GABA can improve acoustic contrast in the rat ventral cochlear nucleus

The effect of microiontophoretically applied -aminobutyric acid (GABA) and its agonists and antagonists on the response pattern of single units in the ventral cochlear nucleus (VCN) of the rat was examined in order to study GABA's physiological function in auditory processing. The effects of the drugs were judged by changes of spontaneous and sound-evoked activity in peristimulus-time histograms (PSTHs) of at least 20 consecutive presentations of acoustic stimuli. GABA inhibited the discharge activity of the majority of neurons. All response types found in the VCN except onset-I responders were sensitive to GABA. The GABAergic inhibition is most probably mediated by GABA_A receptors, since the GABA_A-receptor agonist muscimol, but not the GABA_B-receptor agonist baclofen, mimicked the effect of GABA. The GABA_A-receptor antagonists, bicuculline and picrotoxin, had an excitatory effect on the neurons' spontaneous activity, suggesting a tonic endogeneous release of GABA which exerts a permanent inhibition on VCN neurons. Although inhibitory, iontophoresis of GABA emphasized the response to stimulus onset in the PSTHs by means of a stronger inhibition of spontaneous activity. When using iontophoretical currents which did not suppress the neuronal activity completely, a strong inhibition of spontaneous activity was accompanied by only a small inhibition of tone-evoked activity. Under these conditions, the response to tone onset was frequently not inhibited at all. Therefore, GABA's physiological function is possibly to improve the contrast between transient acoustic signals and ongoing background activity. In order to test this hypothesis, the test tone was masked by continuous background noise. Indeed, GABA reduced the noise-evoked discharge more than the toneevoked discharge, leaving the onset peak in the PSTHs almost unchanged. Thus, GABAergic input improves the signal-to-noise ratio for acoustic transients in VCN neurons. Our data suggest that a functional role of GABA in the VCN is to act as a transmitter within a descending inhibitory feedback loop of the auditory brainstem which serves to improve the transmission of relevant acoustic signals in constant background noise.     

海风藤对犬脑干缺血后BAEP的影响

目的观察海风藤对犬脑干缺血后脑干听觉诱发电位（ＢＡＥＰ）的影响。方法建立犬脑干缺血模型，给药组和对照组各２０只犬，分别于阻断基底动脉前３ｈ向十二指肠注入海风藤溶液（按０．３ｇ／ｋｇ）和等体积生理盐水，于缺血前和缺血后０．５、３、６和１２ｈ分别记录ＢＡＥＰ。结果给药组ＢＡＥＰ的Ⅰ、Ⅲ、Ⅴ波潜伏期和Ⅰ－Ⅲ、Ⅲ－Ⅴ、Ⅰ－Ⅴ波峰间期明显缩短。结论海风藤可改善犬脑干对缺血的耐受程度，减小半暗带的范围，减轻病变的程度。     

Effects of contralateral sound stimulation on unit activity of ventral cochlear nucleus neurons

The cochlear nucleus (CN) commissural connection represents the first opportunity for convergence of binaural information in the auditory brainstem. All major neuron types in the ventral CN (VCN) are innervated by a diverse population of cells in the contralateral VCN. This study examined the effect of contralateral sound stimulation on the spontaneous rates (SRs) of neurons in the VCN. Unit activity was recorded with silicon-substrate multichannel probes which allowed recordings from up to 16 sites simultaneously. On average, 30% of units showed short-latency (often only 2 ms greater than the latencies of ipsilateral sound-evoked responses) inhibition of SR by wideband contralateral noise bursts. Fewer units (4.5%) were excited by contralateral noise at sound levels low enough to exclude excitation by acoustic crossover. Both regular and irregular units in the anterior VCN (AVCN) and posterior VCN (PVCN) were inhibited by contralateral sound. Decrements in SR followed a monotonic function with increases in contralateral sound level, except where responses could be attributed to acoustic crossover. Restricting the contralateral noise bandwidth resulted in a frequency-specific inhibition, dominated by frequencies at and below the ipsilateral BF of the unit, consistent with anatomical findings of the tonotopic organization of the CN commissural pathway. The latencies of these effects are compatible with mono, di and tri-synaptic connections reflecting CN commissural pathway effects.     

Effects of sound intensity on a midlatency evoked response to repeated auditory stimuli in schizophrenic and normal subjects

Inhibitory gating of response to repeated stimuli is demonstrated by several event-related potentials, including the auditory P50 wave. The present study examined the effects of variation in sound intensity on this phenomenon in schizophrenics and normal subjects. Paired clicks, 500 ms apart, were presented 50 dB above threshold to 10 normal subjects and 10 schizophrenics. The normal subjects demonstrated significantly more decrement of response to the second stimulus than did the schizophrenics. When the sounds were noticeably louder(70 dB above threshold), no such difference was observed. Rather, both groups had similarly diminished gating of response. A significant difference between schizophrenics and normal subjects was also observed when the sounds were 30 dB above threshold, but the difference was smaller than that at 50 dB. At any stimulus intensity, concomitant eye movements led to loss of gating of P50 in the normal subjects.     

Acoustically evoked potentials in the rat during sleep and waking

Summary Click-evoked potentials were recorded from the rat's auditory cortex (AC), medial geniculate body (MGB), reticular formation (RF), and hippocampus (HIPP) during natural sleep and waking. Various amplitude measurements made on sliding averages by a computer provided essentially continuous measurement of evoked responses in long experiments. Changes in AC responses were simplest in potentials recorded from a depth of 1.0–1.5 mm, all components of the average waveform being larger during slow-wave sleep (SS) than in waking (W) and low-voltage fast sleep (LVFS). More complex changes in cortical surface responses included increases in the first positive wave, in a second positive deflection, and in a late negative wave during drowsiness (D) and SS. The second positive wave remained large during LVFS, while the late negativity changed form and peaked earlier. Early components of both surface and deep responses were not consistently different in W and LVFS. The only clear change in MGB responses was a reduction in amplitude during LVFS. Late positive waves in RF and HIPP responses were large during SS and small during W and LVFS. In general, increases in the very late components of responses at all sites distinguished periods of cortical synchrony from periods of cortical activation. The first negative deflection and a succeeding positive wave in the HIPP response were markedly increased during arousal.This work was supported principally by the National Institutes of Health (Grant 5 POl GM-14940-03), and in part by the Joint Services Electronics Program (Contract DA 28-043-AMC-02536 (E)). One of us (A.A.B.) was supported in part by a grant from the Swiss National Foundation for Scientific Research. Preliminary reports were presented at the Annual Meeting of the Eastern Psychological Association, April 18, 1969 in Washington, D.C. and in the Quarterly Progress Report of the Research Laboratory of Electronics, No. 90, July 15, 1968.     

癫癎发作对大鼠海马感觉门控的影响

目的：观察癫癎发作对大鼠海马感觉门控的影响。方法：采用青霉素诱导的大鼠癫癎发作模型，将探测电极植入大鼠海马的CA1区，连续7天，记录大鼠海马的听觉诱发电位；采用条件—测试模式的双短音刺激（S1、S2），刺激间隔是500ms，观察大鼠癫癎发作前后S1和S2波的峰—峰值、潜伏期和N40的测试刺激／条件刺激（T／C）比的变化，并与对照组进行比较。结果：与生理盐水对照组相比，实验组大鼠第一天癫癎发作后S2的峰—峰值增大，差异有显著意义（P=0．043）。反复癫癎发作一周，实验组第二天以后每天癫癎发作后总的趋势是：S1的峰—峰值减小，与对照组相比差异有显著意义（P=0．01），N40的T／C比在癫癎发作后增大，差异具有显著意义（P=0．028）。结论：癫癎发作对大鼠海马感觉门控具有急性和潜在的慢性损害作用。     

孤独症患者脑干听觉通路功能的评估与研究

目的：研究孤独症患者脑干听觉通路的功能状态,并探讨其可能的构建模式。方法：采用脑干听觉诱发电位（BAEP）技术对36例孤独症患者（孤独症组）与27例对照者（对照组）进行测试,分析比较BAEP成分的组问差异。结果：孤独症组BAEP中双侧Ⅲ、V波的潜伏期（PL）和各峰间期（IPL）均较对照组延长,其中右侧Ⅲ波PL和双侧V波PL延长之组间差异显著（P〈O．05）,左侧Ⅲ-V波和双侧I—V波IPL延长组间差异显著（P〈0．05）。结论：孤独症患者存在脑干听觉通路功能异常或脑干功能发育不成熟。脑干传导时间延长产生的听觉信息传递失真与中枢性听觉紊乱可能是孤独症形成的构建模式之一。     

Encoding timing and intensity in the ventral cochlear nucleus of the cat

Physiological response properties of neurons in the ventral cochlear nucleus have a variety of features that are substantially different from the stereotypical auditory nerve responses that serve as the principal source of activation for these neurons. These emergent features are the result of the varying distribution of auditory nerve inputs on the soma and dendrites of the various cell types within the nucleus; the intrinsic membrane characteristics of the various cell types causing different responses to the same input in different cell types; and secondary excitatory and inhibitory inputs to different cell types. Well-isolated units were recorded with high-impedance glass microelectrodes, both intracellularly and extracellularly. Units were characterized by their temporal response to short tones, rate vs. intensity relation, and response areas. The principal response patterns were onset, chopper, and primary-like. Onset units are characterized by a well-timed first spike in response to tones at the characteristic frequency. For frequencies less than 1 kHz, onset units can entrain to the stimulus frequency with greater precision than their auditory nerve inputs. This implies that onset units receive converging inputs from a number of auditory nerve fibers. Onset units are divided into three subcategories, OC, OL, and OI. OC units have extraordinarily wide dynamic ranges and low-frequency selectivity. Some are capable of sustaining firing rates of 800 spikes/s at high intensities. They have the smallest standard deviation and coefficient of variation of the first spike latency of any cells in the cochlear nuclei. OC units are candidates for encoding intensity. OI and OL units differ from OC units in that they have dynamic ranges and frequency selectivity ranges much like those of auditory nerve fibers. They differ from one another in their steady-state firing rates; OI units fire mainly at the onset of a tone. OI units also differ from OL units in that they prefer frequency sweeps in the low to high direction. Primary-like-with-notch (PLN) units also respond to tones with a well-timed first spike. They differ from onset cells in that the onset peak is not always as precise as the spontaneous rate is higher. A comparison of spontaneous firing rate and saturation firing rate of PLN units with auditory nerve fibers suggest that PLN units receive one to four auditory nerve fiber inputs. Chopper units fire in a sustained regular manner when they are excited by sound.(ABSTRACT TRUNCATED AT 400 WORDS)     

Central auditory conduction time in the rat

Summary Central conduction time is the time for an afferent volley to traverse the central pathways of a sensory system. In the present study, central auditory conduction time (CACT) was calculated for the rat, the first such formal measurement in any animal. Brainstem auditory evoked potentials (BAEPs) were recorded simultaneously with the primary response of the auditory cortex (P1). The latency of wave II of the BAEP, which arises in the cochlear nucleus, was subtracted from that of P1. This yielded a mean CACT of 6.6 ms. The results confirm a previous theoretical estimate that CACT in the rat is at least twice as long as central soma-tosensory conduction time.     

肝豆状核变性患者VEP、SEP及BAEP的对比研究

目的 :观察肝豆状核变性 (Wilson)病患者及直系亲属视觉诱发电位 (VEP)、体感诱发电位 (SEP)及脑干听觉诱发电位 (BAEP)的变化。方法 :对 10例Wilson病患者及其 18名直系亲属进行VEP、SEP及BAEP检测并分析其结果。结果 :5例患者双侧和 2例患者单侧VEP的P10 0潜伏期 (PL)延长。 1例患者双侧和 3例患者单侧SEP的N13-N2 0的波间潜伏期 (IPL)延长。 1例患者双侧和 2例患者单侧BAEP的Ⅲ -Ⅴ的IPL和Ⅰ -Ⅴ的IPL延长。提示Wilson病患者视觉、躯体感觉及听觉神经传导通路有不同程度的电生理活动障碍。 18名直系亲属中有 4名双侧和 3名单侧VEP的P10 0PL有不同程度的延长 ,2名亲属单侧BAEP的Ⅲ -Ⅴ和Ⅰ -Ⅴ的IPL延长。结论 :Wilson病患者的VEP、SEP及BAEP有明显的变化 ,提示Wilson病患者早期即有感觉通路功能异常     

葛根素对豚鼠卡那霉素耳中毒听觉诱发电位的影响

观察葛根素在豚鼠卡那霉素耳中毒中的作用。将豚鼠 30只随机分两组 :对照组 15只 ,肌注卡那霉素 40 0mg/kg/d ,共 12天 ;葛根素组 15只 ,除肌注卡那霉素 40 0mg/kg/d外 ,腹腔注射葛根素 10mg/kg/d ,共 12天。以听觉诱发电位为指标进行组间比较 ,听觉诱发电位阈值对照组明显高于葛根素组 (P <0 0 5 ) ;对照组诱发电位各波幅值则明显低于葛根素组 (P <0 0 1)。葛根素能减轻卡那霉素耳毒性 ,对卡那霉素耳中毒具有一定的保护作用 ,为耳毒性抗生素致聋的防治提供了一条新的研究途径     

Characteristics of evoked potentials of the human brain during recognition of short acoustic stimuli of different frequencies

We report here studies of the efficiency of recognition of short acoustic signals (11–30 msec) whose presentation did not produce mismatch negativity in evoked potentials in the human brain. Nonetheless, stimuli could still be recognized efficiently in these conditions; processing negativity disappeared from evoked potentials and the efficiency of recognition was significantly worsened on presentation of the shortest stimuli (11 msec). It is suggested that processing negativity also has a critical duration for acoustic signals, though this is significantly shorter than the minimum duration of stimuli needed for generating mismatch negativity.Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 89, No. 8, pp. 913–918, August, 2003.     

Early onset of age-related changes on neural processing in rats

Altered perceptual and emotional processing might bind impaired cognitive mechanisms during aging; however the nature of these sensory perception modifications is still unknown. In the present experiment we analyzed in rats, from early to mature life (2 to 11 months old), the response to unattended auditory evoked stimulation (Auditory evoked potential, AEP) and the power spectrum of spontaneous electroencephalogram (EEG), with the aim of unraveling the onset and target functional effects of aging. Somatosensory and cingulate cortex, mediodorsal thalamus and CA3 hippocampus were chosen for examination based on their involvement in sensory processing and age-related deficits. The main finding of this study is the early onset of age-related changes in adult rats as can be established with both AEP's and frequency analyses, and its diversity between brain regions during normal aging.     

40例听神经瘤病人的脑干听觉诱发电位分析

目的 :探讨听神经瘤患者的脑干听觉诱发电位 (BAEP)变化规律及应用价值。方法 :对听神经瘤患者作常规BAEP检查。结果 :40例听神经瘤肿瘤侧BAEP异常率 10 0 %,非肿瘤侧BAEP异常率 90 %,以Ⅲ Ⅴ间期延长尤显著 (占 90 %) ,Ⅲ Ⅴ /Ⅰ Ⅲ比值异常占 72 %。结论 :听力减退患者进行BAEP测试 ,对听神经瘤的诊断和鉴别诊断具有重要意义。     

Effects of low pass filtering on the brainstem auditory evoked potential in the rat

Summary The effects of low pass filtering on the brainstem auditory evoked potential (BAEP) were studied in the adult male rat. The bandpass of the recording system was progressively widened while the cut-off frequency of the high pass filter remained constant at 3.2 Hz. When the high frequency cut-off was 320 Hz or less, the principal waveform recorded in response to a click stimulus was a slow positive-negative complex. As the high frequency setting was raised from 800 Hz to 3.2 kHz, the slow components of the brainstem were replaced by four fast BAEP waves (I, II, III and IV). As the bandpass widened there was an increase in amplitude and a decrease in the absolute latency of all four fast waves in the order of 0.1 ms although the wave I–IV interpeak latency remained unaffected. The results confirm that the high frequency components of the BAEP are underlain by a slow positivity of uncertain origin followed by a slow negativity which probably arises within the inferior colliculus.This study was supported by the Medical Research Council of New Zealand     

Auditory brainstem responses in the aged cat

Auditory brainstem responses (ABRs) were compared in young adult and aged cats. Mean thresholds for click-evoked ABRs were greater in the aged cats. Clicks normalized to 15 and 30 dB above individual thresholds at rates of 10, 20, 50 and 100/sec evoked ABRs with similar latencies and central conduction times in both groups. Background noise at equal intensity for all cats completely suppressed ABRs evoked by clicks 30 dB above threshold in 2/3 of the young but none of the old cats. As rise time of a 25 msec noise burst at equal intensity for all cats increased 1, 2, 5, and 10 msec, latency of wave 4 increased more for the old cats than for the young. Summed monaural ABRs from both ears were greater than binaural ABRs for waves 4 and 5 in both groups. These data indicate peripheral auditory dysfunction in aged cats but little abnormality in auditory brainstem transmission with click intensity normalized for ABR threshold.     

Divergent projections of physiologically characterized rat ventral cochlear nucleus neurons as shown by intra-axonal injection of horseradish peroxidase

Summary An attempt was made to correlate electrophysiological and morphological characteristics of rat ventral cochlear nucleus neurons. Their axonal course and their soma morphology were investigated using the intra-axonal horseradish peroxidase method. Prior to labeling, neurons were characterized by recording their response patterns to acoustic stimulation with pure tones. Three types of cells were found: Category I (37 neurons) exhibited primarylike responses and a spontaneous firing rate below 10 spikes/s. Category II (21 neurons) showed on responses and little spontaneous activity. Category III (9 neurons) had primarylike responses like neurons in category I. However, the spontaneous activity rate of these neurons was significantly higher (mean: 95 spikes/s). Among the response categories, the morphological characteristics differed in some prominent aspects. Within each category, however, the morphological properties were rather similar. All neurons in category I were globular/bushy cells located in the area of the entrance of the cochlear nerve. The axon of each cell coursed along the ventral acoustic stria and consistently innervated the lateral superior olive ipsilaterally, and the nucleus of the trapezoid body and the nucleus of the lateral lemniscus contralaterally. Some neurons also projected to periolivary nuclei ipsilaterally and contralaterally. Neurons in category II were located in the posteroventral cochlear nucleus and were presumably multipolar/stellate cells. Their axons coursed via the intermediate acoustic stria and innervated mainly contralateral periolivary regions as well as the contralateral nucleus of the lateral lemniscus. Ipsilaterally, the lateral superior olive and the superior periolivary nucleus were innervated by some of the category II neurons. Somata types of neurons in category III could not be identified morphologically, but somata were located in caudal parts of the posteroventral cochlear nucleus that correspond to the octopus cell area. Their axons coursed via the intermediate acoustic stria and innervated periolivary regions and the contralateral nucleus of the lateral lemniscus. Thus, their axonal distribution differed only slightly from neurons in category II. These data confirm and extend previous findings regarding the efferent connections of ventral cochlear neurons. They emphasize the complexity of the axonal projection patterns of single cochlear nucleus cells. Since two types of response patterns and three types of axonal projection patterns have been observed, there remains an ambiguous relation between response pattern and axonal projection site. It is concluded that the response pattern to pure tone stimulation alone is not sufficient to describe physiological characteristics allowing for the establishment of structure-function relations. Only if one considers additional physiological properties like the spontaneous activity rate and the shape of tuning curves, does a correspondence between structure and function become apparent.Abbreviations AVCN anteroventral cochlear nucleus - c contralateral - CF characteristic frequency - CN cochlear nucleus - DCN dorsal cochlear nucleus - dor dorsal - DPO dorsal periolivary region - HRP horseradish peroxidase - i ipsilateral - IAS intermediate acoustic stria - IC inferior colliculus - lat lateral - LL lateral lemniscus - LNTB lateral nucleus of the trapezoid body - LSO lateral superior olive - LVPO lateroventral periolivary nucleus - med medial - MNTB medial nucleus of the trapezoid body - MSO medial superior olive - MVPO medioventral periolivary nucleus - NLL nucleus of the lateral lemniscus - NTB nucleus of the trapezoid body - PSTH peristimulus time histogram - PVCN posteroventral cochlear nucleus - RF reticular formation - rost rostral - RPO rostral periloivary region - SOC superior olivary complex - SPO superior paraolivary nucleus - VAS ventral acoustic stria - VCN ventral cochlear nucleus - VNLL ventral nucleus of the lateral lemniscus - VNTB ventral nucleus of the trapezoid body - 8n cochlear nerve     

Effects of neuronal activity on kainic acid neurotoxicity in the ventral cochlear nucleus

Kainic acid was injected into the brain stem of adult guinea pigs, and the animals were either placed in a sound reducing-chamber or stimulated with 90 dB noise. The pattern and rate of kainic acid-induced degeneration in the anteroventral cochlear nucleus (AVCN) of sound-deprived animals was similar to that in animals exposed to ambient noise [2]. The amount of degeneration was greatly increased in animals stimulated with 90 dB noise. Therefore, although decreased activity in primary auditory fibers does not protect neurons in the AVCN from kainate-induced neurotoxicity, increased auditory stimulation augments the effects of kainic acid in the cochlear nucleus.     

Conscious and preconscious adaptation to rhythmic auditory stimuli: a magnetoencephalographic study of human brain responses

This study was triggered by the experimental evidence that subjects required to tap in synchrony with a heard rhythm spontaneously time their tapping to variations in rhythm frequency even when these variations are so small that they are not consciously detectable. We performed a series of magnetoencephalographic (MEG) measurements, aimed at investigating whether the response of the auditory cortex discriminates randomly administered series of brief tones differing from each other only by their interstimulus intervals (ISI). Moreover, by combining psychophysical measurements, conscious and preconscious adjustments of tapping to rhythm variations were compared with brain cortical responses. The ISIs were varied by 2% or 20% from a "central" value of 500 ms. Subjects always consciously detected the 20% ISI changes and easily adjusted their tapping accordingly, whereas they never consciously detected the 2% ISI changes, even though they always correctly adjusted their tapping to them. Analysis of the auditory evoked fields (AEFs) showed that the intensity of the M100 component decreased with decreasing ISI both for 20% and 2% variations in a statistically significant manner, despite the fact that the 2% variation was not consciously perceived. The M100 behavior indicated that connections between auditory and motor cortexes may exist that are able to use the information on rhythm variations in the stimuli even when these are not consciously identified by the subject. The ability of the auditory cortex to discriminate different time characteristics of the incoming rhythmic stimuli is discussed in this paper in relation to the theories regarding the physiology of time perception and discrimination.