Post-auricular Muscle Response Research Articles

Direct cochlear nerve stimulation monitoring through evoked muscle responses during retrosigmoid vestibular schwannoma resection surgery: technical note.

Cochlear nerve preservation during surgery for vestibular schwannoma (VS) may be challenging. Brainstem auditory evoked potentials and cochlear compound nerve action potentials have clearly shown their limitations in surgeries for large VSs. In this paper, the authors report their preliminary results after direct electrical intraoperative cochlear nerve stimulation and recording of the postauricular muscle response (PAMR) during resection of large VSs. The details for the electrode setup, stimulation, and recording parameters are provided. Data of patients for whom PAMR was recorded during surgery were prospectively collected and analyzed. PAMRs were recorded in all patients at the ipsilateral vertex-earlobe scalp electrode, and in 90% of the patients they were also observed in the contralateral electrode. The optimal stimulation intensity was found to be 1 mA at 1 Hz, with a good cochlear response and an absent response from other nerves. At that intensity, the ipsilateral cochlear response had an initial peak at a mean (± SEM) latency of 11.6 ± 1.5 msec with an average amplitude of 14.4 ± 5.4 µV. One patient experienced a significant improvement in his audition, while that of the other patients remained stable. PAMR monitoring may be useful in mapping the position and trajectory of the cochlear nerve to enable hearing preservation during surgery.

The Influence of Stimulus Repetition Rate on Tone-Evoked Post-Auricular Muscle Response (PAMR) Threshold.

Post-auricular muscle response (PAMR) is a large myogenic potential that can be useful in estimating behavioral hearing thresholds when the recording protocol is optimal. The main aim of the present study was to determine the influence of stimulus repetition rate on PAMR threshold. In this repeated-measures study, 20 normally hearing adults aged between 18 and 30 years were recruited. Tone bursts (500, 1000, 2000, and 4000 Hz) were used to record PAMR thresholds at 3 different stimulus repetition rates (6.1/s, 11.1/s, and 17.1/s). Statistically higher PAMR thresholds were found for the faster stimulus rate (17.1/s) compared with the slower stimulus rate (6.1/s) (p < 0.05). For all stimulus rates and frequencies, significant correlations were found between PAMR and pure-tone audiometry thresholds (r = 0.62 to 0.82). Even though the stimulus rate effect was significant at most of the tested frequencies, the differences in PAMR thresholds between the rates were small (<5 dB). Nevertheless, based on the correlation results, we suggest the use of 11.1/s stimulus rate when recording PAMR thresholds.

Gap-induced inhibition of the post-auricular muscle response in humans and guinea pigs

A common method for measuring changes in temporal processing sensitivity in both humans and animals makes use of GaP-induced Inhibition of the Acoustic Startle (GPIAS). It is also the basis of a common method for detecting tinnitus in rodents. However, the link to tinnitus has not been properly established because GPIAS has not yet been used to objectively demonstrate tinnitus in humans. In guinea pigs, the Preyer (ear flick) myogenic reflex is an established method for measuring the acoustic startle for the GPIAS test, while in humans, it is the eye-blink reflex. Yet, humans have a vestigial remnant of the Preyer reflex, which can be detected by measuring skin surface potentials associated with the Post-Auricular Muscle Response (PAMR). A similar electrical potential can be measured in guinea pigs and we aimed to show that the PAMR could be used to demonstrate GPIAS in both species.In guinea pigs, we compare the GPIAS measured using the pinna movement of the Preyer reflex and the electrical potential of the PAMR to demonstrate that the two are at least equivalent. In humans, we establish for the first time that the PAMR provides a reliable way of measuring GPIAS that is a pure acoustic alternative to the multimodal eye-blink reflex. Further exploratory tests showed that while eye gaze position influenced the size of the PAMR response, it did not change the degree of GPIAS.Our findings confirm that the PAMR is a sensitive method for measuring GPIAS and suggest that it may allow direct comparison of temporal processing between humans and animals and may provide a basis for an objective test of tinnitus.

Rotation of the Eyes (Not the Head) Potentiates the Postauricular Muscle Response

The authors investigated how eye and head rotation modulate the human postauricular muscle response (PAMR), to determine the optimal strategy for potentiating the PAMR, or minimizing it to reduce contamination of small neurogenic responses. The authors recorded the PAMR evoked by binaural bipolar clicks (50 dB SL, 360 µsec per phase with 53-msec interval) from behind the right ear of 12 normally hearing adults, and attempted to enhance it with (a) voluntary ear contraction alone, (b) head rotation alone (with the eyes forward-directed and tracking a target attached to the head), or (c) by lateral eye movement alone (toward the right measurement side, with the head facing forward). When the head alone was rotated with eyes fixed relative to the head, the PAMR increased only slightly in some subjects, as did the ongoing electromyography (EMG) (probably due to EMG activity from nearby neck muscles). On returning the head to the forward control position, the PAMR dropped rapidly to control amplitudes. When the eyes alone were rotated, both the EMG and the PAMR increased markedly in most subjects, and returning the eyes to their control position produced a gradual return to control amplitudes. Voluntary PAM contraction (in those subjects who could accomplish it) increased the EMG tone and the PAMR amplitude concomitantly, with vigorous voluntary PAM contraction saturating the PAMR but not the EMG. Head rotation alone was not effective in potentiating the PAMR when lateral eye movement relative to the head was avoided during the head rotation maneuver. When lateral eye movement was controlled appropriately, the PAMR could be potentiated reliably, or reliably avoided when recording smaller neurogenic responses. If head rotation was used to optimize the PAMR without explicit control of eye movement, a false impression of variability was produced.

Rising-frequency chirps and earphones with an extended high-frequency response enhance the post-auricular muscle response

The purpose of this study was to determine whether rising-frequency chirps presented via earphones with an extended high-frequency response would optimize the post-auricular muscle response (PAMR). The PAMR was recorded in adults using three different stimuli (a click, a rising-frequency chirp, and a truncated speech stimulus, /t/). Conventional ER-3A insert earphones were compared to ER-2 insert earphones to determine whether the PAMR is enhanced by the ER-2's extended high-frequency response. There were significant stimulus and earphone effects on PAMR amplitudes. The PAMR was largest for the chirp stimulus and the ER-2 earphones. The poorest responses were obtained using the /t/ stimulus and conventional ER-3A earphones. The results support previous ABR studies that have demonstrated a significant advantage of chirps over clicks for evoked response audiometry, and indicate that the PAMR is enhanced by inclusion of additional high-frequency stimulus energy.SumarioEl propósito de este estudio fue determinar si los gorjeos de frecuencia ascendente presentados con auriculares de respuesta extendida en las frecuencias agudas, optimizan la respuesta del músculo post-auricular (PAMR). El PAMR se registró en adultos que usaron tres estímulos diferentes (clic, gorjeo de frecuencia ascendente y estimulo truncado de lenguaje, /t/). Se compararon auriculares de inserción convencionales ER-3A con auriculares de inserción ER-2 para determinar si el PAMR mejora con las respuestas de alta frecuencia extendida del ER-2. Se apreciaron efectos significativos en el estímulo y en los auriculares sobre las amplitudes del PAMR. EL PAMR fue más grande para los estímulos con gorjeo y con los auriculares ER-2. Las respuestas mas pobres se dieron usando el estimulo /t/ y los auriculares convencionales ER-3A. Estos resultados apoyan estudios previos de ABR que demostraron una ventaja significativa de los gorjeos sobre los clics en la audiometría de respuestas evocadas e indican que el PAMR se incrementa con la inclusión adicional de la energía de estímulos de altas frecuencias.

The post-auricular muscle response: an objective electrophysiological method for evaluating hearing sensitivity

Post-auricular muscle responses (PAMRs) were recorded in sixteen adults with normal hearing and twenty adults with sensorineural hearing loss. Click stimuli were presented at 20 to 80 dB nHL via insert earphones. Only one ear was tested in hearing-impaired subjects, but normal-hearing subjects were tested monaurally and binaurally. PAMR amplitudes declined and latencies increased with decreasing click intensity. Both binaural stimulation and eye turn enhanced the PAMR. In hearing-impaired subjects, PAMR thresholds were correlated with audiometric thresholds for the eyes-turned condition. All normal-hearing subjects had PAMR when recording conditions were optimized and half had responses for the least optimal condition (20 dB nHL, monaural, eyes front). With eyes turned and monaural clicks at 35 dB nHL, the level widely used for infant hearing screening, most normal-hearing adults had a PAMR. Thus the PAMR is a robust response that may be a useful adjunct to ABR for objective hearing assessment.SumarioLas respuestas del músculo post-auricular (PAMR) fueron registradas en 16 adultos con audición normal y 20 adultos con hipoacusia sensorineural. Se presentaron estímulos con clics a 20 y 80 dB nHL por medio de auriculares de inserción. Solo se evaluó un oído en los hipoacúsicos pero los sujetos normales fueron evaluados mono y binauralmente. Las amplitudes del PAMR declinaron y las latencias aumentaron conforme la intensidad del clíc disminuyó. Tanto la estimulación binaural y el giro ocular aumentaron el PAMR. En hipoacusicos los umbrales PAMR se correlacionaron con los umbrales audiométricos en la condición de ojos girados. Todos los normales tuvieron PAMR cuando se optimizaron las condiciones de registro y la mitad tuvieron respuestas en la condición menos óptima (20 dB nHL, monoaural y con los ojos al frente). Con los ojos girados y con clics monoaurales en 35dB nHL, el nivel mas ampliamente usado para la identificación auditiva neonatal, la mayoría de los adultos con audición normal tuvieron PAMR. Por ello se considera que el PAMR es una respuesta robusta que puede ser un útil accesorio para las ABR en la evaluación objetiva de la audición.

A correlation method for detecting the sound-evoked post-auricular muscle response (PAMR)

We have made detailed measurements of the sound-evoked post-auricular muscle response (PAMR) in four adults and two infants, in an attempt to understand the inter-relationships between sound level, potentiation of the PAMR with voluntary PAM contraction or eye rotation, electromyographic (EMG) noise, amplitude of the PAMR, and a correlation measure of the presence of the PAMR. We have found that the amplitude of the PAMR is a simple linear function of the decibel level of a monophasic click (0.1 ms duration), and that the PAMR amplitude is also a saturating power function of the level of tonic EMG. As a result, PAMR=PAM o.SL.(EMG−EMG noise) 2/[(EMG−EMG noise) 2+ β 2], where SL is the decibel level of a click above subjective threshold, PAM o is a parameter accounting for the differing PAMR amplitude across individuals or with altered electrode placement, EMG noise is the component of EMG not associated with PAMR potentiation, and β determines the initial rate of growth of PAMR at low levels of PAM activation. We have also found that the correlation measure ( C) of the PAMR follows a saturating power function of the signal-to-noise ratio (SNR=PAMR/EMG), with C=SNR 2/(SNR 2+ δ 2), where δ determines the onset of saturation in the correlation as a function of SNR. The combination of these two relationships means that correlation is a non-monotonic function of the EMG (PAM activation): it can be large for moderate levels of EMG, but small for high levels of EMG, because the PAMR amplitude saturates but the EMG does not. The correlation is a fast, convenient means of detecting the PAMR, whether using clicks or tone-bursts, and can be used effectively in adults or infants, as long as the reflex is moderately activated. This moderate activation is most effectively produced by eye rotation towards the recording electrodes.

Effects of eye rotation on the sound-evoked post-auricular muscle response (PAMR)

One objective electrophysiological test for deafness involves presenting a brief acoustic stimulus to a subject and measuring the electrical activity evoked in the muscle located just behind the ear (the post-auricular muscle or PAM). We describe a method for enhancing this post-auricular muscle response (PAMR) using lateral eye movement, which increases both the tonic EMG activity in the PAM and the magnitude of the PAMR, and decreases response latency. EMG activity in most subjects tested (more than 30) increased almost instantly on rotation of the eyes, and thereafter grew more slowly with maintained lateral gaze, with the largest increase occurring with eye rotation towards rather than away from the measurement electrodes over the PAM. The EMG activity returned rapidly to near pre-rotation levels when the eyes were returned to the forwards position, with full recovery taking some minutes. While there was a similar increase and return of the PAMR amplitude with eye rotation, the time-course of these changes was somewhat different, largely because the EMG activity and the PAMR amplitude were not proportional. Rather the PAMR amplitude was a saturating function of EMG level, so that the PAMR response did not fall as markedly as the EMG when the eyes were returned to a forwards gaze, and the recovery of the PAMR amplitude to pre-rotation levels appeared to take longer. We discuss the neural mechanisms that may be responsible for this PAMR potentiation with eye movement and discuss its probable role in increasing variability in early studies which did not control for eye movement. We also discuss the utility of eye rotation in potentiating and stabilising the PAMR to allow its use in screening for deafness.

Basic properties of the sound-evoked post-auricular muscle response (PAMR)

One objective electrophysiological test for deafness involves presenting a brief acoustic stimulus to a subject and measuring the electrical activity evoked in the muscle located just behind the ear (the post-auricular muscle or PAM). Although this electrical response has been known for many years, it has been ignored by most clinicians and frequently misreported in the literature. This paper presents the fundamental properties of the PAM electrical response (the PAMR) and examines ways in which its measurement can be improved by altering the standard electrode position and filtering. The response consists of a simple bipolar compound action potential with a first peak latency of between 12.5 and 15 ms, depending on the stimulus intensity and PAM muscle tone. The largest recordings can be made with an active electrode over the PAM and with the reference electrode on the dorsal surface of the pinna. It can be obtained with click and tone-burst stimuli within 20 dB of the subjective detection threshold, can be evoked with tone-bursts between 500 Hz and 16 kHz and grows either linearly with the click level or approximately exponentially with the tone-burst level, reaching a maximum of as large as 250 μV pp in some subjects. It has a frequency spectrum mostly between 25 and 200 Hz. The response is often visible in raw recordings, with as few as 20 averages required for obtaining a stable waveform. There is very little amplitude and latency difference in stimulating the ear on the same side or opposite side to the recording electrodes and the binaurally evoked response is similar to the simple arithmetic sum of the waveforms obtained with monaural stimulation. The response latency and duration are longer in very young infants, but reach adult values by 12 months of age. In a companion paper, we describe a method of enhancing the PAMR using lateral eye movement (Patuzzi and O’Beirne, 1999a).

Short‐latency evoked response correlations of psychophysical phenomena: Preliminary results from forward masking studies

Human wave V (8 msec latency) responses were recorded under forward masking conditions using vertex‐mastoid electrodes. Masking and masked stimuli were either noise‐burst clicks or sinusoids. When pairs of 1 msec clicks are presented monaurally at 75 dB SPL, the masked‐stimulus wave V response is reduced by about 93% when the interstimulus interval is 1 msec. Amplitude recovery is rapid and largely complete by 10 msec. 4 msec sinusoids presented singly at constant 55 dB sensation levels produce a bandpass frequency response function with a peak at about 3 kHz. When frequency is reduced below about 9 kHz, the wave V complex separates into two components: A fast positive defection with a stable latency of about 8 msec and a slower biphasic response with a latency inversely related to frequency (the later portion of this wave appears to overlap the postauricular muscle response). Forward masking of these responses is restricted to the spectral region of the masking sine wave; work directed toward determining the shape of the wave V “filter” is currently under way.

Distortion of averaged post-auricular muscle responses due to system bandwidth limits

Substantially different waveform details have been reported in various studies of the post-auricular muscle (PAM) response. By examining the high frequency limits of the pass-bands used to record the response it would appear that the system bandwidth limits have affected the waveform. Recordings were made using a very wide bandwidth, and were used to obtain power spectra of these PAM responses. These determined the minimum bandwidth requirements to avoid distortion of the waveform. It seems clear that a substantial proportion of the differences reported have been due to the use of a recording bandwidth which has distorted the response.