Computer techniques for the processing of evoked potentials

A computer technique is described for the systematic characterization of brain evoked potentials. Preprocessing of the data by a causal digital filter is followed by a peak search and identification procedure. A latency histogram of the peaks found is constructed to determine the ranges or clusters of peaks within the single evoked potential. Peaks found within the clusters are then corrected to the mean latency of the cluster and a latency corrected average version of the evoked potential constructed.     

Evoked potential measurement and analysis on a small laboratory computer

A program is described for the collection and subsequent analysis of somatosensory evoked potentials using a LINC-8 computer. The program allows simple evoked-potentials analysis in centers where a small laboratory computer may be available but sophisticated instrumentation such as a computer of average transients is not available. This program provides an efficient method of easily obtaining information concerning the conduction pathways of the nervous system as well as the cerebral function; the program can be implemented on small laboratory computers which most hospitals currently own, without the associated cost or complexity of additional hardware in the laboratory. Combining utilization of a small laboratory computer with an easily programmable method provides an approach for evoked potential analysis which is well within the financial and technical scope of most neurophysiology laboratories.     

A computer system for neurosurgical patient monitoring.

The variables monitored in intensive care units are generally late indicators of neurologic deterioration. A system based on a LINC-8 computer was therefore developed for on-line monitoring of evoked potentials, electroencephalography (EEG), and transcranial and transthoracic impedances as well as conventional parameters. Somatosensory evoked potentials are recorded at either 30 min or 1 h intervals. One minute epochs of EEG are analyzed every 10 min using a peak-detection algorithm. Impedances and conventional parameters are also monitored at 10 min intervals. In a study of 50 patients, the technical feasibility of this type of monitoring with a small laboratory computer has been demonstrated. In some instances, evoked potentials and EEG show changes prior to detectable neurologic changes. The study suggests that this type of monitoring can provide a valuable adjunct for evaluation of physiologic function in neurosurgical intensive care.     

Online Adaptation of a c-VEP Brain-Computer Interface(BCI) Based on Error-Related Potentials and Unsupervised Learning

The goal of a Brain-Computer Interface (BCI) is to control a computer by pure brain activity. Recently, BCIs based on code-modulated visual evoked potentials (c-VEPs) have shown great potential to establish high-performance communication. In this paper we present a c-VEP BCI that uses online adaptation of the classifier to reduce calibration time and increase performance. We compare two different approaches for online adaptation of the system: an unsupervised method and a method that uses the detection of error-related potentials. Both approaches were tested in an online study, in which an average accuracy of 96% was achieved with adaptation based on error-related potentials. This accuracy corresponds to an average information transfer rate of 144 bit/min, which is the highest bitrate reported so far for a non-invasive BCI. In a free-spelling mode, the subjects were able to write with an average of 21.3 error-free letters per minute, which shows the feasibility of the BCI system in a normal-use scenario. In addition we show that a calibration of the BCI system solely based on the detection of error-related potentials is possible, without knowing the true class labels.     

Analysis of visual evoked potentials through Wiener filtering applied to a small number of sweeps

We introduce a method for processing visual evoked potentials, on the basis of a Wiener filter algorithm applied to a small number of consecutive responses. The transfer function of the filter is obtained by taking into account both the average of 99 sweeps (as an estimate of the true signal) and the EEG signal just before the stimulus onset (as an estimate of the noise superimposed on each individual response). The process acts as a sweep-by-sweep filter (in the sense of the mean square error) which considers the possible non-stationarities of the EEG signal during a complete clinical procedure. The average of a small number of consecutive filtered sweeps reveals variations in the morphology of the evoked responses which produce a change in the principal latencies. Applications are foreseen in neurophysiological studies of visual evoked potential responses, and in the clinic, where it is important to evaluate adaptive mechanisms, dynamic changes in single groups of visual evoked potentials and cognitive responses.     

Use of Cognitive Evoked Potentials (P300) as an Approach to Assessing the Frequency of Possible Requests towards the Working Memory of Players during Computer Games

Cognitive potentials measured in players during computer games were used as a tool to assess the number of possible cognitive requests (NPCR) between two mouse clicks. The data obtained in recording cognitive evoked potentials (EP) with pressing a button allowed us to count the frequency of requests towards conscious cognitive processes in the working memory, which was associated with the number of operations of comparison (matching), decision-making, and triggering an action.     

On-line analysis of neuromuscular bioelectric potentials

A computer system is presented which provides for on-line data capture and analysis of evoked end-plate potentials and action potentials, and on-line data capture with off-line analysis of spontaneously occurring miniature end-plate potentials at the end-plate region of the neuromuscular junction. Sampling of evoked waveforms begins after an adjustable delay following the stimulus. Spontaneously occurring waveforms are captured by 'freezing' the contents of a circular buffer. The software provides MENU selectable support functions including storage and retrieval of data and calculated parameters, analog and digital display of waveforms, data calibration and gain modification, data editing, file management, and hardcopy output. Calculated parameters of the waveform are optionally placed in a data base file by the analysis programs. The data base may be used for editing, arithmetic operations, and subsetting of variables as well as statistical analysis and plotting of any selected variables.     

Some comments on the derivation of the Wiener filter for average evoked potentials

The Wiener filtration of average evoked potentials supplies the estimate of evoked response with the least square error. However, this error is dependent on the choice of interstimulating intervals. This dependence was not considered in hitherto applications of the Wiener filter. In this paper the Wiener filter with respect to the concrete choice of interstimulating intervals is derived.     

Source derivation: Application to topographic mapping of visual evoked potentials

The application of a source derivation technique to topographic mapping of the pattern-reversal visual evoked potential is described. Comparisons were made with non-cephalic and common average reference recordings. Source derivation yielded wave forms which were less influenced by activity of reference origin. Source derivation wave forms were similar to those obtained with common average referencing but contour plots showed less spread of regions of maximal activity in the case of source derivation. It is suggested that source derivation may be useful in further studies of the topography and sources of cerebral evoked potentials.     

Electrogenic Absorption of Sugars and Amino Acids in the Small Intestine of the Human Fetus

Some characteristics and the degree of intestinal absorption in the developing human fetus were examined by measuring solute evoked potentials and ¹⁴C-D-glucose uptake into the everted jejunal segments.

In all segments, the Michaelis-Menten relationship was observed between D-glucose concentrations and the evoked potentials or D-glucose uptake. Increase of Na-ion concentrations enhanced both D-glucose evoked potentials and uptake.

Both D-glucose and L-α-alanine evoked potentials increased in a significant correlation to the fetal age; however, the apparent Michaelis constants did not show any significant change. The structural specificity of sugar for generating evoked potentials was the same as that reported for adult mammals. Among amino acids, only the L-form of neutral and acidic amino acids generated markedly high evoked potentials, but the basic ones hardly at all. Oligopeptides such as glycyl-glycine and glycyl-glycyl-glycine also generated high evoked potentials.     

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.     

Changes in the P300 amplitude under the influence of "aggressive" computer game in adolescents with various levels of initial aggression and conflicting behavior

Dynamic changes in the amplitude of component P300 of the evoked potentials in different cortical areas were studied as an index of activity of cortical structures responsible for actualization of a computer game with aggressive content with regard for the level of initial aggression and conflict in behavior of adolescent subjects. Dynamic changes in anxiety and aggression evoked by playing an "aggressive" computer game were shown to be dependent on the initial level of aggression and conflict. An increase in P300 in the frontal and orbitofrontal areas of both hemispheres was observed in adolescents with initially high level of aggression and conflict. In adolescents with initially low aggression and conflict, P300 decreased bilaterally in the frontal areas and did not change significantly in the orbitofrontal areas. These findings testify to the bilateral frontal top-down control over negative emotions.     

痛觉诱发电位的研究进展

痛觉诱发电位的研究在过去的几十年内取得了重要进展 ,出现了许多用于被试的诱发明确疼痛感的刺激技术 ,并与诱发电位方法学联合应用 ,已经成为脑映像学研究中重要的组成部分。本文从刺激技术、痛觉诱发电位成分分析和偶极子源分析等方面出发 ,讨论了痛觉诱发电位的研究进展     

Electrogenic absorption of sugars and amino acids in the small intestine of the human fetus

Some characteristics and the degree of intestinal absorption in the developing human fetus were examined by measuring solute evoked potentials and 14C-D-glucose uptake into the everted jejunal segments. In all segments, the Michaelis-Menten relationship was observed between D-glucose concentrations and the evoked potentials or D-glucose uptake. Increase of Na-ion concentrations enhanced both D-glucose evoked potentials and uptake. Both D-glucose and L-alpha-alanine evoked potentials increased in a significant correlation to the fetal age; however, the apparent Michaelis constants did not show any signficant change. The structural specificity of sugar for generating evoked potentials was the same as that reported for adult mammals. Among amino acids, only the L-form of neutral and acidic amino acids generated markedly high evoked potentials, but the basic ones hardly at all. Oligopeptides such as glycyl-glycine and glycyl-glycyl-glycine also generated high evoked potentials. Our results have indicated that the active transport system of sugars and amino acids in the human fetus have already developed by as early as the sixth month of gestation.     

Visual event-related potentials evoked by using a virtual reality display

This study aimed at investigating whether a virtual reality display (VRD) is an appropriate tool for evoking visual event-related potentials (VEPs). VEPs evoked by VRD stimuli were highly similar in form to VEPs evoked by using a computer monitor, both having two dominant peaks, labeled P100 and N200. Monitor and VRD N200 latencies and amplitudes were highly correlated. However, peak latencies were longer and the peaks were broader when stimuli were presented on the VRD. Besides, VRD P100 amplitude was smaller, and an N75 peak could be seen usually only on monitor VEPs.     

Bioelectrical activity and neuromediator metabolism in different brain structures during chronic haloperidol administration]

First haloperidol administration is followed by the reorganization of evoked potentials in visual cortex. During haloperidol administration (10-12 days after the beginning) variations of evoked potentials is visual cortex and in subcortical structures uniform evoked potentials took place.     

视力与视觉诱发电位的相关分析

对104例病人的图形翻转VEP的瞬态波形各参数,以及9例正常或近视学生的稳态曲线功率谱与视力之间的关系进行了多元相关统计分析,旨在探讨VEP的哪些参数可客观地评估视力.结果表明,瞬态VEP的波形参数中以13’格诱发的N_1P_1、P_1N_2的峰峰值及P_(100)潜伏期与视力的相关系数最大,故认为,分析视力时以平均P_(100)波的波幅值和P_(100)波潜伏期作指标较为灵敏;而稳态、VEP能谱曲线则显示,视力与平均相叶能谱或刺激频率点的能谱相关性较大,与二次谐波的相关性则小.     

Cerebral chemosensory evoked potentials elicited by chemical stimulation of the human olfactory and respiratory nasal mucosa

A stimulation method was employed by which chemosensory evoked potentials were recorded without tactile somatosensory contamination. The purpose of the study was to determine whether potential components evoked by stimulation of the chemoreceptors of the trigeminal nerve can be distinguished from those of the olfactory nerve. The stimulants (vanillin, phenylethyl alcohol, limonene, menthol, anethol, benzaldehyde, carbon dioxide and a mixture of vanilin and carbon dioxide) were presented in a randomized order to 13 volunteers. Chemosensory evoked potentials to substances which anosmics are unable to perceive (vanillin, phenylethyl alcohol) were termed olfactory evoked potentials; potentials to CO₂, which effected no olfactory sensations were termed chemo-somatosensory potentials. Analysis of variance revealed that the different substances resulted in statistically significant changes in the amplitudes and latencies of the evoked potentials, and also in the subjective estimates of intensity. An increased excitation of the somatosensory system resulted in reduced latencies and enhanced amplitudes of the evoked potentials. Responses to the mixture of carbon dioxide and vanillin appeared significantly earlier (50–150 msec) than responses to either substance alone.     

Auditory responses in the torus semicircularis of the cane toad, Bufo marinus. I. Field potential studies

Field potentials have been recorded in the torus semicircularis of the toad, Bufo marinus, in response to brief tones presented in the free field. The amplitude of the potentials varied with the frequency of the stimulus and location of the electrode along the rostro-caudal axis of the torus. All frequencies in the auditory range evoked largest potentials when the stimulus was located in the contralateral auditory field. Potentials evoked by low to mid frequencies were largest when the stimulus was located near the line orthogonal to the long axis of the animal. For progressively higher frequencies, the optimal stimulus position was progressively more anterior in the contralateral field. In animals in which one eighth nerve had been sectioned, field potentials evoked by tones of low to mid frequency were less sensitive to changes in stimulus direction than in normal animals. However, the directional sensitivity of field potentials evoked by mid to high frequencies was similar in monaural and normal animals. These observations suggest that binaural neural integration is important in determining the directional sensitivity of field potentials in the torus evoked by low to mid frequencies but not for potentials evoked by mid to high frequencies.     

Selecting the smoothing parameter for estimation of slowly changing evoked potential signals

Brain evoked potential (EP) data consist of a true response ("signal") and random background activity ("noise"), which are observed over repeated stimulus presentations ("trials"). A signal that changes slowly from trial to trial can be estimated by smoothing across trials and over time within trials. We present a method for selecting the smoothing parameter by minimizing an estimate of the mean average squared error (MASE). We evaluate the performance of this method using simulated EP data, and apply the method to an example set of real flash evoked potentials.