The present study was designed to investigate how ABRs of the rats are influenced by experimental manipulations of central noradrenergic (NA) activities. Experiments were conducted on Wistar strain male rats anesthetized with α-chloralose. ABR waveform patterns had dependencies on electrode positions. A clear pattern with a distinct separation of each peak could be recorded when an electrode was placed on the midline of the skull close to the lambda. A reference electrode was placed on the tail or pinna. Clonidine, an NA α2-agonist, depressed the amplitudes of ABR at intravenous doses of 0.05-0.1mg/kg; larger changes in peaks IIb and IV were noted. These effects were antagonized by yohimbine, an NA α2-antagonist. Electrical stimulation of the locus coeruleus also depressed peak II and beyond in a current-dependent manner. The maximum inhibitory effect was observed at the conditioning-test stimulus interval of about 50msec. Yohimbine suppressed these changes, too. These results suggested that an NA system of α2-type, originating from the locus coeruleus, was involved in the efferent modulatory function on the auditory afferent system.
This study was performed to clarify the origin of PII wave of the rat's ABR. The PII was characterized by the bimodality of PII a and PIIb, and usually this bimodality was clearly recognized using non-cephalic reference electrode. In this study, the reference electrode was set at the base of the tail as a non-cephalic reference point, and special attention was paid to avoid the ECG interference. The development of PII was studied in a series of rats over a postnatal period ranging immediate after birth to 60 days. PII a was appeared at 14 days after birth, while PIIb was recognized at 18 days. PIIa had a large amplitude at the recoding sites of contralateral to the stimuli, whereas PIIb was larger than PIIa at the ipsilateral sites to the stimuli. These results indicate that PII is a complex wave having at least two generators.
In order to varify the frequencial specificity of ABR of rat, the authors recorded ABR on the surface of the brain and the potential of the inferior colliculus (I. C) evoked by click and tone pip from 4k to 500Hz. The results were as follows: 1) Tone pip was more specified than click in the form of power spectral analysis at every frequency. 2) ABR was recorded at every frequency except 1k and 500Hz tone pip. The fast wave of ABR was not evoked by these two stimuli. 3) The tonotopic organization of I. C. was not proved by this experiment. The preceding 2 or 3 waves of the potential in I. C. were not evoked by the stimuli of 1k and 500Hz tone pip. This fact seemed to be the same phenomenon with the diminished fast waves of ABR. The latter nagative potential of I. C. was also reduced by these stimuli which was thought to have less influence upon slow negative 10 (SN10)
Slow components of the auditory brain stem responses (ABRs) were recorded from the scalp and earlobes electrodes using balanced non-cephalic reference electrode method. Active electrodes were placed using. International 10-20 system in coronal (A1, T3, C3, Cz, T4, A2) and in sagittal (Fpz, Fz, Cz, Pz, Oz.) planes. The results were compared with the standard vertex to earlobe deviation. These studies lead us to the following conclusions: 1. The slow components of the ABRs are broadly distributed over the scalp, and they are positive at all recording points with monoaural stimulation. 2. The slow components are of maximal amplitude at the region of Cz in all of the recording points. 3. Amplitude of the slow component from Cz-neck is higher than that from standard vertex-earlobe deviation. In clinical slow components recording, earlobe is usually used as a reference point, however, it was clarified that it was active electrode.
Auditory brainstem response (ABR) was divided into the fast and slow components by computerized digital filter. Digital filtered signals were averaged up to 1000 times. During these procedures, every 100 times' averaged responses were recorded successively, and their latencies and detectability were calculated, in order to compare the modality of the fast and slow components of ABR. In this study, effect of stimulus rise time and duration on two components of ABR were investigated. The results were as follows; (1) The stability of wave I to wave IV was decreased both with increase in stimulus rise time and increase in duration. The stability of both wave V and the slow component, on the other hand, was not decreased with rise time and duration. (2) The latencies of the fast components were prolonged with increase in stimulus rise time and duration. The latency of the slow component, on the other hand, showed no remarkable change with increase in stimulus rise time and duration.
Contralaterally recorded brainstem auditory evoked potentials were compared with ipsilaterally recorded ones in an attempt to apply their differences for wave identification. The method proved to be helpful in; 1) identifying wave I, which is obscured on the contralateral, 2) separating waves IV and V, which are often more discrete contralaterally. But other contralateral findings such as; 3) prolongation of waves II and V latencies, 4) lengthening of III-V interpeak latencies, 5) shortening of II-III interpeak latencies, seem to be of less clinical value, because the latency differences from each counterpart show a relatively wide distribution.
In order to discuss the clinical utility of synchrony measure (SM), advocated by Fridman, a modified statistical test of the brain stem auditory response (component synchrony index=CSI) was designed and investigated. The CSI, which resembles to SM and represents the degree of reproducibility for group averages of ABR, was used as a statistical measure and was calculated from the first peak latency of 10 waves, which were derived from 10 group averages with filtering technique using FFT. The sensitivity of the test was demonstrated on 14 normal ABRs with different intensities (80, 50, 0dB HL) of stimulus from ipsilateral response. From the results, we emphasized that synchrony measure is useful for auditory brain stem evoked response detection.
We investigated a spatial course of the auditory electromotive vector following to sound stimuli (=Vector ABR) delivered from one of the four loudspeakers sequentially, situated at 0° azimuth, 90°, 180°, 270°. Vector ABRs changed in a certain manner with the movement of the sound sources in the horizontal plane. Apparent changes were observed in the responses of right-to-left lead axis. There were no significant diffferences between Vector ABRs to sound stimuli from the front loudspeaker and from the back loundspeaker. It is well known that localization performance of sound sources in the sagittal plane is also difficult psychoacoustically. We recorded responses of three axis of ABR in the performance of sound lateralization.
Topographic mapping of ABRs were performed in various indifferent reference sites on 42 cats. Highest voltage areas (HVA) in isovoltage maps of ABR component (wave I, III and IV) were compared. When indifferent reference sites were bilateral earlobes or ipsilateral one, the pattern of HVA of wave I were similared, concentrated on the contralateral occipital area. The HVA of wave III and IV have also similarity in these groups, and concentrated on the temporal area. However, in cases of posterior neck series, the HVA of wave I was observed on the temporal area. HVA mapping of wave III and IV made a little differences.
Techniques in ABR topography were studied in five normal adults. 1. Noise potentials between a vertex exploring electrode and 6 non-cephalic references were measured and evaluated by time-series and spectrum analyses. A laryngeal prominence reference had the least ECG contamination. 2. To reduce ECG and EMG noises, an aluminum foil strip was wound round the neck. It was effective in reducing the noise. 3. Simultaneous 16chs ABR recordings were obtained by binaural acoustic click stimuli. Exploring electrodes were located according to the 10-20 system. A non-cephalic reference was placed at the laryngeal prominence. A set of peak-to-peak amplitude values of Jewett wave V was employed in computation to obtain amplitude topograms of laryngeal prominence reference, average potential reference and source derivation. The latter two were reference invariant. The test-retest stability of the records were satisfactory. 4. Wave V peak latency distribution topograms were obtained with the same technique as described above. We concluded that the laryngeal prominence reference with metal neck belt was one of the best techniques for multichannel ABR recording; the source derivation topogram may have advantages in clinical neurophysiological investigation.
126 low birth-weight infants (born at 27 to 36 weeks postconceptional age), representing 252 ears, were classified into 5 groups by postconceptional age: 30-36 weeks, 37-42 weeks, 43-57 weeks, 58-73 weeks and 74-105 weeks. ABR waveform detection was made on these infants and detection rates were reviewed. ABR waveforms were detected and stable at 90dBnHL. When measured at 70dBnHL, waveforms were hardly detected if infants were younger in postconceptional age. Judged from the changes in the detection rates of ABR waveforms and of composite waves I-II, III-IV and IV-V among infants, auditory pathway seemed to continue developing even after birth with myelination progressing over the time both in rostral and caudal sides.
A computer system to process auditory evoked responses was developed. In this system examinations were performed as same as conventional method. After completion of the examination the results of addition were sent through parallel interface to micro-computer and processed. The results of processing were indicated on a cathode ray tube or X-Y plotter. In the present stage, the process described as below were performed by this computer system. 1. Amplitude and latency of each component of ABR are automatically measured, and latency-intensity curve of V is written out. 2. A threshold of bone conduction is measured by the method of derived ABR. 3. Responses of ECoG are measured and some graphs about AP and SP are plotted. 4. All data processed by this system are stored to magnetic disc with patients name and diagnosis, and these data can be statistically analysed. This system is very usefull to indicate the results of auditory evoked responses obviously, and to control many records of examinations with low cost.