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Biomedical subjects

J Horikawa

Publications and source records attributed to J Horikawa.

25 records · Page 2Linked to original sources
PubMed1989

[Activities of single cochlear nerve fibers in rats].

Activities of 325 single cochlear nerve fibers in response to pure tones at various frequencies including ultrasonic sounds were observed in rats. The stimulus sounds were measured with a probe tube inserted into an ear canal and a microphone and expressed in dB SPL. The best frequency (BF, characteristic frequency) and the threshold at BF were determined in every fiber. The measured BF ranged from 0.58 kHz to 62.6 kHz. BF and the threshold at BF of a fiber with the lowest BF-threshold were 27.49kHz and 6dB SPL respectively. The highest sensitivity was found in fibers with BF from 20 to 50 kHz. The tuning curve rose from BF and its slope was steeper for the high side than the low one as observed in other animals. The sharpness of the tuning curve was expressed by QN values, where QN is the ratio of BF to the band width at N dB above the BF threshold. Mean and the variance of Q10dB, Q20dB, Q30dB, Q40dB, Q50dB, all increased as the BF did. Almost all fibers had spontaneous discharge. The discharge rate increased with the increase in sound intensity and saturated at about 30 dB above the threshold. The auditory threshold curve obtained from distribution of the lowest BF-threshold of 325 fibers was consistent with the audiograms determined behaviorally.

Acoustic Stimulation↗
PubMed1986

The acoustic middle ear muscle reflex in albino rats.

The acoustic middle ear muscle reflex was studied in albino rats anesthetized with chloralose. The best frequency of the reflex and the threshold at this frequency were on average about 3 kHz and 57 dB SPL, respectively. The threshold increased as frequency increased above, and decreased below, the best frequency at a rate of about 20 dB/octave. Above about 12 kHz, the muscular response showed instability and habituation. Thresholds were similar between stapedius and tensor tympani reflexes and between ipsilateral and contralateral reflexes. The middle ear transmission loss due to the reflex was the greatest and nearly constant below about 1 kHz, where the loss was about 18 dB at the maximal stimulation. Above this frequency the loss decreased as frequency increased up to 20 kHz. Thus the reflex, unlike that in other animals, suppressed transmission over the whole range of reflex-eliciting frequencies. The transfer function of the reflex had a well damped low-pass characteristic with a cut-off frequency of about 20 Hz. From the above characteristics of the reflex, the role of the rat's tympanic muscles in improving ultrasonic hearing under ambient noises was suggested.

Animals↗
PubMed1986

Multiple time axes for representation of echo delays in the auditory cortex of the mustached bat.

The properties of the orientation sound (pulse) of the Jamaican mustached bat, Pteronotus parnellii parnellii is the same as the Panamanian mustached bat, P.p. rubiginosus. It consists of four harmonics, each containing a long constant-frequency (CF) component followed by a short frequency-modulated (FM) component. Thus, there are eight components in total: CF1-4 and FM1-4. The combination-sensitive area of the auditory cortex in P.p. parnellii consists of two major divisions (FM-FM and CF/CF areas) as in P.p. rubiginosus. The FM-FM area projects to the dorsal fringe (DF) and other areas. Response latencies of neurons in the DF area are longer than those in the FM-FM area. The distribution of latencies is unimodal for the FM-FM area, but bimodal for the DF area. In this electrophysiological study of the response properties of neurons in the DF and FM-FM areas, our aim was to find out how signal processing might be different between the two areas. Both the FM-FM and DF areas consist of three types of FM-FM combination-sensitive neurons: FM1-FM2, FM1-FM3, and FM1-FM4. They do not respond or respond poorly to pulse alone, echo alone, single CF tones or single FM sounds. But they show strong facilitation of response to the echo when it is delivered with particular delays from the pulse. The essential elements in the pulse-echo pair for facilitation are the FM1 of the pulse and FM2 or FM3 or FM4 of the echo. In both the FM-FM and DF areas, the great majority of neurons show short-lasting facilitation, and other neurons show long-lasting facilitation. FM-FM neurons are tuned to particular echo delays, i.e., target ranges. In both the FM-FM and DF areas, the width of a delay-tuning curve is linearly related to the value of a best delay. There is no sign that processing of range information is more specialized in the DF area than the FM-FM area. In both the FM-FM and DF areas, three types of FM-FM neurons form independent clusters. Along the major axis of each cluster, best delays for facilitative responses of neurons systematically change according to the loci of the neurons. The more posterior the location, the longer the best delay is. Therefore, there are six time (i.e., range) axes in total. The time axis in the DF area is shorter than that in the FM-FM area.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1986

Biosonar signals and cerebellar auditory neurons of the mustached bat.

In the vermis (VIp, VIIa, VIIp, and VIII), crus, and paraflocculus of unanesthetized mustached bats Pteronotus parnellii parnellii, responses of single neurons to acoustic stimuli were studied. The stimuli delivered were constant-frequency (CF) tones, frequency-modulated (FM) sounds, noise bursts (NBs), and sounds similar to the orientation sounds (pulses) of the species and echoes. The effect of ablation of the cerebellar cortex on vocalization was also investigated to explore whether the cerebellum was involved in sound emission. In the cerebellum of the mustached bat, auditory neurons are predominantly tuned to frequencies within the bands between 23 and 30, 55 and 63, or 85 and 94 kHz, which are found in the first, second, and third harmonics of bat's biosonar signals, respectively. The first harmonic is represented in the paraflocculus. The second harmonic is represented in vermis VIp and VIIa and crus I and IIa. The third harmonic is mainly represented in vermis VIIp and crus IIp. Different lobules represent different frequencies, but there is no systematic tonotopic representation in each lobule. The resting frequency of the CF component of the second harmonic (CF2) of the pulse differs among bats. The majority of auditory neurons in vermis VIp and VIIa and crus IIa are tuned to the CF2 frequency of the bat's own pulse. The frequency-tuning curves of cerebellar neurons are broader than those of peripheral neurons, reflected in significantly lower quality factors of Q-10, -30, and -50 dBs. In vermis VIp and VIIa, there are tiny clusters of FM-FM and CF/CF combination-sensitive neurons. They show strong facilitation of responses when two FM or CF sounds are delivered with particular relationships in the frequency, amplitude, and time domains. Because the clusters of these combination-sensitive neurons in the cerebellum are so small, we found no sign of a systematic representation of certain acoustic parameters, unlike that found in the auditory cortex. In vermis VIp and VIIa, there is a large cluster of NB-sensitive neurons that are more sensitive to NBs than to CF tones. The wider the bandwidth of the NBs, the better are the responses of these NB-sensitive neurons. The ablation of the vermis (VIp, VIIa, and VIIp), crus, and paraflocculus increases the variation of the CF frequency of the pulse. The ablation of the crus and paraflocculus causes a clear increase in the variation of CF frequency. The ablation of vermis (VIp, VIIa, and VIIp) has only a small effect on the variation. Any of the above ablations has little effect on the repetition rate of the pulse emission and the duration of pulses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Mechanical and neural interactions between binaurally applied sounds in cat cochlear nerve fibers.

Most single fibers of the cochlear nerve (CN) in 22 cats exhibited effects of mechanical interaction in one cochlea between two sounds applied binaurally, similarly to results in two cats in which the contralateral CN was transected. In 11 of 189 fibers, the spontaneous and/or the sound-evoked activity was suppressed by a contralateral intense best-frequency sound; this indicates an interaural neural inhibition, probably through the olivocochlear bundle (OCB). The inhibited fiber population was small, and the intensity differences between the binaural sounds were exceptionally large, so that a simple negative feed-back function via the OCB is not likely.

Acoustic Stimulation↗