The effect of perilymphatic perfusion with oxygenated artificial perilymph upon the EP of the ischemic cochlea was investigated in the guinea pig. Perfusion at a high flow rate in the scala vestibuli could well recover and maintain the EP to the level before the ischemia, whereas perfusion in the scala tympani could not recover the EP as effectively. This finding seems to suggest that, in an anoxic cochlea, oxygen when supplied in the scala vestibuli gets easier access to the stria vascularis than when supplied in the scala tympani.
The auditory evoked Slow Vertex Response (SVR) has been used as one of the objective audiometry. However, there are some problems still remain unsolved, such as the false positive response especially in infants under sleeping stages and unstability of the response for low intensity stimuli near the audible threshold. The aim of this paper is to establish a method to improve the detectability of the SVR, and the responses for 20dBSL both in adults and infants have been analized under a series of computerized procedures using PDP 11/60. Methods were as follows; (1) The non-recursive digital bandpass filter using the fast Fourie transform was applied for the SVR in adults and infants. (2) Both non-filtered and digital filtered EEG were averaged 100 times. During these procedures, the averaged EEGs every 25 times were recorded successively, and their signal to noise ratio (S/N) were calculated, in order to analyse the modality of the response. Results were as follows; (1) The most effective pass-band of digital filter in order to detect SVR in adults and infants was 3 to 9Hz. (2) The detectability of digital filtered SVR was increased by 18% in adults, 15% in infants, compared with the non-filtered SVR. The S/N of filtered SVR was significantly increased, compared with non-filtred SVR. (3) The false positive response in digital filtered EEG in infants reduced by approximately 50%, compared with those in non-filtered EEG. (4) Averaged EEGs every 25 times with low intensity stimuli were not always stable as for their latencies and amplitudes. (5) The 25 times averaged EEG with the highest S/N was appeared 20 to 30 seconds after the first stimulus was applied. This phenomenon seemed to be influenced by the attention or habituation to the acoustic stimuli.
Hypothermia was induced by surface cooling in 32 anesthetized guinea pigs' and the effects upon AP, SP, CM and EP of the cochlea were examined. The amplitude of the CM was almost linearly descreased and the latency of the AP was increased as a function of temperature decline. The SP showed variable changes, but this potential still remained when the other potentials were absent. The change of the AP amplitude was the most interesting finding in this experiment. It showed no change or transient increase up to 28°C, followed by gradual decrease with the further temperature decline. The EP was slowly decreased from 36°C to 27°C and rapidly decreased thereafter. The decline of EP in anoxia for 120 sec was decreased as the temperature was lowered. These results are relevant to the animal experiments reported by the others, and they show that hypothermia induced the diminution in the metabolic activity in all cochlear tissue.
The purpose of this study is to confirm whether hearing threshold of young children can be predicted from response threshold of ABR to click or tone pip stimuli. The response threshold of ABR was compared with that of play audiometry which was performed about 6 months to one year after ABR had been done in 35 young children. It was generally found that there was close conelation in speech frequencies between the hearing threshold determined by the click or tone pip evoked ABR and that determined by play audiometry. Consequently, hearing threshold in speech frequencies can be estimated by ABR to click or tone pip stimuli and it is concluded that ABR audiometry is very useful to predict the hearing in young children. We, however, emphasized that determining the hearing in young children must be done very carefully by not only ARR but also behavioral audiometry, because the large discrepancy between the ABR threshold and the behavioral threshold actually existed in some cases.
Scalp distribution and its stability of the auditory brainstem response (ABR) were studied in a normal human subject by computed brain electrical activity mapping. The scalp distribution of the highest electrical activity of ABR components on the scalp was as follows: 1) Wave I: the highest area had many variations. 2) Wave II: the highest area was not uniform, however they tended to distribute in the octipital area. 3) Wave III: the highest area was not uniform, however they tended to distribute in the parietal area and contralateral hemisphere. 4) For the wave IV-V: the highest area was most clearly detected on the parietal area. 5) For the slow component: the highest area Clinical application of topographical display of ABR have to be taken a prudent attitude as far as the results of our data are concerned, because topographical display of ABR had many normal variations.
Changes of modality of 40Hz ERP (40Hz Event Related Potential) through various pass bands of input filter, and power spectra of 40Hz ERP during awake and asleep in adults were examined, and the following results were discussed. 1) 40Hz ERP is commonly recorded through 10-100Hz band pass filter as R. Galambos reported in 1981, but in these examinations its modality was seemed to be more stable when the pass band of input filter was 25-50Hz. 2) At the large intensity of stimuli the power spectra of 40Hz ERP had a peak of 40Hz component but when the intensity of stimuli was smaller for example 20dB and 0dB SL, 20Hz component had another peak and its power was relatively increased against the 40Hz component. 3) When the intensity of stimuli was 30dB SL, power of 20Hz or 15Hz component had another peak and that of 40Hz was decreased during asleep. 4) Considering these facts, it was thought that the more stable 40Hz ERP could be recorded using 25-50Hz band pass filter during not only awake but asleep even with small intensity of stimuli. 5) From the changes of modality of 40Hz ERP through various pass bands of filter and the power spectra of 40Hz ERP during awake and asleep, 40Hz ERP was thought to have a close relation not only to Po but also to Pa component of MLR (Middle Latency Response).