Authors: Sarah Steele¹
¹Macquarie University
Feedback loops linking the auditory cortex to the cochlea form critical neural networks essential for listening, yet their functional mechanisms remain poorly understood. Transcranial Magnetic Stimulation (TMS), a non-invasive method of modulating cortical activity, offers a promising approach to probing these pathways. Although widely applied in the motor cortex, and clinically for tinnitus, there remains no objective method to verify its effects on auditory cortical circuits. This study addresses that gap by examining whether TMS can modulate auditory cortical excitability and cochlear function in a controlled experimental setting.
Twelve normal-hearing participants (9 females; 18-35 years) underwent sham-TMS (no magnetic stimulation) and active TMS sessions following a baseline measurement of auditory cortical responses (N1-P2 complex) and cochlear function, assessed via otoacoustic emissions (OAEs), including medial olivocochlear reflex (MOCR) metrics. Repetitive TMS was delivered using the theta-burst paradigm (x3 50Hz pulses in 5 Hz intervals for 40s) known to modulate cortical networks.
TMS stimulation caused a significant reduction in MOCR magnitude, indicating an effect on brainstem efferent function. This change was not observed after sham stimulation. In contrast, auditory cortical responses (amplitude and latency) remained stable across all conditions.
These findings suggest that TMS can modulate cortical auditory feedback networks. The lack of cortical effects suggest that our single-channel EEG was unable to pick up cortical changes, at least under the current stimulation parameters. Our findings support TMS’s utility as a tool for investigating human auditory feedback circuits and highlights the need for refined protocols to assess and potentially target cortical auditory modulation, critical for both mechanistic research and therapeutic applications such as tinnitus treatment.
