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Results for “Evoked Potentials”

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At least 19 recordsLinked to original sources
PubMed1979

Digital filtering of on-line evoked potentials.

Evoked potentials recorded automatically at frequent intervals are a useful adjunct for monitoring head injury patients; however, unaveraged residual noise due to patient movement and synchronization of th- stimulus to harmonics of the line frequency is sometimes present. A frequency analysis was performed on 23 records with varying degrees of unaveraged noise and the results were used to design a digital filter. The frequency content of the records analyzed was largely contained in a band from D.C. to 200 Hz. A zero phase shift lowpass digital filter with a cutoff frequency of 200 Hz eliminated the majority of noise. Despite the low frequency content, a wide-band amplifier is still required to avoid waveform distortion, particularly latencies. Digital filters can then be applied without causing distortion.

Computers↗
PubMed1977

An objective indicant of binocular vision in humans: size-specific interocular suppression of visual evoked potentials.

Evoked cortical potentials (VEPs) to grid patterns flashed to one eye were suppressed in amplitude when grid patterns were continuously presented to the other eye. The degree of interocular suppression of VEPs was influenced by the stereoacuity of the subjects. VEPs were obtained to each of two grid sizes flashed to one eye (individual squares subtending 15 and 60 min of arc) and changes in amplitude of these VEPs were considered as a function of four stimuli continuously presented to the other eye (diffuse light, 15, 30, and 60 min of arc squares in grids). Interocular suppression of VEPs was greater (a) when the continuously presented grid was of high (38.00 mL) as compared to low (00.38 mL) intensity, (b) when the continuous and flashed grids were of the same as compared to different sizes, and (c) in six subjects who had good as compared to six subjects who had poor binocularity. Eleven of the twleve subjects could be classified correctly as having good or poor binocularity on the basis of statistically significant interocular suppression of VEPs. The results were interpreted in terms of centrally located binocular neurons responsive to specific grid sizes or spatial frequencies and the decreased functioning of such neurons in subjects with poor binocularity.

Evoked Potentials↗
PubMed1978

Iontophoresis of enkephalins potentiates evoked field potentials in the in vitro rat hippocampus.

Effects of iontophoresis of an active opioid peptide, D-Ala2-Met-enkephalinamide (2dA), on evoked field potentials were studied in the hippocampus in vitro preparation. Population spike responses which correspond to the summatory firing of the pyramidal neurons were recorded with glass microelectrodes from the CA1 cell layer. It is found that 2dA greatly enhanced the amplitude of population spike. The excitatory effect was opiate-specific, because it was antagonized by iontophoretically applied naloxone, a potent narcotic antagonist. On the contrary, an inactive enkephalin analog, N-acetyl-(D-Ala2, Lys3)-Met-enkephalinamide, was without effect. It is concluded that opioid peptides exert a specific excitatory action on the pyramidal neurons in the in vitro hippocampus.

Action Potentials↗
PubMed1978

[Brain potentials evoked by stimuli of different intensities in normal subjects and in hysterical psychopathy].

The author studied evoked potentials of 5 different intensitities to electroskin stimula in normals and psychopathic personalities of a hysterical type. It was established that different in their genesis the components of evoked potentials change differently in a change of the stimula intensity. The highest intensity of the stimula is reflected in the early sensory component of evoked potentials, the amplitude of which in normals in an increase of intensity successionaly rises. In hysterical personalities the amplitude of early sensorial components of evoked potentials in an increase of stimula intensity increases only to a certain limit, after which it begins to drop. This phenomenon called "reducing" indicates to a weakness of the sensory systems and relative prevalence of nonspecific brain systems in hysterical psycopathy.

Antisocial Personality Disorder↗
PubMed1976

Evoked potential decrements in auditory cortex. I. Discrete-trial and continual stimulation.

In experiment 1 cats were exposed to sets of clicks (trials) with 1 min inter-trial-intervals to determine if the effects of repetitive stimulation on potentials evoked in the auditory cortex would be cumulative despite discrete-trial stimulation. Evoked potentials were averaged to give one average evoked potential (AEP) for each trial for each electrode; there were four cortical electrodes per subject. To test for dishabituation pawshocks were given between trials 60 and 61. Subjects were paralyzed to insure stimulus constancy. The latency and peak-to-peak amplitude of each component of each AEP was measured; significant amplitude decremented; and decrements were more frequent in components with latencies greater than 15 msec. A few amplitude increments and latency changes were also observed...

Animals↗
PubMedDate not supplied

Auditory nerve and brain stem volume-conducted potentials evoked by pure-tone pips in the CBA/J laboratory mouse.

The short latency (less then 10 ms) auditory nerve and brain stem evoked potentials of Jewett were examined in the inbred CBA/J laboratory mouse. Tone pips, at nine frequencies from 4 to 64 kHz, were used to determine auditory nerve evoked potential (P1) thresholds. Maximum sensitivity occurred at 32 kHz, and a second sensitive area was seen at 56 kHz. With the exception of 32 kHz, as stimulus frequencies were increased in octave intervals, the 90 dB P1 amplitude also increased. P1 latency decreased as the stimulus frequency was increased up to 32 kHz, but this trend reversed with further increases of frequency. However, the P1 amplitude-latency function produced a better agreement of latency and frequency with the travelling wave theory for amplitudes less than 1 micro V, while amplitudes from 2 to 8 micro V were independent of frequency. Latency and amplitude input-output functions for responses from the four auditory brain stem loci suggest that auditory information is differentially processed as a function of frequency at each level, This is especially true for the inferior colliculus, which is most sensitive to 8-KHz stimuli.

Acoustic Stimulation↗
PubMed1978

The cervical somatosensory evoked potential (SEP) in the diagnosis of multiple sclerosis.

Abnormalities of the potential evoked by stimulation of the median nerve and recorded over the cervical spine were found in 59% of patients with multiple sclerosis (MS) this proportion increasing to 69% of those in the definite diagnosis category and to 100% in the severely disabled. Abnormalities were often found in the absence of relevant clinical signs and the method appears to be capable of revealing clinically silent plaques. In patients with a single episode of neurological disease, including retrobulbar neuritis, and at least compatible with the onset of MS, the proportion of abnormalities did not rise above 18%. Only prolonged follow-up will permit assessment of the value of this and other evoked potential techniques in the detection of the early case of the disease.

Adolescent↗
PubMed1979

Brain evoked potentials are functional correlates of induced pain in man.

Electrical potentials evoked by 5 intensities of painful dental stimulation were recorded at the scalp. During testing, volunteers indicated subjective painfulness by verbal pain ratings and visual analogue scales. Evoked potentials (EPs) to each intensity, observed between 50 and 400 msec, were characterized by 4 waveform components. The peak-to-peak amplitudes, but not the peak latencies, of all 4 EP components systematically increased with increased stimulation. The amplitudes of the two earlier components correlated with stimulus intensity when the effect of subjective painfulness was controlled, but this was not the case for the later components. In contrast, the amplitudes of the two later components were associated with subjective painfulness but not with stimulus intensity. A strong linear relationship was observed between subjective painfulness and peak-to-peak amplitude for the EP component observed between 175 and 260 msec. The data suggest that the earlier EP components may reflect sensory transmission processes while the later components indicate brain activity when pain is perceived.

Adult↗
PubMed1977

Differential enhancement of early and late components of the cerebral somatosensory evoked potentials during forced-paced cognitive tasks in man.

1. Cerebral potentials evoked by random sequences of electrical stimuli to four fingers were recorded in intact man performing selective attention tasks. Eye movements and other artifacts were excluded from the averaged traces. Different finger stimuli were designated as targets to be mentally counted in alternate runs of each experiment. The high mean random rate of stimuli (150/min) fully involved the processing capacities of the subject. Vigilance changes or differential expectancy effects were excluded by the reciprocal random design with four different sensory channels. Task-related enhancements of somatosensory evoked potentials (s.e.p.) components were estimated by comparison with the s.e.p.s to physically identical finger stimuli recorded in runs when the subject attended signals in the opposite hand. The experimental design avoided subject's fatigue.2. The primary s.e.p. components N(20) and P(45) were not significantly influenced and this excluded centrifugal gating of the corticipetal signals as a mechanism.3. The earliest task-related changes in s.e.p. occurred 55-135 msec (mean 77.7 msec) after the target finger stimuli. In most cases the negative N(140) component was markedly enhanced both for target signals and for non-targets in the adjacent finger of the same hand. However, in several subjects the targets elicited a positive P(100) component instead. Both N(104) and P(100) were larger at the contralateral parietal focus than ipsilaterally. They were definitely smaller at the vertex and frontal scalp locations.4. Enhancements of N(140) were not observed in similar random four-finger experiments carried out at a 4 times slower mean rate, but they occurred in a bisensory paradigm with finger shocks and acoustic clicks at that slower rate.5. A large positive P(400) component was only elicited by target stimuli. Its voltage was maximum over the parietal region and was equal on both sides.6. At least three categories of components can be differentiated in the cortical s.e.p. on the basis of their time domains (roughly 18-70 msec, 70 to 200-250 msec and over 200 msec after the finger stimuli), cerebral hemispheres topography and cognitive parameters. Verbal instructions defining specific perceptual tasks can to a large extent switch on and off the components of the second and third categories when the processing resources of motivated subjects are fully committed in a well designed forced paced paradigm. In certain individuals physiological evidence for a different ;stimulus set' processing of target (P(100)) and non-target (N(140)) signals was documented for the first time.

Adult↗
PubMed1977

Evaluation of brain function in severe human head trauma with multimodality evoked potentials. Part 1: Evoked brain-injury potentials, methods, and analysis.

Methods for obtaining multimodality evoked potentials, somatosensory, visual, auditory, and auditory brain-stem potentials in patients with severe head trauma are described. A method of analyzing abnormal multimodality evoked potentials (graded evoked brain-injury potentials) is proposed that defines the degree of abnormality of the electrophysiological data and expresses it simply in four grades per modality. Data from 20 normal subjects are given for comparison with the abnormal data obtained from 51 patients with head trauma.

Acoustic Stimulation↗
PubMed1977

Automatisation of a localising technique in aphasia based upon averaged evoked potentials.

Averaged evoked potentials were utilised as a localising technique in aphasia. Based on a set of measurements extracted from various evoked potentials, subjects from four diagnostic categories were correctly classified in more than 70% of the cases. The measurements were derived from amplitudes and latencies of significant peaks which were selected by human judgement from plots of the recorded evoked potentials. An algorithm has been developed which simulates the manual procedure and reduces the processing time per patient by several magnitudes. The automated method yields results which are more consistent with expected results than those from the manual method. The percentage of correct classification is in both cases essentially the same.

Aphasia↗
PubMed1979

Locally evoked potentials in slices of rat neostriatum: a tool for the investigation of intrinsic excitatory processes.

Field potentials, extracellular unitary discharges and intracellular potentials evoked by intrastriatal stimulation were recorded from slices (thickness 200-400 micron) of rat neostriatum maintained in an artificial medium. The field potentials consisted of two negative waves appearing at latencies of 0.5-1.5 ms (N-1) and 2-4 ms (N-2). Extracellular unitary records showed two typed of discharges, one with short but constant latencies at threshold level stimulation and the other with longer and variable latencies. In intracellular recordings the late discharge was seen to arise from EPSPs. Based on the intra- and extracellular unitary records, N-1 was identified as the population spike of antidromically or directly activated unitary discharges and N-2 as that of orthodromically activated discharges. This interpretation was substantiated by the fact that the N-2 potential was blocked in a perfusion medium containing a lower Ca++ or a higher Mg++ concentration than the standard solution. Neither interruption of ascending neostriatal inputs nor decortication 14 days prior to recording altered the configuration of the locally evoked potentials or the probability of synaptically driven discharge occurrence. Thus by intrastriatal stimulation, neostriatal neurons are activated antidromically or directly and/or orthodromically through intrinsic excitatroy synapses. Since the intracellular recordings showed that neostriatal neurons can be well preserved, this preparation can be regarded as a useful tool for electrophysiological and neuropharmacological investigations on intrinsic excitatory processes in the neostriatum.

Afferent Pathways↗
PubMed1979

Field potentials evoked in the subiculum following postsynaptic discharge of hippocampal pyramidal neurons.

Evoked potentials, represented by population spikes and slow waves, have been recorded from the subiculum, along its whole dorso-ventral extent, following postsynaptic activation and discharge of hippocampal pyramidal neurons. These potentials can be associated with synaptic excitatory effects generated on radially oriented neurons by hippocampal impulses reaching the subiculum at any dorso-ventral level, according to a segmental organization.

Animals↗
PubMed1979

The polarity inversion of scalp potentials evoked by upper and lower half-field stimulus patterns: latency or surface distribution differences?

Evoked potentials to patterned stimulation of the upper and lower half of the visual field are generally inverted in polarity. Two conflicting proposals have been made to explain this effect, both based on surface distribution studies of pattern-reversal and/or pattern-onset VEPs. The first suggests that this polarity inversion is due to differences in surface distribution of corresponding components of constant latency; the second that it is due to differences in the latencies of peaks of similar surface distributions in the upper and lower half-field responses. Experimental evidence is here presented which supports the first explanation for the case of the pattern-onset VEPs. These results, which illustrate how different components in the same response can be identified from the selective adaptation effects of pre-exposure to outline patterns, show that there is no difference in latency of components of corresponding properties in the upper and lower half-field VEPs.

Electroencephalography↗
PubMed1979

Hemisphere contributions to the composition of the pattern-evoked potential waveform.

The transverse distribution of scalp-recorded potentials evoked by pattern reversal stimulation was studied in 50 healthy subjects. In most individuals the full-field responses were symmetrical over the occipital scalp, but important variations in distribution, symmetry and waveform were recorded in some cases. Asymmetrical responses were similar for each eye (i.e., they were "uncrossed" or homonymous asymmetries). Full-field peak latencies and amplitudes in the lateral channels were more variable than those at midline electrodes. Half-field responses were markedly asymmetric with well-lateralised components widespread over occipital-parietal scalp. In contrast to the full-field responses, component values measured near the midline were less consistent than those from lateral channels due to waveform distortions in this area ("transitional zone"). Upper field stimulation is particularly likely to produce such midline waveform distortions. Activity recorded from the scalp contralateral to the half-field stimulated shows more inter-individual and inter-hemispheric variation than that recorded from ipsilateral electrodes. Variants in the full-field waveform can be accounted for by relative differences in amplitude and distribution of the ipsilateral and contralateral components from each half field. The algebraic sum of these half-field components does not differ significantly from the components of the separately recorded full-field response. Furthermore, responses from the surviving half-field in patients after total hemispherectomy contain all the ipsilateral and contralateral half-field components seen in healthy subjects.

Dominance, Cerebral↗
PubMed1977

[The relationship of amplitude of visual evoked potentials to side length of rectangular stimulus pattern and to abruptness of stimulus alternation (author's transl)].

Cortical potentials evoked by viewing checkerboard pattern reversal stimuli as well as horizontal and vertical rectangular pattern reversal stimuli were recorded. The amplitude of the cortical evoked responses decreased with increasing side length of the rectangular pattern and decreasing velocity of the pattern reversal. Psychophysical and electrophysiologic findings are compared with these data and their clinical relevance is discussed.

Adaptation, Ocular↗
PubMed1978

Accuracy of evoked potential refractometry using bar gratings.

We recorded cortical potentials evoked by phase-alternating square-wave gratings. Significant effects of varying the refractive power of the eye are obtained only at 5 cycles/degree (cy/deg) and above. The extrapolation to zero amplitude of the evoked response as a function of spatial frequency predicts the psychophysical visual acuity even for the myopic eye. As the sensitivity of meridional refraction using sufficiently fine bar gratings is better than 0.5 D it provides a suitable means for the measurement of astigmatism.

Astigmatism↗