High-fidelity detection and quantification of acoustic startle response in freely moving mice in an open field

Acoustic startle response (ASR) is an involuntary reflex to an intense acoustic stimulus, characterized by rapid muscle contractions. Traditional ASR testing requires animals to be placed in spatially confining chambers to minimize voluntary movements, potentially altering natural behavior and stress levels. A method for detecting and quantifying ASR in free-moving rodents is needed.

This study presents a novel methodology and fully functional setup for measuring ASR in freely moving mice. The approach utilizes acoustic emissions (AE) generated by the animal's startling. The setup features an open field equipped with sensitive AE sensors to capture ASR with high precision and resolution.

In an open field fitted with AE sensors, ASR experiments were conducted on three mouse strains (129S6/EvSv, CBA/CaJ, and C57BL/6J). The system's ability to detect the effects of startle sound level, tone frequency, lighting conditions, stress levels, and genetic differences was evaluated. AE-based measures detected significant strain effects, with C57BL/6J mice showing lower startle intensities and higher latencies. Tone frequency and sound level influenced startle responses, while light/dark conditions had no effect. Stress conditioning resulted in elevated responses, but the difference was not statistically significant.

Alongside AE data, video recordings from three orthogonal viewpoints were acquired and analyzed to quantify startling. Unlike AE-based measures, video analysis failed to detect strain effects but found significant effects of frequency, sound level, and stress conditioning (which the AE data did not detect).

These findings validate AE-based technology for measuring ASR in freely moving rodents.