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N Suga

Publications and source records attributed to N Suga.

At least 37 records · Page 2Linked to original sources
PubMed1997

Syntax processing by auditory cortical neurons in the FM-FM area of the mustached bat Pteronotus parnellii.

Syntax denotes a rule system that allows one to predict the sequencing of communication signals. Despite its significance for both human speech processing and animal acoustic communication, the representation of syntactic structure in the mammalian brain has not been studied electrophysiologically at the single-unit level. In the search for a neuronal correlate for syntax, we used playback of natural and temporally destructured complex species-specific communication calls-so-called composites-while recording extracellularly from neurons in a physiologically well defined area (the FM-FM area) of the mustached bat's auditory cortex. Even though this area is known to be involved in the processing of target distance information for echolocation, we found that units in the FM-FM area were highly responsive to composites. The finding that neuronal responses were strongly affected by manipulation in the time domain of the natural composite structure lends support to the hypothesis that syntax processing in mammals occurs at least at the level of the nonprimary auditory cortex.

Animal Communication↗
PubMed1997

Corticofugal modulation of frequency processing in bat auditory system.

Auditory signals are transmitted from the inner ear through the brainstem to the higher auditory regions of the brain. Neurons throughout the auditory system are tuned to stimulus frequency, and in many auditory regions are arranged in topographical maps with respect to their preferred frequency. These properties are assumed to arise from the interactions of convergent and divergent projections ascending from lower to higher auditory areas; such a view, however, ignores the possible role of descending projections from cortical to subcortical regions. In the bat auditory system, such corticofugal connections modulate neuronal activity to improve the processing of echo-delay information, a specialized feature. Here we show that corticofugal projections are also involved in the most common type of auditory processing, frequency tuning. When cortical neurons tuned to a specific frequency are inactivated, the auditory responses of subcortical neurons tuned to the same frequency are reduced. Moreover, the responses of other subcortical neurons tuned to different frequencies are increased, and their preferred frequencies are shifted towards that of the inactivated cortical neurons. Thus the corticofugal system mediates a positive feedback which, in combination with widespread lateral inhibition, sharpens and adjusts the tuning of neurons at earlier stages in the auditory processing pathway.

Acoustic Stimulation↗
PubMed1997

The inferior colliculus of the mustached bat has the frequency-vs-latency coordinates.

In the mustached bat, the central auditory system contains FM-FM (delay-tuned) neurons which are specialized for processing target-distance information carried by echo delays. Mechanisms for creating the FM-FM neurons involve delay lines, coincidence detection and amplification. A neural basis for delay lines can be a map representing response latencies. The aim of the present study is to explore whether the central nucleus of the inferior colliculus has a latency axis incorporated into iso-best frequency slabs. Responses of single or multiple neurons were recorded from the inferior colliculus of unanesthetized mustached bats with tungsten-wire electrodes, and their response latencies were measured with tone bursts at their best frequencies and best amplitudes or 65 dB SPL. In the dorsoventral electrode penetrations across the inferior colliculus, response latency systematically shortens from approximately 12 to approximately 4 ms. Tonotopic representation in the inferior colliculus is somewhat complex. Iso-best frequency slabs are tilted and/or curved, but they orient more or less ventrodorsally. Nevertheless, the latency axis is evident in each iso-best frequency slab, regardless of best frequency. The inferior colliculus has the frequency-vs-latency coordinates.

Acoustic Stimulation↗
PubMed1997

Binaural and commissural organization of the primary auditory cortex of the mustached bat.

In the mustached bat, the primary auditory cortex (AI) can be divided into three subdivisions: the Doppler-shifted constant-frequency processing (DSCF) area, and the anterior (AIa) and posterior (AIp) regions. The DSCF area is composed of two subdivisions: excitatory-excitatory (E-E) and inhibitory-excitatory (I-E). The E-E division is located in the ventral portion of the DSCF area and mainly consists of neurons excited bilaterally, while the I-E division is located in the dorsal portion and mainly consists of neurons which are inhibited by ipsilateral ear stimuli, but excited by contralateral ear stimuli. The E-E division is bilaterally connected by commissural fibers, while the I-E division is not. The AIa and AIp regions have neither E-E neurons nor commissural connections. In the AI of the cat, E-E and I-E neurons form alternating bands which are parallel to the frequency axis. E-E bands are bilaterally connected by commissural fibers, but I-E bands are not. The DSCF area shares a similar functional organization with the AI of the cat.

Acoustic Stimulation↗
PubMed1997

NMDA-mediated facilitation in the echo-delay tuned areas of the auditory cortex of the mustached bat.

We recorded the responses of single delay-tuned neurons in the dorsal fringe (DF) area and the FM-FM area of the auditory cortex of the mustached bat using multi-barreled carbon-fiber electrodes. An iontophoretic application of N-methyl-D-aspartate (NMDA) or kainate (KA) to a DF neuron evoked a burst of discharges from the neuron. The burst of discharges evoked by NMDA was always smaller than that evoked by KA. Simultaneous application of D-2-Amino-5-phosphonovalerate (APV) with NMDA and KA abolished the NMDA-evoked but not the KA-evoked discharges. APV did not evoke any significant changes in the auditory responses of 43 out of the 47 delay-tuned neurons studied in the DF area, and in all 20 neurons studied in the FM-FM area. In the remaining four DF neurons, however, APV either increased the initial discharges of their auditory response or decreased the late discharges of their response. These results indicate that in the majority of neurons in the DF and FM-FM areas NMDA receptors do not play a significant role in the processing of target-distance information, and that their facilitative auditory responses are basically created by synaptic interactions occurring in the subcortical auditory nuclei.

2-Amino-5-phosphonovalerate↗
PubMed1997

Sharpening of frequency tuning by inhibition in the thalamic auditory nucleus of the mustached bat.

Unlike the quasitriangular frequency-tuning curves of peripheral neurons, pencil- or spindle-shaped frequency-tuning curves (excitatory areas) have been found in the central auditory systems of many species of animals belonging to different classes. Inhibitory tuning curves (areas) are commonly found on both sides of such "level-tolerant" sharp frequency-tuning curves. However, it has not yet been examined whether sharpening of frequency tuning takes place in the medial geniculate body (MGB). We injected an inhibitory transmitter antagonist, bicuculline methiodide (BMI), into the MGB of the mustached bat to examine whether frequency tuning is sharpened by inhibition in the MGB and whether this sharpening, if any, occurs in addition to that performed in prethalamic auditory nuclei. Thirty-seven percent of thalamic Doppler-shifted constant frequency (DSCF) neurons mostly showing a level-tolerant frequency-tuning curve had an inhibitory area or areas. BMI changed the inhibitory areas of these neurons into excitatory areas, so that their excitatory frequency-tuning curves became broader. However, the BMI-broadened excitatory frequency-tuning curves were still much narrower than those of peripheral neurons. Our results indicate that level-tolerant frequency tuning of thalamic DSCF neurons is mostly created by prethalamic auditory nuclei and that it is further sharpened in 37% of thalamic DSCF neurons by lateral inhibition occurring in the MGB. The comparisons in sharpness (quality factors) of frequency-tuning curves between peripheral, thalamic, and cortical DSCF neurons indicate that the skirt portion of tuning curves is sharper in the above order, and that their tip portion is not significantly different between the peripheral and thalamic DSCF neurons, but significantly sharper in the cortical DSCF neurons than in the thalamic DSCF neurons. Therefore the central auditory system has inhibitory mechanisms for the progressive sharpening of frequency tuning. DSCF neurons in the primary auditory cortex were recently found to show facilitative responses to paired sounds. That is, they are combination sensitive. In the present studies, we found that thalamic DSCF neurons also showed facilitative responses to paired sounds. The responses of thalamic DSCF neurons to acoustic stimuli consisted of a slow and a fast component. BMI mainly increased the slow component and an excitatory transmitter antagonist, D-2-amino-5-phosphonovalerate mainly suppressed the slow component. Therefore the response pattern of these thalamic neurons is shaped by both gamma-aminobutyric acid-mediated inhibition and N-methyl-D-aspartate-mediated facilitation.

Acoustic Stimulation↗
PubMed1997

Corticofugal amplification of subcortical responses to single tone stimuli in the mustached bat.

Since 1962, physiological data of corticofugal effects on subcortical auditory neurons have been controversial: inhibitory, excitatory, or both. An inhibitory effect has been much more frequently observed than an excitatory effect. Recent studies performed with an improved experimental design indicate that corticofugal system mediates a highly focused positive feedback to physiologically "matched" subcortical neurons, and widespread lateral inhibition to "unmatched" subcortical neurons, in order to adjust and improve information processing. These results lead to a question: what happens to subcortical auditory responses when the corticofugal system, including matched and unmatched cortical neurons, is functionally eliminated? We temporarily inactivated both matched and unmatched neurons in the primary auditory cortex of the mustached bat with muscimol (an agonist of inhibitory synaptic transmitter) and measured the effect of cortical inactivation on subcortical auditory responses. Cortical inactivation reduced auditory responses in the medial geniculate body and the inferior colliculus. This reduction was larger (60 vs. 34%) and faster (11 vs. 31 min) for thalamic neurons than for collicular neurons. Our data indicate that the corticofugal system amplifies collicular auditory responses by 1.5 times and thalamic responses by 2.5 times on average. The data are consistant with a scheme in which positive feedback from the auditory cortex is modulated by inhibition that may mostly take place in the cortex.

Acoustic Stimulation↗
PubMed1996

Corticofugal modulation of time-domain processing of biosonar information in bats.

The Jamaican mustached bat has delay-tuned neurons in the inferior colliculus, medial geniculate body, and auditory cortex. The responses of these neurons to an echo are facilitated by a biosonar pulse emitted by the bat when the echo returns with a particular delay from a target located at a particular distance. Electrical stimulation of cortical delay-tuned neurons increases the delay-tuned responses of collicular neurons tuned to the same echo delay as the cortical neurons and decreases those of collicular neurons tuned to different echo delays. Cortical neurons improve information processing in the inferior colliculus by way of the corticocollicular projection.

Acoustic Stimulation↗
PubMed1996

Facilitative responses to species-specific calls in cortical FM-FM neurons of the mustached bat.

FM-FM neurons in the auditory cortex of the mustached bat are highly specialized for echolocation, responding facilitatively to the combination of frequency modulated (FM) components of biosonar pulse and its echo. Here we propose they are also specialized for processing bat communication calls. FM-FM neurons respond facilitatively to natural call syllable pairs, and exhibit inter-syllable interval tuning to the natural range of intervals. Our results support a role for 'combination-sensitive' neurons in communication, and suggest that cortical neurons can possess multiple distinct specialized modes of response.

Animal Communication↗
PubMed1996

The midbrain creates and the thalamus sharpens echo-delay tuning for the cortical representation of target-distance information in the mustached bat.

Mustached bats emit complex biosonar 'pulses' for echolocation. A delay of an echo from the emitted pulse carries target-distance information. At the auditory periphery, distance information is expressed by a time interval between the responses of neurons to the emitted pulse and its echo. In the auditory cortex (AC), however, it is mapped by 'FM-FM' neurons which are tuned to particular echo delays. FM-FM neurons have been found not only in the AC but also in the inferior colliculus (IC) of the midbrain and the medial geniculate body (MGB) of the thalamus. In the present study, we found that the IC has a precursor of the cortical echo-delay axis for the systematic representation of target-distance information and that the MGB shows the improved neural representation of target-distance information.

Animals↗
PubMed1995

Sharpening of frequency tuning by inhibition in the central auditory system: tribute to Yasuji Katsuki.

Frequency analysis is a fundamental function of the auditory system. Békésy and Katsuki believed that sharpening of frequency tuning by lateral inhibition takes place in the central auditory system. However, most 'cat' auditory physiologists have believed that frequency tuning of neurons is not sharpened in the central auditory system, so that there is no lateral inhibition. Unlike quasi-triangular frequency-tuning curves of peripheral neurons, pencil- or spindle-shaped frequency-tuning curves have been found in the central auditory systems of many species of animals belonging in different classes. Inhibitory tuning curves are commonly associated with such 'level-tolerant' sharp excitatory tuning curves. It is that frequency-tuning curves of some central auditory neurons are sharpened by inhibition. Yasuji Katsuki (Professor, M.D., Ph.D.) passed away on 6 March 1994 at the age of 88. I have written this article as a tribute to him, focusing on his major contribution to auditory neurophysiology: the finding of the sharpening of frequency tuning in the cat's central auditory system. Neural sharpening of frequency tuning is an old yet still current topic, as you will read in this article dedicated to Professor Katsuki.

Animals↗
PubMed1995

Delay-tuned neurons in the midbrain of the big brown bat.

1. The auditory midbrain in Eptesicus contains delay-tuned neurons that encode target range. Most delay-tuned neurons respond poorly to tones or individual frequency-modulated (FM) sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned. The index of facilitation (IF), a coefficient measuring combination sensitivity for individual delay-tuned neurons, ranged from 0.14 to 1.0, with an average of 0.64 +/- 0.24 (mean +/- SD). Of the 33 facilitated responses from 29 neurons, 23 (70%) exhibited IFs > 0.5, which corresponds to a facilitated response 3 times greater than the sum of the responses to individual pulse and echoes. Thus the responses of midbrain delay-tuned neurons are highly combination sensitive. 2. The response of midbrain delay-tuned neurons is phasic, with an average of 0.7 +/- 0.4 action potentials elicited per optimal pulse-echo pair. Thus midbrain delay-tuned neurons in Eptesicus act as probability encoders. 3. The distribution of best echo delays (BDs) of midbrain delay-tuned neurons ranged from 8 to 30 ms. As an ensemble, midbrain delay-tuned neurons encode target ranges of 138-516 cm. There is a basic correspondence between the physiologically determined span of midbrain BDs between 8 and 30 ms and the behaviorally determined borders of the approach (8- to 17-ms echo delay) and search stages (17- to 30-ms echo delay) of the insect pursuit sequence. Midbrain delay-tuned neurons can be separated into two subpopulations on the basis of the difference in distributions of the echo best amplitude (EBA) tuning at BD. The BDs of one subpopulation correspond to the span of search stage echo delays, and the BDs of the other subpopulation correspond to the span of approach stage echo delays. 4. EBAs of neurons in each subpopulation are tailored to the specific perceptual requirements of the corresponding behavioral stage. EBAs of midbrain neurons tuned to echo delays between 17 and 30 ms (N = 12) correspond to the search stage and are suited to the requirements of target detection. EBAs of midbrain neurons tuned to echo delays between 17 and 30 ms (N = 21) correspond to the approach stage and are suited to the requirements of target size discrimination. 5. The best FM sweeps for the pulse (PFM) and echo (EFM) were determined for each midbrain neuron. PFMs appear to cluster at frequencies corresponding to the three harmonic peaks in the emitted pulse power spectra.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1995

Long delay lines for ranging are created by inhibition in the inferior colliculus of the mustached bat.

1. The central auditory system of the mustached bat has arrays of delay-tuned (FM-FM combination-sensitive) neurons in the inferior colliculus, the medial geniculate body, and the auditory cortex. These neurons are tuned to particular echo delays, i.e., target distances. The neural mechanisms for creating the delay-tuned neurons involve delay lines, coincidence detection, and amplification. We have hypothesized that delay lines longer than 4 ms are created by inhibition occurring in the anterolateral division (ALD) of the central nucleus of the inferior colliculus. If this hypothesis is correct, suppression of inhibition occurring in the ALD must shorten the best delays of the collicular, thalamic, and cortical delay-tuned neurons. The aim of the present study is to test this hypothesis. Responses of single delay-tuned neurons in the FM-FM area of the auditory cortex were recorded with a tungsten-wire microelectrode, and the effects of iontophoretic microinjections of strychnine (STR) and/or bicuculline methiodide (BMI) into the ALD were examined on the responses of these neurons. 2. STR (glycine receptor antagonist) and/or BMI [gamma-aminobutyric acid-A (GABAA) receptor antagonist] injections into the ALD shortened the best delays of delay-tuned neurons in the FM-FM area with little change in their response patterns. The longer the best delay of a delay-tuned neuron, the larger the amount of shortening. 3. Inhibition mediated by glycine receptors plays a larger role in creating delay lines than that mediated by GABAA receptors, because STR and BMI, respectively, shortened the best delay of 91 and 74% of the neurons with best delays longer than 4.5 ms. 4. BMI has no effect on the best delays of delay-tuned neurons that were tuned to echo delays shorter than 4.5 ms. 5. The present data support the hypothesis that long delay lines utilized by delay-tuned neurons are created by inhibition occurring in the ALD of the inferior colliculus. However, the amount of shortening in delay lines by STR and/or BMI was generally smaller than that predicted by a neural network model. Therefore the present study partially answers the questions of where and how long delay lines were created.

Acoustic Stimulation↗
PubMed1994

After-discharges in the auditory cortex of the mustached bat: No oscillatory discharges for binding auditory information.

Action potentials of single or multi-neurons were recorded from the DSCF, FM-FM and DF areas in the auditory cortex of the mustached bat to study stimulus-induced neural oscillation in the auditory system. Out of 125 neurons 120 recorded in these three areas showed after-discharges to a best stimulus. Durations of after-discharges of 120 neurons ranged between 4.8 and 217 ms. In the remaining 5 neurons, the duration of the discharges was shorter that of the stimulus. The PST histograms displaying responses of these 125 neurons showed no oscillatory component locked to the stimulus. 98% of the autocorrelograms of responses (122/125) showed no sign of oscillation, but the remaining two percent showed a very weak oscillatory component that was not stimulus-locked. The duration of the after-discharges had no correlation with the best delay or cortical depth of neurons. After-discharges are common in the auditory cortex of the mustached bat, but oscillatory discharges are very rare, so that neural oscillations play no role in binding various types of biosonar information processed in the different 'specialized' areas in the auditory cortex.

Action Potentials↗
PubMed1994

Liposteroid against refractory pulmonary haemorrhage in idiopathic pulmonary haemosiderosis.

We describe two Japanese children with idiopathic pulmonary haemosiderosis (IPH), whose refractory haemorrhages were treated with an intravenous lipid emulsion containing dexamethasone (liposteroid). A 22-month-old boy and a 14-month-old girl have been observed with similar symptoms; periodic bouts of anaemia, reticulocytosis, diffuse infiltrates on chest X-ray and the finding of siderophages in sputum or gastric lavage fluid. The MRI of the lung was useful for the diagnosis. Methylprednisolone pulse therapy was successful in treating acute massive bleeding. Subsequent oral prednisolone could not prevent chronic recurrent haemorrhages. However, the intermittent administration of liposteroid (0.05 mg/kg/dose IV) led to a cessation of bleeding; the haemoglobin concentration rose to normal levels. This observation emphasizes the usefulness of liposteroid in the management of refractory IPH.

Dexamethasone↗
PubMed1994

Analysis of acoustic elements and syntax in communication sounds emitted by mustached bats.

Mustached bats, Pteronotus parnellii parnellii spend most of their lives in the dark and use their auditory system for acoustic communication as well as echolocation. The sound spectrograms of their communication sounds or "calls" revealed that this species produces a rich variety of calls. These calls consist of one or more of the 33 different types of discrete sounds or "syllables" that are emitted singly and/or in combination. These syllables can be further classified as 19 simple syllables, 14 composites, and three subsyllables. Simple syllables consist of characteristic geometric patterns of CF (constant frequency), FM (frequency modulation), and NB (noise burst) sounds that are defined quantitatively using statistical criteria. Composites consist of simple syllables or subsyllables conjoined without any silent interval. Most syllable types exhibit a large intrinsic variation in their physical structure compared to the stereotypic echolocation pulses. Syllable domains are defined on the basis of multiple parameters, although these can be collapsed onto three dimensions that capture 99% of the measured variation among different types of syllables. Temporal analysis of multisyllabic constructs reveals several syntactical rules for syllable transitions.

Acoustics↗