Elsevier

Hearing Research

Volume 151, Issues 1–2, January 2001, Pages 115-120
Hearing Research

Brainstem auditory evoked potentials (BAEPs) in the cynomolgus macaque monkey: Equivalence with human BAEPs and proposal of a new nomenclature

https://doi.org/10.1016/S0378-5955(00)00215-XGet rights and content

Abstract

Several groups have studied brainstem auditory evoked potentials (BAEPs) in non-human primates. However, the nomenclature of the waves elicited and their correspondence with human waves I–V differ among authors. BAEPs were recorded from six anaesthetised young cynomolgus macaques (Macaca fascicularis), using different sound stimuli parameters. A constant pattern of four main waveforms was present in all the animals with stimulus intensities over 60 dB SPL, although up to four smaller waveforms were observed in some of the individuals. Latency values increased with decreasing stimulus intensities and with increasing repetition rates. These results were similar to the BAEPs observed in other species of macaques. Although an approximate equivalence between human and monkey BAEPs is possible, some discrepancies suggest that there may be generators which contribute to different waves in both species. This is the reason for our proposal of a new nomenclature for BAEP waveforms in monkeys, following a descriptive order with arabic numerals preceded by the letter M.

Introduction

Brainstem auditory evoked potentials (BAEPs) are constituted by a series of waveforms obtained after averaging the first 10 ms of the EEG responses evoked by auditory stimulation with clicks. This potential is characteristically formed by seven vertex-positive waveforms in man in a vertex–ipsilateral earlobe montage (Vx–Ai) (Jewett and Williston, 1971). Evoked responses to auditory stimuli have been obtained in many different species (Huang, 1980), even in reptiles (Strain et al., 1986) and fish (Bullock and Corwin, 1979). Several species of macaques have been studied, but not Macaca fascicularis, widely used as an experimental primate model at this moment (Insausti et al., 1999, Manrique et al., 2000). The results of the studies in monkeys have shown a series of 4–9 waveforms, named with roman or arabic numerals, whose human equivalence has not been clearly established (Allen and Starr, 1978, Velasco et al., 1982, Doyle et al., 1983, Velasco et al., 1984, Doyle and Fria, 1985, Möller and Burgess, 1986, Legatt et al., 1986a, Legatt et al., 1986b, Pineda et al., 1989, Kamada et al., 1991, Lasky et al., 1995). The aim of our study was to describe the characteristics of the BAEPs in M. fascicularis, as an initial step for further research on brainstem auditory prosthesis, and to try to establish an equivalence with human BAEPs, if possible, based on previous studies and on the response of the different waveforms to changes in stimulus parameters.

Section snippets

Materials and methods

Six young male cynomolgus macaque monkeys (M. fascicularis), weighing between 3.8 and 5.4 kg, were used in this study. The protocol was approved by the Institutional Animal Care and Use Committee. The animals were anaesthetised with intramuscular ketamine (10 mg/kg) and midazolam (1 mg/kg), with a second half-dose injection if necessary. The body temperature was kept at 37±1° C during the whole procedure. All BAEPs were obtained in recording sessions of approximately 90 min of length. Each

Standard condition

A constant pattern of waveforms was observed in all the macaques examined (Fig. 1A). A minimum of four vertex-positive high amplitude waves (which we named with the letter M (monkey) followed by arabic numbers) were observed in the Vx–Ai mastoid (Vx–Mi) montage. M1 was the first vertex-positive wave clearly observed. The last of the high amplitude waveforms (M4) was followed by a slow negativity which typically included another small positive wave (M5). M4 had also the largest peak-to peak

Discussion

Monkey BAEPs have been studied by several authors in at least five different species (squirrel monkey-Saimiri sciureus (Pineda et al., 1989), Japanese monkey (Kamada et al., 1991), rhesus monkey Macaca mulatta (Allen and Starr, 1978, Velasco et al., 1982, Doyle et al., 1983, Velasco et al., 1984, Doyle and Fria, 1985, Möller and Burgess, 1986, Legatt et al., 1986b, Legatt et al., 1986a), and Macaca nemestrina (Legatt et al., 1986b, Legatt et al., 1986a). Even though the conditions and

Acknowledgments

This work was partially supported by the University of Navarra Research program and Cochlear Limited.

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