Context-dependent modulation of natural approach behavior in mice

Specific features of visual objects innately draw approach responses in animals, and provide natural signals of potential reward. However, visual sampling behaviors and the detection of salient, rewarding stimuli are context and behavioral state-dependent. The neural mechanisms underlying how the brain encodes naturally appetitive stimuli and conditionally transforms them into approach behavior remain unclear. To mechanistically understand this process, we probed natural approach behavior in mice by employing a virtual stimulus orienting paradigm based on prey capture to quantify the conditional expression of visual stimulus-evoked innate approach in freely moving mice. We found that specific combinations of stimulus features selectively evoked innate approach versus freezing behavioral responses when stimuli were unexpected. However, we discovered that prey capture experience, and therefore the expectation of prey in the environment, selectively modified a range of visually-evoked appetitive behaviors, as well as altered those visual features that evoked approach. Thus, we found that mice exhibit robust and selective orienting responses to parameterized visual stimuli that can be readily modified via natural experience. This work provides critical insight into how natural appetitive behaviors are driven by both visual motion and internal state. 

Methods
DeepLabCut was used to process videos of mice responding to two-dimensional visual stimuli moving across a video monitor that made up one side of an open field arena. Mouse nose, ears, tailbase and stimulus were tracked in 2D (x,y) pixel coordinates which were subsequently transformed into centimeters using customized Matlab scripts. These scripts were also used to determine when mice approached or froze in response to the stimulus. Frequencies of approach and freeze responses were quantified, as were mouse locomotive speeds, ranges and bearings with respect to the stimulus. Angular sizes and speeds of the visual stimulus were also calculated during each behavioral event.