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At least 253 records · Page 14Linked to original sources
PubMed1993

Study of neural activities of the primary auditory cortex and middle latency auditory evoked potentials.

This study was undertaken to clarify the relationship between the neural activities of the auditory cortex and components of middle latency auditory evoked potentials (ML-AEPs) (NI and PI) in the cat. Extracellular single-unit activities in the auditory cortex AI (AC-AI) were recorded simultaneously with ML-AEPs. In addition, the effects of removal of the AC-AI and AII and the cerebral hemisphere on ML-AEPs were also studied. ML-AEPs of humans consist of Na, Pa, and Nb components with preceding VI and VII, and those of the cat consist of NI, PI and NII with preceding P6 and P7. Among the 21 unit activities obtained from the AC-AI, 14 showed time-locked responses to click stimuli. The positive and negative waves of these unit activities have a phase reversal relation to N7 and P7, respectively. They are not related in latencies to NI and PI. Recording of ML-AEPs from the surface of the AC-AI showed large negative potentials (No), which also had a phase reversal relation to P7. The amplitude of P7 and No decreased after the unilateral and the bilateral removal of the AC-AI and AII. NI and PI decreased in amplitude after the unilateral removal of the cerebral hemisphere and further decreased after the bilateral removal. The above mentioned findings indicate that the neural activities of the primary AC are the ones mostly related to P7 and that NI and PI reflect neural activities of the cerebral hemispheres.

Acoustic Stimulation↗
PubMedDate not supplied

Convergent but temporally separated inputs to lateral amygdala neurons from the auditory thalamus and auditory cortex use different postsynaptic receptors: in vivo intracellular and extracellular recordings in fear conditioning pathways.

The lateral nucleus of the amygdala (LA), a key component of the fear conditioning circuitry, receives a rapid but relatively impoverished auditory input from the auditory thalamus and a slower but richer input from the auditory cortex. We examined in urethane anesthetized rats whether individual cells in the LA receive convergent inputs from these two areas, and whether different postsynaptic receptors contribute to the temporally separated excitations over the two pathways. With both extracellular and intracellular recordings, individual cells could be activated by stimulation of each pathway. In extracellular recordings iontophoretic application of the N-methyl-D-aspartate (NMDA) receptor antagonist APV and the L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor antagonist CNQX demonstrated that synaptic transmission in both pathways depends on AMPA receptors, whereas transmission in the thalamic pathway also depends on the involvement of NMDA receptors. The involvement of NMDA receptors in synaptic activation of the LA from the thalamus but not the cortex was confirmed in intracellular recordings using systemic injections of the NMDA antagonist MK-801. The slow time course of NMDA currents could provide LA cells with a mechanism to integrate the inputs arriving rapidly from the thalamus and somewhat later from the cortex, thus allowing the LA to integrate signals in the two pathways during the acquisition and expression of conditioned fear reactions.

Amygdala↗
PubMed1989

Human brainstem auditory evoked potentials fail to provide evidence of efferent modulation of auditory input during attentional tasks.

Efferent modulation of auditory input at the level of the brainstem during attention-demanding tasks has been described in animal studies. Attempts to demonstrate these effects in humans have produced conflicting results, however. These studies are reviewed with particular reference to those animal experiments that have demonstrated peripheral effects. The human experiments have used a number of attentional conditions which have not been related either to each other or to the successful animal work. Two of the most important conditions in these studies--the use of an intermodal attention task and the manipulation of attentional states--have been examined rarely or not at all in the human research. Two experiments were conducted to investigate the possibility of attention-related effects on the human brainstem auditory evoked potential. These experiments were designed to examine experimental conditions common to both successful and unsuccessful attempts to demonstrate attention-driven efferent modulation at the periphery in humans. Also examined was the gradation of attention effects on efferent modulation demonstrated in animals but never studied in humans. No significant changes in either the latency or the amplitude of the brainstem auditory evoked potential were found in any of the attention-demanding conditions. Results are discussed in terms of psychophysiological theories of attention. Also, the interpretation of the most recent animal work is questioned.

Adolescent↗
PubMed2005

Auditory brainstem responses in the Eastern Screech Owl: an estimate of auditory thresholds.

The auditory brainstem response (ABR), a measure of neural synchrony, was used to estimate auditory sensitivity in the eastern screech owl (Megascops asio). The typical screech owl ABR waveform showed two to three prominent peaks occurring within 5 ms of stimulus onset. As sound pressure levels increased, the ABR peak amplitude increased and latency decreased. With an increasing stimulus presentation rate, ABR peak amplitude decreased and latency increased. Generally, changes in the ABR waveform to stimulus intensity and repetition rate are consistent with the pattern found in several avian families. The ABR audiogram shows that screech owls hear best between 1.5 and 6.4 kHz with the most acute sensitivity between 4-5.7 kHz. The shape of the average screech owl ABR audiogram is similar to the shape of the behaviorally measured audiogram of the barn owl, except at the highest frequencies. Our data also show differences in overall auditory sensitivity between the color morphs of screech owls.

Acoustic Stimulation↗
PubMed2006

Comment on "Auditory-nerve first-spike latency and auditory absolute threshold: a computer model" [J. Acoust. Soc. Am. 119, 406-417 (2006)].

A recent paper by Meddis [J. Acoust. Soc. Am. 119, 406-417 (2006)] shows that an existing model of the auditory nerve [Meddis and O'Mard, J. Acoust. Soc. Am. 117, 3787-3798 (2005)] is consistent with experimentally-measured first-spike latencies in the auditory nerve [Heil and Neubauer, J. Neurosci. 21, 7404-7415 (2001)]. The paper states that this consistency emerges because in the model, the calcium concentration inside the inner hair cell builds up over long periods of time (up to at least 200 ms) during tone presentation. It further states that integration over long time-scales happens despite the very short time constants (< 1 ms) used for the calcium dynamics. This letter demonstrates that these statements are incorrect. It is shown by simulation that calcium concentration inside the hair cell stage of the Meddis model rapidly reaches a steady state within a few milliseconds of a stimulus onset, exactly as expected from the short time-constant in the simple first-order differential equation used to model the calcium concentration. The success of the Meddis model in fitting experimental data actually confirms earlier results [Krishna, J. Comput. Neurosci. 13, 71-91 (2002a)] that show that the experimental data are a natural result of stochasticity in the synaptic events leading up to spike-generation in the auditory nerve; integration over long time scales is not necessary to model the experimental data.

Action Potentials↗
PubMed2006

Auditory cortical responses to electrical stimulation of the inferior colliculus: implications for an auditory midbrain implant.

The success and limitations of cochlear implants (CIs) along with recent advances in deep brain stimulation and neural engineering have motivated the development of a central auditory prosthesis. In this study, we investigated the effects of electrical stimulation of the inferior colliculus central nucleus (ICC) on primary auditory cortex (A1) activity to determine the potential benefits of an auditory midbrain implant (AMI). We recorded multiunit activity in A1 of ketamine-anesthetized guinea pigs in response to single-pulse (200 micros/phase) monopolar stimulation of the ICC using multisite silicon-substrate probes. We then compared measures of threshold, dynamic range, and tonotopic spread of activation for ICC stimulation with that of published data for CI stimulation. Our results showed that compared with cochlear stimulation, ICC stimulation achieved: 1) thresholds about 8 dB lower; 2) dynamic ranges > or = 4 dB greater; and 3) more localized, frequency-specific activation, even though frequency specificity was partially lost at higher stimulus levels for low-frequency ICC regions. Our results also showed that stimulation of rostral ICC regions elicited lower thresholds but with greater activation spread along the tonotopic gradient of A1 than did stimulation of more caudal regions. These results suggest that an AMI may improve frequency and level coding with lower energy requirements compared with CIs. However, a trade-off between lower perceptual thresholds and better frequency discrimination may exist that depends on location of stimulation along the caudorostral dimension of the ICC. Overall, this study provides the foundation for future AMI research and development.

Acoustic Stimulation↗
PubMed1991

Auditory nerve compound action potentials and brain stem auditory evoked potentials in patients with various degrees of hearing loss.

Click-evoked compound action potentials recorded in normal-hearing patients through a monopolar electrode placed on the intracranial portion of the eighth nerve were compared with the responses recorded in patients with high-frequency hearing loss or with high- and low-frequency hearing losses. That multiple peaks appear in the compound action potential in patients with hearing loss implies that click sounds elicit successive and separated volleys of neural excitation in the ascending auditory pathway, whereas click sounds in patients with normal hearing mainly give rise to a single volley of neural activity. This difference in the pattern of auditory nerve activity might explain why there are often multiple peaks in the brain stem auditory evoked potentials in patients with hearing loss and that the peaks are often less well-defined than peaks in patients with normal hearing.

Audiometry, Evoked Response↗
PubMed1980

Middle components of the auditory evoked response in bilateral temporal lobe lesions. Report on a patient with auditory agnosia.

An investigation of the middle components of the auditory evoked response (10--50 msec post-stimulus) in a patient with auditory agnosia is reported. Bilateral temporal lobe infarctions were proved by means of brain scintigraphy, CAT scanning, and regional cerebral blood flow measurements. The middle components were found to be normal regarding latency (pa approximately 30 msec) and configuration of the recordings, when evaluated relative to the peripheral hearing loss in the patient and to the corresponding normative template. Based upon the combined procedures, it is concluded that the middle components cannot be generated exclusively, if at all, in the primary auditory cortex, located in the temporal lobe. Furthermore, the responses are found to be of neurogenic origin according to the methodological procedure applied.

Aged↗
PubMed2005

Attentional modulation of electrophysiological activity in auditory cortex for unattended sounds within multistream auditory environments.

In three experiments, we addressed the issue of attention effects on unattended sound processing when one auditory stream is selected from three potential streams, creating a simple model of the cocktail party situation. We recorded event-related brain potentials (ERPs) to determine the way in which unattended, task-irrelevant sounds were stored in auditory memory (i.e., as one integrated stream or as two distinct streams). Subjects were instructed to ignore all the sounds and attend to a visual task or to selectively attend to a subset of the sounds and perform a task with the sounds (Experiments 1 and 2). A third (behavioral) experiment was conducted to test whether global pattern violations (used in Experiments 1 and 2) were perceptible when the sounds were segregated. We found that the mismatch negativity ERP component, an index of auditory change detection, was evoked by infrequent pattern violations occurring in the unattended sounds when all the sounds were ignored, but not when attention was focused on a subset of the sounds. The results demonstrate that multiple unattended sound streams can segregate by frequency range but that selectively attending to a subset of the sounds can modify the extent to which the unattended sounds are processed. These results are consistent with models in animal and human studies showing that attentional control can limit the processing of unattended input in favor of attended sensory inputs, thereby facilitating the ability to achieve behavioral goals.

Acoustic Stimulation↗
PubMed1992

A possible collicular component of the auditory evoked potential and its relationship to brainstem and cerebellar auditory potentials.

Auditory evoked potentials were recorded from the rat using skull screw electrodes inserted over the inferior colliculus and the cerebellum. In addition, brainstem auditory evoked potentials (BAEPs) were also recorded. The response recorded from over the inferior colliculus consisted of a slow positive potential with one of two possible peak latencies. The mean latency of the earlier potential was 5.6 ms and that of the later potential was 6.4 ms. A hypothetical generator for the first collicular potential is the termination of the lateral lemniscus in the ventrolateral inferior colliculus, while the later collicular potential could have its origins within the brachium of the inferior colliculus. None of the principal nor minor BAEP waves corresponded to either of the collicular responses. Nor did the trough of negativity between BAEP waves IV and V which is often thought to reflect activity generated within the midbrain. The potential recorded over the cerebellum also consisted of a slow positivity but with a slightly sharper contour than that of the collicular response. The mean latency of the cerebellar potential was 4.9 ms. As there was no temporal relationship between collicular and cerebellar potentials, the present study provided no support for the theory that cerebellar auditory potentials are artefactual and simply far field reflections of activity generated in the inferior colliculus. Judging by the timing of the BAEP waves, it is also concluded that the afferent volley most likely projects to the cerebellum via a collateral pathway branching off the caudal part of the lateral lemniscus.

Acoustics↗
PubMed1976

The influence of early auditory experience on later auditory and tactual variation seeking in the rat.

Albino rats were raised under 1 of 4 conditions of auditory stimulation from 22-35 days of age. At 40 days, preferences for auditory and tactual variation were assessed in separate runway tests. Results were analyzed in a split-plot design for each of 2 measures of variation seeking. Subjects experiencing more-variable early stimulation scored higher than subjects receiving less-variable stimulation on 1 measure of variation-seeking and lower on the 2nd measure. The effect was intermodal since these results were obtained for tactual as well as auditory variation seeking.

Acoustic Stimulation↗
PubMed1991

Auditory-evoked brain-stem responses and auditory disorders in patients with Bell's palsy.

Out of 121 patients examined with acute unilateral facial paralysis, 93 were determined to have idiopathic facial palsy (Bell's palsy). The examination included pure-tone and speech audiometry, stapedial reflex recordings, temporal bone radiography and auditory-evoked brain-stem response testing (ABR). If a retrocochlear lesion was suspected, computed tomography or magnetic resonance imaging was performed. Patients with sensorineural hearing loss affecting all frequencies were compared to one group with hearing loss affecting only high frequencies and to another group with ABR findings suggesting a cochlear lesion. No association could be made between the etiology of these pathological results and the concurrent facial paresis. Most of them were probably caused by unrelated disorders of the auditory system. In cases with prolonged inter-peak latencies representing brain-stem responses, abnormal ABRs could be caused by the same pathology as the paralysis. This might well suggest the presence of a neuropathy in both the central auditory system and the facial tracts.

Adolescent↗
PubMed1992

Auditory cortex neurons sensitive to correlates of auditory motion: underlying mechanisms.

Neuronal response properties such as phasic vs. tonic, onset vs. offset, monotonicity vs. non-monotonicity, and E/E vs. E/I, can be shown to act synergistically suggesting underlying mechanisms for selectivity to binaural intensity correlates of auditory sound source motion. Both identical (diotic), and oppositely directly dichotic AM ramps were used as stimuli in the lightly anesthetized cat, simulating motion in four canonical directions in 3-dimensional space. Motion in either azimuthal direction evokes selective activity in cells which respond best to the onset of monaural sound in one ear and show a decreased response to binaural stimulation (E/I or I/E). In some cells specificity is increased by "off" components in the non-dominant ear. Although these cells fire only at the onset of stationary sound, they fire throughout oppositely directed AM ramps. Motion toward or away from the head evokes responses from EE cells; strong binaural facilitation increases selectivity for motion in depth. The sharpness of direction of tuning was related to the degree of binaural facilitation in E/E cells. Selectivity for sound moving away from the head is correlated with "off" responses, while "on" responses correlate with preference for motion toward the head. Most units showed a monotonic rate function as AM ramp excursion and rate was increased. One third were selective for slower rates of intensity change and may therefore encode slower rates of stimulus motion, as well as direction of movement. The findings suggest that neural processing of auditory motion involves neural mechanisms distinct from those involved in processing stationary sound location and that these mechanisms arise from interactions between the more traditionally studied response properties of auditory cortex neurons.

Acoustic Stimulation↗
PubMed1984

Correlation between EEG and auditory perceptual measures in auditory agnosia.

We describe a child who acquired a gradual sustained speech deficit for which no specific etiology was found, and who had an associated epileptogenic abnormality on EEG. Assessment of auditory perceptual skills and receptive language confirmed that gradual parallel improvement occurred with the EEG after therapeutic anticonvulsant blood levels were obtained. Prospective trials of anticonvulsant drugs in conjunction with serial measures of central auditory abilities are necessary to establish their value in the management of the linguistic deficit in children with auditory agnosia.

Agnosia↗
PubMed1985

Uncertainties of topodiagnosis of auditory nerve and brain-stem auditory evoked potentials due to rarefaction and condensation stimuli.

Auditory nerve and brain-stem auditory evoked potentials (AN and BAEP) were elicited after separate stimulation with rarefaction and condensation stimuli. There were only few persons with identical patterns in the two opposite phases. Rarefaction stimuli showed a tendency to evoke AN and BAEP with shorter latencies and better synchronization. In diseases of the auditory nerve and brain-stem the phase-dependent differences were even more prominent, indicating different topodiagnostic levels of lesions. The results point to the need for stimulus presentation with rarefaction and condensation stimuli separately and an evaluation of both curves. The alternating mode is the result of summating rarefaction and condensation stimuli.

Brain Stem↗
PubMedDate not supplied

Binaural interaction of the auditory brain-stem potentials and middle latency auditory evoked potentials in infants and adults.

Binaural interactions in brain-stem auditory evoked potentials and in middle latency auditory evoked potentials were studied in 18 normal hearing adults and 10 normal term infants. Binaural interactions at the times of ABR waves V and VI were comparable in term infants and adults. Binaural interaction during the time domain of the middle latency auditory evoked potentials was the greatest at N20 in term infants and at N40 in adults. Measurement of binaural interaction during maturation may be a useful tool in assessing neurologically affected infants.

Acoustic Stimulation↗
PubMedDate not supplied

Mismatch negativity (MMN) for sequences of auditory and visual stimuli: evidence for a mechanism specific to the auditory modality.

ERPs to sequences of standard and deviant sinusoidal 100 msec tone pips, high-contrast sinusoidal gratings and to their simultaneously presented combinations were recorded. Mismatch negativity (MMN), an ERP component elicited by deviant stimuli, was estimated for the different stimulus sequences in order to find out whether it reflects modality-specific processes or non-specific attentive phenomena. In addition to the auditory modality, we studied whether the mismatch response could be evoked by a deviant visual stimulus in a visual sequence or by a deviant stimulus in either modality. The results show that only auditory stimuli produced the mismatch response, suggesting that MMN is not a manifestation of a general attentional mechanism but is probably specific to the auditory modality.

Acoustic Stimulation↗
PubMed1994

Similar structural dimensions in bushcricket auditory organs in spite of different foreleg size: consequences for auditory tuning.

The bushcricket species Decticus albifrons, Decticus verrucivorus and Pholidoptera griseoaptera (Tettigoniidae) belong to the same subfamily (Decticinae) but differ significantly in body size. In spite of the great differences in the dimensions of the forelegs, where the auditory organs are located, the most sensitive range of the hearing threshold lies between 6 and 25 kHz in each case. Only in the frequency range from 2 to 5 kHz and above 25 kHz, significant differences are present. The anatomy of the auditory receptor organs was compared quantitatively, using the techniques of semi-thin sectioning and computer-guided morphometry. The overall number of scolopidia and the length of the crista acustica differs in the three species, but the relative distribution of scolopidia along the crista acustica is very similar. Additionally, the scolopidia and their attachment structures (tectorial membrane, dorsal tracheal wall, cap cells) are of equal size at equivalent relative positions along the crista acustica. The results indicate that the constant relations and dimensions of corresponding structures within the cristae acusticae of the three species are responsible for the similarities in the tuning of the auditory thresholds.

Acoustic Stimulation↗