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Biomedical subjects

N Kraus

Publications and source records attributed to N Kraus.

105 records · Page 6Linked to original sources
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Intracranial and extracranial recordings of the auditory middle latency response.

Simultaneous epidural and cortical depth recordings of the auditory middle latency response (MLR) were obtained from 18 anesthetized guinea pigs. Microelectrodes were advanced at a right angle to the cortical surface at sites shown to be optimal for recording surface MLRs. Transcortical polarity reversals of waves A (14 msec) and B (24 msec) of the MLR were recorded in depth penetrations initiated at sites on the temporal lobe with large amplitude surface potentials. In 6 of 18 penetrations yielding phase inversions, wave polarities changed abruptly as microelectrodes were advanced into the cortex. In the remaining penetrations, the reversals were preceded by gradual decreases in wave latencies at progressively deep sites. As electrodes were advanced beyond the depth at which polarity reversals were encountered, decreases in amplitude and only minor changes in latency were observed. Surface and depth MLR activity were temporarily eliminated immediately after electrolytic lesions were made at polarity reversal sites. Recovery of responses occurred within 30-60 min. Lesions produced in penetrations initiated at sites with no surface MLR activity had no effect. Histologic examination confirmed the location of the phase reversal sites as being within grey matter of the temporal lobe. These results are consistent with previous investigations in experimental animals which demonstrated transcortical polarity reversals, and provide evidence for dipolar generating systems of the early components of the MLR at the cortical level.

Animals↗
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Binaural stimulation reveals functional differences between midline and temporal components of the middle latency response in guinea pigs.

Two morphologically distinct auditory middle latency response (MLR) wave forms can be recorded from the surface of the guinea pig brain. The temporal response is recorded from the temporal lobe contralateral to the stimulus ear, and the midline response is recorded over the posterior midline. Experimental evidence suggests that different neural generators contribute to the two responses. Furthermore, it appears that the temporal response principally reflects activity of the primary auditory pathway while the midline response reflects non-primary pathways. Although it is known that neurons throughout the auditory pathway exhibit distinct binaural interaction (BI) properties, thus far there have been no systematic attempts to differentiate the MLR wave forms in response to binaural stimulation. The purpose of this study was to determine if binaural click stimulation could functionally differentiate the midline and temporal MLR responses in the guinea pig. Binaural click stimulation caused a significant decrease in temporal MLR peak amplitudes, and a significant increase in midline MLR amplitudes. The fact that different BI patterns were observed suggests that the two MLR components are functionally distinct. The data further support the hypothesis that the midline and temporal MLR in guinea pigs reflect different neural generators and pathways.

Acoustic Stimulation↗
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Acoustic versus phonetic representation of speech as reflected by the mismatch negativity event-related potential.

The concept of categorical perception of speech and speech-like sounds has been central to models of speech perception for decades. Event-related potentials (ERPs) provide a neurophysiologic perspective of this important phenomenon. In the present experiment the mismatch negativity (MMN) event-related potential, which is sensitive to fine acoustic differences, was recorded in adults. Of interest was whether the MMN reflects the acoustic or categorical perception of speech. The MMN was elicited by stimulus pairs (along a continuum varying in place of articulation from /da/ to /ga/) which had been identified as the same phoneme /da/ (within category condition) and as different phonemes /da/ and /ga/ (across categories condition). The acoustic differences between these two pairs of stimuli were equivalent. The MMN was observed in all subjects both in the within and across category conditions. Furthermore, the MMN did not differ in latency, amplitude or area within and across categories. That is, the MMN indicated equal discrimination both across and within categories. These results suggest that the MMN appears to reflect the processing of acoustic aspects of the speech stimulus, but not phonetic processing into categories. The MMN appears to be an extremely sensitive electrophysiologic index of minimal acoustic differences in speech stimuli.

Acoustic Stimulation↗
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Mismatch negativity in school-age children to speech stimuli that are just perceptibly different.

The mismatch negativity event-related potential (MMN) was elicited in normal school-age children in response to just perceptibly different variants of the speech phoneme /da/. A significant MMN was measured in each subject tested. Child and adult MMNs were similar with respect to peak latency and duration. Measures of MMN magnitude (peak-to-peak amplitude and area) were significantly larger in children than in adults. The results of the present study indicate that the MMN can be elicited in response to minimal acoustic stimulus differences in complex speech signals in school-age children. The results support the feasibility of using the MMN as a tool in the study of deficient auditory perception in children.

Acoustic Stimulation↗
PubMedDate not supplied

Auditory middle latency responses in the guinea pig.

Auditory middle latency responses (latencies 6 to 50 msec in guinea pigs) were recorded from eight awake, restrained guinea pigs. Before recording, screw electrodes were implanted in the skull in a coronal plane in line with the bregma. Another electrode, which served to monitor auditory brainstem responses, was placed 1 cm posterior to the bregma. All electrodes were referenced to a lead positioned 2 cm anterior to the bregma. During the recording session, click stimuli of various repetition rates and intensity levels were delivered monaurally in a closed sound system. Auditory brainstem responses were monitored to ensure normal functioning of the peripheral auditory system. Responses from electrodes at the midline and over the temporal area ipsilateral to the stimulus ear were greatly attenuated or absent. From an electrode over the temporal area contralateral to the stimulus ear, two positive peaks occurred at latencies of approximately 12 and 27 msec. A negative trough was identified at approximately 17 msec. Latency and amplitude functions for this waveform were determined for various stimulus levels. Response amplitude increased as stimulus repetition rate was decreased. Anesthesia greatly altered waveform structure and prolonged peak latencies. These effects were more marked at stimulus repetition rates faster than 10/sec than at slower rates. Properties of the guinea pig middle latency response are compared with those previously reported for cats and humans.

Animals↗
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Effects of chloral hydrate, pentobarbital, ketamine, and curare on the auditory middle latency response.

Changes in threshold, latency, and amplitude of the auditory middle latency response (MLR) with anesthesia and neuromuscular paralysis were studied in guinea pigs. Although each component of the surface-recorded MLR was altered by barbiturate and nonbarbiturate agents, the early positive wave (wave A) was always present, and the later waves were generally identifiable at moderate levels of anesthesia. MLR threshold was not affected by anesthesia or curare. Pentobarbital, chloral hydrate, and ketamine each caused an increase in the latency of all MLR components, with increases progressively marked for later waves. Amplitude changes were more complex. Wave A increased in amplitude with anesthesia, while wave C decreased or disappeared temporarily. Wave B showed mixed amplitude changes. Changes in MLR associated with anesthesia were generally more pronounced at a stimulation rate of 10/sec as compared to 4/sec. No changes in waveform morphology or latency were seen with neuromuscular paralysis. The results provide evidence in support of separate neurogenic substrates for the different components of the guinea pig temporal lobe MLR. The presence of the MLR with moderate levels of anesthesia indicates that this animal is an appropriate model for studying the MLR in experiments requiring anesthesia and immobilization.

Animals↗
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The hearing-impaired infant: patterns of identification and habilitation.

The 1982 Position Statement by the Joint Committee on Infant Hearing recommends that infants at risk for hearing impairment be screened by 3 mos of age and that the diagnostic process be completed an habilitation begun by 6 mos of age. How close to this ideal actual practice comes in an urban setting is the subject of this study, Data on 88 infants referred to a hospital-based parent-infant program were retrospectively examined to determine the occurrence of risk factors and at what ages: (1) hearing loss was first suspected, (2) hearing loss was diagnosed, and (3) habilitation was initiated. Results indicate that over one-quarter of all hearing-impaired infants will not manifest any of the risk factors proposed in the 1982 Position Statement and that regardless of whether the infant graduates from a neonatal intensive care unit or well-baby nursery, the median age for enrollment in a parent-infant program is a year or more later than the 1982 recommendation.

Age Factors↗
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Speech sound representation, perception, and plasticity: a neurophysiologic perceptive.

Historically, auditory research has focused predominately upon how relatively simple acoustic signals are represented in the neuronal responses of the auditory periphery. However, in order to understand the neurophysiology underlying speech perception, the ultimate objective is to discover how speech sounds are represented in the central auditory system and to relate that representation to the perception of speech as a meaningful acoustic signal. This paper reviews three areas that pertain to the central auditory representation of speech: (1) the differences in neural representation of speech sounds at different levels of the auditory system; (2) the relation between the representation of sound in the auditory pathway and the perception/misperception of speech, and (3) the training-related plasticity of speech sound neural representation and speech perception.

Auditory Cortex↗
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Speech sound representation in the brain.

Biologic processes underlying speech sound perception and learning have been addressed using the mismatch negativity (MMN) evoked response. First is a consideration of how the acoustic properties of the signal affect the neural mechanisms and brain regions engaged. Because the MMN differs depending on the acoustic characteristics of the stimuli used to elicit the response, it has been used to probe mechanisms underlying the neural representation of stimuli along the auditory pathway. Second is a consideration of neurophysiologic correlates of speech sound perception and learning. Detailed is a 'behavioral-neurophysiologic, acoustic-phonetic approach', used to link perception with underlying physiologic processes in humans. The focus here is on children and what has been learned about normal maturation of speech sound perception and its disruption in certain children with learning disorders. The last topic is a consideration of central nervous system changes with perceptual learning. This includes long-term experience with one's native language and short-term auditory training in the laboratory. Limitations and future challenges are discussed.

Auditory Pathways↗
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Auditory pathway encoding and neural plasticity in children with learning problems.

An inability to process auditory information, especially speech, characterizes many children with learning and attention problems. Our working hypothesis is that these speech-sound perception problems arise, at least in some cases, from faulty representation of the speech signal in central auditory centers. Preconscious neurophysiologic representation of sound structure by central auditory pathway neurons can be reflected by subcortical and cortical aggregate neural responses. These neurophysiologic responses can be modified by perceptual learning. Our research has shown that some children with learning problems demonstrate abnormal perception and neural representation of certain speech sounds. Differences between normal and learning-impaired groups can be attributable to aspects of neural synchrony that are reflected in aggregate neural responses. Deficiencies in neural synchrony in these children are apparent in subcortical (as well as cortical) representations of speech-sound structure, and these timing deficits are related to performance on speech-sound perception and learning measures. Moreover, impaired perception and neurophysiologic encoding of speech sounds can be improved with cue enhancement and can be modified by perceptual learning associated with auditory training.

Child↗