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PubMed1993

Visual projections induced into the auditory pathway of ferrets: II. Corticocortical connections of primary auditory cortex.

Although the development of corticocortical projections has been well studied, less is known about the role of sensory inputs in the specification of these connections. As part of an ongoing series of studies in our laboratory, we have examined the role of thalamic input modality in the development of corticocortical connections. These studies involve making unilateral lesions and inducing retinal inputs into the auditory thalamus (MGN) during early development in ferrets, thereby conferring visual responsiveness on primary auditory cortex (AI). In this way we can examine the role of input identity in cortical specification in general, and connectivity patterns specifically. A previous paper (Pallas et al. [1990] J. Comp. Neurol. 298:50-68) described the pattern of thalamocortical and corticothalamic connections of auditory cortex in normal and lesioned animals. This study compares the pattern of auditory corticocortical connections in normal and lesioned animals. We injected neuroanatomical tracers into AI and mapped out the distribution of retrogradely labelled cells in the cortex. We report that the cortical inputs to ferret AI resembled those in cats, and that the pattern of ipsi- and contralateral corticocortical connections of ferret AI with visual input was similar to the normal pattern. Auditory cortex with visual input did not make ectopic connections with visual cortex, but maintained its connections with other auditory cortical areas. These results suggest that the overall corticocortical connections of an area are not influenced by the modality or activity pattern of its inputs. In particular, altering the input activity to a cortical area does not seem to promote the formation of entirely new connections, although small changes in the strength of existing connections are possible (Sur et al. [1990] Trends Neurosci. 13:227-233).

Animals↗
PubMed2001

SPET monitoring of auditory cortex activation by electric stimulation in a patient with auditory brainstem implant.

Auditory cortex activation following multifrequency acoustic stimulation has been evaluated by means of single photon emission tomography (SPET) in one patient before and after an auditory brainstem implant (ABI). No activation could be observed after acoustic stimulation before ABI. After ABI stimulation in the coronal and axial slices, the activation within the temporal cortex contralateral to the stimulated ear was twice (43.76%) that of normal controls (23.94 +/- 2.74%). This marked difference was not present in other selected cortical auditory areas (homolateral temporal, homolateral and contralateral parietal cortices). The temporal cortex was also examined with six consecutive sagittal slices from 18.75 mm up to 56.25 mm lateral to the midline. A very strong activation (51.20%) compared with that of normal controls (9.94 +/- 7.45%) was detected in the 25.26-mm sagittal slice of the temporal cortex contralateral to the stimulated side. The remaining sagittal slices showed an almost normal post-stimulatory activation. As the 25.26-mm sagittal slice corresponds to the medial part of the auditory temporal cortex, its activation suggests that electrode stimulation is concentrated on the region of the cochlear nucleus in which the neurons that transduce high frequencies are located. SPET can be considered useful, in combination with electric auditory-evoked potentials, to obtain information on ABI placement and function, effectiveness of acoustic stimulation, degree of cortical stimulation and tonotopic spatial distribution of auditory cortex activation.

Adult↗
PubMed2003

fMRI of the auditory system: understanding the neural basis of auditory gestalt.

Functional magnetic resonance imaging (fMRI) has rapidly become the most widely used imaging method for studying brain functions in humans. This is a result of its extreme flexibility of use and of the astonishingly detailed spatial and temporal information it provides. Nevertheless, until very recently, the study of the auditory system has progressed at a considerably slower pace compared to other functional systems. Several factors have limited fMRI research in the auditory field, including some intrinsic features of auditory functional anatomy and some peculiar interactions between fMRI technique and audition. A well known difficulty arises from the high intensity acoustic noise produced by gradient switching in echo-planar imaging (EPI), as well as in other fMRI sequences more similar to conventional MR sequences. The acoustic noise interacts in an unpredictable way with the experimental stimuli both from a perceptual point of view and in the evoked hemodynamics. To overcome this problem, different approaches have been proposed recently that generally require careful tailoring of the experimental design and the fMRI methodology to the specific requirements posed by the auditory research. The novel methodological approaches can make the fMRI exploration of auditory processing much easier and more reliable, and thus may permit filling the gap with other fields of neuroscience research. As a result, some fundamental neural underpinnings of audition are being clarified, and the way sound stimuli are integrated in the auditory gestalt are beginning to be understood.

Auditory Cortex↗
PubMed1998

Role of the primary auditory cortex in auditory selective attention studied by whole-head neuromagnetometer.

In order to identify the human cortical areas involved in the auditory attention, neuromagnetic fields were recorded from 12 healthy adults with a 122-channel whole-head magnetometer while the subjects performed the auditory selective attention task. Randomized sequence of 900 Hz (P=0.9) and 950 Hz (P=0.1) tones was presented to each ear with random interstimulus intervals across ears ranging from 300 to 500 ms. Subjects were asked to pay attention to the designated ear (attended ear) and to count the number of the 950 Hz tones presented to the attended ear. Twelve sessions were performed for each subject, among which the attended ear was changed alternately in a counterbalanced order among subjects. In seven out of twelve subjects, averaged neuromagnetic fields in response to frequent tones presented to the attended ear showed attention-related deflection over the bilateral temporal areas starting at around 100 ms after the stimulus presentation. Although the dipole moment for N100m in the attended condition showed significant increase compared to that in the non-attended condition, locations of the two equivalent current dipoles in the auditory cortex were not significantly different from each other. Moreover, a simulation study supported the enhancement of N100m rather than participation of additional dipoles in the auditory selective attention task. These results suggest that the primary auditory cortex plays a main role in the auditory selective attention starting as early as 100 ms after the stimulus presentation.

Adult↗
PubMed2004

Role of auditory stimulation in maturation of the auditory pathway.

OBJECTIVE: To compare the maturation of the auditory pathway, as shown by electrical brainstem auditory potentials (EABRs), in ears with and without prior auditory stimulation. MATERIAL AND METHODS: Electrophysiological data were collected prospectively from ears which had received cochlear implants. Implant-evoked (Imp)EABRs were recorded. Thirty children, implanted after January 2000, were selected according to a strict inclusion/exclusion protocol. All the children had received a 22-channel Nucleus cochlear implant (CI24 series). Intraoperatively, ImpEABRs were recorded using the Medelec Synergy Evoked Response system in conjunction with Nucleus Neural Response Telemetry software. The ImpEABR latencies of waves eII, eIII and eV and the morphology of wave eV were assessed. RESULTS: ImpEABRs alter during the first 12 months of life. The latency becomes shorter during this period and the morphology of wave eV alters from a broad shape to a more distinct waveform. This appears to occur independently, even in the absence of auditory stimulation. CONCLUSION: The development of electrical brainstem auditory potentials is not dependent on auditory stimulation.

Acoustic Stimulation↗
PubMed2006

Functional cerebral reorganization for auditory spatial processing and auditory substitution of vision in early blind subjects.

Early blind (EB) individuals can recognize bidimensional shapes using a prosthesis substituting vision with audition (PSVA) and activate right dorsal extrastriate visual cortex during the execution of this task. The present study used repetitive transcranial magnetic stimulation (rTMS) to further examine the functional role of this structure in the successful use of the PSVA. Moreover, we investigated which auditory parameter used in the prosthesis (pitch, intensity, or spatial location) might contribute to this occipital activation. Results revealed that rTMS applied to right dorsal extrastriate cortex in EB subjects interferes with both the PSVA use and the auditory spatial location task but not with pitch and intensity discriminations. By contrast, rTMS targeting the same cortical areas in sighted subjects did not affect performance on any auditory tasks. Early visual deprivation thus leads to functional cerebral cross-modal reorganization in the processing of auditory information and auditory-to-visual sensory substitution. The findings also point to the specific involvement of the dorsal visual stream for auditory spatial processing in blind subjects. Moreover, this suggests that sensory substitution prostheses can be developed using these additional neural resources to perform tasks that partially compensate for the loss of vision.

Adult↗
PubMed1994

Improvement in auditory function following pentazocine suggests a role for dynorphins in auditory sensitivity.

The pharmacologic specificity of potentially beneficial drug effects on the auditory system were investigated. Changes in auditory sensitivity were evaluated in chinchillas following the infusion of an opioid narcotic. This drug (pentazocine) mimics endogenous opioid peptides (dynorphins), postulated to be chemical neurotransmitters (or neuromodulators) within the mammalian cochlea. In this study, two pentazocine enantiomers were investigated over a range of stimulus intensities. Significant baseline-relative changes in compound action potential (CAP) amplitudes were observed following intravenous administration of the kappa-opioid agonist (-)pentazocine (8 mg/kg). The sigma-receptor drug agonist (+)pentazocine (8 mg/kg) produced no measurable auditory effects. The magnitude of the (-)pentazocine effects were inversely related to stimulus intensity, up to 10 dB above threshold (i.e., 10 dB SL). Consistent with the observed amplitude doubling, auditory sensitivity was also improved an average 5-7 dB sound pressure level (SPL) following the administration of (-)pentazocine, while CAP response latencies and cochlear microphonic (CM) amplitudes remained unchanged. Results indicate stereospecific kappa-receptor mediated actions of pentazocine at the auditory nerve, and suggest an auditory role for neuroactive dynorphin peptides contained within the lateral efferent olivocochlear neurons.

Animals↗
PubMed2004

Central auditory deficits associated with compromise of the primary auditory cortex.

The subject of this study was a 46-year-old female who had suffered a cerebrovascular accident (CVA). Magnetic resonance imaging revealed damage in the area of the distribution of the middle cerebral artery involving most, if not all, of the primary auditory area of the left hemisphere. No auditory problems were noted prior to the CVA; however, following the CVA, the subject reported a number of auditory difficulties. Pure-tone thresholds were normal post-CVA, and performance on speech recognition testing was good in both ears if ample time was provided between a response and the presentation of the next test item. Duration pattern, intensity discrimination, and middle latency response test results were abnormal for both ears, and right ear deficits were evident on an auditory fusion test and two dichotic speech tests (digits and rhymes). This case is significant in that it demonstrates a good correlation between damage to known key auditory regions and central auditory test results.

Audiometry, Pure-Tone↗
PubMed2004

Auditory temporal processes in normal-hearing individuals and in patients with auditory neuropathy.

OBJECTIVE: To study objectively auditory temporal processing in a group of normal hearing subjects and in a group of hearing-impaired individuals with auditory neuropathy (AN) using electrophysiological and psychoacoustic methods. METHODS: Scalp recorded evoked potentials were measured to brief silent intervals (gaps) varying between 2 and 50ms embedded in continuous noise. Latencies and amplitudes of N100 and P200 were measured and analyzed in two conditions: (1) active, when using a button in response to gaps; (2) passive, listening, but not responding. RESULTS: In normal subjects evoked potentials (N100/P200 components) were recorded in response to gaps as short as 5ms in both active and passive conditions. Gap evoked potentials in AN subjects appeared only with prolonged gap durations (10-50ms). There was a close association between gap detection thresholds measured psychoacoustically and electrophysiologically in both normals and in AN subjects. CONCLUSIONS: Auditory cortical potentials can provide objective measures of auditory temporal processes. SIGNIFICANCE: The combination of electrophysiological and psychoacoustic methods converged to provide useful objective measures for studying auditory cortical temporal processing in normals and hearing-impaired individuals. The procedure used may also provide objective measures of temporal processing for evaluating special populations such as children who may not be able to provide subjective responses.

Acoustic Stimulation↗
PubMed1998

Subdivisions of auditory cortex and ipsilateral cortical connections of the parabelt auditory cortex in macaque monkeys.

Auditory cortex of macaque monkeys can be divided into a core of primary or primary-like areas located on the lower bank of the lateral sulcus, a surrounding narrow belt of associated fields, and a parabelt region just lateral to the belt on the superior temporal gyrus. We determined patterns of ipsilateral cortical connections of the parabelt region by placing injections of four to seven distinguishable tracers in each of five monkeys. Results were related to architectonic subdivisions of auditory cortex in brain sections cut parallel to the surface of artificially flattened cortex (four cases) or cut in the coronal plane (one case). An auditory core was clearly apparent in these sections as a 16- to 20-mm rostrocaudally elongated oval, several millimeters from the lip of the sulcus, that stained darkly for parvalbumin, myelin, and acetylcholinesterase. These features were most pronounced caudally in the cortex assigned to auditory area I, only slightly reduced in the rostral area, and most reduced in the narrower rostral extension we define as the rostrotemporal area. A narrow band of cortex surrounding the core stained more moderately for parvalbumin, acetylcholinesterase, and myelin. Two regions of the caudal belt, the caudomedial area, and the mediolateral area, stained more darkly, especially for parvalbumin. Rostromedial and medial rostrotemporal, regions of the medial belt stained more lightly for parvalbumin than the caudomedial area or the lateral belt. The parabelt region stained less darkly than the core and belt fields. Injections confined to the parabelt region labeled few neurons in the core, but large numbers in parts of the belt, the parabelt, and adjacent portions of the temporal lobe. Injections that encroached on the belt labeled large numbers of neurons in the core and helped define the width of the belt. Caudal injections in the parabelt labeled caudal portions of the belt, rostral injections labeled rostral portions, and both caudal and rostral injections labeled neurons in the rostromedial area of the medial belt. These observations support the concept of dividing the auditory cortex into core, belt, and parabelt; provide evidence for including the rostral area in the core; suggest the existence of as many as seven or eight belt fields; provide evidence for at least two subdivisions of the parabelt; and identify regions of the temporal lobe involved in auditory processing.

Animals↗
PubMedDate not supplied

Contributions from the auditory nerve to the brain-stem auditory evoked potentials (BAEPs): results of intracranial recording in man.

Intraoperative recordings obtained from electrodes placed on the scalp (vertex and earlobe or ear canal) in response to click stimulation were compared with recordings made directly from the auditory nerve in patients undergoing microvascular decompression (MVD) operations to relieve hemifacial spasm (HFS) and disabling positional vertigo (DPV). The results support earlier findings that show that the auditory nerve is the generator of both peak I and peak II in man, and that it is the intracranial portion of the auditory nerve that generates peak II. The results indicate that the second negative peak in the potentials recorded from the earlobe is generated by the auditory nerve where it passes through the porus acusticus into the skull cavity, and that the proximal portion of the intracranial portion of the auditory nerve generates a positive peak in the potentials that are recorded from the vertex. This peak appears with a latency that is slightly longer than that of the second negative peak in the potentials recorded from the earlobe (or ear canal). The second negative peak in the recording from the ear canal and the positive peak in the vertex recording contribute to peak II in the differentially recorded BAEP. Since our results indicate that the difference in the latency of the second negative peak in the recording from the earlobe and that of the positive peak in the vertex recording represents the neural travel time in the intracranial portion of the auditory nerve, this measure may be valuable in the differential diagnosis of eighth nerve disorders such as vascular compression syndrome.

Brain Stem↗
PubMed1990

A four-day period of bimodality auditory and visual experience is sufficient to permit normal emergence of the map of auditory space in the guinea pig superior colliculus.

Previous work has shown that if guinea pigs are deprived of simultaneous visual and auditory experience during a 4-day period 26-30 days after birth (DAB), this prevents the normal emergence of an auditory space map in the superior colliculus. The present work reports that if this 4-day period is the only developmental period in which the animals have simultaneous bimodality experience, the auditory space map appears at the normal time. Apart from this time-window animals were deprived of either visual experience (by dark-rearing) or of normal auditory experience (by rearing in an environment of omnidirectional masking noise). We conclude that the period 26-30 DAB is a crucial developmental period during which coincident auditory and visual experience is utilized in the initial formation of the collicular map of auditory space.

Animals↗
PubMed2005

Echolocation, vocal learning, auditory localization and the relative size of the avian auditory midbrain nucleus (MLd).

The avian nucleus mesencephalicus lateralis, pars dorsalis (MLd) is an auditory midbrain nucleus that plays a significant role in a variety of acoustically mediated behaviours. We tested whether MLd is hypertrophied in species with auditory specializations: owls, the vocal learners and echolocaters. Using both conventional and phylogenetically corrected statistics, we find that the echolocating species have a marginally enlarged MLd, but it does not differ significantly from auditory generalists, such as pigeons, raptors and chickens. Similarly, all of the vocal learners tend to have relatively small MLds. Finally, MLd is significantly larger in owls compared to all other birds regardless of how the size of MLd is scaled. This enlargement is far more marked in asymmetrically eared owls than symmetrically eared owls. Variation in MLd size therefore appears to be correlated with some auditory specializations, but not others. Whether an auditory specialist possesses a hypertrophied MLd appears to be depend upon their hearing range and sensitivity as well as the ability to resolve small azimuthal and elevational angles when determining the location of a sound. As a result, the only group to possess a significantly large MLd consistently across our analyses is the owls. Unlike other birds surveyed, owls have a battery of peripheral and other central auditory system specializations that correlate well with their hearing abilities. The lack of differences among the generalists, vocal learners and echolocaters therefore reflects an overall similarity in hearing abilities, despite the specific life history requirements of each specialization and species. This correlation between the size of a neural structure and the sensitivity of a perceptual domain parallels a similar pattern in mammals.

Analysis of Variance↗
PubMed2004

Brain-stem auditory impairment during the neonatal period in term infants after asphyxia: dynamic changes in brain-stem auditory evoked response to clicks of different rates.

OBJECTIVE: To explore dynamic changes in brain-stem auditory electrophysiology during the neonatal period in term infants after perinatal asphyxia. METHODS: Sixty-eight term newborn infants who suffered asphyxia were studied on days 1, 3, 5, 7, 14 and 30 after birth. Brain-stem auditory evoked response (BAER) was recorded with clicks, delivered at 21, 51 and 91 s(-1) and > or =40 dB above BAER threshold of each subject. RESULTS: During the neonatal period wave I latency in the infants after asphyxia increased slightly while later BAER components changed more significantly. On the first day after birth wave III and V latencies and I-V and III-V intervals increased significantly at all rates of clicks (ANOVA P<0.01-0.001). On day 3, the latencies and intervals increased further. III-V/I-III interval ratio increased at 51 and 91 s(-1), suggesting a relatively more significant increase in III-V interval than in I-III interval at higher rates. Thereafter, wave III and V latencies and all intervals decreased progressively, although these BAER variables were still significantly longer than in normal controls on days 5 and 7 (P<0.05-0.001) On day 30, all latencies and intervals approached near normal values, with a slight increase in wave V latency and I-V and III-V intervals at 51 and 91 s(-1). CONCLUSIONS: Perinatal asphyxia has a major effect on central auditory function, resulting in acute impairment. The impairment progresses during the first 3 days and then tends towards recovery. By 1 month the impaired auditory function has largely returned to normal. Significant increase in click rates can moderately improve the detection of auditory impairment. SIGNIFICANCE: After perinatal asphyxia early detection of hypoxic-ischaemic damage to the central auditory system and initialisation of neuroprotective and therapeutic measures during the first hours after birth are critical to prevent or reduce deterioration of central impairment.

Acoustic Stimulation↗
PubMed2006

Mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy.

Auditory neuropathy is a particular type of hearing impairment in which neural transmission of the auditory signal is impaired, while cochlear outer hair cells remain functional. Here we report on DFNB59, a newly identified gene on chromosome 2q31.1-q31.3 mutated in four families segregating autosomal recessive auditory neuropathy. DFNB59 encodes pejvakin, a 352-residue protein. Pejvakin is a paralog of DFNA5, a protein of unknown function also involved in deafness. By immunohistofluorescence, pejvakin is detected in the cell bodies of neurons of the afferent auditory pathway. Furthermore, Dfnb59 knock-in mice, homozygous for the R183W variant identified in one DFNB59 family, show abnormal auditory brainstem responses indicative of neuronal dysfunction along the auditory pathway. Unlike previously described sensorineural deafness genes, all of which underlie cochlear cell pathologies, DFNB59 is the first human gene implicated in nonsyndromic deafness due to a neuronal defect.

Amino Acid Sequence↗
PubMed2006

The auditory midbrain implant: a new auditory prosthesis for neural deafness-concept and device description.

The auditory midbrain implant (AMI) is a new central auditory prosthesis designed for penetrating stimulation of the human inferior colliculus. The major group of candidates for the AMI consists of neurofibromatosis type 2 (NF2) patients who develop neural deafness because of growth and/or surgical removal of bilateral acoustic neuromas. Because of the absence of a viable auditory nerve, these patients cannot benefit from cochlear implants. An alternative solution has been the auditory brainstem implant (ABI), which stimulates the cochlear nucleus. However, speech perception performance in NF2 ABI patients has been limited. The fact that the ABI is able to produce high levels of speech perception in nontumor patients (with inaccessible cochleae or posttraumatic damage to the cochlear nerve) suggests that limitations in ABI performance in NF2 patients may be associated with cochlear nucleus damage caused by the tumors or the tumor removal process. Thus, stimulation of the auditory midbrain proximal to the damaged cochlear nucleus may be a better alternative for hearing restoration in NF2 patients. We propose the central nucleus of the inferior colliculus (ICC) as the potential site. A penetrating electrode array aligned along the well-defined tonotopic gradient of the ICC should selectively activate different frequency regions, which is an important elementfor supporting good speech understanding. The goal of this article is to present the ICC as an alternative site for an auditory implant for NF2 patients and to describe the design of the first human prototype AMI. Practical considerations for implementation of the AMI will also be discussed.

Algorithms↗
PubMed1997

Contribution of auditory cortex to acoustical orientation in cats under conditions of discordant auditory reafference.

Head-orienting responses (ORs) evoked by a stationary source of sound typically terminate in small undershoots in normal hearing cats or in large undershoots (hypometria) if the auditory cortex is ablated bilaterally. In the present study, ORs executed by cats were studied using a procedure in which the OR produced an isogonal rotation of the sound source, i.e., response-produced change (reafference) in the acoustic stimulus was distorted. Under this condition (discordant auditory reafference), ORs terminated in large overshoots (hypermetria) in the normal hearing cats. This result indicates that experimental distortion of response-produced auditory feedback resulted in an "on-line" modification of ORs by the normal hearing cats. In the cats with auditory cortex ablated, ORs terminated in large undershoots (hypometria), suggesting that auditory cortex is a necessary component of the central auditory system for processing reafferent acoustic stimuli that normally occur during head rotation in a sound field.

Acoustic Stimulation↗
PubMed1999

A new class of auditory warning signals for complex systems: auditory icons.

This simulator-based study examined conventional auditory warnings (tonal, nonverbal sounds) and auditory icons (representational, nonverbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under 6 display configurations, 2 vehicle speeds, and 2 levels of headway. Accident occurrence was measured for impending side collision scenarios under 2 vehicle speeds, 2 levels of visual workload, 2 auditory displays, absence/presence of mirrors, and absence/presence of a dash-mounted iconic visual display. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impending front-to-rear collision scenarios using the longer headway condition. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multimodal displays over single-modality displays. Actual or potential applications for this research include auditory displays and warnings, information presentation, and the development of alternative user interfaces.

Accidents, Traffic↗