The frequency-following response to continuous tones in humans

Area of Science:

• Auditory Neuroscience
• Neurophysiology

Background:

• The frequency-following response (FFR) is believed to originate from multiple sources, but precise identification has been challenging.
• Previous methods using tone bursts produced transient responses, complicating amplitude and latency measurements of the FFR.

Purpose of the Study:

• To systematically examine the frequency and intensity ranges for evoking FFRs using continuous tones.
• To compare FFRs evoked by continuous tones versus tone bursts.
• To analyze FFRs to continuous tones to identify their sources.

Main Methods:

• Utilized continuous tones and Fast Fourier Transform (FFT) for accurate FFR assessment.
• Compared FFRs evoked by continuous tones with those evoked by tone bursts.
• Analyzed FFR latency and amplitude to differentiate response sources.

Main Results:

• FFRs to both continuous tones and tone bursts exhibited similar thresholds (65-90 dB SPL) and frequency ranges.
• Neurogenic FFRs in humans were observed only below 1000 Hz, with a latency of 8.2 ± 0.1 ms, consistent with a midbrain origin.
• At higher frequencies, FFRs showed latencies under 1 ms, likely representing cochlear microphonic potentials.

Conclusions:

• Continuous tones provide a reliable method for FFR measurement, overcoming limitations of transient stimuli.
• Distinguishing between midbrain (neurogenic) and cochlear (microphonic) FFR sources is possible based on frequency and latency.
• The consistent latency of the neurogenic FFR suggests its potential as a biomarker for neurological disorders.