Behavioral Evidence of Transient versus Persistent Tinnitus Induced by Loud Noise Exposure in a Novel Rat Model
Authors: Beh Krystal , Typlt Marei , Sigel Greg , Schormans Ashley , Stolzberg Dan , Allman Brian L 
Published: November 2023

It is well known that excessive exposure to loud noise can result in permanent hearing loss. A common corollary to this noise‐induced hearing loss is tinnitus, the subjective perception of a phantom sound which is often described as a “ringing in the ears.” It is estimated that as many as 10–15% of adults suffer from persistent tinnitus, and for ~1% of the general population it becomes debilitating. Despite the prevalence of tinnitus, a lack of understanding of the underlying brain changes has hindered efforts to devise effective treatment. In order to ultimately investigate the neural basis of tinnitus, our lab first endeavored to design a behavioral model that would allow us to accurately screen laboratory animals for noise‐induced tinnitus. To that end, we have developed a two‐alternative forced choice appetitive behavioral paradigm for rats that closely replicates the conditions under which humans experience tinnitus (i.e., people perceive a steady noise in quiet conditions). In order to eventually screen for tinnitus in the hours, days and/or weeks following loud noise exposure, the rats were first trained to nose‐poke a left feeder trough during various steady narrow‐band noises, and a right feeder trough during quiet trials (speaker off). Correct feeder choices were reinforced with a food pellet. In subsequent testing sessions (i.e., following tone/sham exposure), performance during quiet trials were neither reinforced nor punished so as to avoid biasing the test day results. Once trained to correctly identify the various acoustic conditions, rats were then screened for the presence/absence of tinnitus: (1) immediately after intense 15‐minute tone exposure (12 kHz tone at 110 dB SPL) or sham; or (2) up to two weeks after a one‐hour intense tone exposure (12 kHz tone at 120 dB SPL) or sham. Following sham exposures, rats correctly chose the right feeder during quiet trials, even when they had experienced a substantial layoff from training. Conversely, after the 15‐minute tone exposure, all rats (n=10) mistakenly went to the left (steady noise) feeder during the quiet trials indicating the rats perceived a steady phantom sound (i.e., tinnitus). Tinnitus induced by the 15‐minute tone exposure was transient, however, as all rats returned to normal baseline performance 24 hours post‐exposure. As predicted based on human studies, only a subset of rats (~75%) screened positive for tinnitus one week following the hour‐long tone exposure. Collectively, these data suggest that our appetitive operant conditioning model is able to reliably screen rats for both transient and persistent noise‐induced tinnitus, as the learned behavior does not extinguish when a testing session occurs several days after tinnitus induction. Future experiments will record cortical activity in behaving rats in an effort to investigate the neural correlates of transient and persistent noise‐induced tinnitus.

Support or Funding Information

CIHR Open Operating Grant