Yasuji Katsuki

Neural Mechanism of the Peripheral and Central Auditory System in Monkeys

The cochlear nerve of the monkey is composed only of the axons of the primary neurons. In Part I of this article, the properties of the primary auditory neuron—i.e., tonotopic organization, response pattern, and response area—have been studied. Two groups of neurons could be stochastically separated in terms of threshold in the low‐ and middle‐frequency range and not in the high‐frequency range. The rate of increase of impulse frequency with the change of sound intensity was examined at the characteristic frequency (CF) of a neuron after the measurement of its response area. The rate of increase and the threshold of a neuron were found to be well‐correlated. This result seems to show the validity of Bekesys hypothesis on the pitch‐intensity coordinate system of the inner and outer hair cells.Part II is concerned with the responses of the cortical neurons of unanesthetized monkeys. Two types of response areas, wide as well as narrow, were obtained with single‐tone bursts. By the simultaneous delivery of t...

Cortical efferent flow influencing unit responses of medial geniculate body to sound stimulation

SummarySingle units in the medial genioulate body and inferior colliculus of the cat were activated by acoustic stimulation and their activity was tested by orthodromic conditioning stimulation of the auditory cortex with the following findings;1.Two groups of the cells in the medial geniculate body and the inferior colliculus, activated by both cortical electric stimulation and tonal stimulation, have been classified as „modification” units and “no modification” units.2.Corticofugal stimulation inhibited or facilitated “modification” units. “No modification” units were subdivided into a) units with no electrical response, b) units with independent responses to both auditory and electrical stimulation, c) units with electrical response only. These were believed to be, respectively, principal neurons, inhibitory interneurons and excitatory (efferent) interneurons.3.In general, fibers from AI elicit inhibitory while those from AII elicit facilitatory effects in the medial geniculate body.4.Cortical stimulation produced a threshold change on the response area of “modification” units.5.It is concluded that a number of, not very many, centrifugal fibers innervate the ipsilateral geniculate neurons.6.In agreement with anatomical findings, physiological evidence suggests that corticofugal fibers from both auditory cortices innervate inferior colliculus neurons. Their modification patterns were same as those of geniculate units except the latency of responses was much longer.7.A centrifugal control mechanism may play an important role in the frequency selective gating mechanism of the central auditory system.

Structure of warm fiber terminals in the pit membrane of vipers

The free nerve endings in the infrared receptor organ (the so-called “pit organ”) of an oriental pit viper, Trimeresurus f. flavoviridis, were studied with the electron microscope. The free nerve endings in this organ form a conglomeration of nonmyelinated nerve branchlets surrounding a few Schwann cells. We regard this conglomeration as a receptive unit, and have termed it the “terminal nerve mass”. Terminal nerve masses are about 40 μ in diameter and 10 μ thick; they are found in a single layer throughout the innervated membrane suspended in the pit cavity. The nerve branchlets comprising the masses contain a high concentration of mitochondria. Thin processes of the Schwann cells partially cover the surface of the branchlets, leaving certain areas completely bare. The structural relation between the Schwann cells and the branchlets seems functional, i.e., to provide the necessary nutrition for the cells without obstructing the reception of radiated energy over all the surface of the nerve mass. There are no synapses in the masses, indicating the absence of receptor interaction at this level of the receptor system.

Tetraethylammonium and Tetrodotoxin: Effects on Cochlear Potentials

Tetraethylammonium chloride, which is believed to decrease potassium conductance, and tetrodotoxin, which apparently decreases sodium conductance in nerve fibers, were introduced iontophoretically into the organ of Corti or the scala media of guinea pig cochlea. The former depressed the direct-current endocochlear potential and also the alternating-current cochlear microphonics (the receptor potential of the ear), but tetrodotoxin was ineffective except on the nerve impulses.

Frequency discrimination in the central nerve cords of locusts

Abstract The auditory mechanism in locusts, especially the central mechanism of frequency analysis, was examined electrophysiologically. The central auditory response had a sharp rise of threshold at a certain frequency range, and it showed a remarkable change when all peripheral fibres except the tympanic nerve were cut off. The response pattern was also changed by this procedure. These results indicate the presence of an inhibitory interaction mechanism of various auditory inputs. It can be concluded that locusts are able to discriminate sound frequency to some degree by this interactive mechanism.

Efferent system of lateral-line organ of fish

Abstract 1. 1. The efferent feedback system of the lateral-line organ of a fish, Japanese sea eel, was confirmed electrophysiologically by the following observations. 2. 2. An inhibitory effect to the afferent neural activity is caused by the descending electrical stimulation of the lateral-line nerve. 3. 3. The descending spontaneous activity of the lateral-line nerve is responsive to the mechanical stimulation of the contra-lateral or ipsilateral intact end organs. 4. 4. The efferent system might adjust the sensitivity of the receptor to various environmental conditions. 5. 5. The crosed efferent might also play an important role in identifying the stimulus location in the environmental free space.

Shark Pit Organs: Enhancement of Mechanosensitivity by Potassium Ions

The mandibular pit organs of pelagic sharks, which respond sensitively to monovalent cations, often show neural discharges synchronized with respiratory gill movement. The mechanosensitivity of the organs is remarkably enhanced by application of potassium ions on the same end organ, respiratory movement remaining constant. In view of their michanosensitivity to an incr-ease of potassium ions in the cell environment, as well as their chemosensitivity,the pit organs of sarks, rather than the canal organs which have no chemosensitivity, may be designated as a better model of the inner ear of higher animals.

Enhancement of the Mechanosensivity of Hair Cells of the Lateral‐Line Organs by Environmental Potassium Ions

The cochlear hair cell has a remarkably high sensitivity to the displacement of the basilar membrane of the inner ear. However, the detailed mechanism of the receptor process, especially for the high sensitivity, has not been fully established. The present article is concerned with the enhancement of the mechanosensitivity of the receptor hair cells of the lateral‐line organ of aquatic animals by the environmental potassium ions. The potassium ion on the receptor surface of the lateral‐line organ, the free standing neuromast, modified the receptor sensitivity to vibratory mechanostimuli. Studies on the free neuromast rather than on the canal neuromast may better contribute to the understanding of the excitation mechanism of the cochlear hair cell.

Pitch Discrimination in the Higher Level of the Brain

Since the publication of Galambos and Davis″ work, electrophysiological data have been accumulated which show that the analysis of sound is performed in a special way in the cochlea. The examination of discharge patterns and the response areas of single primary auditory neurons in the cochlear nerve bundle reveals that they are sending enough informatoion about intensity of sound, but not about the frequency of analysed sound. This fact recalls to us Rutherfords telephone theory which had once been supplanted by Helmholtzs place theory of the cochlear function. The telephone theory tells us that the frequency analysis of sound is not performed in the cochlea at all, but it is done in the auditory cortex. This hypothesis seems in a sense to be valid for us, because the primary auditory neurons send only very poor information about the frequency of sound in spite of the fact that cats and monkeys and, especially, human beings are remarkably capable of discriminating the freqency of sound. In order to expl...

Neural Mechanism of Hearing in Cats and Monkeys

Publisher Summary This chapter describes neural mechanism of hearing in cats and monkeys. The single neuron analysis in that field had been performed at the cochlear nuclei and other regions. Cats as used as experimental animals, and under light anesthesia with nembutal, various regions of the skull were opened to expose a part of brain that were desired for the study. In order to finish successive experiments of measuring thresholds of a neuron for sounds with various frequencies within a short time, an automatic sound producing apparatus was designed using a rotatory switch driven by a motor. The mechanism of the initiation of impulses at the ending of the cochlear nerve fiber, which makes contact with the base of the hair cell, is so far not clear; there are two hypotheses, one is electrical and the other chemical. It has been reported that electrical stimulation of the crossed olivo-cochlear bundle inhibits neural response in the cochlea and augments the CM. This inhibitory effect is suppressed by intravenous injection of strychnine. It is found that the latencies of the responses of a neuron were different to sounds with different frequencies and intensities. The latencies of the responses to the same sound were also different from neuron to neuron.