Background: Defensive and threat-related behaviors are common models for aspects of human mental illness.These behaviors are typically quantified by potentially laborious and/or computationally intensive video recording and post hoc analysis. Depending on the analysis method, the resulting measurements can be noisy or inaccurate. Other defensive behaviors, such as suppression of operant reward seeking, require extensive animal pre-training. Inertial tracking and accelerometry can be computationally efficient, but require specialized hardware.
New method: We quantified rodent defensive behavior using a commercially available electrophysiology headstage with 3-axis accelerometry integration during a threat conditioning and extinction paradigm. We tested multiple pre-processing and smoothing methods and correlated them against video-derived freezing and suppression of operant bar pressing.
Results: The best approach to tracking defensive behavior from accelerometry was Gaussian filter smoothing of the first derivative. Behavior scores from this method reproduced canonical conditioning and extinction curves. Timepoint-to-timepoint correlations between accelerometry,video, and bar press metrics were statistically significant but modest (largest r = 0.53, between accelerometry and bar press). These increased when traditional thresholding-based analyses were used, at the cost of a loss of temporal resolution (r = 0.97 between thresholded accelerometry and percent time freezing).
Comparison with existing methods: Accelerometry's integration with standard electrophysiology systems and relatively light weight signal processing may make it particularly well suited to detect behavior in resource-constrainedor real-time applications.
Conclusions: Accelerometry allows researchers already using electrophysiology to assess defensive behaviors without the need for additional behavioral measures or video. The modest correlations between metrics suggest that each measures a distinct aspect of defensive behavior. Accelerometry is a viable alternative to current defensive measurements, and its non-overlap with other metrics may allow for more sophisticated dissection of threat responses.
Keywords: Bar press; Electrophysiology; Fear conditioning; Freezing; Motion tracking; Rats.
Published by Elsevier B.V.