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Biomedical subjects

M Don

Publications and source records attributed to M Don.

53 records · Page 3Linked to original sources
PubMed1980

Analysis of the click-evoked brainstem potentials in humans using high-pass noise masking. II. Effect of click intensity.

Derived narrow-band brainstem responses were obtained for click levels of 10--60 dB SL in normal hearing subjects. The amplitudes and latencies of the wave I, wave III, and wave V components in the derived BSER were studied as a function of click intensity. Characteristic differences were found between the input-output behavior of waves I and III on one hand and wave V on the other hand, especially for the low-frequency narrow bands (center frequencies of 0.5 and 1.0 kHz). While the wave I and wave III (peak-to-succeeding trough) amplitude showed a small (20--30 dB) dynamic range with saturation effects, the wave V amplitude continued to increase across the intensity range studied. At the high-frequency end (narrow-band center frequencies of 4 and 8 kHz), wave V also showed saturation. It is suggested that this difference across center frequency (place of origin along the cochlear partition) is responsible for the dominance of wave V at low-frequency stimulation (e.g., with tonebursts). The latencies of the three waves studied maintained their constant interwave delays across the observed intensity range in each narrow band. Quite large (up to 3.5 ms) increases in the narrow-band latencies were found for decreasing click levels; this is comparable in value with those for the unmasked BSER although the mechanism seems to be different. The major contribution to the BSER which determines its latencies, originates at 60 dB SL from the 8-kHz region but at low SL (10 and 20 dB) from the 2-kHz region. At these low intensity levels, the contribution from the apical part of the cochlea, however, is still of the same size as that from the high-frequency end.

Acoustic Stimulation↗
PubMed1978

Analysis of the click-evoked brainstem potentials in man unsing high-pass noise masking.

Brainstem electrical responses (BSER) to 60-dB-SL click in noise high passed at various cutoff frequencies separated b 1/2-octave steps were recorded in normal-hearing adult subjects. By applying a derived response technique, narrow-band contributions to the BSER from specific portions of the basilar membrane were revealed. Latencies and amplitudes of the various waves in the derived BSER were recorded. Results indicate that nearly the whole cochlear partition can contribute to the brainstem response. The shifts in latency of waves I, III, and V and amplitude changes of waves I and III as a function of CF appear to be fully comparable to those of the AP. In contrast, the amplitude behavior of wave V as a function of CF is different from waves I and III depending upon frequency range. The discrepency in the behavior of wave V with respect to the earlier waves suggests some sort of neural reorganization at the level where was V is generated. The fact that there are contributions to the brainstem response from apical portions of the cochlea opens the possibility for extending the brainstem technique in assessing the higher cochlear turn function.

Acoustic Stimulation↗
PubMed1975

On the application of affinity chromatography to turnover studies on the lactate dehydrogenase isoenzymes.

1. The suitability of a combined application of the techniques of affinity chromatography, double labelling and gel electrophoresis in the determination of the turnover characteristics of the lactate dehydrogenase isoenzymes (L-lactate:NAD+ oxidoreductase EC 1.1.1.27) in rat tissues has been studied. 2. Affinity chromatography was established as affording the advantages of rapidity, high yield and purity to such studies, and the double-labelling procedure was modified to encompass the differential decay kinetics in the separate rat tissues. In addition, a convenient method for the resolution and separate collection of radioactively labelled isoenzymes has been described. 3. Using this methodology, comparative turnover values for the isoenzymes of lactate dehydrogenase and for total soluble protein have been determined. 4. The comparability of these results with other methodologies, and the advantages of this approach in facilitating broad comparative studies on turnover are discussed.

Animals↗
PubMedDate not supplied

Spatio-temporal source modeling of evoked potentials to acoustic and cochlear implant stimulation.

Spatio-temporal source modeling (STSM) of event-related potentials was used to estimate the loci and characteristics of cortical activity evoked by acoustic stimulation in normal hearing subjects and by electrical stimulation in cochlear implant (CI) subjects. In both groups of subjects, source solutions obtained for the N1/P2 complex were located in the superior half of the temporal lobe in the head model. Results indicate that it may be possible to determine whether stimulation of different implant channels activates different regions of cochleotopically organized auditory cortex. Auditory system activation can be assessed further by examining the characteristics of the source wave forms. For example, subjects whose cochlear implants provided auditory sensations and normal hearing subjects had similar source activity. In contrast, a subject in whom implant activation evoked eyelid movements exhibited different source wave forms. STSM analysis may provide an electrophysiological technique for guiding rehabilitation programs based on the capabilities of the individual implant user and for disentangling the complex response patterns to electrical stimulation of the brain.

Acoustic Stimulation↗
PubMedDate not supplied

Maturation of the mismatch negativity: effects of profound deafness and cochlear implant use.

The use of cochlear implants to restore auditory sensation in deaf children is increasing, with a trend toward earlier implantation. However, little is known about how auditory deprivation and subsequent cochlear implant use affect the maturing human central auditory system. Our previous studies have demonstrated that the obligatory auditory evoked potentials (AEPs) of implanted children are very different from those of normal-hearing children. Unlike the obligatory potentials, which primarily reflect neural responses to stimulus onset, the mismatch negativity (MMN) provides a neurophysiological measure of auditory short-term memory and discrimination processes. The purpose of this investigation is to review our studies of the effects of auditory deprivation due to profound deafness and cochlear implant use on the maturation of the MMN in children, placed in the context of overall age-related changes in the AEPs. The development and application of a statistical technique to assess the MMN in individuals is also reviewed. Results show that although the morphology of the obligatory AEPs is substantially altered by the absence of a normal N(1) peak, the MMN is robustly present in a group of implanted children who have good spoken language perception through their device. Differences exist in the scalp distribution of the MMN between implanted and normal-hearing children. Specifically, the MMN appears to be more symmetrical in amplitude over both hemispheres, whereas it is initially much larger over the contralateral hemisphere in normal-hearing children. These findings suggest that, compared to N(1), the MMN is a better measure of basic auditory processes necessary for the development of spoken language perception skills in profoundly deaf children and adults who use a cochlear implant.

Adult↗
PubMedDate not supplied

Effect of click rate on the latency of auditory brain stem responses in humans.

Auditory brain stem responses are the far-field reflections of electrical activity originating in the auditory pathway in its course from the cochlea to cortex that can be recorded from scalp electrodes using computer averaging techniques. There are seven components in the initial 10 msec following a click signal which have been shown to have an orderly change in latency as a function of signal intensity. The results of this study show that click repetition rate can also significantly affect the response latency measure. Responses were measured in six normal hearing subjects at click rates of 10, 30, 50 and 100/sec and af four intensity levels (30, 40, 50, and 60 dB sensation level). The mean latency shift of component V was approximately 0.5 msec when the responses at 10 and 100/sec were compared. This is equivalent to a 15-20 dB decrease in signal intensity at the 10/sec click rate. An analysis of the time of occurrence of this shift using brief click trains at 100/sec showed the shift in latency to be complete by the fifth click. The latency shift was similar at the four signal levels tested. The latency shift was similar at the four signal levels tested. The latency shift of component V appeared to be a monaural and therefore a potentially peripheral process. The results are interpreted as an objective measure of adaptation in the human auditory system with implications for the measurement in disorders of hearing.

Acoustic Stimulation↗
PubMedDate not supplied

Reconstruction of the audiogram using brain stem responses and high-pass noise masking.

Contributions to the brain stem electrical responses (BSER) presumably initiated from specific frequency regions of the cochlea with center frequencies similar to the major audiometric frequencies (0.5, 1, 2, 4, and 8 kHz) are derived by the application of a high-pass noise masking technique utilizing click stimuli. In normal hearing subjects, these derived narrow-band responses from the midfrequency regions (4, 2, and 1 kHz) can be recognized at click levels as low as 10 dB HL. For the frequency regions around 8 kHz and 0.5 kHz, these derived responses can be discerned at click levels of 30 dB HL and higher. When one uses the lowest click level at which these derived responses can be obtained from a given frequency region, the differences between a patient with a hearing loss and a normal hearing subject correlate well with the amount of hearing loss (air conduction) recorded by conventional pure tone audiometry. Use of the high-pass noise masking technique to reconstruct the audiogram may be of great potential value in assessing young children and other individuals who cannot or will not respond to conventional audiometry.

Adolescent↗
PubMedDate not supplied

Electrocochleography and auditory brainstem electric responses in patients with pontine angle tumors.

In 45 patients with surgically proven pontine angle tumors, compound action potential (AP) and summating potential (SP) were recorded with transtympanic electrocochleography (ECochG) together with brainstem electric responses (BSER). The aims were to quantify the mechanism by which tumors cause hearing loss and evaluate the diagnostic potentials of ECochG and BSER for detecting eighth nerve and brainstem tumors. Except for AP latency and narrow band AP waveform, response parameters recorded by ECochG are uncorrelated. Four uncorrelated parameters were abnormal in only 10% of the cases, three in 25%, two in 40%, and one in 90%. The BSER criterion was the latency delay between waves I and IV and resulted in about 90% detection, improving to 95% when used in combination with ther interaural wave V delay criterion. ECochG results provide evidence that, for hearing losses up to 60 dB HL, the origin is cochlear, resembling that caused by Meniere's disease. Evidence is presented that the increase in I-V delay in the BSERs is caused by differential action of the tumor upon low and high frequency fibers in the auditory nerve and that desynchronization of the firings of the nerve fibers is of more importance than an increase in neural conduction time. ECochG as the sole test for detection of pontine angle tumors appears to be of limited value. Brainstem response on its own has great merits; however, it should be emphasized that no wave I was detected in about 30% of the cases. The 95% detection score obtained with BSER depends on specifying the latency of wave I. For these cases, we substituted the latency of the AP recorded by ECochG.

Acoustic Stimulation↗