

Summary

Introduction

The quest for a principle underlying human behavior is considered to be a difficult task, since actions are subject to the individual’s constant conscious deliberation and psyche, resulting in a continuously changing type and level of activity, arising from interaction with dynamically changing environmental demands. Nakamura et al [3] studied the nature of human behavioral organization, how resting and active periods are interwoven throughout daily life, and found that the duration statistics exhibit universal behavior, which can be generalized across individuals. We show that in experiments wild-type mice with minimal environmental demands display exactly the same behavioral organization as healthy humans, suggestive of the presence of an underlying principle governing behavioral organization across these mammalian species. Considering the reported chronobiological abnormality in depression [5,6,7], our findings have potential implications for the development of a novel mouse model of depression

Methods

Results

Conclusion