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PubMed1991

Effects of opioid be drugs on auditory evoked potentials suggest a role of lateral olivocochlear dynorphins in auditory function.

Multiple gene products of opioid peptide families (e.g., enkephalins, dynorphins) with differing opioid receptor specificities are present within olivocochlear efferent terminals. Enkephalins activate mu- and delta-opioid receptors, and are generally inhibitory in the nervous system, and dynorphins are kappa-receptor agonists, which may be excitatory to postsynaptic neurons. We have examined the effects of intravenously administered opioid agonists and antagonists on click-evoked N1 and N2 amplitudes and latencies of the compound action potential in the chinchilla recorded at the round window. Parenteral administration of the opioid receptor antagonist naloxone or the potent mu-receptor agonist fentanyl did not alter N1 and N2 amplitudes or latencies. The kappa-receptor agonist, mu-receptor antagonist pentazocine caused marked increases in N1 and N2 amplitudes over baseline values at threshold intensities. These effects were not abolished by naloxone. No effects were seen on the cochlear microphonic, supporting a site of action of these effects at the lateral olivocochlear efferent terminals on auditory nerve dendrites under inner hair cells. Similar results were obtained when far field auditory evoked responses were recorded. Results were obtained under ketamine/pentobarbital anesthesia, which provided stable recording baselines in contrast to tiletamine/zolezepam/pentobarbital, with which an upward drift in auditory potentials was observed. This stimulatory action of kappa-agonists on auditory-evoked potential amplitudes appears to represent a physiological role of the lateral olivocochlear efferent innervation. The different neurotransmitters of the olivocochlear efferents (e.g. enkephalins, dynorphins, acetylcholine) may have antagonistic actions on auditory potentials, as may the lateral and medial systems themselves.

Animals↗
PubMed2004

Auditory lexical decision, categorical perception, and FM direction discrimination differentially engage left and right auditory cortex.

Recent neuroimaging and neuropsychological data suggest that speech perception is supported in bilaterally auditory areas. We evaluate this issue building on well-known behavioral effects. While undergoing positron emission tomography (PET), subjects performed standard auditory tasks: direction discrimination of frequency-modulated (FM) tones, categorical perception (CP) of consonant-vowel (CV) syllables, and word/non-word judgments (lexical decision, LD). Compared to rest, the three conditions led to bilateral activation of the auditory cortices. However, lateralization patterns differed as a function of stimulus type: the LD task generated stronger responses in the left, the FM task a stronger response in the right hemisphere. Contrasts between either words or syllables versus FM were associated with significantly greater activity bilaterally in superior temporal gyrus (STG) ventro-lateral to Heschl's gyrus. These activations extended into the superior temporal sulcus (STS) and the middle temporal gyrus (MTG) and were greater in the left. The same areas were more active in the LD than the CP task. In contrast, the FM task was associated with significantly greater activity in the right lateral-posterior STG and lateral MTG. The findings argue for a view in which speech perception is mediated bilaterally in the auditory cortices and that the well-documented lateralization is likely associated with processes subsequent to the auditory analysis of speech.

Acoustic Stimulation↗
PubMed2004

Auditory neglect: what and where in auditory space.

A sound that we hear in a natural setting allows us to identify the sound source and to localise it in space. Several lines of evidence indicate that the two aspects are processed in anatomically distinct cortical networks. Auditory areas that are part of the What or Where processing streams have been identified recently in man and in non-human primates. Comparison between anatomical and activation studies suggests that processing within either stream can be modulated by specific attentional factors. Attending to auditory events can be affected in neglect. Bisiach et al. (1984) described systematic directional errors to the ipsilesional space, which was considered a manifestation of hemispatial neglect and interpreted as a disruption of the neural network providing the internal representation of egocentric space. The other manifestation of auditory neglect is contralesional extinction in dichotic listening condition (Heilman and Valenstein, 1972). Recently two types of auditory neglect have been described, one corresponding to a primarily attentional deficit associated with basal ganglia lesions and the other to distortions of auditory space representations associated with parieto-prefrontal lesions (Bellmann et al., 2001). Based on studies of sound detection and sound recognition following hemispheric lesions we argue that the two types of neglect correspond to disturbed processing in either the What or the Where stream.

Attention↗
PubMed1993

Modulation of early sensory processing in human auditory cortex during auditory selective attention.

Neuromagnetic fields were recorded from human subjects as they listened selectively to sequences of rapidly presented tones in one ear while ignoring tones of a different pitch in the opposite ear. Tones in the attended ear evoked larger magnetic brain responses than did unattended tones in the latency ranges 20-50 msec and 80-130 msec poststimulus. Source localization techniques in conjunction with magnetic resonance imaging placed the neural generators of these early attention-sensitive brain responses in auditory cortex on the supratemporal plane. These data demonstrate that focused auditory attention in humans can selectively modulate sensory processing in auditory cortex beginning as early as 20 msec poststimulus, thereby providing strong evidence for an "early selection" mechanism of auditory attention that can regulate auditory input at or before the initial stages of cortical analysis.

Acoustic Stimulation↗
PubMed2004

Evaluation of selected auditory tests in school-age children suspected of auditory processing disorders.

OBJECTIVE: To compare the auditory function of normal-hearing children attending mainstream schools who were referred for an auditory evaluation because of listening/hearing problems (suspected auditory processing disorders [susAPD]) with that of normal-hearing control children. DESIGN: Sixty-five children with a normal standard audiometric evaluation, ages 6-14 yr (32 of whom were referred for susAPD, with the rest age-matched control children), completed a battery of four auditory tests: a dichotic test of competing sentences; a simple discrimination of short tone pairs differing in fundamental frequency at varying interstimulus intervals (TDT); a discrimination task using consonant cluster minimal pairs of real words (CCMP), and an adaptive threshold task for detecting a brief tone presented either simultaneously with a masker (simultaneous masking) or immediately preceding it (backward masking). Regression analyses, including age as a covariate, were performed to determine the extent to which the performance of the two groups differed on each task. Age-corrected z-scores were calculated to evaluate the effectiveness of the complete battery in discriminating the groups. RESULTS: The performance of the susAPD group was significantly poorer than the control group on all but the masking tasks, which failed to differentiate the two groups. The CCMP discriminated the groups most effectively, as it yielded the lowest number of control children with abnormal scores, and performance in both groups was independent of age. By contrast, the proportion of control children who performed poorly on the competing sentences test was unacceptably high. Together, the CCMP (verbal) and TDT (nonverbal) tasks detected impaired listening skills in 56% of the children who were referred to the clinic, compared with 6% of the control children. Performance on the two tasks was not correlated. CONCLUSIONS: Two of the four tests evaluated, the CCMP and TDT, proved effective in differentiating the two groups of children of this study. The application of both tests increased the proportion of susAPD children who performed poorly compared with the application of each test alone, while reducing the proportion of control subjects who performed poorly. The findings highlight the importance of carrying out a complete auditory evaluation in children referred for medical attention, even if their standard audiometric evaluation is unremarkable.

Adolescent↗
PubMed1990

Auditory association cortex lesions impair auditory short-term memory in monkeys.

Monkeys that were trained to perform auditory and visual short-term memory tasks (delayed matching-to-sample) received lesions of the auditory association cortex in the superior temporal gyrus. Although visual memory was completely unaffected by the lesions, auditory memory was severely impaired. Despite this impairment, all monkeys could discriminate sounds closer in frequency than those used in the auditory memory task. This result suggests that the superior temporal cortex plays a role in auditory processing and retention similar to the role the inferior temporal cortex plays in visual processing and retention.

Animals↗
PubMed1997

First-spike timing of auditory-nerve fibers and comparison with auditory cortex.

First-spike timing of auditory-nerve fibers and comparison with auditory cortex. J. Neurophysiol. 78: 2438-2454, 1997. The timing of the first spike of cat auditory-nerve (AN) fibers in response to onsets of characteristic frequency (CF) tone bursts was studied and compared with that of neurons in primary auditory cortex (AI), reported previously. Tones were shaped with cosine-squared rise functions, and rise time and sound pressure level were parametrically varied. Although measurement of first-spike latency of AN fibers was somewhat compromised by effects of spontaneous activity, latency was an invariant and inverse function of the maximum acceleration of peak pressure (i.e., a feature of the 2nd derivative of the stimulus envelope), as previously found in AI, rather than of tone level or rise time. Latency-acceleration functions of all AN fibers were of very similar shape, similar to that observed in AI. As in AI, latency-acceleration functions of different fibers were displaced along the latency axis, reflecting differences in minimum latency, and along the acceleration axis, reflecting differences in sensitivity to acceleration [neuronal transient sensitivity (S)]. S estimates increased with spontaneous rate (SR), but values of high-SR fibers exceeded those in AI. This suggests that S estimates are biased by SR per se, and that unbiased true S values would be less tightly correlated with response properties covarying with SR, such as firing threshold. S estimates varied with CF in a fashion similar to the cat's audiogram and, for low- and medium-SR fibers, matched those for AI neurons. Minimum latency decreased with increasing SR and CF. As in AI, the standard deviation of first-spike timing (SD) in AN was also an inverse function of maximum acceleration of peak pressure. The characteristics of the increase of SD with latency in a given AN fiber/AI neuron and across AN fibers/AI neurons revealed that the precision of first-spike timing to some stimuli can actually be higher in AI than in AN. The data suggest that the basic characteristics of the latency-acceleration functions of transient onset responses seen in cortex are generated at inner hair cell-AN fiber synapses. Implications for signal processing in the auditory system and for first-spike generation and adaptation in AN are discussed.

Acoustic Stimulation↗
PubMedDate not supplied

Neural correlates of auditory repetition priming: reduced fMRI activation in the auditory cortex.

Repetition priming refers to enhanced or biased performance with repeatedly presented stimuli. Modality-specific perceptual repetition priming has been demonstrated behaviorally for both visually and auditorily presented stimuli. In functional neuroimaging studies, repetition of visual stimuli has resulted in reduced activation in the visual cortex, as well as in multimodal frontal and temporal regions. The reductions in sensory cortices are thought to reflect plasticity in modality-specific neocortex. Unexpectedly, repetition of auditory stimuli has resulted in reduced activation in multimodal and visual regions, but not in the auditory temporal lobe cortex. This finding puts the coupling of perceptual priming and modality-specific cortical plasticity into question. Here, functional magnetic resonance imaging was used with environmental sounds to reexamine whether auditory priming is associated with reduced activation in the auditory cortex. Participants heard environmental sounds (e.g., animals, machines, musical instruments, etc.) in blocks, alternating between initial and repeated presentations, and decided whether or not each sound was produced by an animal. Repeated versus initial presentations of sounds resulted in repetition priming (faster responses) and reduced activation in the right superior temporal gyrus, bilateral superior temporal sulci, and right inferior prefrontal cortex. The magnitude of behavioral priming correlated positively with reduced activation in these regions. This indicates that priming for environmental sounds is associated with modification of neural activation in modality-specific auditory cortex, as well as in multimodal areas.

Acoustic Stimulation↗
PubMed2006

Multiple auditory steady-state responses in children and adults with normal hearing, sensorineural hearing loss, or auditory neuropathy.

OBJECTIVES: We tested the clinical effectiveness of multiple auditory steady-state responses (ASSRs) for the objective assessment of hearing thresholds in patients with and without hearing loss, candidates for cochlear implants, and children with auditory neuropathy. METHODS: The study sample included 29 subjects with sensorineural hearing loss (SNHL), 18 candidates for cochlear implants, 11 subjects with auditory neuropathy, and 18 subjects with normal hearing thresholds. Behavioral hearing thresholds and ASSRs to carrier frequencies of 0.5, 1, 2, and 4 kHz were obtained. Special care was taken to minimize possible aliasing and high-intensity multiple stimulation effects. Differences and correlations between the ASSRs and the behavioral thresholds were determined. RESULTS: The ASSR estimation of behavioral thresholds in the normal-hearing group was elevated, whereas very close predictions were found for the SNHL group. The correlations between the two measures ranged from 0.86 at 0.5 kHz carrier frequency to 0.94 at 2 kHz. In the cochlear implant candidates and the auditory neuropathy group, the ASSR thresholds generally overestimated the behavioral audiogram. In these groups the number of detected ASSRs was higher than the number of behavioral responses, especially for the high-frequency carrier stimuli. CONCLUSIONS: Multiple ASSRs may reliably predict the behavioral threshold in subjects with SNHL and may serve as a valuable objective measure for assessing the hearing threshold across different frequencies in candidates for cochlear implants and children with auditory neuropathy.

Adolescent↗
PubMed2002

Effects of early auditory deprivation and stimulation on auditory brainstem responses in the rat.

The purpose of this study was to investigate the effect of auditory sound deprivation or stimulation on auditory brainstem responses (ABRs) during the maturation period of the rat auditory system. At postnatal day (PND) 21, 40 newborn Norway Brown male rats were categorized into 3 groups: (i) an auditory deprivation group in which a bilateral average conductive hearing loss of 27 dB was induced; (ii) an auditory activation group exposed to 65-90 dB sound pressure level; and (iii) a control group. ABR recordings were made on PND 84. In order to compare group differences in interpeak latency (IPL), sensation level (SL), defined as stimulus intensity above threshold, was used. IPL measurements and analysis were restricted to the 20-60 dB SL range. No differences were observed in the IPLs of peaks I-IV between the three groups. Small, but not statistically significant, differences in mean estimated IPLs of peaks I-IV were shown in the ranges > 50 dB SL and < 25 dB SL. Possible confounding factors explaining the apparent discrepancy between these results and those of other animal studies are reviewed.

Acoustic Stimulation↗
PubMed2003

Functional asymmetry for auditory processing in human primary auditory cortex.

Structural asymmetries in the supratemporal plane of the human brain are often cited as the anatomical basis for the lateralization of language predominantly to the left hemisphere. However, similar asymmetries are found for structures mediating earlier events in the auditory processing stream, suggesting that functional lateralization may occur even at the level of primary auditory cortex. We tested this hypothesis using functional magnetic resonance imaging to evaluate human auditory cortex responses to monaurally presented tones. Relative to silence, tones presented separately to either ear produced greater activation in left than right Heschl's gyrus, the location of primary auditory cortex. This functional lateralization for primary auditory cortex is distinct from the contralateral dominance reported for other mammals, including nonhuman primates, and may have contributed to the evolution of a unique role for the left hemisphere in language processing.

Adult↗
PubMed1995

Convergence of somatosensory and auditory projections in the avian torus semicircularis, including the central auditory nucleus.

Projections of dorsal column, spinal, and cochlear nuclei upon the central nucleus of the torus semicircularis (otherwise known as nucleus mesencephalicus lateralis, pars dorsalis, or MLd) and upon other toral nuclei were investigated in pigeon by anterograde and retrograde tracing and electrophysiological methods. The anatomical results showed that caudal regions of the dorsal column nuclei and medial lamina V of the upper four cervical spinal segments have extensive projections upon the contralateral central auditory nucleus and upon other nuclei of the torus, in particular the core portion of the preisthmic superficial area of Puelles et al. (L. Puelles, C. Rrobles, M. Martiez-de-la-Torre, and S. Martinez, 1994, J. Comp. Neurol. 340:98-125). The projections of nucleus angularis were found to terminate throughout most of the contralateral central nucleus except the dorsomedial portion at rostral levels, where the majority of the projections of nucleus laminaris were concentrated. Nucleus angularis (and to a lesser extent nucleus laminaris) was also found to have substantial projections to certain noncentral toral nuclei, in particular to the caudomedial shell nucleus of Puelles et al. (1994). As shown positively with both Nissl and cytochrome oxidase staining and negatively with substance P labeling, this nucleus is a medial extension of more caudal regions of the central nucleus, and it is suggested that it should be included as part of the auditory midbrain. The electrophysiological results confirmed the anatomical findings by showing that evoked potentials and multiunit activity can be recorded throughout the central and noncentral toral nuclei by using electrical stimulation of the radial nerve and auditory click stimuli. The core portion of the preisthmic superficial area, however, can be regarded as a distinct somatosensory nucleus of the midbrain. It is concluded that there is substantial convergence of somatosensory and auditory inputs within both central auditory and noncentral nuclei of the torus semicircularis in pigeon.

Animals↗
PubMed1991

Auditory corticocortical interconnections in the cat: evidence for parallel and hierarchical arrangement of the auditory cortical areas.

The origin and laminar arrangement of the homolateral and callosal projections to the anterior (AAF), primary (AI), posterior (PAF) and secondary (AII) auditory cortical areas were studied in the cat by means of electrophysiological recording and WGA-HRP tracing techniques. The transcallosal projections to AAF, AI, PAF and AII were principally homotypic since the major source of input was their corresponding area in the contralateral cortex. Heterotypic transcallosal projections to AAF and AI were seen, originating from the contralateral AI and AAF, respectively. PAF received heterotypic commissural projections from the opposite ventroposterior auditory cortical field (VPAF). Heterotypic callosal inputs to AII were rare, originating from AAF and AI. The neurons of origin of the transcallosal connections were located mainly in layers II and III (70-92%), and less frequently in deep layers (V and VI, 8-30%). Single unit recordings provided evidence that both homotypic and heterotypic transcallosal projections connect corresponding frequency regions of the two hemispheres. The regional distribution of the anterogradely labeled terminals indicated that the homotypic and heterotypic auditory transcallosal projections are reciprocal. The present data suggest that the transcallosal auditory interconnections are segregated in 3 major parallel components (AAF-AI, PAF-VPAF and AII), maintaining a segregation between parallel functional channels already established for the thalamocortical auditory interconnections. For the intrahemispheric connections, the analysis of the retrograde tracing data revealed that AAF and AI receive projections from the homolateral cortical areas PAF, VPAF and AII, whose neurons of origin were located mainly in their deep (V and VI) cortical layers. The reciprocal interconnections between the homolateral AAF and AI did not show a preferential laminar arrangement since the neurons of origin were distributed almost evenly in both superficial (II and III) and deep (V and VI) cortical layers. On the contrary, PAF received inputs from the homolateral cortical fields AAF, AI, AII and VPAF, originating predominantly from their superficial (II and III) layers. The homolateral projections reaching AII originated mainly from the superficial layers of AAF and AI, but from the deep layers of VPAF and PAF. The laminar distribution of anterogradely labeled terminal fields, when they were dense enough for a confident identification, was systematically related to the laminar arrangement of neurons of origin of the reciprocal projection: a projection originating from deep layers was associated with a reciprocal projection terminating mainly in layer IV, whereas a projection originating from superficial layers was associated with a reciprocal projection terminating predominantly outside layer IV.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1985

Transneuronal transport in the vestibular and auditory systems of the squirrel monkey and the arctic ground squirrel. II. Auditory system.

Transneuronal transport in the auditory system of the squirrel monkey and the arctic ground squirrel was studied after implantation of tritiated protein or glycoprotein precursors into the ampulla of a single semicircular duct. In both species, essentially the same pattern of transneuronal transport extended beyond the cochlear nuclei to the central nucleus of the inferior colliculus (CNIC), after survival periods ranging from 9 to 33 days. Animals displayed dense labeling over nearly all auditory receptors, nearly all portions of the spiral ganglion and throughout the cochlear nuclei (CN). Labeled fibers, mainly in the ventral acoustic stria, terminated over the ipsilateral lateral superior olive (LSO) and the lateral aspect of medial superior olive (MSO). Fibers continuing medially, decussated in an orderly manner, and terminated over the opposite medial nucleus of the trapezoid body (MNTB) and medial aspect of MSO. Labeled fibers projecting into the opposite lateral lemniscus (LL) terminated in the ventral nucleus of the lateral lemniscus (VNLL) and the CNIC. Fibers, but few terminals, were noted over the dorsal nucleus of the LL. The ipsilateral LL contained comparatively few labeled fibers, but sparse terminations occurred over portions of VNLL and CNIC. No transport of [3H]precursors was noted in the peripheral nuclei of the inferior colliculus or in the medial geneculate body on either side. Massive transport via the contralateral LL and the profuse terminals in the opposite CNIC suggested transneuronal transport via secondary and higher order auditory fibers. Although the largest number of fibers in the contralateral LL probably arose from the cochlear nuclei, higher order fibers also may have arisen from the ipsilateral LSO and the contralateral MSO and VNLL. Small numbers of fibers in both species descended from the region of the superior olivary complex (SOC) ventral to the facial motor nucleus. In the ground squirrel, scant auditory projections were traced into the opposite cochlear nuclei. Tritiated precursors in the endolymph passed most readily from labyrinth to cochlea, and transneuronal transport was more extensive in the auditory pathways than in the vestibular system at comparable times. Centrally transported [3H]fucose was cleared more promptly than [3H]proline in monkeys.

Animals↗
PubMed1996

Development of vestibular and auditory function: effects of hypothyroidism and thyroxine replacement therapy on nystagmus and auditory evoked potentials in the pigmented rat.

The functional development of semicircular canals and some brainstem structures of the auditory system was followed in parallel with time in control and propylthiouracyl-induced hypothyroid pigmented rats by respective recording of postrotatory nystagmus response and auditory evoked brainstem potentials, with the aim of discovering the timing of permanent alterations of these responses in congenital hypothyroidism. A group of hypothyroid rats which under went thyroxine-replacement therapy from postnatal day 12 onward was also included in our studies to corroborate the involvement of thyroid hormones in these effects. Postrotatory nystagmus and auditory evoked responses were absent in congenital hypothyroid rats. In the thyroxine-replaced group postrotatory nystagmus values showed no differences from the control group from postnatal day 28 onward. Auditory evoked potentials in thyroxine-replaced animals could not be elicited at 30 dB, but by increasing the intensity of stimulus to 70 dB, values of latencies of the four waves composing the response were indistinguishable from controls from postnatal day 39 and thereafter. These results show that hypothyroidism affects both semicircular canal and auditory function, the latter more severely than the former, but that these effects can be prevented when thyroxine replacement treatment is started in early stages of postnatal development.

Animals↗
PubMed1987

Fetal auditory brain stem response: effect of increasing stimulus rate during functional auditory development.

The fetal auditory brain stem response to increasing stimulus rates of 16, 32, 45, 64, 87, and 100 clicks/sec were determined in eight fetal lambs of 115 to 136 days' gestation (term = 145 days). To conduct these studies, a hysterotomy was performed on the pregnant ewe at 110 to 118 days' gestation to implant stainless steel electrodes in the fetal scalp and a hearing aid receiver in the fetal external ear canal. The fetus was returned to the uterus and the pregnancy was allowed to continue. Auditory brain stem responses from younger fetuses (115 to 125 days' gestation) were present at the slower click rates but were not observed consistently at the fast click rates until the fetuses were older (125 to 136 day's gestation). Latency values of the auditory brain stem response peaks decreased with increasing fetal age and increased with increasing stimulus rates. From a two-way analysis of variance, the influence of age and click rate alone and more important, the interaction of age and click rate were determined to have highly significant effects (p less than 0.001) on latency values of wave 1, wave V, and central conduction time. These auditory brain stem response results suggest that the cochlear component of the fetal auditory system undergoes rapid change in late gestation to process incoming stimuli at a faster rate.

Acoustic Stimulation↗
PubMed1999

The case for early identification of hearing loss in children. Auditory system development, experimental auditory deprivation, and development of speech perception and hearing.

Human infants spend the first year of life learning about their environment through experience. Although it is not visible to observers, infants with hearing are learning to process speech and understand language and are quite linguistically sophisticated by 1 year of age. At this same time, the neurons in the auditory brain stem are maturing, and billions of major neural connections are being formed. During this time, the auditory brain stem and thalamus are just beginning to connect to the auditory cortex. When sensory input to the auditory nervous system is interrupted, especially during early development, the morphology and functional properties of neurons in the central auditory system can break down. In some instances, these deleterious effects of lack of sound input can be ameliorated by reintroduction of stimulation, but critical periods may exist for intervention. Hearing loss in newborn infants can go undetected until as late as 2 years of age without specialized testing. When hearing loss is detected in the newborn period, infants can benefit from amplification (hearing aids) and intervention to facilitate speech and language development. All evidence regarding neural development supports such early intervention for maximum development of communication ability and hearing in infants.

Acoustic Stimulation↗
PubMed2000

Early unilateral auditory deprivation increases 2-deoxyglucose uptake in contralateral auditory cortex of juvenile Mongolian gerbils.

The effects of early onset, unilateral conductive hearing loss on tone-induced 2-deoxyglucose (2-DG) uptake in the auditory cortex of juvenile Mongolian gerbils (Meriones unguiculatus) were studied. Atresia of the left ear canal was induced at postnatal day 9 (P9) to achieve reversible auditory deprivation prior to onset of hearing (around P12). Atresia either persisted (ATR, n=4) or the canal was opened 15 min before the 2-DG experiments (RE, n=4) at P27. Control animals were either non-deprived (CON, n=4), or their left ears were plugged acutely (PAX, n=4). In PAX, 2-DG uptake in primary auditory cortex (AI) and anterior auditory field (AAF) was lower in right than in left AI and AAF. In contrast, in ATR and RE, uptake was significantly higher on the right side contralateral to the atresia. Hence, atresia during early development leads to plastic changes resulting in an interhemispheric imbalance of functional metabolism in favor of the auditory cortex contralateral to the manipulated ear. Distances between tone-induced 2-DG labeling in AI and AAF were increased in PAX, but smaller in ATR in the right compared to the left hemisphere, suggesting effects of atresia also on spatial relations in cortical tonotopic maps.

Acoustic Stimulation↗