Frequency following response

Frequency following response (FFR), also referred to as Frequency Following Potential (FFP), is an evoked response generated by continuous presentation of low-frequency tone stimuli.[1] Part of the auditory brainstem response (ABR), the FFR reflects sustained neural activity integrated over a population of neural elements; "the brainstem response...can be divided into transient and sustained portions, namely the onset response and the frequency-following response (FFR)".[2] It is phase-locked to the individual cycles of the stimulus waveform and/or the envelope of the periodic stimuli.[3] It has not been well studied with respect to its response characteristics and clinical utility.

History

In 1930, Weaver and Bray discovered a potential called the "Weaver-Bray Response".[4][5] They originally believed the potential originated from the cochlear hair cells, but later discovered that the response was from the auditory nerve. The original discovery of this potential may have been accidentally discovered back in 1930; however, renewed interest in defining the FFR did not occur until the mid-1960s. While several researchers raced to publish the first detailed account of the FFR, the term "FFR" was originally coined by Worden and Marsh in 1968, to describe the cochlear microphonic (CM)-like neural components recorded directly from several brainstem nuclei (research based on Jewett and Williston’s work on click ABR's).[6]

Stimulus parameters

The recording procedures for the scalp-recorded FFR is essentially the same as the ABR. The primary differences are related to the stimulus and response parameters. The FFR can be evoked to tone bursts below 2000 Hz, complex tones, steady-state vowels, tonal sweeps, and consonant-vowel syllables. The duration of those stimuli are generally between 15-150 milliseconds, with a rise time of 5 milliseconds. The polarity of the stimulus can either be fixed or alternating, however alternating polarity causes the extinction of the CM and a doubling of FFR frequency.[7]

Clinical applicability

Due to the lack of specificity at low levels FFR has yet to make its way into the clinical setting. Only recently has FFR been evaluated for encoding complex sound and binaural processing.[8][9][10] There may be uses for the information FFR can provide regarding steady state, time-variant, and speech signals for better understanding of individuals with hearing loss and its effects. FFR Distortion Products (FFR DPs) could supplement low frequency (< 1000 Hz) DPOAEs.[11] FFRs have the potential to be used to evaluate the nature of neural representation of speech sounds processed by different strategies employed in cochlear implants, primarily identification and discrimination of speech. Also phase-locked neural activity reflected in the auditory steady state responses have been successfully used to predict auditory thresholds.[12]

Research directions

Currently, there is renewed interest in using the FFR to evaluate: the role of neural phase-locking in encoding of complex sounds in normally hearing and hearing impaired subjects, encoding of voice pitch, binaural hearing, and evaluating the characteristics of the neural version of cochlear nonlinearity.[13]

See also

References

  1. ↑ Burkard, R., Don, M., & Eggermont, J. J. Auditory evoked potentials: Basic principles and clinical application. Philadelphia: Lippincott Williams & Wilkins.
  2. ↑ Russo, N.; Nicol, T.; Musacchia, G.; Kraus, N. (September 2004). "Brainstem responses to speech syllables". Clinical Neurophysiology 115 (9): 2021–2030. doi:10.1016/j.clinph.2004.04.003. PMC 2529166. PMID 15294204.
  3. ↑ Moushegian, G.; Rupert, A. L. (1973). "Response diversity of neurons in ventral cochlear nucleus of kangaroo rat to low-frequency tones". Journal of Neurophysiology 33: 351–364.
  4. ↑ Wever, E. G. & Bray, C. W. (1930a) Proc. Nat. Acad. Sci. Wash. 16. 344.
  5. ↑ Wever, E. G. & Bray, C. W. (1930b). J. Exp Psychol. 13, 373.
  6. ↑ Worden, F.G.; Marsh, J.T. (July 1968). "Frequency-following (microphonic-like) neural responses evoked by sound". Electroencephalography and Clinical Neurophysiology 25 (1): 42–52. doi:10.1016/0013-4694(68)90085-0.
  7. ↑ Burkard, R., Don, M., & Eggermont, J. J. Auditory evoked potentials: Basic principles and clinical application. Philadelphia: Lippincott Williams & Wilkins.
  8. ↑ Krishnan, A. (2002). Human frequency–following responses: Representation of steady-state synthetic vowels. Hearing Research, 166, 192-201.
  9. ↑ Krishnan, A., Parkinson, J. (2000). Human frequency-following response: Representation of tonal sweeps. Audiology and Neurootology, 5, 312-321.
  10. ↑ Krishnan, A., Xu, Y., Gandour, J. T., Cariani, P. A. (2004). Human frequency-following response: Representation of pitch contours in Chinese tones. Hearing Research, 189, 1-12.
  11. ↑ Burkard, R., Don, M., & Eggermont, J. J. Auditory evoked potentials: Basic principles and clinical application. Philadelphia: Lippincott Williams & Wilkins.
  12. ↑ Krishnan, A. (2002). Human frequency–following responses: Representation of steady-state synthetic vowels. Hearing Research, 166, 192-201.
  13. ↑ Burkard, R., Don, M., & Eggermont, J. J. Auditory evoked potentials: Basic principles and clinical application. Philadelphia: Lippincott Williams & Wilkins.