On the optimal pulse duration in electrical stimulation of the brain

Rats ran a runway for brain stimulation reward. From data relating running speed to current intensity at different pulse durations, we determined the strength-duration function. This function describes how much of an increase in current is required to compensate for a given decrease in pulse duration. From this function we calculated total charge (Current × Duration) as a function of duration. This quantity tends toward a constant minimum at short durations (0.1 msec or less). Short pulse durations should minimize the deleterious electrochemical effects of stimulation delivered through chronic electrodes.     

The brainstem auditory evoked potential: effects of high frequency filtering

The effects of low pass filtering on the brainstem auditory evoked potential (BAEP) were studied in the lightly anaesthetised rat. The high pass filter was kept fixed at 100 Hz in order to exclude the slow components on which the four fast waves of the BAEP are superimposed. The cut-off frequency of the low pass filter was systematically raised from 160 to 32 k HZ. With a band pass of 100-160 Hz, the BAEP waveform could barely be discerned. With a bandpass of 100-320 Hz, all four BAEP waves were apparent but of diminutive amplitude. With subsequent increases in the high frequency cut-off, the BAEP waveform became more clearly defined with increases in the amplitudes and decreases in the latencies of all four waves. However, beyond 8 k Hz, there was little additional change in waveform morphology. With widening of the bandpass, there was only a small concomitant decrease in brainstem transmission time. This implies that the effects of low pass filtering acted in a basically uniform manner on all four BAEP waves.     

脑干听觉诱发电位测试参量重要性的探讨

对国内外各家ＢＡＥＰ资料进行统计分析，以及对４１例健康人（１５～５６岁，男１９例，女２２例）８１只听力正常耳分别用短声和滤波短声进行ＢＡＥＰ测试，结果表明，在ＢＡＥＰ正常值检测中，刺激声是影响其结果的最重要参量之一。因此，各实验室应有自己的正常值，如果测试条件及仪器符合规格。那么在测试方法学和测试参量统一的条件下，各实验室的ＢＡＦＰ正常值应该是可以相互参考的。     

gamma-Aminobutyric acid immunoreactivity in brainstem auditory nuclei of the chicken

Using an antiserum directed against gamma-aminobutyric acid (GABA), the presence of presumed GABAergic neurons is demonstrated in the chicken auditory brainstem nuclei: nucleus laminaris, nucleus angularis, superior olive, and the ventral nuclei of the lateral lemniscus. Nucleus magnocellularis contains no immunopositive neurons but numerous GABA-positive terminals surrounding the cells. Terminal labeling is also present in the other auditory nuclei, though scarcer and not always associated with cell bodies. These data suggest an involvement of GABAergic inhibition in auditory processing in the lower auditory pathway of birds.     

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。     

Reorganization of the frequency map of the auditory cortex evoked by cortical electrical stimulation in the big brown bat

In a search phase of echolocation, big brown bats, Eptesicus fuscus, emit biosonar pulses at a rate of 10/s and listen to echoes. When a short acoustic stimulus was repetitively delivered at this rate, the reorganization of the frequency map of the primary auditory cortex took place at and around the neurons tuned to the frequency of the acoustic stimulus. Such reorganization became larger when the acoustic stimulus was paired with electrical stimulation of the cortical neurons tuned to the frequency of the acoustic stimulus. This reorganization was mainly due to the decrease in the best frequencies of the neurons that had best frequencies slightly higher than those of the electrically stimulated cortical neurons or the frequency of the acoustic stimulus. Neurons with best frequencies slightly lower than those of the acoustically and/or electrically stimulated neurons slightly increased their best frequencies. These changes resulted in the over-representation of repetitively delivered acoustic stimulus. Because the over-representation resulted in under-representation of other frequencies, the changes increased the contrast of the neural representation of the acoustic stimulus. Best frequency shifts for over-representation were associated with sharpening of frequency-tuning curves of 25% of the neurons studied. Because of the increases in both the contrast of neural representation and the sharpness of tuning, the over-representation of the acoustic stimulus is accompanied with an improvement of analysis of the acoustic stimulus.     

Fos-like immunoreactivity in auditory and nonauditory brain structures of hamsters previously exposed to intense sound

Fos-like immunoreactivity (FLI) was evaluated in auditory and nonauditory brain structures in hamsters that had been exposed previously to intense sound and tested behaviorally for tinnitus. The immunocytochemical results demonstrated a significant increase in exposed animals of FLI in auditory brain structures such as the lateral lemniscus, central nucleus of inferior colliculus, and auditory cortex, as well as in some nonauditory brain structures such as the locus coeruleus, lateral parabrachial nucleus, certain subregions of the hypothalamus, and amygdala. The behavioral scores suggest that animals that had been exposed to intense sound developed tinnitus. This is consistent with the hypothesis that FLI induced by intense sound exposure might represent a neural correlate of tinnitus or of plasticity associated with tinnitus. The possibility and the mechanisms underlying the increased FLI are discussed.     

Somatostatin and substance P-like immunoreactivity in the auditory brainstem of the adult rat

The superior olivary complex (SOC) of the adult rat brainstem was studied in detail with regard to its innervation by neural elements showing immunoreactivity for two neuroactive peptides, somatostatin and substance P. Nerve fibres and varicosities showing positive immuno-reactivity for both peptides were particularly dense immediately dorsal and lateral to the lateral superior olivary nucleus (LSO) and dorsal to the superior paraolivary nucleus (SPN). Penetration of this curtain-like innervation into the SPN was limited, and the LSO showed only a very minor innervation by somatostatin-positive structures in its most medial (high frequency) lobe. Dense fibre labelling and varicosities were also apparent for both peptides immediately medial to the ventral and dorsal nuclei of the lateral lemniscus, and in the external cortex and dorsomedial zones of the inferior colliculus (IC). Labelled fibres and endings were also seen in the granule cell regions of anteroventral cochlear nucleus (AVCN) and the most dorsomedial parts of the dorsal cochlear nucleus (DCN). The majority of cells in the medial nucleus of the trapezoid body (MNTB) showed a prominent innervation by nerve terminals that stained positive for somatostatin only whereas the medial superior olivary nucleus (MSO) was devoid of label for both peptides. The ventral nucleus of the trapezoid body (VNTB) showed sparse but significant innervation by both somatostatin and substance P-positive structures. Hence the VNTB was the only defined nucleus of the SOC to show a significant substance P-positive innervation. Neuronal somata immuno-reactive for somatostatin were found in anteroventral and posteroventral cochlear nuclei (AVCN and PVCN) and the A5 and A7 cell groups adjacent to the LSO and the VNLL and DNLL and in all subdivisions of the inferior colliculus (IC). Somata showing only faint immunoreactivity for substance P were found in the VNLL, AVCN and PVCN. These results suggest a potential role for both peptides in auditory signal processing in the adult rat brain.     

犬脑干缺血后脑干听觉诱发电位的研究

建立犬脑干局灶性缺血模型，观察脑干局灶性缺血后脑干听觉诱发电位（ＢＡＥＰ）的变化。结果发现犬脑干缺血０．５、１、１．５、３、６和１２ｈ缺血组（ＩＳ）ＢＡＥＰ的Ⅰ、Ⅲ、Ｖ各波潜伏期（ＰＬ）及Ⅰ－Ⅲ、Ⅲ－Ｖ、Ⅰ－Ｖ波的峰间期（ＩＰＬ）与假手术组（ＳＨ）相比较均非常明显地延长（Ｐ＜０．０１），以１～１．５ｈ延长最显著（ｒ＜０．０１），３ｈ后各值逐渐缩短。提示ＢＡＥＰ可反映犬脑干缺血后的脑干损害，可客观地评价脑干功能。     

婴儿痉挛症脑干听觉诱发电位的奇异性初步分析

目的运用建立在子波变换基础上的Lipschitz指数和模极大值两种奇异性检测方法分析婴儿痉挛症患儿脑干听觉诱发电位,试图解释婴儿痉挛症患儿智能迟滞的原因,从神经电生理的信息传递的角度来证明脑干是责任病灶。方法本实验病例分为2组,正常组12例,平均年龄(6.325±3.210)岁;婴儿痉挛症组13例,平均年龄(4.638±3.986)岁。所有病例均行脑干听觉诱发电位检查,并用建立在子波变换基础上的Lipschitz指数和模极大值两种奇异性检测方法进行分析。结果Lipschitz指数尖峰在正常幼儿0～2ms和5～7ms各出现1次,在婴儿痉挛症患儿尖峰出现在0～2ms和5～7ms之后。正常幼儿模极大值在一定范围内连续性好,而在婴儿痉挛症患儿则中断。结论研究发现在婴儿痉挛症患儿的脑干、尤其是上部脑干对上行传导的信息耦合性差,从而影响患儿的智能发育。     

Sensory gating of auditory evoked potentials in rats: effects of repetitive stimulation and the interstimulus interval

In the P50 gating or conditioning-testing (C-T) paradigm, the P50 response, a small positive midlatency ( approximately 50 ms after stimulus onset) component of the human auditory evoked potential (AEP), is reduced towards the second click (S2) as compared to the response to the first click (S1). This phenomenon is called sensory gating. The putative function of sensory gating is thought to protect subjects from being flooded by irrelevant stimuli.Comparative studies have been done in rats in order to elucidate the underlying neural substrate of sensory gating. However, for a direct comparison of rat and human AEP components, it is imperative for both components to show similar characteristics. The amount of sensory gating in humans is dependent on repetitive stimulation and the interstimulus interval (ISI). In the present study effects of repetitive stimulation (Experiment 1) and various ISIs (Experiment 2) were determined on rat AEP components. The results demonstrate that gating is not limited to a restricted cortical area or a single midlatency component and that repetitive stimulation and ISI affect gating of several rat AEP components. Components such as the vertex P17 and N22 show a decrease in gating within several S1-S2 presentations, mainly due to a decrease in amplitude to S1 (Experiment 1). Gating for vertex components (such as the P17, N22 and N50) is ISI dependent (Experiment 2), but there is no interval in the 200-600 ms range at which optimal gating occurs. The ISI effects on gating are due to an increase of the amplitude to S2. The results have implications for the discussion about the rat homologue of the human P50.     

Effect of frequency and pulse duration on human muscle fatigue during repetitive electrical stimulation

Different combinations of stimulation frequency and intensity can generate a targeted force during functional electrical stimulation (FES). This study compared isometric performance and muscle fatigue during repetitive stimulation with three different combinations of frequency and pulse duration that produced the same initial peak forces: protocol 1 used long pulse duration (fixed at 600 micros) and 11.5 +/- 1.2 Hz (low frequency); protocol 2 used 30 Hz (medium frequency) and medium pulse duration (150 +/- 21 micros); and protocol 3 used 60 Hz (high frequency) and short pulse duration (131 +/- 24 micros). Twenty and 60 Hz pre- and postfatigue testing trains were delivered at the pulse duration used by the fatiguing trains and at 600 micros pulse duration. The percentage decline in peak force between the first and last fatiguing train of each protocol was the measure of muscle performance. The declines in peak force of the 60 Hz testing trains were used to measure muscle fatigue. The 20 Hz:60 Hz peak force ratio was used as a measure of low-frequency fatigue. The results showed that protocol 1 produced the least decline in peak force in response to the fatiguing trains, as well as the least muscle fatigue and low-frequency fatigue when the pulse duration was maintained at the level used by the fatiguing trains. Interestingly, protocol 2 produced the least muscle fatigue, and there were no differences in the levels of low-frequency fatigue across protocols when a comparable motor unit population was tested using 600 micros pulse duration. The results suggest that if the frequency and intensity are kept constant during FES, using the lowest frequency and longest pulse duration may maximize performance.     

Analysis and detection of binaural interaction in auditory evoked brainstem responses by time-scale representations

The beta-wave of the binaural interaction component (BIC) in auditory evoked brainstem responses has been shown to be an objective measure of binaural interaction. However, a reliable and automated detection of this component capable of clinical use still remains a challenge. In this study, wavelet based time-scale representations of auditory evoked brainstem responses were investigated for the analysis of binaural interaction and for an automated detection of the beta-wave. Twenty normal hearing subjects with verified normal directional hearing and speech intelligibility in noise were included in our study. In all of these subjects, the BICs exhibited a characteristic concentration of energy in the time-scale domain which allowed for an automated detection of the beta-wave. Moreover, our study provides an explanation why the beta-wave is hard to detect for larger interaural time delays using time-scale entropy based arguments. It is concluded that time-scale representations of auditory brainstem responses are well suited for the analysis of binaural interaction and allow for an automated detection of the beta-wave.     

早产儿的脑干听觉诱发电位及听力检测

目的:探讨早产儿脑干听觉诱发电位(BAEP)的特征及听力损失情况.方法:对46例不同出生胎龄早产儿进行BAEP及听力检测,分析BAEP主要波形成分Ⅰ、Ⅲ、Ⅴ波的峰潜伏期(PL),波幅及Ⅰ-Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ峰问期(IPL).以单侧耳Ⅴ波反应阈值作为听反应阈.结果:以30例正常足月儿为对照,不同出生胎龄新生儿BAEP Ⅰ、Ⅲ、Ⅴ波的PL,Ⅰ～Ⅲ、Ⅲ-Ⅴ、Ⅰ-Ⅴ波的IPL比较差异有显著意义(P＜0.05).46例早产儿存在听力损失27例(59%),30例足月儿存在听力损失2例(7%),差异有非常显著意义(γ2=20.62,P＜0.01).胎龄＜30周的4例均发生听力损失(100%),且均为中重度以上听力损失;胎龄30～33周23例中,发生听力损失13例(68%),其中中重度以上听力损失者占37%;胎龄≥34～36 6周23例,发生听力损失10例(43%),其中中重度以上听力损失者占11%.不同胎龄组间发生听损失的差异有非常显著意义(x2=16.56,P＜0.01),中重度以上听力损失的发生率差异尤为显著(x2=27.6,P＜0.01).结论:胎龄是影响新生儿BAEP的重要因素,早产儿胎龄越小,听力损失的发生率越高,听损失的严重程度越重.     

Comparison of saccades evoked by visual stimulation and collicular electrical stimulation in the alert monkey

In the alert monkey we have compared the properties of saccades elicited by a visual stimulus (V-saccades) with those generated by electrical stimulation in the superior colliculus (E-saccades). We found that whereas there exists a graded relation between E-saccade amplitude and current strength, E-saccade direction is remarkably independent of electrical stimulation parameters. At sufficiently high current strengths (about 20 microA), E-saccades are consistently directed toward the center of the movement field of nearby cells, except when stimulation is performed at sites near the collicular borders. Further interesting differences between the amplitude and direction behaviour were observed when the variability in E-saccade vectors, obtained with fixed stimulation parameters, was analyzed. In all cases, E-saccade amplitude scatter exceeds direction scatter, suggesting the possibility of a polar coordinate organization for the coding of saccade metrics. These data are compared with V-saccade scatter data, recently obtained in the human (Van Opstal and Van Gisbergen 1989c). Finally, an analysis of saccade dynamics shows that E-saccades can reach V-saccadic velocities at higher current strengths. However, at near-threshold current strengths, where E-saccade amplitude decreases, we found at most stimulation sites (22/37) that E-saccades are consistently slower than V-saccades of the same amplitude. Possible mechanisms underlying the collicular role in saccade generation are discussed.     

Effects of aversive and rewarding electrical brain stimulation on auditory evoked responses in albino rat tectum

Auditory evoked responses in rat tectum yielded recovery functions to aversive electrical brain stimulation of either contralateral mesencephalic central gray or deep superior colliculus. Effects of stimulation on inferior colliculus auditory potentials are abolished by pentobartital and curare, implying tympanic muscle mediation due to reticular activation. Brain stimulation effects survive identical pharmacological manipulations when auditory responses are led from deep superior colliculus, showing independence from reticular processes or events occurring in inferior colliculus, one synapse previous. Rewarding brain stimulation also effects deep superior colliculus potentials, but interacts in an undetermined manner with nonspecific processes.