High-pass filter settings affect the detectability of MLRs in humans

Early Maturation of Frequency-Following Responses to Voice Pitch in Infants with Normal Hearing

Neural plasticity of pitch processing mechanisms at the human brainstem, as reflected by the scalp-recorded frequency-following response (FFR) to voice pitch, has been reported for normal-hearing adults. Characteristics and maturation of such a response during the first year of life have remained unclear. The purpose of this study was to examine the characteristics of FFR to voice pitch in normal-hearing infants and to make a direct comparison with adults using the same stimulus and recording parameters. 9 infants and 9 adults were recruited. A Chinese monosyllable that mimics the English vowel /i/ with a rising pitch was used to elicit the FFR to voice pitch. The results demonstrated that infant FFRs showed slightly larger Pitch Strength but comparable Frequency Error, Slope Error, and Tracking Accuracy to those obtained from adults. Early maturation of FFRs was also observed in the infants starting from 1 to 3 mo. of age.

Attenuated human auditory middle latency response and evoked 40-Hz response to self-initiated sounds

For several modalities, it has been shown that the processing of sensory information generated by our own actions is attenuated relative to the processing of sensory information of externally generated stimuli. It has been proposed that the underlying mechanism builds predictions about the forthcoming sensory input and forwards them to the respective sensory processing levels. The present study investigated whether early auditory processing is suppressed by the top-down influences of such an internal forward model mechanism. To this end, we compared auditory middle latency responses (MLRs) and evoked 40-Hz responses elicited by self-initiated sounds with those elicited by externally initiated but otherwise identical sounds. In the self-initiated condition, the amplitudes of the Pa (27-33 ms relative to sound onset) and Nb (40-46 ms) components of the MLRs were significantly attenuated when compared to the responses elicited by click sounds presented in the externally initiated condition. Similarly, the evoked activity in the 40-Hz and adjacent frequency bands was attenuated. Considering that previous research revealed subcortical and auditory cortex contributions to MLRs and 40-Hz responses, our results support the existence of auditory suppression effects with self-initiated sounds on temporally and structurally early auditory processing levels. This attenuation in the processing of self-initiated sounds most probably contributes to the optimal processing of concurrent external acoustic events.

Middle-latency auditory evoked potentials in children at high risk for alcoholism

PURPOSE

In the course of a high-risk study for alcoholism, the middle-latency auditory evoked potentials (MAEPs) of children of alcoholics were explored.

MATERIAL AND METHODS

A series of auditory clicks (0.1 ms, 60 dB SL, 1.1/s) were used to record the Pa and Pb peaks of the MAEPs in 15 children of alcoholics with a multigenerational family history of alcoholism, and 17 control subjects, ranging from 10 to 14 years of age.

RESULTS

The latency of Pb was shorter in the high-risk than in the control group, and there was also a significant risk group by age interaction on Pa latency. The amplitude of Pa was smaller in the children of alcoholics.

CONCLUSIONS

The characteristics of the MAEPs of the high-risk subjects did not match the pattern of abnormalities previously observed in chronic alcoholics, which are supposed to be a consequence of the neurotoxic effects of ethanol. Nonetheless, the results showed significant differences in MAEPs between children of alcoholics and controls, pointing to an anomalous pattern of information transmission from thalamus to cortex that should be further analyzed using larger samples in a broader age range.

Area-Under-the-Curve Measure of the Auditory Middle Latency Response (AMLR) From Birth to Early Adulthood

The area-under-the-curve (AUC) measure of the auditory middle latency response (AMLR) waveform was derived and analyzed from recordings in 50 subjects with normal hearing. The AUC metric is believed to represent the total amount of neural energy contributing to the evoked response. This proposed method of measure, therefore, may provide an alternative method of quantifying the response. The subjects were divided into five age groups ( n = 10 for each group): infants, children, preteens, teens, and adults. Ipsilateral and contralateral recordings of the AMLR were obtained at two stimulus levels (70 and 40 dB nHL) and at two stimulus rates (11.3 and 3.3/s). AUC measures were obtained for each recording at 70 and 40 dB nHL and at 3.3 and 11.3 clicks/s. These area measurements were compared among the five age groups for significant differences due to age. According to the results, no significant differences in the AUC of the AMLR waveform existed as a function of age.

Effect of stimulus level and frequency on ABR and MLR binaural interaction in human neonates

Auditory brainstem (ABR) and middle latency (MLR) responses were evoked by click and tone-burst stimuli from human neonates. Electrophysiologic evidence of binaural interaction was measured by subtracting waveforms obtained for binaural stimulus conditions from waveforms obtained for the sum of right ear monaural and left ear monaural stimulus conditions. The effects of stimulus level and stimulus frequency on binaural interaction were evaluated by measuring the number, latency and amplitude of components found in the derived binaural interaction waveform, that is, binaural interaction components (BIC). BICs were more prevalent in the latency range of ABRs than for MLRs. Click and tonal stimuli were equally effective for deriving ABR-BICs, while tone-bursts were somewhat less effective than clicks for deriving MLR-BICs. Stimulus-response dependencies for ABR and MLR component latencies were apparent in monaural, binaural and binaural interaction waveforms. Normalized amplitudes for BICs showed that low-frequency tone-burst stimuli resulted in the largest values compared to click and high-frequency tonal stimuli. Comparison of these results with published results from adults demonstrated immaturity of binaural interaction in neonates.

The temporal relationship between the brainstem and primary cortical auditory evoked potentials

Many methods are employed in order to define more precisely the generators of an evoked potential (EP) waveform. One technique is to compare the timing of an EP whose origin is well established with that of one whose origin is less certain. In the present article, the latency of the primary cortical auditory evoked potential (PCAEP) was compared to each of the seven subcomponents which compose the brainstem auditory evoked potential (BAEP). The data for this comparison was derived from a retrospective analysis of previous recordings of the PCAEP and BAEP. Central auditory conduction time (CACT) was calculated by subtracting the latency of the cochlear nucleus BAEP component (wave III) from that of the PCAEP. It was found that CACT in humans is 12 msec which is more than double that of central somatosensory conduction time. The interpeak latencies between BAEP waves V, VI, and VII and the PCAEP were also calculated. It was deduced that all three waves must have an origin rather more caudally within the central auditory system than is commonly supposed. In addition, it is demonstrated that the early components of the middle latency AEP (No and Na) largely reside within the time domain between the termination of the BAEP components and the PCAEP which would be consistent with their being far field reflections of midbrain and subcortical auditory activity. It is concluded that as the afferent volley ascends the central auditory pathways, it generates not a sequence of high frequency BAEP responses but rather a succession of slower post-synaptic waves. The only means of reconciling the timing of the BAEP waves with that of the PCAEP is to assume that the generation of all the BAEP components must be largely restricted to a quite confined region within the auditory nerve and the lower half of the pons.

The effects of anterior temporal lobectomy (ATL) on the middle-latency auditory evoked potential (MLAEP)

The anatomical and physiological origins of the middle-latency auditory evoked potential (MLAEP) are not well understood. The present investigation was conducted to determine whether the MLAEP derives its origins in part from the anterior temporal lobe. Twelve subjects with intractable seizures were evaluated with the MLAEP pre and post excision of the anterior-mesial temporal lobe (ATL) unilaterally. In our study, component Pa latency was unaffected by the ATL. The Na latency and the Na/Pa amplitude showed significant increases after ATL. The results we interpreted as being consistent with currently held beliefs regarding the origins of Pa. The changes in Na latency and Na/Pa amplitude are hypothesized to reflect a loss of the modulating influence of the cortex on the subcortical generators of Na.

Filter effects and low stimulation rate on the middle-latency response in newborns

Auditory middle-latency responses (MLR) have been recorded in 25 newborns at 60 dB nHL using two wide band-pass filter conditions and a slow stimulation rate of 2/s. With both types of filter, the MLR consisted in an initial positive wave followed by a negative component (Na) and a positive component (Pa). In newborns, this positive component appears in the vicinity of 45 ms and is more prolonged than the Pa of the MLR in adults. The probability of obtaining MLR after averaging only 500 signals was higher with a high-pass filter setting of 10 Hz (12 dB/octave), as compared with 5 Hz (12 dB/octave). No significant differences were found in the detectability rate of MLR between the two-filter band-pass settings. It is important to note that some MLR were unstable and not easily replicable. Therefore, the clinical application of these components is still doubtful.

Human middle-latency auditory evoked potentials: vertex and temporal components

We recorded middle-latency (20-70 msec) auditory evoked potentials (MLAEPs) to monaural and binaural clicks in 30 normal adults (ages 20-49 years) at 32 scalp locations all referred to a balanced non-cephalic reference. Our goal was to define the MLAEP components that were present at comparable latencies and comparable locations across the subject population. Group and individual data were evaluated both as topographic maps and as MLAEPs at selected electrode locations. Three major components occurred between 20 and 70 msec, two well-known peaks centered at the vertex, and one previously undefined peak focused over the posterior temporal area. Pa is a 29 msec positive peak centered at the vertex and present with both monaural and binaural stimulation. Pb is a 53 msec positive peak also centered at the vertex but seen consistently only with binaural and right ear stimulation. TP41 is a 41 msec positive peak focused over both temporal areas. TP41 has not been identified in previous MLAEP studies that concentrated on central scalp locations and/or used active reference electrode sites such as ears or mastoids. Available topographic, intracranial, pharmacologic, and lesion studies indicate that Pa, Pb and TP41 are of neural origin. Whether Pa and/or Pb are produced in Heschl's gyrus, primary auditory cortex, remains unclear. TP41 is probably produced by auditory cortex on the posterior lateral surface of the temporal lobe. It should prove of considerable value in experimental and clinical evaluation of higher level auditory function in particular and of cortical function in general.

Sensorial substitution using sound-vibratory stimuli on the teeth: a new approach to the rehabilitation of the profoundly deaf

In 20 normal-hearing subjects, hypoacusics and anacusics ranging from 4 to 44 years of age, we have developed a study related to the analysis of brain evoked potential: B E R, E R P 40 Hz, cochlear microphonic responses and P 300 stimulating sound in the ear, and vibration to the teeth. With vibratory stimuli to the teeth, the brainstem potential didn't appear in anacusics; however, it appeared in subjects with perception deafness and transmission deafness. The potential type E R P 40 Hz (Galambos et al, 1981) appeared in hypoacusics, but not in anacusics; however, the subjective sensation of the vibration remained with them in absence of all the auditory registrable responses; nevertheless, we were able to record the P 300. We recorded perfectly cochlear responses in anacusics using vibratory stimuli of 500 Hz and higher applied to their teeth, even though they didn't have any other type of normal auditory response. The potential P 300 was obtained in normal hearing, hypocusics and anacusics, with the proper latencies according to their ages.

Changes in the auditory middle latency responses during all-night sleep recording

The middle latency response (MLR) using wide band-pass filters shows marked changes in amplitude, latency and configuration in sleep. The components with latencies greater than 20 ms show the greatest variability. There is a significant increase in Pa latency in stages 2 and stages 3/4, and in some cases a disappearance of the Nb component with the development of a broad positivity of latency intermediate to Pa and Pb which dominates the response. The responses in REM are of similar latency and configuration as in wakefulness but of reduced amplitude. The 40 Hz response is markedly reduced in amplitude in all sleep stages reflecting a decrease in the contribution of the middle latency components to this composite response. This appears to arise through a loss of 40 Hz periodicity in slow wave sleep and an increase in the slow 10 Hz component. In REM sleep, there is an overall reduction in amplitude. Much of the reported variability of the MLR in the literature arises from the widely differing band-pass filters used and the inadequate control for level of arousal. Both these factors have been shown to produce significant changes in the response.

Development of the middle latency response in an animal model and its relation to the human response

Although the clinical use of the middle latency response (MLR) in adults is fairly straightforward, its use is complicated by maturational changes that continue throughout the first decade of life. In order to telescope the time period of this long developmental course, we have approached the study of MLR maturation using the gerbil as an animal model. The course of MLR obtained over the temporal lobe development was characterized in the Mongolian gerbil ranging in age from 10 days to 3 months of life. The adult gerbil MLR consists of two positive peaks (A and C) at 11 and 25 ms, respectively, and a negative component (B) at 16 ms. These components emerge in a systematic fashion as a function of age. The present work supports a strong age effect of increased MLR detectability in the gerbil, similar to findings reported for humans. Wave A was infrequently detected in young animals, but when present, it occurred at adult latencies. The latency of waves B and C decreased systematically with age. The amplitude of all components increased with age, similar to findings in humans. The fact that adult-like thresholds were obtained shortly after birth indicates that when present, MLRs may be a good index of hearing threshold. Effects of stimulating across a wide range of intensities were described. The gerbil model appears appropriate for the study of development of the central auditory system function.