Tone-evoked acoustic change complex (ACC) in an animal model

The auditory change complex (ACC) is a cortical evoked potential complex generated in response to a change (e.g., frequency or level) within an ongoing auditory stimulus. The ACC has been recorded in both normal-hearing human subjects and in cochlear implant users, suggesting that the ACC would be useful in clinical applications. Here, we investigate the feasibility of recording ACC in response to frequency or level changes in sedated cats. Five purpose-bred cats were sedated with ketamine and acepromazine. Continuous tones alternated between high and low frequencies or levels in 500-ms blocks. Frequency and level steps were varied parametrically. Scalp potentials were recorded with needle electrodes (two active electrodes = one on each hemisphere, reference: mastoid, ground = back of the cat). ACC was successfully elicited in all cats by both frequency and level steps. In many cases, ACCs were markedly greater for increasing or for decreasing stimulus steps. The discrimination thresholds measured were in...