Estimation of Neural Phase Locking from Stimulus-Evoked Potentials

Abstract

The frequency extent over which fine structure is coded in the auditory nerve has been physiologically characterized in laboratory animals but is unknown in humans. Knowledge of the upper frequency limit in humans would inform the debate regarding the role of fine structure in human hearing. Of the presently available techniques, only the recording of mass neural potentials offers the promise to provide a physiological estimate of neural phase locking in humans. A challenge is to disambiguate neural phase locking from the receptor potentials. We studied mass potentials recorded on the cochlea and auditory nerve of cat and used several experimental manipulations to isolate the neural contribution to these potentials. We find a surprisingly large neural contribution in the signal recorded on the cochlear round window, and this contribution is in many aspects similar to the potential measured on the auditory nerve. The results suggest that recording of mass potentials through the middle ear is a promising approach to examine neural phase locking in humans.

Medial olivocochlear efferent reflex inhibition of human cochlear nerve responses

“…While we quantified MOC reflex inhibition on click-evoked cochlear nerve responses using an electrode on the human tympanic membrane, the amount of time needed for adequate response averaging will limit its clinical utility. Measurements with a trans-tympanic electrode (e.g., Verschooten & Joris 2014) would likely require fewer averages, but nonetheless this has limitations for clinical utility: the procedure does not avoid the requirement that patients remain awake and mentally alert, the hole in the tympanic membrane can cause problems for in situ measurement of sound pressure levels, and these measurements would certainly not be possible for challenging cases of, for example, children with Autism – in whom MOC measurements may be helpful (Danesh & Kaf 2012). …”

Development of a method for determining binaural sensitivity to temporal fine structure

“…Amplitude modulation cannot be detected for higher rates, except when spectral cues are available (Kohlrausch, Fassel, and Dau 2000). TFS information is conveyed by neural synchrony (phase locking) to individual cycles of the TFS, and phase locking becomes very weak for frequencies above 4000-5000 Hz, although the exact upper limit in humans is not known (Verschooten and Joris 2014).…”

Mass Potentials Recorded at the Round Window Enable the Detection of Low Spontaneous Rate Fibers in Gerbil Auditory Nerve

“…Due to the non-linear nature of the ANF response [16,17,34,35], the low-frequency neurophonic response consists of multiple harmonics (dominated by a strong 1 st and 2 nd harmonic). These harmonics were divided over the sum and difference responses (see Fig 1 and Fig 2).…”

“…Although the number of synapses per IHC reached about 20–25 synapses per IHC (see [36]) in the 1–2 kHz region of the cochlea, a drastic reduction in the neural gain index was seen for probe frequencies below 2 kHz. This neural cancelation may be due to the phase-locking behavior of the ANFs to fine structure presented in alternating phase (Fig 2E and 2J, [16,34,35]). At these low-frequencies of stimulation, the fine-structure of the waveform follows the stimulus polarities, eliciting phase-locked firing of the ANFs in a 180° phase shift (i.e., 1/2 cycle shift).…”

“…To do this, we analyzed mass potentials from an electrode placed on the round-window niche [16,17]. In absence of sound stimulation, this activity is known to reflect the asynchronous activity of the ANFs assembly [18,19,20] which is dominated by the high-SR fiber pool.…”