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This study investigated the relation between severity of auditory comprehension impairment in aphasia and the functional integrity of the posterior superior temporal region as evaluated by middle- and long-latency auditory evoked potentials and dipole source analysis. AEPs were studied in 20 stroke patients and in age-matched controls. AEPs and language data were collected 1 year or more post onset, and were compared to performance early after onset. Patients were differentiated in a group with severe and a group with moderate to recovered auditory comprehension impairment. Significant asymmetries of auditory evoked dipole source potentials were more frequent in the severely impaired group. However, a severe auditory comprehension deficit was not incompatible with normal AEPs. The results confirm the importance of the posterior superior temporal region for auditory language comprehension, but the correlation between AEP asymmetry and auditory comprehension seems due to the close spatial relation of AEP generating substrate and posterior language area rather than to partial overlap. Dipole source analysis of AEPs proved to be a valuable method for the assessment of interhemispheric asymmetries, enhancing the sensitivity of AEPs to unilateral damage of auditory cortex.
CONCLUSION: Peripheral auditory threshold does not correlate with brainstem auditory function in preterm infants. Infants with peripheral auditory abnormality seem not to be necessarily more prone to brainstem auditory abnormality than those without the elevation, although further studies are needed in a larger number of subjects. OBJECTIVE: To investigate whether peripheral auditory threshold correlates with brainstem auditory function in preterm infants and shed light on whether preterm infants with threshold elevation are prone to central auditory abnormality. PATIENTS AND METHODS: Brainstem auditory evoked response (BAER) was recorded with clicks at term in preterm infants (gestation 28-36 weeks). Analysis of correlation was made between BAER threshold and various BAER components. BAER data were compared between preterm infants with thresholds < or = 20 dB nHL (n = 113) and those > 20 dB (n = 32). RESULTS: Although BAER threshold correlated significantly with BAER wave latencies and amplitudes, the threshold did not correlate significantly with I-V, I-III and III-V intervals. No significant differences were found between preterm infants with BAER thresholds < or = 20 dB and those > 20 dB in I-V, I-III intervals, although III-V was longer in the infants with thresholds > 20 dB nHL (p < 0.05).
The aim of this study was to investigate auditory cortex function in the context of auditory stimuli in a patient with auditory agnosia due to bilateral lesions confined to the auditory radiations. A male patient experienced mild left temporal hemiplegia because of right putaminal hemorrhage at the age of 43 years. Thereafter he recovered completely but hypertension persisted. When he was 53 years old, he suffered left putaminal hemorrhage and went into a coma. After recovering from the coma and right hemiplegia he could hear but could not discriminate speech sounds. Brain CT and MRI demonstrated small bilateral lesions confined to the auditory radiations. Magnetoencephalography demonstrated the disappearance of middle latency responses and auditory-evoked potential studies showed a very small Pa peak. In contrast, a positron emission tomography study demonstrated a marked increase in blood flow in the bilateral auditory cortex in response to both click and monosyllable stimuli. It is speculated that the auditory cortex receives functional projections from the cochlea via non-specific pathways in the cerebral hemispheres.
Children of women who smoke cigarettes during pregnancy display cognitive deficits in the auditory-verbal domain. Clinical studies have implicated developmental exposure to nicotine, the main psychoactive ingredient of tobacco, as a probable cause of subsequent auditory deficits. To test for a causal link, we have developed an animal model to determine how neonatal nicotine exposure affects adult auditory function. In adult control rats, nicotine administered systemically (0.7 mg/kg, s.c.) enhanced the sensitivity to sound of neural responses recorded in primary auditory cortex. The effect was strongest in cortical layers 3 and 4, where there is a dense concentration of nicotinic acetylcholine receptors (nAChRs) that has been hypothesized to regulate thalamocortical inputs. In support of the hypothesis, microinjection into layer 4 of the nonspecific nAChR antagonist mecamylamine (10 microM) strongly reduced sound-evoked responses. In contrast to the effects of acute nicotine and mecamylamine in adult control animals, neither drug was as effective in adult animals that had been treated with 5 days of chronic nicotine exposure (CNE) shortly after birth. Neonatal CNE also impaired performance on an auditory-cued active avoidance task, while having little effect on basic auditory or motor functions. Thus, neonatal CNE impairs nicotinic regulation of cortical function, and auditory learning, in the adult. Our results provide evidence that developmental nicotine exposure is responsible for auditory-cognitive deficits in the offspring of women who smoke during pregnancy, and suggest a potential underlying mechanism, namely diminished function of cortical nAChRs.
OBJECTIVE: To study the auditory function and auditory nerve pathological changes of the experimental allergic neuritis (EAN) animal model in Guinea pigs. METHOD: To establish the animal model of EAN, heterologous myelin basic protein (MBP) of peripheral nerve was used to the immunize Guinea pigs. Serum anti-MBP-IgG levels, sciatic nerve conduction velocity (NCV), hearing thresholds and wave latencies, and pathological changes in auditory nerve, sciatic nerve and cochlea were observed. The immune lesions in inner ear were examined with immunohistochemistry. Auditory brainstem response (ABR) and compound action potential (CAP) were assayed weekly before and after immunization for a period of seven weeks. In the control group, antigen was replaced by the 0.9% saline. RESULT: Serum anti-MBP-IgG levels increased significantly in experimental group comparing with the control group (P < 0.01). Seiatic nerve conduction velocity decreased after immunization, as comparing with the control group (P < 0.01). Sciatic nerve and auditory nerve showed the existence of demyelination. There was significant increase of ABR and CAP thresholds and the latencies of wave I, III, V and N1 in experimental group when compared to the controls (P < 0.01), but no significant changes in inter-peak latencies of I-III, III-V were found( P > 0.05). In addition, there were 4 Guinea pigs (8 ears) in which only appeared lengthened wave latencies with normal hearing thresholds. Immunohistochemistry indicated that antibodies to inner ear from the MBP-sensitized animals distributed in cochlear nerve, neurofiber of inner ear and spiral ganglion cells. Cochlear scanning electron microscopy showed the pathology of inner hair cell with stereociliary disorder and cytoplasmic protrusions. CONCLUSION: The results suggest that auditory nerve demyelination are involved in this experimental allergic neuritis animal model and sciatic nerve demyelination as well, and the auditory abnormalities are elicited. This animal model seems to be a promising one of auditory dysfunction due to demyelination disorders.
The combined findings of "normal evoked otoacoustic emissions (EOAE) and absent or markedly disturbed auditory evoked potentials from the brainstem and/or cortex" has been named auditory neuropathy in the English literature. The pure tone thresholds in these patients range from mild to severe loss. The loss of speech comprehension is out of proportion in comparison to the pure tone threshold elevation. This combination of findings suggests that cochlear function and in particular outer hair cell function, is normal in these patients but also suggests that the inner hair cell / VIII nerve functional unit is abnormal. Disruption in neural synchrony has previously been postulated as a reasonable explanation for the absent auditory brainstem response while otoacoustic emissions are preserved. Because the long-latency auditory evoked potentials, not having the stringent synchrony requirements of the ABR, may also be missing, the term synchrony - disruption may be somewhat misleading. The literature about auditory neuropathy is reviewed here: We now know that a set of salient features distinguishes these patients from the majority of patients with sensorineural hearing loss or other described syndromes. The symptoms defining auditory neuropathy are mild, moderate or severe elevation of auditory thresholds to pure tone stimuli by air and bone conduction, absent to severely abnormal ABRs to high level stimuli, present otoacoustic emissions (that do not suppress with contralateral noise), word recognition ability poorer than expected from the pure tone hearing loss configuration (in cases with mild to moderate hearing threshold elevation) and absent acoustic reflexes to both ipsilateral and contralateral tones. The entire set of findings, consistently seen in these patients, supports the importance of the crosscheck principle in diagnostic evaluation especially in children with delayed and/or impaired language acquisition. It is of ponderous importance that this disorder is not being confused with sensory hearing loss.
The extent of a region containing acoustically responsive neurons within the anterior ectosylvian sulcus and its relationship to surrounding gyral auditory cortical fields was examined in chloralose-anaesthetized cats. Multiple microelectrode penetrations were made orthogonal to the middle and anterior ectosylvian gyral surfaces, and longer penetrations were made into the dorsal and ventral banks and fundus of the anterior ectosylvian sulcus. The quantitative and qualitative auditory response characteristics of neurons and neuron clusters in the sulcal banks and surrounding regions were mapped in detail, and the degree of overlap of auditory and visual neurons within the sulcus was determined by routinely testing for responsiveness to a gross light flash. The detailed results from three animals and a summary of all penetrations into the sulcus are presented. The anterior ectosylvian sulcal field (Field AES) lay deep within the banks and fundus of the posterior three quarters of the sulcus. A combination of changes in the auditory response characteristics of neurons (i.e., in optimal stimulus, latency, and frequency tuning), and the presence of visually responsive cells, distinguished this field from surrounding fields. The distinction between the anterior ectosylvian field and extensions of the nearby tonotopic fields (i.e., primary and anterior auditory fields) into the dorsal and ventral banks of the dorsoposterior sector of the sulcus was readily made on the basis of these characteristics. The distinction between the anterior ectosylvian field and extensions of the second auditory field into the ventral bank of the middle sector of the sulcus was more difficult and there were differences between animals in the transition between these fields. Anterior ectosylvian sulcal field responses did not extend into the dorsal bank in anterior parts of the sulcus but were restricted to fundal regions, an observation consistent with the presence of the fourth somatosensory field in the dorsal bank of this sector of the sulcus. The majority of penetrations into the sulcus revealed coextensive auditory and visual activity, an observation apparently at variance with the identification of a purely visual field in this region. Barbiturate anaesthesia, which has been used in experiments demonstrating an anterior ectosylvian visual area, was found to have a depressing effect on auditory responses within the anterior ectosylvian sulcal field.
A topographic representation of the auditory azimuth has been described in the external nucleus of the inferior colliculus (ICX) of the guinea-pig [3]. This representation is characterized by directional multi-unit responses, at threshold stimulation intensities, with directional preferences organized in such a way as to represent the auditory azimuth along the rostro-caudal axis of the ICX. The following paper considers the emergence of that map and the role of developmental experience in its elaboration. Multi-unit responses to free-field broad-band auditory stimuli were recorded in the ICX. At threshold stimulation intensities, multi-unit receptive fields (MURFs) obtained from younger animals showed the same discrete spatial tuning as found in MURFs from animals older than 35 DAB (days after birth). However, a normal adult topographic representation was not present until animals were at least 30-32 DAB. Visual deprivation, by dark-rearing from birth until mapping (at 35-43 DAB), had no obvious detrimental effects on auditory receptive field size or topographic order in the ICX. Auditory deprivation was achieved by rearing animals in an environment of continuous omnidirectional noise from birth until mapping (47-53 DAB). Following auditory deprivation, receptive fields remained relatively discrete, but no correlation between rostro-caudal position of the recording site and the angle of the best response was observed. Thus, the representation of auditory azimuth in the ICX appears to be unperturbed by developmental visual deprivation but is susceptible to developmental auditory deprivation.
NMDA receptors have been well shown to be involved in neuronal plasticity. In order to understand the role of NR2B subtype NMDA receptors in auditory function development, the present study investigated the effect of early auditory deprivation on the expression of NR2B mRNA in rat auditory cortex (AC) during postnatal development. For normal rats, the NR2B mRNA expression was highest at birth (postnatal day 1 [P1]) and declined rapidly to low level during adulthood. However, during the critical period of rat auditory development (two to three weeks after birth), there was a transient NR2B expression peak on postnatal day 21 (P21). For the auditory-deprived rats, the general declining trend of NR2B mRNA expression from birth to adult was similar to that observed in the normal group, whereas the expression level from P15 to P27 was significantly lower than normal and the transient peak on P21 disappeared. In both groups, the distribution pattern of NR2B mRNA-positive neurons was also examined in various layers and dorsal, medial and ventral subdistricts of AC. There is no significant effect on the spatial expression of the NR2B mRNA in the AC between normal and deprived group. Our results indicated that the early auditory deprivation decreased the expression levels of NR2B mRNA in AC during the critical period of rat auditory development, suggesting that NR2B plays an important role in the developmental plasticity of auditory function in rats.
Developmental dyslexia is characterized by a phonological processing deficit and impaired low-level auditory processing may contribute to this problem. However, this remains controversial because not all dyslexic individuals show psychophysical deficits on auditory processing tasks; hence it has been argued that auditory processing deficits are not a causal factor in dyslexia. Because behavioral psychophysical tasks include both bottom-up processing and top-down strategies, dyslexics' successful coping strategies may positively influence their performance on auditory behavioral measures. Therefore we have studied whether dyslexics who perform adequately on auditory psychophysical tasks nevertheless show electrophysiological evidence of impaired auditory processing. We compared auditory event-related mismatch negativity (MMN) potentials to frequency modulated (FM) tones at 5, 20 and 240 Hz between dyslexic adults and controls. Groups were matched for age, cognitive ability and psychophysical FM detection thresholds. The dyslexic group showed significantly smaller MMNs in the 20 Hz FM condition in both the early (150-300 ms, P=0.010) and late (300-500 ms, P=0.049) time frames. A 2-way ANOVA showed a significant group by FM rate interaction (P=0.012). There were no significant differences between the groups in the 5 Hz or 240 Hz conditions. The magnitude of the 20 Hz FM MMN correlated with the degree of discrepancy between cognitive and literacy skills (0.66, P=0.003) in the entire group. Thus, even among compensated dyslexics with above-average cognitive abilities and adequate performance on auditory psychophysical tasks, the MMN responses of some dyslexic adults were found to be abnormal.
The development of brain stem auditory-evoked potentials (BAEP) was studied in devocalized ducklings reared in auditory isolation and in vocal ducklings exposed to enhanced species-specific auditory stimulation with embryonic contact-contentment calls (CTs). Thresholds and latency of BAEP wave P1 in the mute ducklings indicated that even short-term auditory deprivation affected the development of auditory sensitivity, substantially reducing the rate of decline in BAEP thresholds and latencies of P1, especially in the low-frequency (500 and 750 Hz) and high-frequency (above 2.0 kHz) ranges. The ducklings exposed to enhanced stimulation, on the other hand, showed an accelerated decline in BAEP thresholds and latencies of P1 across all test frequencies, with the most marked influence on low (below 1.5 kHz) and high (above 2.5 kHz) frequencies. The influence of species-specific auditory experience had its most potent effect during the embryonic critical period for postnatal auditory perceptual (behavioral) development, at which time the embryo produces and hears a special low-frequency (1.5-2.5 kHz) version of its own contact-contentment vocalization.
Auditory disability increases with both hearing threshold level and age. It is often suggested that some or most of the age effect in auditory disability is underpinned by deficits in central auditory function. A sample of 240 individuals aged between 50 and 75 years was examined to provide a balance across the major variables of hearing level and age. The central auditory indices investigated were: the binaural masking difference, the effects of dichotic competition on the staggered spondaic word tests, the binaural advantage for dichotically presented words, the binaural advantage for dichotically presented sentences, the effect of increasing the rate of presentation of speech, and the effect of nonsense as opposed to sensible sentences. In addition, the non-auditory variables of verbal and non-verbal IQ and the peripheral auditory factors of frequency and temporal resolution were assessed. Auditory disability was assessed using a performance index derived from a sentence identification-in-noise procedure and a procedure containing sense or nonsense sentences. Aspects of self-reported disability were determined using the MRC Institute of Hearing Research's Hearing Disability Questionnaire and the American Hearing Performance Inventory. There were significant correlations between the derived central variables and measured disability after control for hearing threshold levels and age. Central variables were correlated with self-reported disability for only the specific sub-score reflecting disability in localisation. On a multiple regression, the central variables explained 11.1% of the variance in performance index of disability above the 21.1% explained by hearing threshold levels and age.(ABSTRACT TRUNCATED AT 250 WORDS)
A 53-year-old man showed central auditory disturbance with recurrent cerebral hemorrhage. At his acute stage he had deafness and auditory anosognosia. Two or three months later, there was no deafness and auditory anosognosia, but he could not comprehend words, environmental sounds and music. Auditory brainstem responses showed no peripheral or brainstem damage, and the lesion of bilateral auditory radiation was detected by MRI. His auditory agnosia did not improve over one and a half year. There is no report like such permanent auditory agnosia with the lesion of bilateral subcortical temporal lobe.
Research has shown that speaking in a deliberately clear manner can improve the accuracy of auditory speech recognition. Allowing listeners access to visual speech cues also enhances speech understanding. Whether the nature of information provided by speaking clearly and by using visual speech cues is redundant has not been determined. This study examined how speaking mode (clear vs. conversational) and presentation mode (auditory vs. auditory-visual) influenced the perception of words within nonsense sentences. In Experiment 1, 30 young listeners with normal hearing responded to videotaped stimuli presented audiovisually in the presence of background noise at one of three signal-to-noise ratios. In Experiment 2, 9 participants returned for an additional assessment using auditory-only presentation. Results of these experiments showed significant effects of speaking mode (clear speech was easier to understand than was conversational speech) and presentation mode (auditory-visual presentation led to better performance than did auditory-only presentation). The benefit of clear speech was greater for words occurring in the middle of sentences than for words at either the beginning or end of sentences for both auditory-only and auditory-visual presentation, whereas the greatest benefit from supplying visual cues was for words at the end of sentences spoken both clearly and conversationally. The total benefit from speaking clearly and supplying visual cues was equal to the sum of each of these effects. Overall, the results suggest that speaking clearly and providing visual speech information provide complementary (rather than redundant) information.
OBJECTIVE: Mismatch negativity (MMN), a change-specific component of the auditory event-related potential (ERP), is sensitive to deficits in central auditory processing associated with many clinical conditions. The aim of this study was to obtain a comprehensive multi-dimensional profile of central auditory processing by extending the recently developed fast multi-feature MMN paradigm [Näätänen R, Pakarinen S, Rinne T, Takegata R. The mismatch negativity (MMN): towards the optimal paradigm. Clin Neurophysiol 2004;115:140-144]. METHODS: MMN responses to changes in sound duration, frequency, intensity, and perceived sound-source location at six different magnitudes of deviation were recorded from healthy young adults by using the multi-feature MMN paradigm. In addition, behavioural discrimination accuracy and speed were measured to examine the relationship between MMN and behavioural performance. RESULTS: All the 24 sound changes elicited significant MMNs. MMN amplitude increased and latency decreased with increasing magnitude of sound change. Furthermore, the MMN amplitude and latency predicted the subjects' accuracy and speed in detecting these deviations. CONCLUSIONS: This new paradigm provides an extensive auditory discrimination profile for several auditory attributes at different deviation magnitudes in a minimal recording time. SIGNIFICANCE: The auditory discrimination profiles can offer a comprehensive view of the development, plasticity, and deficits of central auditory processing.
We examined efferent connections of the cortical auditory field that receives thalamic afferents specifically from the suprageniculate nucleus (SG) and the dorsal division (MGD) of the medial geniculate body (MG) in the rat [Neuroscience 117 (2003) 1003]. The examined cortical region was adjacent to the caudodorsal border (4.8-7.0 mm posterior to bregma) of the primary auditory area (area Te1) and exhibited relatively late auditory response and high best frequency, compared with the caudal end of area Te1. On the basis of the location and auditory response property, the cortical region is considered identical to "posterodorsal" auditory area (PD). Injections of biocytin in PD revealed characteristic projections, which terminated in cortical areas and subcortical structures that play pivotal roles in directed attention and space processing. The most noticeable cortical terminal field appeared as dense plexuses of axons in area Oc2M, the posterior parietal cortex. Small terminal fields were scattered in area frontal cortex, area 2 that comprises the frontal eye field. The subcortical terminal fields were observed in the pontine nucleus, the nucleus of the brachium inferior colliculus, and the intermediate and deep layers of the superior colliculus. Corticostriatal projections targeted two discrete regions of the caudate putamen: the top of the middle part and the caudal end. It is noteworthy that the inferior colliculus and amygdala virtually received no projection. Corticothalamic projections terminated in the MGD, the SG, the ventral zone of the ventral division of the MG, the ventral margin of the lateral posterior nucleus (LP), and the caudodorsal part of the posterior thalamic nuclear group (Po). Large terminals were found in the MGD, SG, LP and Po besides small terminals, the major component of labeling. The results suggest that PD is an auditory area that plays an important role in spatial processing linked to directed attention and motor function. The results extend to the rat findings from nonhuman primates suggesting the existence of a posterodorsal processing stream for auditory spatial perception.
We examined effects of eye position on auditory cortical responses in macaques. Laminar current-source density (CSD) and multiunit activity (MUA) profiles were sampled with linear array multielectrodes. Eye position significantly modulated auditory-evoked CSD amplitude in 24/29 penetrations (83%), across A1 and belt regions; 4/24 cases also showed significant MUA AM. Eye-position effects occurred mainly in the supragranular laminae and lagged the co-located auditory response by, on average, 38 ms. Effects in A1 and belt regions were indistinguishable in amplitude, laminar profile, and latency. The timing and laminar profile of the eye-position effects suggest that they are not combined with auditory signals at a subcortical stage of the lemniscal auditory pathways and simply "fed-forward" into cortex. Rather, these effects may be conveyed to auditory cortex by feedback projections from parietal or frontal cortices, or alternatively, they may be conveyed by nonclassical feedforward projections through auditory koniocellular (calbindin positive) neurons.