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At least 37 records · Page 2Linked to original sources
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↗
PubMed1979

Acoustically evoked potential: dependence upon age.

The slow components of the potentials evoked acoustically by pure tones (1 kHz, 0 to 90 dB HL) were compared between two groups of subjects. All subjects of one group were 22 years old; the members of the other group had an average age of 63 years. The P2-latencies of the older subjects were significantly shorter for 60, 75 and 90 dB HL than those of the younger group. This finding was interpreted as a sign of a decreased efferent inhibition of several nuclei of the auditory pathway in the older subjects. No significant difference between the two groups could be found for the amplitudes (N1/P2), the exponent of the intensity function, or the latencies of P1 and N1.

Acoustic Stimulation↗
PubMed1977

Influence of succinylcholine on middle component auditory evoked potentials.

Auditory evoked potentials in the middle component time domain (post-stimulus, 8 to 50 msec) were recorded in response to 1,000-Hz tone pips in a normal-hearing adult subject. Electromyographic (EMG) responses in response to ulnar nerve shocks were recorded from the ipsilateral hypothenar muscles. With the assistance of an anesthesiologist, data were collected during a normal resting state, a state of light sedation, and a state of complete skeletal muscle paralysis from succinylcholine administration. During the paralyzed state, there was abolition of the normal EMG responses seen in the resting and sedated states. The auditory evoked potentials, however, appeared unchanged during the paralyzed state, indicating that they were not of myogenic origin.

Acoustic Stimulation↗
PubMed1975

Actions and interactions of dipropylacetate and penicillin on evoked potentials of excised prepiriform cortex of guinea pig.

Slices from guinea pig brain containing the lateral olfactory tract (LOT) and the prepiriform cortex were studied in vitro. Field potentials, evoked by stimulation of the LOT, were recorded extracellularly. This field potential comprises a compound action potential, a surface negative wave (identified as EPSP), and superimposed positive peaks ("population spikes" or PSs) reflecting postsynaptic activity. In a previous article the penicillin-induced increase of EPSP and of both amplitude and number of PSs was described. Now we are reporting the slight depression of EPSP and PSs and the prevention of the appearance of penicillin-induced PSs by an antiepileptic drug sodium dipropylacetate (Depakine). The effect was dose-dependent. Models explaining the effects of penicillin and dipropylacetate are discussed.

Animals↗
PubMed1976

Localization of evoked potentials in the digastric, masseteric, supra- and intertrigeminal subnuclei of the cat.

Extracellular focal potentials were evoked and mapped in the trigeminal motor nucleus and its surrounding borderzone in the cat. Graded electrical stimulation was used for orthodromic and antidromic excitation of the masseteric and digastric motoneurones and for orthodromic stimulation of the lingual and inferior alveolar nerves. The method of referring Horsley Clarke coordinates of microelectrode recording positions to their location of the actual histological section was studied and the total error affecting the method was calculated for the H, AP and L axes. The characteristics and the distribution of the evoked focal potentials were described and related to the histological section from the actual experiment. A phase reversal of the negative focal potential evoked by the lingual and inferior alveolar nerves in the main sensory nucleus and in the intertrigeminal nucleus was observed to indicate the dorso-lateral border of the motor nucleus. Other borders were given by the antidromic potentials evoked in the nucleus. Digastric motoneurones were found medially in the caudal third and ventro-medially in the middle third of the motor nucleus. The masseteric motoneurones were located laterally in the middle and rostral thirds of the nucleus. Potentials evoked in the supratrigeminal and intertrigeminal subnuclei, adjacent to the motor nucleus, were considered and discussed in relation to the available evidence of interneurones subserving trigeminal reflex arcs.

Action Potentials↗
PubMed1976

Somatosensory evoked potential in man: far field potentials.

Three short latency positive potentials evoked by median nerve stimulation were recorded from the scalp, nose and ear of 11 normal adult subjects in leads where the hand or knee contralateral to the side of stimulation was used as the reference site. The short latencies and positive polarity of these components suggest that they are volume conducted far field potentials. Evidence is presented which suggests that the first potential arises in peripheral nerve fibers. Brain stem and dicencephalic structures are suggested as possible sources for the second and third potentials. The configuration of the response to median nerve stimulation recorded over the cervical spine in ear and hand reference recordings was different. Evidence is presented which suggests that this occurs because the electrode placed on the ear records the far field potentials described in the above paragraph. A far field potential was also recorded in hand--knee leads contralateral to the stimulated median nerve.

Adolescent↗
PubMed1979

Effect of stimulus intensity on short latency somatosensory evoked potentials.

The peripheral and central potentials evoked by percutaneous electrical stimulation of the median nerve were investigated in a group of neurologically normal subjects. We found: (1) Motor threshold stimulation gave consistently submaximal responses and probably does not represent an optimal intensity for routine use. (2) The sum of motor plus sensory threshold gave potentials which were consistently at, or close to, maximal in amplitude. This intensity was comfortable for all subjects. (3) When stimulating at intensities above motor threshold, the increase in amplitude of peripheral potentials markedly exceeded that of the central potentials. There was evidence suggesting that amplitudes would decline at very high stimulus intensities. (4) The P13 peak latency and the P13--N9 interpeak latency declined and the N17--P13 interpeak latency increased with increasing intensities of stimulation. The N9 and N18 peak latencies remained stable.

Adult↗
PubMedDate not supplied

Diagnostic role of brain-stem auditory evoked potentials in neurobrucellosis.

Evoked potential audiometry and brain-stem auditory evoked potentials were evaluated in 15 patients with systemic brucellosis in whom brucella meningitis was suspected clinically. In 8 patients cerebrospinal fluid (CSF) was abnormal with high brucella titre, and evoked potentials were abnormal in all of them. In 7 patients the CSF was normal and evoked potentials were also normal. Brain-stem auditory evoked potential abnormalities were categorised into 4 types: (1) abnormal wave I, (2) abnormal wave V, both irreversible, (3) prolonged I-III interpeak latencies, and (4) prolonged I-V interpeak latencies, both reversible. These findings are of important diagnostic value and correlate well with the clinical features, aetiopathogenesis and final outcome.

Adolescent↗
PubMed1979

Contrast sensitivity of the human neonate measured by the visual evoked potential.

Visual evoked potentials (VEPs) were recorded from a total of 97 1- to 10-day-old infants, with phase-reversing sinusoidal grating stimuli. The grating contrast or spatial frequency for which 50% of infants gave a statistically significant VEP was taken as a measure of threshold. This procedure yielded an estimate of neonatal acuity of 0.85 cycles/degree and an optimal contrast threshold of 50%. VEPs from an older infant showed good agreement with behavioral measures of sensitivity on the same individual. Comparison of the neonatal VEP results with behavioral data from 5-week-old infants, suggests little change in visual performance over the first month of life.

Evoked Potentials↗
PubMed1976

Parameters of temporal recovery of the human auditory evoked potential.

Auditory evoked potentials (AEPs) to tone pips at three monopolar scalters were systematically varied: tone intensity (3.0, 1.5 and 0.75 sec), and direction of attention. Interstimulus intervals were computed separately for the 9 different combinations of the three possible first prior intervals (intervals between the test stimulus and the stimulus immediately preceding it) and the three possible second prior intervals (intervals between the stimulus preceding the test stimulus and the stimulus prior to that). Our results show that temporal amplitude recovery of N1 and P2 can be based solely on the first prior interval had not effect on amplitude. Furthermore, they show that it is inadvisable to use combined N1-P2 amplitude measures since the two peaks appear to be governed by separate processes. Recovery for N1 was different from that of P2, N1 showed no intensity effects while P2 did, and N1 and P2 had different topographic distributions. Directing attention to the tones did not affect N1 or P2 amplitudes but caused a highly significant increase in both N1 and P2 latency. Attention to the tones also produced a frontal negative baseline shift following them.

Adult↗