Electrically-Evoked Frequency-Following Response (EFFR) in the Auditory Brainstem of Guinea Pigs

It is still a difficult clinical issue to decide whether a patient is a suitable candidate for a cochlear implant and to plan postoperative rehabilitation, especially for some special cases, such as auditory neuropathy. A partial solution to these problems is to preoperatively evaluate the functional integrity of the auditory neural pathways. For evaluating the strength of phase-locking of auditory neurons, which was not reflected in previous methods using electrically evoked auditory brainstem response (EABR), a new method for recording phase-locking related auditory responses to electrical stimulation, called the electrically evoked frequency-following response (EFFR), was developed and evaluated using guinea pigs. The main objective was to assess feasibility of the method by testing whether the recorded signals reflected auditory neural responses or artifacts. The results showed the following: 1) the recorded signals were evoked by neuron responses rather than by artifact; 2) responses evoked by periodic signals were significantly higher than those evoked by the white noise; 3) the latency of the responses fell in the expected range; 4) the responses decreased significantly after death of the guinea pigs; and 5) the responses decreased significantly when the animal was replaced by an electrical resistance. All of these results suggest the method was valid. Recording obtained using complex tones with a missing fundamental component and using pure tones with various frequencies were consistent with those obtained using acoustic stimulation in previous studies.     

VEP Correlates of Feedback in Human Cortex

It is known that neural responses become less dependent on the stimulus size and location along the visual pathway. This study aimed to use this property to find evidence of neural feedback in visually evoked potentials (VEP). High-density VEPs evoked by a contrast reversing checkerboard were collected from 15 normal observers using a 128-channel EEG system. Surface Laplacian method was used to calculate skull-scalp currents corresponding to the measured scalp potentials. This allowed us to identify several distinct foci of skull-scalp currents and to analyse their individual time-courses. Response nonlinearity as a function of the stimulus size increased markedly from the occipital to temporal loci. Similarly, the nonlinearity of reactivations (late evoked response peaks) over the occipital, lateral-occipital, and frontal scalp regions increased with the peak latency. Response laterality (contralateral vs. ipsilateral) was analysed in lateral-occipital and temporal loci. Early lateral-occipital responses were strongly contralateral but the response laterality decreased and then disappeared for later peaks. Responses in temporal loci did not differ significantly between contralateral and ipsilateral stimulation. Overall, the results suggest that feedback from higher-tier visual areas, e.g., those in temporal cortices, may significantly contribute to reactivations in early visual areas.     

Amplitude and latency characteristics of spinal cord motor evoked potentials in the rat

The motor evoked potential (MEP) has become a valuable component of neurophysiological monitoring. A better understanding of the characteristics of the normal MEP is needed before one can fully appreciate the effects of injury on the MEP. We describe characteristic patterns of spinal cord MEPs, recorded epidurally, in response to transcranial (dura-to-palate) brain stimulation in a rat model. Series of signal averaged MEP responses at a duration of 100 μ sec were recorded at T_10/11, T_12/13, and L_1/2 in 8 normal rats. We used a much greater range of current intensities (0.5–65 mA) than has been studied previously. Also, we studied the gradual development of the MEP wave form using smaller increments of current strength than have been reported previously. We confirmed in rats our earlier report in cats that long latency peaks appear first at low intensities while short latency peaks appear with higher intensities (Konrad et al. 1988). We also report average peak latencies over the range of stimulus intensities used for each recording level in each rat. In some rats, conduction velocities of several MEP peaks were calculated, and they range from 35 to 42 m/sec. These velocities are consistent with values reported in the literature for extrapyramidal pathways. Our rat model provides a method of measuring spinal cord potentials at three levels with no trauma to the spinal cord. Therefore, it can be used to repeatedly test motor function in chronic studies of spinal cord injury.     

基于小波变换的婴儿痉挛症脑干听觉诱发电位复杂性分析

采用多尺度小波变换计算脑干听觉诱发电位近似熵的方法,对比婴儿痉挛症患儿与正常幼儿的近似熵值,按照脑干听觉诱发电位成份波对应的解剖位置,分段、分尺度计算并统计近似熵值,从神经信息传递角度探讨阻碍婴儿痉挛症患儿智能发育的原因。采集12例正常儿童和13例婴儿痉挛症患儿的脑干听觉诱发电位,将它们进行60尺度小波分解,分段、分尺度计算各尺度近似熵值。发现婴儿痉挛症组患儿脑干听觉诱发电位中代表脑干活动的3~7ms段的分尺度近似熵明显高于正常组(P<0.01),小尺度上表现尤为显著。结果表明婴儿痉挛症患儿脑干传导通路不畅通,其中的随机成份增多,阻碍信息在脑干的传递,进而影响患儿大脑皮层的发育。     

A dipole localization method in analyzing the auditory brain-stem evoked potential]

The localization of generators of brainstem auditory evoked response (BAER) has been studied in one patient using the method of dipole localization based on the spatial distribution of BAER over the surface of the head. It has been found that in formation of all BAER waves the activity of several generators overlaps. It is especially marked for the peaks I', II', III and III'--their potential distribution can not be described by single-dipole model, thus preventing the defining of their generation site. Distribution of potential for other peaks corresponds to the single-dipole model. The coordinates of the equivalent sources of these peaks are in the vicinity of the auditory structures: I--near the distal part of the auditory nerve, II--near the auditory nerve in the place of its entering the brainstem, V--near contralateral auditory pontine structures, V--near lateral lemniscus while V', VI and VI'--near mesencephalic auditory structures.     

Auditory evoked responses in tropical men during sojourn over the arctic region

The influence of an arctic environment on auditory evoked responses, both brainstem and cognitive, were evaluated in 10 Indian soldiers. They were first tested in Delhi and then flown to an arctic region where they were tested in the first week and again in the eighth week of their stay. Two migrants from Moscow, their usual place of residence, and six natives, born and brought up in the arctic, were also tested for comparison. The Indians, on their return to India, were tested again. The auditory evoked responses were recorded using the Nicolet (USA) Compact 4 Instrument. The Indians showed a delay in all the waves of the auditory brainstem response (ABR) during their induction in the arctic and these persisted even on their return to India whereas the migrants and the natives had relatively higher ABR latency values.     

Auditory evoked responses to rhythmic sound pulses in dolphins

The ability of auditory evoked potentials to follow sound pulse (click or pip) rate was studied in bottlenosed dolphins. Sound pulses were presented in 20-ms rhythmic trains separated by 80-ms pauses. Rhythmic click or pip trains evoked a quasi-sustained response consisting of a sequence of auditory brainstem responses. This was designated as the rate-following response. Rate following response peak-to-peak amplitude dependence on sound pulse rate was almost flat up to 200 s⁻¹, then displayed a few peaks and valleys superimposed on a low-pass filtering function with a cut-off frequency of 1700 s⁻¹ at a 0.1-amplitude level. Peaks and valleys of the function corresponded to the pattern of the single auditory brain stem response spectrum; the low-pass cut-off frequency was below the auditory brain stem response spectrum bandwidth. Rate-following response frequency composition (magnitudes of the fundamental and harmonics) corresponded to the auditory brain stem response frequency spectrum except for lower fundamental magnitudes at frequencies above 1700 Hz. These regularities were similar for both click and pip trains. The rate-following response to steady-state rhythmic stimulation was similar to the rate-following response evoked by short trains except for a slight amplitude decrease with the rate increase above 10 s⁻¹. The latter effect is attributed to a long-term rate-dependent adaptation in conditions of the steady-state pulse stimulation. Accepted: 18 June 1998     

Improving spatial and temporal resolution in evoked EEG responses using surface Laplacians

Spline generated surface Laplacian temporal wave forms are presented as a method to improve both spatial and temporal resolution of evoked EEG responses. Middle latency and the N1 components of the auditory evoked response were used to compare potential-based methods with surface Laplacian methods in the time domain. Results indicate that surface Laplacians provide better estimates of underlying cortical activity than do potential wave forms. Spatial discrimination among electrode sites was markedly better with surface Laplacian than with potential wave forms. Differences in the number and latencies of peaks, and their topographic distributions, were observed for surface Laplacian, particularly during the time period encompassing the middle latency responses. Focal activities were observed in surface Laplacian wave forms and topographic maps which were in agreement with previous findings from auditory evoked response studies. Methodological issues surrounding the application of spline methods to the time domain are also discussed. Surface Laplacian methods in the time domain appear to provide an improved way for studying evoked EEG responses by increasing temporal and spatial resolution of component characteristics.     

Evaluation of brain-stem auditory evoked potentials using dynamic time warping

Dynamic time warping is a procedure whereby portions of a temporal sequence of values are stretched or shrunk to make it similar to another sequence. This procedure can be used to align the brain-stem auditory evoked potentials recorded from different subjects prior to averaging. The resultant warp-average more closely resembles the wave form of a typical subject than the conventional average. Dynamic time warping can also be used to compare one brain-stem auditory evoked potential to another. This comparison can show the differences that result from changes in a stimulus parameter such as intensity or repetition rate. When a patient's wave form is compared to a normal template, warping can identify the peaks in the patient's wave form that correspond most closely to the peaks in the normal template. Compared to an experienced human interpreter, warping is very accurate in identifying the waves of normal brain-stem auditory evoked potentials (error rate between 0 and 4%) and reasonably accurate in identifying the peaks in abnormal wave forms (error rate between 3 and 18%).     

Topography of alpha and theta oscillatory responses upon auditory and visual stimuli in humans

Brain resonance phenomena and induced rhythms in the brain recently gained importance in electroencephalographic, magnetoencephalographic and cellular studies (Ba\c sar and Bullock 1992). It was hypothesized that evoked potentials are superpositions of induced rhythms caused by resonance phenomena in neural populations (Ba\c sar et al. 1992). According to Ba\c sar (1972), such resonance phenomena are reflected in the main peaks of the amplitude frequency characteristics computed from EEG responses. The present study is based on a frequency domain approach for the evaluation of topography- and modality-dependent properties of oscillatory brain responses. EEG and evoked potentials were recorded from vertex, parietal and occipital scalp locations in 24 volunteers. Two combined methods were applied: (1) amplitude frequency characteristics were computed from the transient evoked responses, and (2) frequency components of the transient responses were obtained by adaptive digital filtering. Our main goal was to investigate theta (4--7 Hz) and alpha (8--15 Hz) response components. (1) Amplitude frequency characteristics. Auditory stimuli elicited theta-alpha compound responses in the 4--11 Hz frequency band (e.g. typical peaking frequency around 7 Hz for vertex recordings). Visual stimuli elicited alpha responses (e.g. typical peaking frequency for vertex recordings around 9--12 Hz). Frequency maxima for visual stimuli thus had main peaks at higher frequency values than frequency maxima for auditory stimuli. (2) Digital filtering confirmed these results: for vertex recordings, theta vs. alpha response amplitudes were 9 vs 6 for auditory stimuli and 5 vs 5 for visual stimuli, thus confirming a shift towards higher frequencies, i.e. a more prominent contribution of the alpha range, in the case of visual stimulation. We hypothesize that these properties might reflect site- and modality-specific features of stimulus encoding in the brain in which resonance properties of neuron populations are involved. Furthermore we emphasize the utility of the systems theory approach for a better understanding of brain function by means of EPs. Received: 25 February 1994 / Accepted in revised form: 5 August 1994     

The effects of synaptic noise on measurements of evoked excitatory postsynaptic response amplitudes.

Spontaneously occurring synaptic events (synaptic noise) recorded intracellularly are usually assumed to be independent of evoked postsynaptic responses and to contaminate measures of postsynaptic response amplitude in a roughly Gaussian manner. Here we derive analytically the expected noise distribution for excitatory synaptic noise and investigate its effects on amplitude histograms. We propose that some fraction of this excitatory noise is initiated at the same release sites that contribute to the evoked synaptic event and develop an analytical model of the interaction between this fraction of the noise and the evoked postsynaptic response amplitude. Recording intracellularly with sharp microelectrodes in the in vitro hippocampal slice preparation, we find that excitatory synaptic noise accounts for up to 70% of the intracellular recording noise, when inhibition is blocked pharmacologically. Up to 20% of this noise shows a significant correlation with the evoked event amplitude, and the behavior of this component of the noise is consistent with a model which assumes that each release site experiences a refractory period of approximately 60 ms after release. In contrast with classical models of quantal variance, our models predict that excitatory synaptic noise can cause the apparent variance of successive peaks in an excitatory synaptic amplitude histogram to decrease from left to right, and in some cases to be less than the variance of the measured noise.     

Unified neurophysical model of EEG spectra and evoked potentials

 Evoked potentials – the brain's transient electrical responses to discrete stimuli – are modeled as impulse responses using a continuum model of brain electrical activity. Previous models of ongoing brain activity are refined by adding an improved model of thalamic connectivity and modulation, and by allowing for two populations of excitatory cortical neurons distinguished by their axonal ranges. Evoked potentials are shown to be modelable as an impulse response that is a sum of component responses. The component occurring about 100 ms poststimulus is attributed to sensory activation, and this, together with positive and negative feedback pathways between the cortex and thalamus, results in subsequent peaks and troughs that semiquantitatively reproduce those of observed evoked potentials. Modulation of the strengths of positive and negative feedback, in ways consistent with psychological theories of attentional focus, results in d istinct responses resembling those seen in experiments involving attentional changes. The modeled impulse responses reproduce key features of typical experimental evoked response potentials: timing, relative amplitude, and number of peaks. The same model, with further modulation of feedback, also reproduces experimental spectra. Together, these results mean that a broad range of ongoing and transient electrocortical activity can be understood within a common framework, which is parameterized by values that are directly related to physiological and anatomical quantities. Received: 22 May 2001 / Accepted in revised form: 8 January 2002     

Cough and laryngeal muscle discharges in brainstem lesioned anaesthetized cats

Experiments were carried out to determine whether there are separate drives from the selected neuronal networks of the brainstem affecting the discharge patterns of laryngeal and respiratory pump muscles during cough. Twenty-four non-decerebrate spontaneously breathing cats anesthetized with sodium pentobarbitone were used. Microinjections of kainic acid into the lateral tegmental field of the medulla, medullary midline or pontine respiratory group eliminated the cough evoked by mechanical stimulation of the tracheobronchial and laryngopharyngeal mucosa. These stimuli, in most cases, provoked irregular bursts of discharges in the posterior cricoarytenoid and thyroarytenoid laryngeal muscles (or they had no effect on them). No pattern of laryngeal muscle activities following lesions resembled the laryngeal cough response. Lesions of the target regions did not result in any apparent changes in the eupnoeic pattern of laryngeal activity. Neurons of the medullary lateral tegmental field, raphe nuclei and the pontine respiratory group seem to be indispensable for the configuration of the central cough motor pattern. However, these neurons do not appear to be essential for the discharge patterns of laryngeal motoneurons during eupnoea. The residual laryngeal "cough" responses are probably mediated by an additional motor drive.     

Methods for determining auditory evoked brain-stem response thresholds in human newborns

Previous investigators have reported that newborn auditory evoked brain-stem responses (ABRs) are 20–30 dB higher than adult psychophysical thresholds to the same stimuli. These investigators reduced the intensity of the stimulus until they no longer reported an ABR to the stimulus. We adapted 2 widely used psychophysical methods, the up-down-transformed response (UDTR) method and the method of constant stimuli, for ABR threshold determination of human newborns. Response judgments were made blindly. ABR thresholds of healthy normal newborns by both procedures were no more than 10–15 dB higher than adult psychophysical thresholds. The differences between the newborn ABR thresholds we reported and those in the literature were probably explained by different procedures including the method used to estimate adult psychophysical thresholds. The correlations between ABR thresholds and suprathreshold ABR latencies and amplitudes and latency and amplitude/intensity functions were modest at best. In normal newborns suprathreshold ABR measurements are of little value in predicting ABR thresholds.     

Properties of auditory brainstem responses evoked by intra-operative electrical stimulation of the cochlear nucleus in human subjects

Electrically evoked auditory brainstem response (EABR) testing can aid placement of the stimulating electrodes during surgical implantation of an auditory brainstem implant (ABI). To facilitate efficient testing, this study of EABR properties examined the effects of various stimulating and recording parameters on the magnitude and clarity of the EABRs obtained from 9 successive ABI patients during intra-operative monitoring. Both stimulus polarities elicited EABRs; the response waveforms were similar and no significant differences between the latencies were found. Stimulus-response relationships displayed thresholds and non-linear growth, characteristic of neural activity, and provided a stimulus amplitude that elicited readily detectable EABRs in all subjects. The stimulus rate could be increased without degrading the EABRs, but usually 50 Hz was used with a 10 ms sampling sweep so that muscle responses, which occurred later than EABRs, could be detected. When 3 stimulating electrodes in a line were tested, the pair with the largest separation consistently provided the largest response. A recording filter passband of 10–3000 Hz was useful for attenuating interference signals because there is negligible energy in the EABR at frequencies above 3 kHz, but there is some energy below 100 Hz.     

Auditory evoked blink reflex and posterior auricular muscle response: Observations in patients with HFS and PFS

Our goal was to investigate the characteristics of the auditory brainstem reflexes in patients with hemifacial spasm (HFS) and postparalytic facial syndrome (PFS).The spasm activities and responses by supraorbital and auditory stimuli were recorded from the orbicularis oculi, the posterior auricular and the mentalis muscles in 27 HFS and 21 PFS patients. The results were compared with those of 20 controls.Blink reflex (BR) was obtained by supraorbital stimulation in normal controls and on both sides of HFS and PFS patients whereas sound evoked bilateral auditory blink reflex (ABR) in 96.3%, 90.5% and 100%, respectively. Both BR and ABR showed synkinetic spread on symptomatic sides in all patients. The posterior auricular muscle response (PAMR) was observed bilaterally in 59.3%, 42.9% and 75.0% of groups, respectively. However, there was no synkinetic spread of PAMR.Since PAMR does not show synkinetic spread even in the presence of synkinetic spread of ABR and BR, we may suggest that a distal origin may be responsible of the synkinetic spread, or PAM is probably governed by a smaller nucleus in the brainstem. Thus it may be speculated that its excitability is insufficient to stimulate the ABR nucleus, whereas the reverse process is possible.     

Effects of pentobarbital and ketamine-xylazine anaesthesia on somatosensory, brainstem auditory and peripheral sensory-motor responses in the rat.

Somatosensory, brainstem auditory evoked and peripheral sensory-motor responses were recorded in rats anaesthetized with either pentobarbital or a ketamine-xylazine combination. This was carried out in order to assess which of these agents degraded responses to a lesser extent and thus would be more suitable for monitoring experimental effects. Neither of the anaesthetic agents affected peripheral sensory or motor conduction, nor were there any interpeak latency changes of the early components of the brainstem auditory response. However, pentobarbital anaesthesia resulted in an increase in latency of the initial positive component of the somatosensory cortical evoked potential and attenuation of the following negative component. During the recovery stages of ketamine-xylazine anaesthesia the longer latency evoked potential components were observed to emerge.     

Cluster analysis of visual cortical responses evoked by moving lines

The cortical evoked responses to a bar of light (line) moving in 8 different directions across the visual field of 6 unanaesthetized, immobilized cats were compared in 18 experimental sessions. The shape of the response is unique for each direction. This is particularly apparent during the first 350 msec of the response. Cluster analysis of the evoked potentials revelas that the recognition of the direction of the moving line is probably less distinct when the line moves in a downward direction. This finding is more pronounced in the left hemisphere. The results of the cluster analysis indicate that the technique may be a useful tool in the analysis and classification of large numbers of evoked potentials. Furthermore, such clustering may eventually reveal some of the physiological mechanisms that contribute to the shape of the evoked response.     

用子波变换的能量最大准则分析婴儿痉挛症脑干诱发电位

借鉴流体力学中用子波变换识别湍流相干结构的能量最大准则,解释婴儿痉挛症发病的三联征,尤其想说明智能迟滞的原因.从电生理的角度来说明,为什么脑干是婴儿痉挛症的责任病灶——这个生化及病理已经做出的推测.研究发现婴儿痉挛症患儿的脑干通道对外界刺激的反应能力和信息的传递能力与正常儿童有明显差异,借用能量最大准则在湍流中的解释,认为是因为信息传导阻滞引起患儿智能发育的迟滞,并试着提出评价最理想治疗效果的标准.     

Reduced variability of ongoing and evoked cortical activity leads to improved behavioral performance

Sensory responses of the brain are known to be highly variable, but the origin and functional relevance of this variability have long remained enigmatic. Using the variable foreperiod of a visual discrimination task to assess variability in the primate cerebral cortex, we report that visual evoked response variability is not only tied to variability in ongoing cortical activity, but also predicts mean response time. We used cortical local field potentials, simultaneously recorded from widespread cortical areas, to gauge both ongoing and visually evoked activity. Trial-to-trial variability of sensory evoked responses was strongly modulated by foreperiod duration and correlated both with the cortical variability before stimulus onset as well as with response times. In a separate set of experiments we probed the relation between small saccadic eye movements, foreperiod duration and manual response times. The rate of eye movements was modulated by foreperiod duration and eye position variability was positively correlated with response times. Our results indicate that when the time of a sensory stimulus is predictable, reduction in cortical variability before the stimulus can improve normal behavioral function that depends on the stimulus.