Abstract
SummaryInstinctive defensive behaviors, consisting of stereotyped sequences of movements and postures, are an essential component of the mouse behavioral repertoire. Since defensive behaviors can be reliably triggered by threatening sensory stimuli, the selection of the most appropriate action depends on the stimulus property. However, since the mouse has a wide repertoire of motor actions, it is not clear which set of movements and postures represent the relevant action. So far, this has been empirically identified as a change in locomotion state. However, the extent to which locomotion alone captures the diversity of defensive behaviors and their sensory specificity is unknown. To tackle this problem, we developed a method to obtain a faithful 3D reconstruction of the mouse body that enabled to quantify a wide variety of motor actions. This higher dimensional description revealed that defensive behaviors are more stimulus specific than indicated by locomotion data. Thus, responses to distinct stimuli that were equivalent in terms of locomotion (e.g., freezing induced by looming and sound) could be discriminated along other dimensions. The enhanced stimulus specificity was explained by a surprising diversity. A clustering analysis revealed that distinct combinations of movements and postures, giving rise to at least 7 different behaviors, were required to account for stimulus specificity. Moreover, each stimulus evoked more than one behavior, revealing a robust one-to-many mapping between sensations and behaviors that was not apparent from locomotion data. Our results indicate that diversity and sensory specificity of mouse defensive behaviors unfold in a higher dimensional space, spanning multiple motor actions.
Highlights
Mice are innately able to respond to changes in their sensory landscape by producing sequences of actions aimed at maximizing their welfare and chances for survival
Five different landmarks on the mouse body were tracked using four cameras mounted at the top of an open-field arena that we used throughout the study (Figures S1A and S1B)
We have previously shown that these two stimuli evoke distinct and opposite behavioral responses, with the former inducing an increase in locomotor activity while the latter abolishes locomotion by inducing freezing behavior [7]
Summary
Mice are innately able to respond to changes in their sensory landscape by producing sequences of actions aimed at maximizing their welfare and chances for survival. Realizing the full power of this approach, relies upon a description of evoked behaviors that is sufficiently complete to encompass the full complexity of the motor responses and to capture the relevant variations across different stimuli or repeated presentations of the same stimulus. Instinctive defensive behaviors, such as escape or freeze, have been defined on the basis of a clear phenotype—a sudden change in locomotion state. Until now, a lack of tools to objectively measure types of movement other than locomotion has left that possibility unexplored
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