Transmuscular vocal fold injury reduces frequency complexity of rat ultrasonic vocalizations

Rapid and precise activation of the laryngeal musculature, particularly the thyroarytenoid (TA), is required for the production of rat ultrasonic vocalizations (USVs). Although the role of the TA in USV production has been established through denervation and excised larynx studies, how TA muscle dysfunction affects USV acoustics remains unknown. This study examined how iatrogenic, transmuscular vocal fold injury influences USV production by comparing acoustic parameters between rats receiving bilateral transmuscular vocal fold injury (including the TA muscle) versus sham surgery. Twenty adult male rats were randomly assigned to injury or sham groups and assessed at 30 or 60 days post-surgery. USVs were recorded at each timepoint (pre- and post-surgery) and analyzed for changes in principal frequency, frequency complexity (standard deviation and sinuosity), power (intensity of the USV), tonality, and duration. Injury significantly decreased USV frequency complexity and reduced the likelihood of producing frequency-modulated vocalizations in both post-surgical time groups. These findings demonstrate that while TA muscle integrity is crucial for frequency modulation, it is not necessary for basic USV production, offering new insights into the biomechanical role of the TA muscle in rat vocalization and laying the groundwork for investigating therapeutic interventions targeting laryngeal muscle function.