Acoustic neuroma diagnosis.

Pure tone audiometry, PTA, has been regarded as an initial step when starting acoustic neuroma, AN, diagnostic service. If observing unilateral/asymmetrical sensorineural hearing loss, electronystagmography, ENG, and registration of auditory brainstem responses, ABRs, are instructed to perform. The measures of the methods are listed appearing particularly effective for AN detecting. Efficacy of ENG and ABR approaches in verification of ANs of even initial stages has been stated to reach the absolute identification score, 100%. In tinnitus and/or vertigo complaints, ENG and ABR examinations are recommended to utilize under normal PTA even. The positive evidence of ANs via ENG and ABR has to validate by contrasting magnetic resonance imaging, MRI, while MRI data are advised to utilize for assessment of concrete strategy of surgical intervention. Under negative ENG and ABR outcomes, on the other hand, MRI is considered as a hardly urgent procedure.

[The psychoacoustic phenomenon of masking level differences in the human subject studied by auditory evoked potentials]. / Issledovanie psikhoakusticheskogo fenomena "razlichie v urovniakh maskirovki" u cheloveka po slukhovym vyzvannym potentsialam.

Auditory brainstem responses (ABRs), middle latency responses (MLRs), and slow cortical potentials (SCPs) were recorded in normal-hearing adults to trains of low-frequency acoustic signals delivered binaurally against a background of a continuous masking noise. Two stimulus conditions, labelled as binaural homophasic and binaural antiphasic paradigms, respectively, were systematically compared. In the homophasic paradigm both the signals and the masker were in-phase at two ears. In the antiphasic paradigm the signals were 180 degrees out-of-phase at two ears, while the masker was in-phase. The psychoacoustic release from masking in the antiphasic vs. the homophasic paradigm 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 homophasic and the antiphasic 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.

[Effect of masking on interhemispheric and bilateral asymmetry of long-latency auditory evoked potentials]. / Vliianie pomekhi na mezhpolusharnuiu i bilateral'nuiu asimmetriiu dlinolatentnykh slukhovykh vyzvannykh potentsialov.

Considering the effects of noise on the amplitude of long-latent auditory evoked potentials, it is concluded that masking interference diminishes the right hemisphere dominance in the processing of the non-speech acoustic information. The decrease is observed both with the monotic and dichotic delivery of signals and noise. With monotic presentation masking interference also decreases the extent of the lateralization of monaurally delivered information predominantly to the contralateral hemisphere.

Sources of the human brainstem auditory evoked potential.

Most components of the human brainstem auditory evoked potential (BEP), elicited by monaural clicks are greater on ipsilateral than on contralateral scalp areas. The major BEP component, Wave V, on ipsilateral areas has also a shorter peak-latency. Under binaural vs monaural stimulation all the BEP components duplicate in amplitudes. Proceeding from these results the sublemniscal (cochleo-olivary-trapezoid) origin of all the BEP components is suggested.

[Age and changes in the latent periods of the slow human auditory potential]. / Vozrastnye izmeneniia latentnykh periodov medlennogo slukhovogo vyzvannogo potentiala cheloveka

Regular changes in latencies of slow auditory evoked potentials were found with age. In particular, peak-latencies of comparatively early deflections, i.e. P1, N1 and P2, progressively diminished. The shortening of latencies was 50-60 ms for the age between 3-7, 8-13, and 25-35 msec further on. The latencies of the later waves, namely P3, N3 and P4, increased by 35-65 ms for the age between 3-7 and 8-13. After these ages, the latency of deflection P3 did not change, while deflections N3 and P4 disappeared. Of all the evoked potential components deflection N2 was the most stable, its latency negligibly shortened with age. In children aged 3-7 two complexes of waves (P1N1P2 and P2N2P3) often overlapped, forming a broad nondifferentiated deflection. The division of the latter was completed at the age of about 8. Long-term developmental changes in wave-shape and parameters of the slow evoked potentials are considered as supporting their mainly nonspecific (extralemniscal) orgin. Basing on correlation revealed between the late evoked potential components and EEG synchronization level, a hypothesis is advanced according to which these components are generated with participation of the nonspecific synchronizing system.

[Intramodal and interaural specificity of the human slow auditory evoked potential]. / Ob intramodal'noi i interaural'noi spetsifichnosti medlennogo slukhovogo vyzvannogo potentsiala cheloveka.

Parameters of slow auditory evoked potentials (SAEPs) evoked by monotonal monaural stimuli were compared with those evoked by a series of tone stimuli of different frequencies. In one version of polytonal stimulation the side of sound application was alternately varied. In the case of polytonal stimulation the amplitude of SAEPs was consistently greater than that in the case of monotonal stimulation. The maximal amplitudes were obtained during alternating polytonal stimulation. In the case of polytonal stimulation, together with the amplitude increase, a regular decrease in its variability was noticed. SAEPs recorded during polytonal stimulation were also characterized by greater peak-latency values. It is concluded that SAEPs possess intramodal and interaural specific properties. It is proved that the tonotopic and bilaterally symmetric organization of SAEP generating system is better manifested at lower sound intensities. The data demonstrate that neuron populations of the SAEP generating system which perceive slightly different sound stimuli overlap each other more than those which perceive more different sounds. The data on intramodal and interaural specificity of SAEP are discussed from the point of view of extralemniscal origin of this potential.

[The relationship between the parameters of the early and late oscillations of human cortical evoked potentials and the rhythm of acoustic stimulation]. / Zavisimost' parametrov rannikh i pozdnikh kolebanii korkovykh vyzvennykh potentsialov cheloveka ot ritma zvukovoi stimuliatsii

The amplitudes of all deflections of the slow auditory evoked potential (AEP) regularly decrease in alert subjects with the increase of stimulation rate. As compared with the late deflections (P2N2), the decrease of the amplitude of comparatively early deflections (N1P2) is more pronounced. It is a rather logarithmic, than a linear function of the interstimulus interval. The degree of amplitude diminution of slow AEPs due to a greater stimulation rate depends on the intensity of acoustic stimul: at greater sound intensities the decrease is more pronounced. The higher rates of stimulation produce, along with a decreased amplitude, a shorter peak latencies of all slow AEP deflections (except the peak of deflection P1). In narcotic (chloralhydrate) sleep higher rates of stimulation are not attended with any regular changes in the amplitude and peak latencies of the slow AEP.