Since several years the authors have been clinicaly investigating acoustic neural mechanisms. This study was designed to solve some problems on acoustic neural mechanism through effects of TTFD on neural level. As psychoacoustic method of measurement, Temporary Threshold Shift (TTS) and Temporary Auditory Summation were used in this work, and were conducted in normal ears.
A series of experiments carried out before and after intra-venous administration of TTFD 50mg in this study were as follows.
(1) TTS: Each TTS recovery curves after exposures to interrupted intensive tones were observed.
(2) Aural Reflex: Effects of the Acoustic Reflex of the Intra-Aural Muscle on the TTS recovery curves were taken into consideration.
(3) Temporary Auditory Summation: Observing the phenomena of Temporary Auditory Summation before and after intra-venous injection of TTFD, we estimated its mechanism of effects at neural level.
Next results were obtained.
(1) Within about 6 hours after TTFD 50mg intra-venous injection, TTS caused by high level sound exposure was decreased.
(2) No change was found on Acoustic Reflex of the intra-aural muscle after TTFD injection.
(3) After injection of TTFD, hearing acuity was improved temporalily. It continued for about 6 hours. The threshold was improved about 5 dB in the frequency range higher than 2000 cps. The improvement was found to be influenced by the duration of testing stimulus, and considerable improvement was obtained at 100msec duration but slight improvement at the duration shorter than 30msec.
(4) As the result of psychoacoustic study, this hearing improvement could be considered as a effect of TTFD on synaptic level of acoustic neural mechanism. In order to obtain more exact findings for a affected level, more careful watches should be done. This problem will be studied in the future.
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