Abstract
Recently, methods of hearing testing in children have been advanced, but these objective methods are not so satisfactory for young children under 3 years old.
We studied the changes in microvibration of the thenar eminence of young children incident to auditory stimuli. In our records, a special pick-up was always used which was connected with an amplifier (Nihon Koden Co. Tokyo). The recording was done through the pick-up which was applied to the thenar eminence of the subjects. In analyzing the records, we divided the vibrations into three categories θ(4-8 cps), α (8-13cps), and β (13-20cps). We simulta- neously recorded the electroencepalogram bilaterally from the parietal and frontal lobes in order to note any coincident changes in it.
The subjects consisted of 11 normal children and 20 children with diminished hearing under 6 years of age. All were sedated with Nembutal. The stimulating sounds were of five kinds 1000 cps pure tone, white noise and sounds of toys (tambourine, castanets and triangle), which were recorded on tape at the same intensity. They were given to one ear through a receiver at 70, 90 and 110 db (sensation level) one by one for 3 seconds with an interval of 3 minutes.
We found that microvibration could be changed with auditory stimuli during sleep as well as in the relaxed awake state. The chief changes were as follows
1) Rapid acceleration during stimulation in some cases and after stimulation in other cases.
2) In analysis, two types of responses were found One was the acceleration of a and β wave components for few seconds after stimulation. The other was the inhibition of them, especially β, continuing for several seconds after stimulation. The latter was more common than the former. Changes of θ wave component was very uncommon. The electroencephalogram exhibited K-complexs, spindle waves, suppression, etc., as many authors have previously reported.
The stimulation at 110 db produced changes which were very clear in both microvibrations and the electroencephalogram. They seemed to be the result of a startle response, but we thought they were different from it. The weaker the stimuli, the fainter the changes in comparison to the electroencephalogram. However, we found that there was a correlation between the response of the electroencephalograph and the microvibration recording.
As the stimulating sound became weaker than 70db, changes in microvibration were very faint. However, with more sensitive methods of recording, we could have picked up such faint changes.
Overall, we found that the microvibration of the thenar eminence of young children could be changed by auditory stimuli during sleep.
