Frequency-Following Responses to Complex Tones at Different Frequencies Reflect Different Source Configurations

Area of Science:

• Auditory Neuroscience
• Neurophysiology

Background:

• The neural basis of the frequency-following response (FFR), crucial for studying the human auditory system, is not fully understood.
• Evidence suggests a variable balance between cortical and subcortical contributions to the FFR, potentially influenced by stimulus frequency.

Purpose of the Study:

• To investigate if variations in FFR generation extend to subcortical nuclei at higher frequencies where cortical activity is minimal.
• To clarify the subcortical contributions to the FFR across different stimulus frequencies.

Main Methods:

• Evoked FFRs in 17 normal-hearing listeners using complex tones with missing fundamentals (C4, E4, G4) presented to one or both ears.
• Applied source imaging techniques to analyze FFR components and compared FFR topographies with auditory brainstem responses (ABR) to clicks.

Main Results:

• Source imaging confirmed dominant subcortical activity for both fundamental frequency (F0) and second harmonic (H2) FFR components.
• FFR features like spatial complexity and scalp distributions systematically varied with stimulus F0, suggesting dynamic subcortical source configurations.
• Topographic comparisons revealed F0 component similarity to click-ABR at earlier latencies with higher stimulus F0, and H2 component similarity at fixed latencies.

Conclusions:

• Subcortical nuclei play a dominant role in generating the FFR, with their relative contributions dynamically changing based on stimulus frequency.
• The findings provide insights into the neural generation of the FFR and its frequency-dependent characteristics, impacting future auditory system research.