No close correlation between brainstem auditory function and peripheral auditory threshold in preterm infants at term age.

OBJECTIVE: To determine whether central auditory function in preterm infants correlates with peripheral auditory threshold and whether threshold elevation affects central auditory function. METHODS: Brainstem auditory evoked response (BAER) was recorded at term age using maximum length sequence (MLS) with 91-910/s clicks in 133 preterm infants (gestation 28-36 weeks). The relationship between MLS BAER variables and BAER threshold was analyzed. RESULTS: The latencies and amplitudes of all MLS BAER waves correlated significantly with BAER threshold. However, no correlation was found between MLS BAER interpeak intervals and BAER threshold at any rates. In preterm infants with a threshold >20dB nHL (n=30), MLS BAER wave latencies were all significantly longer than in those with a threshold < or = 20dB nHL (n=103) (P<0.01-0.001). MLS BAER wave amplitudes were significantly smaller than in those 20dB nHL (P<0.05-0.001). However, no interpeak intervals differed significantly between the two groups of infants. V/I amplitude ratio was similar in the two groups. These findings were true of all click rates. Click rate-dependent changes in MLS BAER of the preterm infants with an elevated BAER threshold are generally similar to those with a normal threshold. CONCLUSIONS: Brainstem auditory function does not closely correlate with peripheral auditory threshold at term in preterm infants. Elevation in peripheral threshold due to middle ear disorders does not significantly affect functional status of the auditory brainstem. SIGNIFICANCE: Short term peripheral conductive auditory abnormality does not significantly affect the immature central auditory function.     

Sustained depression of brainstem auditory electrophysiology during the first months in term infants after perinatal asphyxia.

OBJECTIVE: To gain further insights into the pathophysiological processes of neuronal impairment in neonatal brainstem after perinatal asphyxia. METHODS: Maximum-length sequence brainstem auditory-evoked response (MLS BAER) was recorded with clicks at 91, 227, 455 and 910/s on days 1, 3, 5, 7, 10, 15 and 30 after birth in 108 term infants who suffered perinatal asphyxia. Wave amplitude variables in the MLS BAER were analysed in detail at 40 dB above BAER threshold in 86 infants who had no peripheral hearing impairment. RESULTS: On day 1 the amplitudes of MLS BAER waves I, III and V were all reduced significantly at all click rates, especially at higher ones (91-910/s, ANOVA P<0.05-0.001). On day 3 these amplitudes were reduced further. On days 5 and 7, the amplitude reduction persisted and did not show any significant further changes. On days 10 and 15 the reduced amplitudes were increased slightly. On day 30 all amplitudes were still reduced significantly (P<0.05-0.0001). During the first month, the reduction of wave amplitudes was more significant for the later MLS BAER components than for the earlier ones, and occurred most significantly at 455 and 910/s clicks. By comparison, the amplitude reduction in conventional BAER was much less significant. CONCLUSIONS: During the first month after perinatal asphyxia the amplitudes of MLS BAER waves were reduced significantly and persistently, which was more significant at higher rates of clicks than at lower rates. The reduction is much more persistent than the increase in wave latencies and intervals we previously reported. SIGNIFICANCE: There is sustained depression of brainstem auditory electrophysiology, indicating neuronal damage of the auditory brainstem, in infants after perinatal asphyxia. This may have important clinical implications.     

Age-related changes in the guinea pig auditory cortex: relationship with brainstem changes and comparison with tone-induced hearing loss

Elderly people often show degraded hearing performance and have difficulties in understanding speech, particularly in noisy environments. Although loss in peripheral hearing sensitivity is an important factor in explaining these low performances, central alterations also have an impact but their exact contributions remained unclear. In this study, we focus on the functional effects of aging on auditory cortex responses. Neuronal discharges and local field potentials were recorded in the auditory cortex of aged guinea pigs (> 3 years), and several parameters characterizing the processing of auditory information were quantified: the acoustic thresholds, response strength, latency and duration of the response, and breadth of tuning. Several of these parameters were also quantified from auditory brainstem responses collected from the same animals, and recordings obtained from a population of animals with trauma-induced hearing loss were also included in this study. The results showed that aging and acoustic trauma reduced the response strength at both brainstem and cortical levels, and increased the response latencies more at the cortical level than at the brainstem level. In addition to the brainstem hearing loss, aging induced a 'cortical hearing loss' as judged by additive changes in the threshold and frequency response seen in the cortex. It also increased the duration of neural responses and reduced the receptive field bandwidth, effects that were not found in traumatized animals. These effects substantiate the notion that presbycusis involves both peripheral hearing loss and biological aging in the central auditory system.     

Age-related changes in human middle latency auditory evoked potentials

We recorded middle latency auditory evoked potentials (MAEPs) in young (20-40 years) and elderly (60-80 years) subjects with normal hearing. The Pa component was prolonged in latency and markedly enhanced in amplitude in the elderly subjects. No changes were found in Na, or in the binaural interaction of the MAEP. Differences in Pa amplitude and latency were not due exclusively to changes in auditory thresholds, since they were not duplicated by changes in stimulus intensity, and persisted when MAEPs from selected young and old subjects were compared at similar SPL levels. The enhancement of Pa amplitude appears to reflect age-related central modifications in auditory processing.     

Altered peripheral and brainstem auditory function in aged rats

A technique for conducting free-field brainstem auditory evoked potential (BAEP) audiometry in unanesthetized, unrestrained rats revealed a non-recruiting 18 dB elevation of click threshold in aged rats. BAEPs were first recorded in young and aged rats to clicks of equal intensity (80 dB SPL). Compared to the young group, aged animals exhibited longer wave I and wave IV latencies with no difference seen in the I–IV central conduction time. The prominent negative wave (No) following wave IV was also delayed and the I-No and IV-No conduction times increased in the aged group. When BAEPs were recorded to clicks with intensities adjusted to 35 dB above individual threshold, no differences in wave I or wave IV latencies or in the I–IV central conduction time were found between groups. However, the No component was delayed and the I-No and IV-No conduction times remained prolonged in the aged group. The results suggest that in addition to changes in peripheral auditory structures, changes in the rostal auditory brainstem accompany age-related hearing loss in rats.     

Asymmetry in the auditory brainstem response following experience of monaural amplification

Hearing aids can induce perceptual changes in some elderly listeners and there is recent evidence that this might be associated with reorganization within the auditory system. We compared the click-evoked auditory brainstem response in adults with and without monaural hearing aid experience. In listeners with monaural hearing aid experience, the mean peak-to-peak amplitude between wave V and SN10 was approximately 100 nV larger in the ear with hearing aid experience and this difference was statistically significant (P<0.01). The response was symmetrical in adults with no hearing aid experience. This suggests that hearing aids can induce physiological changes at the level of the auditory brainstem in elderly monaural hearing aid users.     

Brain-stem auditory evoked responses during microvascular decompression for trigeminal neuralgia: predicting post-operative hearing loss

CONTEXT: The importance of brainstem auditory evoked potential monitoring in reducing hearing loss during microvascular decompression for trigeminal neuralgia is now accepted. However the extent of the changes in the pattern of these potentials and the safe limits to which these changes are relevant in reducing postoperative hearing loss have not been established. AIMS: The aim of this study is to quantify these changes and relate these to the postoperative hearing loss. SETTINGS AND DESIGN: This study was done at the Walton Centre for neurology and neurosurgery, Liverpool, United Kingdom. The study was designed to give a measure of the change in the wave pattern following microvascular decompression and relate it to postoperative hearing loss. MATERIALS AND METHODS: Seventy-five patients undergoing microvascular decompression for trigeminal neuralgia had preoperative and postoperative hearing assessments and intraoperative brainstem auditory evoked potential monitoring. STATISTICAL ANALYSIS USED: Chi-square tests. RESULTS: It was found that the wave V latency was increased by more than 0.9 ms in nine patients, eight of whom suffered significant postoperative hearing loss as demonstrated by audiometry. It was also seen that progressive decrease in amplitude of wave V showed progressive hearing loss with 25% loss when amplitude fell by 50 and 100% loss when wave V was lost completely. However most of the patients did not have a clinically manifest hearing loss. CONCLUSIONS: A per-operative increase in the latency of wave V greater than 0.9 ms and a fall of amplitude of wave V of more than 50% indicates a risk to hearing.     

Speech‐in‐noise understanding in older age: The role of inhibitory cortical responses

Studies of central auditory processing underlying speech‐in‐noise (SIN) recognition in aging have mainly concerned the degrading neural representation of speech sound in the auditory brainstem and cortex. Less attention has been paid to the aging‐related decline of inhibitory function, which reduces the ability to suppress distraction from irrelevant sensory input. In a response suppression paradigm, young and older adults listened to sequences of three short sounds during MEG recording. The amplitudes of the cortical P30 response and the 40‐Hz transient gamma response were compared with age, hearing loss and SIN performance. Sensory gating, indicated by the P30 amplitude ratio between the last and the first responses, was reduced in older compared to young listeners. Sensory gating was correlated with age in the older adults but not with hearing loss nor with SIN understanding. The transient gamma response expressed less response suppression. However, the gamma amplitude increased with age and SIN loss. Comparisons of linear multi‐variable modeling showed a stronger brain–behavior relationship between the gamma amplitude and SIN performance than between gamma and age or hearing loss. The findings support the hypothesis that aging‐related changes in the balance between inhibitory and excitatory neural mechanisms modify the generation of gamma oscillations, which impacts on perceptual binding and consequently on SIN understanding abilities. In conclusion, SIN recognition in older age is less affected by central auditory processing at the level of sensation, indicated by sensory gating, but is strongly affected at the level of perceptual organization, indicated by the correlation with the gamma responses.     

Functional abnormality of the auditory brainstem in high-risk late preterm infants

ObjectiveTo examine whether late preterm infants with perinatal problems are at risk of brainstem auditory impairment.Methods68 high-risk late preterm infants (gestation 33–36 weeks) with perinatal problems or conditions were studied at term using maximum length sequence brainstem auditory evoked response. The controls were 41 normal term infants and 37 low-risk late preterm infants.ResultsCompared with normal term infants, the high-risk late preterm infants demonstrated a significant abnormal increase in MLS BAER variables that mainly reflect more central function of the brainstem auditory pathway, including wave V latency, III–V and I–V interpeak intervals, and III–V/I–III interval ratio. The abnormalities were more significant at higher than at lower click rates. The slopes of MLS BAER-rate function for these variables were increased. Compared with low-risk late preterm infants, the high-risk infants showed similar, though slightly less significant, abnormalities, mainly a significant increase in III–V and I–V intervals.ConclusionsMaximum length sequence brainstem auditory evoked response components that mainly reflect central function of the auditory brainstem were abnormal at term in high-risk late preterm infants.SignificanceMore central regions of the auditory brainstem are impaired in high-risk late preterm infants, which is mainly caused by associated perinatal problems or conditions.     

Age and gender contributions to intersubject variability of the auditory brainstem potentials

This study of auditory brainstem potentials in 123 normal hearing subjects examines the contributions of age and gender to intersubject variability of the response form and latency. The main features, wave I, wave III, and wave V, and the I-V interval were separately examined in premature infants, neonates, infants, children, and young adults. Perinatal changes in response latency were confirmed and significant additional shortening in the I-V interval was observed through childhood and adolescence. Significant gender differences in I-V interval were also observed in both children and adults. Whereas the age changes were consistent with the effects of myelination on conduction time, the nature and magnitude of the gender differences were in keeping with the differential growth changes in the central nervous system, reflected in the skull diameters of females and males. These two sources of intersubject variability, age and gender, should be considered when using the auditory brainstem potentials in clinical studies.     

Development and aging of superficial white matter myelin from young adulthood to old age: Mapping by vertex‐based surface statistics (VBSS)

Superficial white matter (SWM) lies immediately beneath cortical gray matter and consists primarily of short association fibers. The characteristics of SWM and its development and aging were seldom examined in the literature and warrant further investigation. Magnetization transfer imaging is sensitive to myelin changes in the white matter. Using an innovative multimodal imaging analysis approach, vertex‐based surface statistics (VBSS), the current study vertexwise mapped age‐related changes of magnetization transfer ratio (MTR) in SWM from young adulthood to old age (30–85 years, N = 66). Results demonstrated regionally selective and temporally heterochronologic changes of SWM MTR with age, including (1) inverted U‐shaped trajectories of SWM MTR in the rostral middle frontal, medial temporal, and temporoparietal regions, suggesting continuing myelination and protracted maturation till age 40–50 years and accelerating demyelination at age 60 and beyond, (2) linear decline of SWM MTR in the middle and superior temporal, and pericalcarine areas, indicating early maturation and less acceleration in age‐related degeneration, and (3) no significant changes of SWM MTR in the primary motor, somatosensory and auditory regions, suggesting resistance to age‐related deterioration. We did not observe similar patterns of changes in cortical thickness in our sample, suggesting the observed SWM MTR changes are not due to cortical atrophy. Hum Brain Mapp 37:1759–1769, 2016. © 2016 Wiley Periodicals, Inc.     

Altered Response Dynamics and Increased Population Correlation to Tonal Stimuli Embedded in Noise in Aging Auditory Cortex

Age-related hearing loss (presbycusis) is a chronic health condition that affects one-third of the world population. One hallmark of presbycusis is a difficulty hearing in noisy environments. Presbycusis can be separated into two components: alterations of peripheral mechanotransduction of sound in the cochlea and central alterations of auditory processing areas of the brain. Although the effects of the aging cochlea in hearing loss have been well studied, the role of the aging brain in hearing loss is less well understood. Therefore, to examine how age-related central processing changes affect hearing in noisy environments, we used a mouse model (Thy1-GCaMP6s X CBA) that has excellent peripheral hearing in old age. We used in vivo two-photon Ca²⁺ imaging to measure the responses of neuronal populations in auditory cortex (ACtx) of adult (2–6 months, nine male, six female, 4180 neurons) and aging mice (15–17 months, six male, three female, 1055 neurons) while listening to tones in noisy backgrounds. We found that ACtx neurons in aging mice showed larger responses to tones and have less suppressed responses consistent with reduced inhibition. Aging neurons also showed less sensitivity to temporal changes. Population analysis showed that neurons in aging mice showed higher pairwise activity correlations and showed a reduced diversity in responses to sound stimuli. Using neural decoding techniques, we show a loss of information in neuronal populations in the aging brain. Thus, aging not only affects the responses of single neurons but also affects how these neurons jointly represent stimuli.SIGNIFICANCE STATEMENT Aging results in hearing deficits particularly under challenging listening conditions. We show that auditory cortex contains distinct subpopulations of excitatory neurons that preferentially encode different stimulus features and that aging selectively reduces certain subpopulations. We also show that aging increases correlated activity between neurons and thereby reduces the response diversity in auditory cortex. The loss of population response diversity leads to a decrease of stimulus information and deficits in sound encoding, especially in noisy backgrounds. Future work determining the identities of circuits affected by aging could provide new targets for therapeutic strategies.     

Age-related differences in auditory evoked responses during rapid perceptual learning.

OBJECTIVE: Young and older adults can learn to rapidly discriminate between elementary visual and auditory features. While growing evidence supports the notion that such behavioral improvement is paralleled by neuroplastic changes in corresponding sensory areas during adulthood, studies have not examined practice-related improvement in older adults and the corresponding changes in neural activity. METHODS: We used event-related potentials (ERPs) to investigate the effects of age on rapid learning-related changes in listeners' ability to identify two phonetically different vowels presented simultaneously. RESULTS: During the first hour of testing, young and older listeners showed comparable behavioral improvement in identifying both vowels. In young adults, learning was paralleled by enhanced amplitudes of early (130 ms) and late (320 ms) ERP waves over the right temporal lobe, as well as an increased negative wave over the midline parietal region, peaking at about 400 ms after sound onset. The practice-related changes over the right temporal lobe were not present in older adults whereas the learning effect observed over the parietal region was present in both young and older adults. In older adults, behavioral improvement was also associated with reduced N1 amplitude recorded at inferior and posterior temporal/occipital scalp sites while no such changes were observed in young adults. CONCLUSIONS: Age-related differences in neural activity during learning suggest that neural networks supporting behavioral improvements in speech segregation and identification change during the course of aging. SIGNIFICANCE: This research highlights the role of practice on concurrent sound perception and may facilitate the development of training programs that may help older listeners to parse the auditory scene into component sound sources.     

A comparative study of age-related changes in inhibitory processes and long-term potentiation in the lateral septum of mice

Anaesthetized C57 BL/6 mice of different ages (young: 5 months; middle-aged: 15 months; and old: 21 months) were used to determine whether aging alters the efficiency of synaptic inhibition and long-term potentiation (LTP) in the lateral septum (LS). Electrical stimulation of the fimbria induced field potentials in the ipsilateral LS comprising two initial negative components (N2 and N3) followed by a positive wave of low amplitude. Paired-pulse experiments showed a facilitation of the N2 component and a concomitant depression of the N3 component: Facilitation of the N2 component was stronger in both middle-aged and old mice as compared to young mice, whereas an inverse pattern of changes was observed for inhibition of the N3 component. High-frequency stimulation of the fimbria produced a persistent increase in the N3 amplitude. This LTP was of significantly higher amplitude in both young and middle-aged mice as compared to old mice. These results suggest that aging impairs both inhibitory processes and synaptic plasticity in the mouse LS, but that inhibitory processes appear to be affected earlier.     

Intraoperative electrophysiological monitoring for hearing preservation in acoustic neurinoma surgery

Five acoustic neurinomas have been operated with hearing preservation as a goal. We monitored intraoperative brainstem auditory evoked potentials (BAEP) in all five cases, electrocochleogram (ECoG) using needle electrode in external auditory meatus in four, and compound action potentials directly recorded from the cochlear nerve (CAP VIII) in three. In all five cases the tumor was totally resected and cochlear nerve was anatomically preserved. However, in only one case useful hearing was preserved with preservation of all wave forms of the BAEP. Another patient with preservation of all wave forms of BAEP and the ECoG showed postoperative severe hearing loss. Other three patients showed postoperative severe hearing loss: only Wave I of BAEP and ECoG were preserved without preservation of the CAP VIII in one whose cochlear nerve was thought to be damaged in cerebellopontine angle cistern; Wave I of BAEP, ECoG and CAP VIII were preserved in one in whom it was suggested cochlear nerve near brainstem or cochlear nucleus was damaged; none of the BAEP, ECoG and CAP VIII was preserved in one in whom it was suggested distal cochlear nerve, or internal auditory artery was damaged. These different patterns of changes suggested that different causes for the hearing loss and difficulties in hearing preservation during acoustic neurinoma surgery. Having identified the putative mechanism of the hearing loss by monitoring those potentials, suggestions are made about how such hearing loss might be avoided. For preservation of the hearing in acoustic neurinoma surgery, all of those potentials including all wave forms of BAEP, ECoG and CAP VIII should be preserved during surgery.(ABSTRACT TRUNCATED AT 250 WORDS)     

The pattern of auditory brainstem response wave V maturation in cochlear-implanted children.

OBJECTIVE: Maturation of acoustically evoked brainstem responses (ABR) in hearing children is not complete at birth but rather continues over the first two years of life. In particular, it has been established that the decrease in ABR wave V latency can be modeled as the sum of two decaying exponential functions with respective time-constants of 4 and 50 weeks [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9]. Here, we investigated the maturation of electrically evoked auditory brainstem responses (EABR) in 55 deaf children who recovered hearing after cochlear implantation, and proposed a predictive model of EABR maturation depending on the onset of deafness. The pattern of EABR maturation over the first 2 years of cochlear implant use was compared with the normal pattern of ABR maturation in hearing children. METHODS: Changes in EABR wave V latency over the 2 years following cochlear implant connection were analyzed in two groups of children. The first group (n=41) consisted of children with early-onset of deafness (mostly congenital), and the second (n=14) of children who had become profoundly deaf after 1 year of age. The modeling of changes in EABR wave V latency with time was based on the mean values from each of the two groups, allowing comparison of the rates of EABR maturation between groups. Differences between EABRs elicited at the basal and apical ends of the implant electrode array were also tested. RESULTS: There was no influence of age at implantation on the rate of wave V latency change. The main factor for EABR changes was the time in sound. Indeed, significant maturation was observed over the first 2 years of implant use only in the group with early-onset deafness. In this group maturation of wave V progressed as in the ABR model of [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9] of normal hearing children: a sum of two decaying exponential functions, one showing an early rapid decrease in latency and the other a slower decrease. Remarkably, the time-constants fell well within the ranges described by Eggermont and Salamy (i.e., 3.9 and 68 weeks), consistent with the time-course of the neurophysiological mechanisms presumably involved in auditory pathway maturation during the first 2 years of life: i.e., myelination and increased synaptic efficacy. In contrast, relatively little change in wave V was evident in children with late-onset deafness. In agreement with the notion that EABR maturation follows an apex-to-base gradient as described for ABR, we observed that wave V latencies were longer for the basal than the apical end of the implant electrode array and remained so throughout the study period, whatever the time of onset of deafness. CONCLUSIONS: The findings in the early-onset of deafness group support the theory that auditory pathways remain "frozen" during the period of sensory deprivation until cochlear implant rehabilitation restores the normal chronology of maturational processes. In children with late-onset deafness, however, some maturational processes may occur before the onset of deafness, and thus less additional maturation is required during the first two years of implant use resulting in no significant EABR latency changes being observed in this period. The results suggest that the rehabilitation-induced plasticity of the auditory pathways is, in case of late auditory deprivation, unlikely to result in neurophysiological outcomes similar to those observed in children with early auditory deprivation. SIGNIFICANCE: Changes in EABR wave V latency over the first 2 years of cochlear implant use were found to be well fitted by the sum of two decaying exponential functions in children with early-onset deafness. This is in line with the maturation of ABR wave V latency in normal-hearing children over the first two years of life. Further studies are needed to assess whether the differences observed in terms of auditory pathways maturation are associated with consistent differences in terms of language development.     

Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children.

OBJECTIVE: The role of apical versus basal cochlear implant electrode stimulation on central auditory development was examined. We hypothesized that, in children with early onset deafness, auditory development evoked by basal electrode stimulation would differ from that evoked more apically. METHODS: Responses of the auditory nerve and brainstem, evoked by an apical and a basal implant electrode, were measured over the first year of cochlear implant use in 50 children with early onset severe to profound deafness who used hearing aids prior to implantation. RESULTS: Responses at initial stimulation were of larger amplitude and shorter latency when evoked by the apical electrode. No significant effects of residual hearing or age were found on initial response amplitudes or latencies. With implant use, responses evoked by both electrodes showed decreases in wave and interwave latencies reflecting decreased neural conduction time through the brainstem. Apical versus basal differences persisted with implant experience with one exception; eIII-eV interlatency differences decreased with implant use. CONCLUSIONS: Acute stimulation shows prolongation of basally versus apically evoked auditory nerve and brainstem responses in children with severe to profound deafness. Interwave latencies reflecting neural conduction along the caudal and rostral portions of the brainstem decreased over the first year of implant use. Differences in neural conduction times evoked by apical versus basal electrode stimulation persisted in the caudal but not rostral brainstem. SIGNIFICANCE: Activity-dependent changes of the auditory brainstem occur in response to both apical and basal cochlear implant electrode stimulation.     

Tinnitus with a normal audiogram: physiological evidence for hidden hearing loss and computational model

Ever since Pliny the Elder coined the term tinnitus, the perception of sound in the absence of an external sound source has remained enigmatic. Traditional theories assume that tinnitus is triggered by cochlear damage, but many tinnitus patients present with a normal audiogram, i.e., with no direct signs of cochlear damage. Here, we report that in human subjects with tinnitus and a normal audiogram, auditory brainstem responses show a significantly reduced amplitude of the wave I potential (generated by primary auditory nerve fibers) but normal amplitudes of the more centrally generated wave V. This provides direct physiological evidence of "hidden hearing loss" that manifests as reduced neural output from the cochlea, and consequent renormalization of neuronal response magnitude within the brainstem. Employing an established computational model, we demonstrate how tinnitus could arise from a homeostatic response of neurons in the central auditory system to reduced auditory nerve input in the absence of elevated hearing thresholds.     

Impaired neural conduction in the auditory brainstem of high-risk very preterm infants

ObjectiveTo test the hypothesis that neural conduction in the auditory brainstem is impaired in high-risk very preterm infants.MethodsEighty-two very preterm infants (gestation 28–32 weeks) with various perinatal problems or complications were studied at term using maximum length sequence (MLS) brainstem auditory evoked response (BAER) with click rates 91–910/s. The data were compared with those in 31 age-matched low-risk very preterm infants and 44 normal gestation (term) infants.ResultsHigh-risk very preterm infants showed a general increase in MLS BAER wave latencies and interpeak intervals. Wave V latency, and III–V and I–V intervals in high-risk very preterm infants were significantly longer than in normal term infants at all click rates, particularly higher rates. I–III interval was significantly longer, and III–V/I–III interval ratio was significantly greater at higher rates. These latency and intervals in high-risk very preterm infants were also longer, though relatively less significantly, than in low-risk very preterm infants. Click rate-related changes in major MLS BAER variables in high-risk infants were more significant than in the two groups of controls.ConclusionsThere were major abnormalities in MLS BAER variables that mainly reflect central neural conduction in high-risk very preterm infants. The abnormalities were relatively less significant when compared with low-risk very preterm infants than with normal term infants.SignificanceNeural conduction in the auditory brainstem, mainly the more central regions, is impaired in high-risk very preterm infants. The impairment is largely attributed to the associated perinatal problems, and partially related to very preterm birth.     

Electrophysiological study of the central and peripheral hearing system of aphasic individuals

SUBJECT: Electrophysiology of the auditory system. OBJECTIVE: Electrophysiological evaluation of the peripheral and central auditory system of brain injured patients. METHOD: Experimental group: eleven brain injured and aphasic subjects, both genders and with ages ranging from 43 to 75; control group: eleven individuals without hearing complaints, equalized as to gender and age. The subjects were evaluated through auditory brainstem response (ABR); auditory middle latency response (AMLR) and auditory P300 response. RESULTS: An increase in the V wave latency and I-V interpeak in both groups, due to the age factor. The presence of statistically significant hemispheric differences when compared to the Pa component in MLAEP research, registered in the C3 (left hemisphere) and the C4 (right hemisphere). In researching the P300 Cognitive Potential, there was an absence or increase in P300 latency and a decrease in P300 amplitude in the presence of the N2 component. CONCLUSION: The AMLR and auditory P300 response have proven to be effective instruments for evaluating aphasic individuals.