Laszlo Stein

Auditory middle latency responses (MLRs) in patients with cortical lesions

Auditory middle latency response (MLRs) and auditory brain stem responses (ABRs) were simultaneously recorded in 24 patients with cortical lesions primarily affecting the temporal lobes. Site of lesion was documented by computerized tomography (CT) scan and behavioral profiles assessing language and other higher cortical functions were obtained. In patients with normal ABRs and either left or right hemisphere lesions, MLR components Na and Pa obtained at the vertex were of normal shape and latency. Exceptions to this occurred in 2 patients: one with bilateral temporal lobe lesions, the second with an infraventricular left temporal lobe lesion extending into the thalamic radiations. Although Na and Pa shape and latency were for the most part unaltered, Pa amplitude tended to cluster at the low end and below normal values. MLR recorded in the coronal plate showed Pa amplitude to be attenuated or absent over the damaged temporal lobe relative to the vertex or the intact hemisphere. This finding contrasts with data from normal subjects where Pa amplitude is largest at the vertex and essentially symmetrical about the temporal lobes. Patients showing an atypical amplitude distribution tended to have lesions involving auditory cortex and adjacent white matter projections. No obvious correlations between MLR abnormalities and behavioral findings regarding receptive and expressive language processes were found. Pa appears to be affected by temporal lobe lesions involving auditory cortex and thalamic projections. Our findings support the hypothesis that Pa is bilaterally generated by two symmetrical, vertically oriented dipole sources located about the temporal lobes.

Consequences of neural asynchrony: a case of auditory neuropathy.

AbstractAbstract The neural representation of sensory events depends upon neural synchrony. Auditory neuropathy, a disorder of stimulus-timing-related neural synchrony, provides a model for studying the role of synchrony in auditory perception. This article presents electrophysiological and behavioral data from a rare case of auditory neuropathy in a woman with normal hearing thresholds, making it possible to separate audibility from neuropathy. The experimental results, which encompass a wide range of auditory perceptual abilities and neurophysiologic responses to sound, provide new information linking neural synchrony with auditory perception. Findings illustrate that optimal eighth nerve and auditory brainstem synchrony do not appear to be essential for understanding speech in quiet listening situations. However, synchrony is critical for understanding speech in the presence of noise.

Absent auditory brain stem response: Peripheral hearing loss or brain stem dysfunction?

Interpretation of auditory brain stem response (ABR) findings can be problematic in cases where waves III and V are absent. Such findings can be attributed to profound hearing loss, brain stem neuropathology, or both. Over a 3‐year period, 48 patients with no known brain stem damage and on whom audiologic data were available were found to have no response by ABR or absent waves III and V. Severe to profound hearing loss was documented in 38 cases, audiometric data were equivocal in 3 cases, and 7 patients showed pure tone sensitivity ranging from normal hearing to moderate impairment. Thus 15% had better hearing sensitivity than might have been expected from their ABR findings. Each of these patients also exhibited abnormal acoustic reflex findings. We report the electrophysiological (ABR, MLR, acoustic reflex}, medical (history, neurological, EEG, CT scan) and behavioral (audiometric, speech and language, learning disabilities, psychological) data which characterize this group of patients.

AUDITORY MIDDLE LATENCY RESPONSES IN CHILDREN: EFFECTS OF AGE AND DIAGNOSTIC CATEGORY

The nature of auditory middle latency responses (MLRs) in children has been the subject of considerable debate. In order to study MLRs as a function of age, MLRs were obtained in 217 subjects ranging in age from 6 days to 20 years, all with normal auditory brain-stem responses (ABRs). Subjects were classified into several diagnostic categories: normal; communicative disorders (language delay, learning disability); mentally retarded, multiply handicapped; and post-meningitic. Age effects, the effects of diagnostic category, and possible differences in MLRs of males vs. females and right vs. left ears were examined. The detectability of both Na and Pa was found to increase significantly as a function of age. Detection of these MLR components became similar to adult values (approaching 100% detectability) at approximately 10 years of age. No significant differences were found among diagnostic categories. There were also no significant differences in the detectability of MLRs in males as compared to females, and there were no right vs. left ear differences. The strong age effect which appears to exist in the MLR influences their clinical use. When responses are present, they may be useful indicators of hearing sensitivity, but the absence of MLRs in children cannot be taken as an indication of hearing loss. Similarly, absent or abnormal MLRs cannot be interpreted as a manifestation of auditory pathway dysfunction, since there appears to be little difference in MLRs in normal subjects and MLRs in patients with a wide range of neurologic, cognitive, and speech and language disorders.

Follow-up of infants screened by auditory brainstem response in the neonatal intensive care unit

Auditory brainstem response screening at 40 and 60 dB was conducted in 100 infants in the neonatal intensive care unit to determine initial failure rate and prevalence of abnormality on follow-up. Of our NICU population, 20% failed one or both of the screening levels: 9% failed at 60 dB in both ears, and 11% failed at 40 dB in one or both ears. On follow-up, half of the 60 dB failure group were found to have sensorineural or conductive impairment and represent the 2% to 4% prevalence of serious otologic-audiologic problems generally found in an NICU population. Subsequent improvement (reversal) of the retest ABR records of the remaining infants in the 60 dB failure group was thought to be related to neural changes in the brainstem associated with recovery from hypoxic episodes. A transient or reversible conductive deficit appeared to account for the majority of failures at 40 dB. We recommend the screening protocol be expanded to include threshold and latency measures in infants who fail the initial screening. The transient nature of many ABR abnormalities makes postdischarge ABR, otologic, audiologic, and neurologic examinations mandatory before any inferences are made about hearing loss or neurodevelopmental disorders.

The hearing-impaired infant: patterns of identification and habilitation revisited.

This study is a follow-up of an 1980-1982 study that examined the occurrence of risk factors and the patterns of identification and habilitation in a group of hearing-impaired infants from an urban setting. Current findings covering the period 1983-1988, indicate that only one out of three hearing-impaired infants can be expected to be identified through audiological screening programs in Neonatal Intense Care Units (NICUs) and although the age at diagnosis for NICU graduates is significantly earlier than for Well Baby Nursery (WBN) graduates, age at enrollment in a parent-infant program for both NICU and WBN infants is around 20 months. Over the 8 year period covered by our two studies, the age hearing-impaired infants are enrolled in habilitation has remained a year or more later than the 6 month ideal recommended in 1982 by the Joint Committee on Infant Hearing.

The hearing-impaired infant: Patterns of identification and habilitation

The 1982 Position Statement by the Joint Committee on Infant Hearing recommends that infants at risk for hearing impairment be screened by 3 mos of age and that the diagnostic process be completed and habilitation begun by 6 mos of age. How close to this ideal actual practice comes in an urban setting is the subject of this study. Data on 88 infants referred to a hospital-based parent-infant program were retrospectively examined to determine the occurrence of risk factors and at what ages: (1) hearing loss was first suspected, (2) hearing loss was diagnosed, and (3) habilitation was initiated. Results indicate that over one-quarter of all hearing-impaired infants will not manifest any of the risk factors proposed in the 1982 Position Statement and that regardless of whether the infant graduates from a neonatal intensive care unit or well-baby nursery, the median age for enrollment in a parent-infant program is a year or more later than the 1982 recommendation.

Absence of sensorineural hearing loss in treated infants and children with congenital toxoplasmosis.

Educationally significant hearing loss has been reported in 10% to 15% of children with congenital toxoplasmosis. As part of a pilot study to assess feasibility and safety of prolonged therapy for congenital toxoplasmosis, 30 congenially infected infants and children were evaluated for auditory function. Serial testing, beginning within 2 months of birth, was performed. Availability of auditory brainstem response (ABR) testing made evaluation at an earlier age than previously possible. Six (20%) of the 30 infants had mild to moderate conductive type hearing loss associated with otitis media. No infant or child had sensorineural hearing loss. The better outcome we observed compared to previous reports of a 15% to 26% incidence of sensorineural hearing loss and 10% to 15% incidence of educationally significant, bilateral hearing impairment may be related to early initiation and/or prolonged institution of antimicrobial therapy. Continued followup to exclude progressive hearing impairment and study of larger numbers of children are needed to verify these preliminary findings.

Auditory brain-stem responses in hydrocephalic patients.

Auditory brain-stem response (ABR) was measured in 40 patients (80 ears) with confirmed hydrocephalus. Eighty-eight percent of these patients showed some form of ABR abnormality. Responses indicative of brain-stem dysfunction consisted of prolonged I-V interwave latency (38%), reduced V/I amplitude ratio (33%), and abnormalities in wave-shape of components III (27%) and V (53%). In addition, 70% of the patients had elevated ABR thresholds; 45% had responses in excess of 20 dB HL and the remaining 25% had no ABR activity. The etiology of the hydrocephalus, head circumference and brain-stem symptoms were not associated with particular ABR abnormalities. Communicating hydrocephalus correlated significantly with both prolonged I-V conduction time and absence of ABR activity, compared with non-communicating hydrocephalus. Four of the 9 patients retested showed ABR improvement on follow-up; one patient showed deterioration. The results were compared to our prior studies of ABR in 60 post-meningitic patients and in 100 severely neurologically impaired institutionalized children in whom the incidence of intrinsic brainstem abnormalities was one-third and two-thirds that of the hydrocephalic group, respectively. The results of this study suggest that ABR can be used to document clinically unsuspected brain-stem pathology that may accompany hydrocephalus. Auditory brain-stem dysfunction is likely to complicate the assessment of hearing sensitivity in hydrocephalic patients.

Listener-assessed intelligibility of a hearing aid self-adaptive noise filter.

A principal complaint of hearing aid users is the inability to understand speech in the presence of competing background noise. Efforts at reducing the adverse effects of external noise on amplification systems have centered on manually adjusted or low frequency activated high-pass filtering; however, there has been recent interest in the potential of self-adaptive noise reduction systems. In this study we investigate the performance of normals and three groups of sensonneural loss subjects under five noise conditions with a self-adaptive noise filter incorporated in a conventional hearing aid. Significant improvement in monosyllabic word scores with the self-adaptive noise filter were recorded by 30 to 65% of the hearing-impaired subjects under four of the five noise conditions.