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Z Kevanishvili

Publications and source records attributed to Z Kevanishvili.

At least 19 recordsLinked to original sources
PubMed2002

Auditory brainstem, middle-latency, and slow cortical responses in multiple sclerosis.

The efficacy of auditory brainstem responses (ABRs), middle-latency responses (MLRs), and slow cortical potentials (SCPs) has been evaluated in 40 patients with multiple sclerosis (MS). ABRs and MLRs were averaged to clicks and SCPs to 1-kHz tone bursts of 70-dB nHL intensity. ABR, MLR, and SCP abnormalities were detected in 65.0, 42.5, and 30.0% of the sample, respectively. The combined sensitivity of ABRs and MLRs amounted to 80.0%, of ABRs and SCPs to 75.0%, and of MLRs and SCPs to 60.0%. The joint aptitude of all three responses equalled 87.5%. All three responses were capable to detect MS in seven of nine patients, failing to display neurological signs of brainstem lesion. The responses were also abnormal in three of five subjects with negative magnetic resonance imaging. It is concluded that the combined application of ABRs, MLRs, and SCPs promotes both detecting and confirming MS loci.

Acoustic Stimulation↗
PubMed1998

[Effect of stimulus rise time and high-pass masking on early auditory evoked potentials].

BACKGROUND: Problems of frequency-specific objective assessment of hearing threshold by means of auditory brainstem response (ABR) have been discussed recently. While a number of workers have recommended methods of selective masking to improve the frequency specificity, others believe that frequency-specific potentials can also be obtained without masking. In this context, the effects of rise-decay time and high-pass masking on ABRs were investigated. METHOD: ABRs were recorded in normal-hearing subjects and patients with high and low frequency hearing loss by means of surface electrodes between the vertex and the ipsilateral mastoid. The frequency of the stimulus was 1 kHz, and the rise-decay time 1 ms (1-0-1) or 2 ms (2-0-2). High-pass filtered noise (cutoff frequency 1.5 kHz; filter slope 250 dB/octave) was employed for masking. Particular attention was paid to the problem of efficient masking. RESULTS: In normal-hearing subjects under the influence of high-pass masking compared to non-masked ABRs, longer mean latencies and diminished means of the amplitudes of wave V were found, with differences in the near-threshold domain being less pronounced. Similar results were observed in patients with high frequency hearing loss. In patients with low frequency hearing loss, the influence of high-pass masking was especially marked distinctly near to threshold. Furthermore, latency and amplitude differences of wave V of the 1-0-1 and the 2-0-2 stimuli were determined from the ABRs obtained with and without high-pass masking. The differences between the latency differences of both stimuli in the suprathreshold range (70 dB nHL) only were statistically significant. CONCLUSIONS: The results are suggestive of an inadequate frequency specificity of unmasked stimuli in the suprathreshold range. Evaluation of the latencies revealed for both rise-decay times a similar frequency specificity near the threshold and a higher frequency specificity of the longer stimulus in the suprathreshold range.

Acoustic Stimulation↗
PubMed1997

Auditory brainstem response, middle-latency response, and slow cortical potential in patients with partial epilepsy.

Auditory brainstem responses (ABRs), middle-latency responses (MLRs), and slow cortical potentials (SCPs) have been recorded in patients with partial epilepsy previously untreated by anticonvulsants. Peak latencies, interpeak intervals, and amplitudes were estimated and the mean group values were compared with the respective data in age- and gender-matched healthy individuals. Neither ABRs nor MLRs in the patients differed significantly from those in the control group. Conversely, the SCP characteristics demonstrated regular differences: the P2 peak latency in the patients was prolonged and both the P1N1 and N1P2 amplitudes were increased. Considering the mechanisms of the ABR and MLR, it has been suggested that the specific structures of central auditory pathway up to the primary cortex do not play any essential role in the pathogenesis of partial epilepsy. Furthermore, it is speculated that the SCP-generating cortical areas, being primarily of non-specific qualities, are intimately involved in the mechanisms of epilepsy.

Adolescent↗
PubMed1997

[Contralateral modification of transitory evoked otoacoustic emissions].

BACKGROUND: In recent publications the influence of contralateral white noise on transient evoked otoacoustic emissions (TEOAE) is discussed with regard on contributions of the efferent auditory system. METHODS: In the present study the effects have been investigated with regards to middle-ear muscles, efferents and cross hearing. TEOAE to monaural 40-80 dB SPL clicks were recorded in normal-hearing adults under simultaneous presentation of 20-60 dB SPL broadband noise to the contralateral ear. Control runs were performed before, during a short break of, and after contralateral stimulation. The control run before contralateral stimulation was used as a reference. RESULTS: Decrease in TEOAE, and increase in accompanying noise floor, were found to follow the contralateral stimulation. In particular a 1-3 dB decrease was found for contralateral noise levels of 40 and 60 dB SPL, even though the readings at 60 dB only were statistically significant (paired-samples t test, p = 0.05). For both TEOAE and noise floor no systematic dependence on click intensity was seen. The control runs during temporary break and after contralateral noise revealed an increase in both TEOAE and noise floor. As a rule, the TEOAE adapted to the reference within 2-3 min following the cessation of contralateral stimulation, whereas the increased noise floor level was still noted after 10 min. CONCLUSIONS: Traditionally, suppressing effects of contralateral stimulation on TEOAE have been attributed to cochlear efferents (CEs). Occasionally, the middle-ear muscle and cross hearing involvement have been considered as well. Substantially, the present results and findings of other workers are inconsistent with the basic knowledge of CE functioning: (I) The decrease in TEOAE under contralateral stimulation is in conflict with an increase in cochlear microphonics and summating potentials observed during activation of CEs: (II) contralateral suppression of TEOAE exhibited no significant dependence on the test-stimulus level while the CEs are known to be efficient in the range of the low signal intensities only, and (III) acoustic activation of the CEs can hardly be expected to reach levels sufficient to influence the TEOAE mechanism. The present findings, i.e. decrease in TEOAE and increase in noise floor level, can more reasonably be explained as being mainly attributable to activation of the middle-ear muscles.

Adult↗
PubMed1996

Effects of the conditioning click on click-evoked otoacoustic emission.

The effects of the preceding (conditioning) click on the evoked otoacoustic emission (EOAE) to the following (test) click were investigated in normally hearing adults. To overcome distortions due to superimposition of the test EOAE on the EOAE to the conditioning click, a special stimulation and response subtraction procedure was utilized. The conditioning stimulus was found to suppress the test EOAE. The suppression lessened with a decrease in the conditioning stimulus level and an increase in the time interval between the conditioning and the test stimuli. Nevertheless, the influence was traced even with the level of the conditioning stimulus as low as 5 dB SL, and lasted for the interval between the conditioning and the test stimuli, as long as 7.5 ms. An attempt at theoretical comprehension of the obtained results is made and their usefulness in differentiation of EOAEs from acoustic reflections is proposed.

Acoustic Stimulation↗
PubMed1993

Auditory middle-latency response: intramodal and intermodal interactions.

Intramodal and intermodal interactions have been studied in generators of the auditory middle-latency response (MLR). The MLRs were recorded to the wide-band clicks. Similar clicks or electric shocks to the median nerve served as conditioning stimuli. A procedure was employed permitting to avoid distortions of test MLRs due to superimposition upon potentials to the conditioning stimuli. A rapid recovery of responsiveness in MLR generators was revealed in intramodal experiments. Poorly discernible test MLRs were identified at conditioning interval of 10 ms, while already at interval of 50 ms the MLR restoration was completed. No effects of shocks upon MLRs were evident in intermodal experiments. The starting knee was only altered in most test MLRs, outlining a narrow strip of intermodal interaction. The sources of the MLR are discussed and a subcortical rather than cortical, polylevel rather than monolevel, monomodal rather than polymodal nature of the MLR is proposed.

Acoustic Stimulation↗
PubMed1992

Evoked otoacoustic emission: behaviour under the forward masking paradigm.

The behaviour of evoked otoacoustic emission (EOAE) has been studied in normally hearing adults under the conventional forward masking paradigm. The clicks and tone pips served as signals, and the noise bursts were used as maskers. At noise burst levels, defined as psychoacoustic masking thresholds of signals (postmasking threshold), attenuation of EOAEs was just noticeable but did not occur in all records. The EOAEs were not completely eliminated even at noise levels exceeding the post-masking threshold by 30 dB. Central or neural and peripheral or receptor mechanisms are suggested to be the constituents of the masking phenomenon. The receptor mechanism effectively joins the neural one at masker levels, well exceeding the thresholds of psychoacoustic masking. The increase in masker duration and decrease in interval between masker and signal seem to accentuate the neural mechanism. As a result, the difference between masker levels, leading to psychoacoustic masking of the signal and having marked attenuating effects upon the EOAEs, respectively, is increased.

Acoustic Stimulation↗
PubMed1992

Behaviour of delayed evoked otoacoustic emission under forward masking paradigm.

The behaviour of delayed evoked otoacoustic emission (DEOAE) has been studied in normally hearing adults under a conventional forward-masking paradigm, and subjective measurements were carried out additionally for comparison. The clicks served as signals and the noise bursts were used as masker. In different experimental sets, signal and masker intensity, masker duration, and the interval between masker and maskee were altered. At masker levels corresponding to the subjective post-masking threshold of the clicks, the DEOAE was unaffected, i.e. had no noticeable alteration, compared with click stimulation without masking. Even at higher masker levels the inaudible clicks elicited clearly discernible DEOAEs. The forward-masking detection threshold of DEOAE ('DEOAE post-masking threshold') was reached at masker levels approximately 35 dB above the subjective post-masking threshold. The gap between subjective and DEOAE post-masking threshold vis-à-vis the masker level was also evident at different masker durations and different time intervals between masker and maskee. Central neural and peripheral receptor mechanisms are suggested to be the constituents of the masking phenomenon. The neural mechanism is involved at low masker levels. The receptor mechanism effectively joins the neural one at masker levels exceeding the threshold of psychoacoustic masking. The progressive increase in the number of auditory units from the periphery to the centre in the hearing system, linked with an increase in inhibition, can help to explain these effects.

Acoustic Stimulation↗
PubMed1990

[Frequency spectra and filtering of the early auditory evoked potential].

We analysed the spectral content of click-evoked fast auditory evoked potentials (FAEPs) at stimulus levels of 80 dB nHL and were able to demonstrate the influence of the different frequency bands of the FAEP spectrum on the shape of the FAEP. The different kinds of filter and their typical effects are discussed, and some examples are demonstrated. Analogue high-pass filters with a steep slope change the shape of the FAEP markedly, because of the great phase distortion (non-linearity of the phase function). Therefore only one-pole filters (6 dB/octave) with a low cut-off frequency below about 70 Hz should be used. Higher cut-off frequencies can be used with digital zero-phase or linear-phase highpass filters. However, such frequency components which are essential for amplitudes and/or latencies of the FAEP should not be attenuated strongly by the filtering. Therefore, the low cut-off point should not exceed about 200 Hz.

Cerebral Cortex↗
PubMed1987

Masking level difference: an electrophysiological approach.

Auditory brainstem responses (ABRs), middle latency responses (MLRs), and slow cortical potentials (SCPs) were registered in normal-hearing adults to trains of low-frequency signals delivered binaurally on a background of a continuous masking noise. Two stimulus conditions, labelled as S0M0 and S pi M0 paradigms, respectively, were systematically compared. In the S0M0 paradigm, both the signals and the masker were in-phase at two ears. In the S pi M0 paradigm, the signals were out-of-phase at two ears, while the masker was in-phase. The psychoacoustic release from masking in S pi M0 vs. S0M0 paradigms was regularly accompanied by an increase in amplitudes and a shortening in peak latencies of the SCPs. In contrast, no differences were evidenced between the S0M0 and the S pi M0 paradigms with respect to the ABRs and the MLRs. Considering the generation loci of the studied electric responses, it is concluded that the binaural psychoacoustic phenomenon, referred to as the masking level difference, is operated primarily at the cortical level.

Adult↗
PubMed1985

Frequency-specific contributions to the auditory brain stem response derived by means of pure-tone masking.

The pure-tone masking technique has been employed to determine the contributions of neural activity from different cochlear regions to the click-evoked auditory brain stem response (compound ABR). ABR to broad-band clicks were recorded without and with simultaneous presentation of pure tones of frequencies ranging from 8 to 0.5 kHz. Derived ABRs for individual frequency bands were obtained by subtracting the masked responses from the unmasked ones. To determine the contributions to the compound ABR, masked and derived ABRs were compared with unmasked responses. The frequency specificity of the contributions was more distinct at lower rather than at higher stimulus intensities. Independent of stimulus intensity, the 8- to 2-kHz regions turned out to be the main sources of waves I-V in the compound ABR, whereas waves VI and VII seem to be predominantly generated by contributions from regions specific for 1 and 0.5 kHz. The main advantage of the pure-tone masking technique as compared with the tone pip stimulation is that contributions from the low-frequency regions become more clearly detectable. The validity of this technique has been proved by comparing the compound ABR with the sum of the derived ABRs. The comparison of ABRs derived by pure-tone masking with those derived by conventional high-pass noise masking did prove the validity of the technique as well.

Acoustic Stimulation↗
PubMed1985

Interpeak intervals of auditory brainstem response, interaural differences in normal-hearing subjects and patients with sensorineural hearing loss.

ABR recordings were made on 31 normal-hearing subjects and 253 patients with sensorineural hearing loss (86 patients with unilateral hearing loss, 61 patients with asymmetrical hearing loss, 34 patients with symmetrical hearing loss, 55 patients with noise-induced hearing loss and 17 patients in the late chronic stage of Menière's disease). In the patient group with unilateral hearing loss, the mean interpeak interval (IPI) I-V was significantly shorter than in normal-hearing subjects. The interaural IPI differences provide a sharp criterion for early detection of acoustic neuroma. The calculation of the 95%-limits (means + 1.96 SD) showed that in patients with normal hearing or with unilateral or symmetrical hearing loss an interaural difference in the IPII-V greater than 0.2 ms has to be considered as an indication of a neuroma or any other brainstem abnormality. In patients with asymmetrical or with noise-induced hearing loss, the limit is 0.3 ms. In contrast to the frequently recommended interaural wave V latency difference criterion, the interaural IPI difference criterion requires no correction for audiogram differences.

Brain Stem↗
PubMed1981

Click polarity inversion effects upon the human brainstem auditory evoked potential.

Parameters of the brainstem auditory evoked potentials (BAEPs) to high-intensity clicks of initial rarefaction (R) and condensation (C) phases differed. The amplitudes of Waves I, II and IV were greater with R clicks, while that of Wave V was greater with C clicks. The peak-latencies of Waves I and VI were shorter with R clicks and those of the remaining components tend to shorten with C clicks. At low stimulus intensities the preserved BAEP components (Waves III, V and VI) did not change noticeably with click phase inversion.

Acoustic Stimulation↗
PubMed1981

Considerations of the sources of the human brainstem auditory evoked potential on the basis of bilateral asymmetry of its parameters.

Possible sources of individual components of the human brainstem auditory evoked potential (BAEP) were previously considered proceeding from the bilateral asymmetry of their parameters, the latter being determined with the centro-periaural electrode position. It is proved that such considerations are misleading: with more adequate derivation paradigm, i.e. with extracephalic placement of the reference electrode, the bilateral asymmetry of BAEP parameters has mainly the opposite sign.

Acoustic Stimulation↗
PubMed1979

Frequency composition of brain-stem auditory evoked potentials.

It has been demonstrated by digital filtration and power spectra analysis that main energies of different components of human brain-stem auditory evoked potentials are concentrated in the following frequency bands: 400--1 000 Hz for waves I and II, 100--900 Hz for wave III, and 100--500 Hz for waves IV--VI. The data obtained are compared with those published in Scand Audiol by Terkildsen et al. (1975) and Elberling (1976).

Acoustic Stimulation↗
PubMedDate not supplied

Effects of carbamazepine on auditory brainstem response, middle-latency response, and slow cortical potential in epileptic patients.

Auditory brainstem responses, middle-latency responses, and slow cortical potentials (ABRs, MLRs, SCPs) were recorded in 21 epileptic patients before and during treatment with carbamazepine (CBZ). The peak-latencies, interpeak intervals, and amplitudes were estimated and evaluated statistically. CBZ monotherapy resulted in prolongation of peak latencies of ABR waves I, III, and V as well as of interpeak intervals I-III and I-V. A significant increase in the peak-latencies of MLR components Na, Pa, and Nb and of interpeak intervals V-Pa and Na-Nb was also observed along with the systematic NaPa amplitude reduction. CBZ also prolonged the peak-latencies of SCP components P1 and N1. Based on the obtained results, we suggest that CBZ exerts suppressive influences both on modally specific (lemniscal) and modally nonspecific (extralemniscal) auditory structures.

Acoustic Stimulation↗