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At least 379 records · Page 21Linked to original sources
PubMed1986

Brain responses to sine wave modulated light (SML): reliability and relationship to spontaneous EEG.

Brain activity elicited by sine wave modulated light and spontaneous EEGs were obtained from 11 healthy adult males on two separate occasions. Within-subject correlations (test-retest correlation coefficients) for SML responses were high, and comparable to reliability estimates of spontaneous EEG activity in this sample. Reliability of the spontaneous EEG was evaluated using two measures: absolute and relative power. Although their magnitudes were comparable, the test-retest correlation coefficients for the right occipital were consistently higher than those of the left using absolute measures; this pattern was not reflected by test-retest correlations based on relative EEG measures. Finally, the SML responses to 5, 15, 18 and 24 Hz stimulation frequency rates correlated most highly with absolute measures of spontaneous EEG beta, whereas the SML response to 10 Hz stimulation yielded the highest correlations with spontaneous alpha activity.

Adult↗
PubMed1980

Computer identification of waves in the auditory brain stem evoked potentials.

The high reliability with which the waves I through V can be identified in auditory brain stem potential (BAEP) recordings suggests the possibility of using the computer to identify the peaks. This paper examines the application of a smoothing algorithm in which detection of zero crossings in the derivative array of the averaged potentials is used to identify waves I--V in clinical BAEP recordings. A comparison of computer wave identification with human evaluation is presented. The results suggest that computer evaluation cannot entirely replace 'manual' evaluation of the waves, but can expedite analysis and alert the clinician to potentially abnormal responses.

Acoustic Stimulation↗
PubMed1986

Development of auditory-evoked potentials in the cat. II. Wave latencies.

Brain stem and forebrain auditory-evoked potentials were studied parametrically during the first 90 postnatal days in unanesthetized kittens using tonal and click stimuli. This paper describes changes that occur in transmission time through the auditory pathway during development by analyses of the maturational time courses of latencies associated with waves of both auditory brain stem responses (ABR's) and late-occurring auditory-evoked potentials (AER's), recorded subdermally from the vertex. In response to click stimuli, ABR latencies were found to decay rapidly early in postnatal life and more slowly after the third postnatal week. Those trends were modeled as a two-stage sequential process, with a linear stage occurring between 7 and 18 postnatal days followed by an exponential stage during which adult latencies were achieved. AER latencies changes during development were less complicated, and followed a single-stage exponential time course. When threshold influences were taken into account--that is, when data were adjusted so that sensation level (SL) was constant across age--the latency-maturation curves associated with all ABR waves were adequately described by a single exponential, and latencies recorded from young animals were substantially shorter than latencies associated with the same aged animals when analyses were carried out with constant sound-pressure level (SPL) stimuli across age. In addition, the difference function, generated when isoasymptotic SPL and SL latency versus age functions were subtracted from one another, was also represented by an exponential curve, suggesting that at least two processes underlie the latency decay that occurs during postnatal development. Evoked responses to tonal stimuli throughout development were consistent with the basoapical developmental gradient that is observed anatomically.

Aging↗
PubMed1987

[The effect of glycerol on EEG-abnormality (polymorphic delta wave) in patients with brain tumors].

The effect of intravenous infusion of 10% glycerol on polymorphic delta waves of EEG was investigated in 13 patients (15 studies) with brain tumors in cerebral hemisphere. The delta waves were analyzed by two-dimensional EEG topography and power spectrum of delta waves (P(delta)) over the tumor, adjacent, and distant regions in the same hemisphere to the tumor, and ipsi- and contralateral hemispheres to the tumor. The data focus of EEG topography was well corresponded to the tumor and surrounding brain edema which visualized by x-ray CT-scan. In the patient with brain tumors with marked brain edema (group A, 11 studies), EEG topography showed marked reduction of delta focus within 20 minutes from the end of intravenous infusion of glycerol, and returned to preinfusion distribution within 60 minutes. In patients with absent to minimum brain edema (group B, 4 studies), delta focus showed the tendency to enlarge and returned to preinfusion state at 60 minutes after the end of glycerol infusion. In patients of group A, P(delta) of ipsilateral hemisphere to tumor decreased at the end of glycerol infusion, and showing maximal reduction ratio (30%, p less than 0.01) at 20 minutes, re-increased there-after. In group B, P(delta) of ipsilateral hemisphere showed no definite changes after the glycerol infusion. P(delta) of contralateral hemispheres in patients of both group A and B, showed similar reduction ratio and time course to those of ipsilateral hemisphere of group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Computer recognition of brain stem auditory evoked potential wave V by a neural network.

A neural network simulator was used to create a connectionist model for the recognition of the peak of wave V of the brain stem auditory evoked potential (BAEP) test. Wave forms were selected from BAEPs performed in the last four years at the University of Pittsburgh Presbyterian University Hospital (PUH). The ipsilateral and contralateral wave forms were digitized and then sampled at 0.1 msec intervals using linear interpolation. The resulting amplitudes were normalized to the range less than -1, 1 greater than. The normalized amplitudes were used as the initial activation values for the processing elements of the input layer. The desired outputs (the target locations for wave V) were determined by adjusting the latencies recorded by the physician interpreter for any distortion in the digitizing process. The location of wave V was represented in the output layer by setting the output element which correspond to the target location and its immediate neighbors to high activation levels and all the remaining output units to zero activity. Two network architectures, differing only in the hidden unit layer, with 40 and 16 hidden units respectively, were used. The networks were trained using standard back-propagation. Several trials from different starting points were performed for each architecture. The training set was composed of the wave forms resulting from the stimulation of 50 ears. The best network, found after 60 epochs (3000 presentations) was able to correctly identify 17 out of 20 cases (85%) from a set of test cases which were independent from the training set.

Diagnosis, Computer-Assisted↗
PubMed1980

A study of cases with partial disappearance of the waves in the auditory brain stem response.

Twenty cases which showed partial loss of ABR waves were reported. Only wave I was recorded in 18 ears tested. Wave I and II; I-III; and I-IV responses were observed in four, eight, and five ears tested, respectively. Cases included pontine glioma (8), acoustic tumor (4), West syndrome (2), leukodystrophy (2), facial neurinoma (1), epidermoid tumor (1), pontine bleeding (1), and unknown cause (1). Fourteen of 20 were tumor cases. This fact indicates that if the ABR shows partial loss of waves, the examiner should first suspect the space-occupying lesions of the brain stem.

Brain Neoplasms↗
PubMed1992

Computer recognition of brain stem auditory evoked potential wave V by a neural network.

A neural network simulator was used for the recognition of the presence and location of the peak of wave V of the brain stem auditory evoked potential (BAEP) test. Waveforms selected from BAEPs performed in the last 4 years at the University of Pittsburgh Presbyterian University Hospital were digitized and sampled, and the resulting amplitudes were normalized. A training set was composed of the waveforms resulting from the stimulation of 50 ears. The normalized amplitudes were used as the initial activation values for the networks. The desired outputs (the target locations for wave V) were represented in the output layer by setting the output element, which corresponded to the target location and its immediate neighbors, to high activation levels, and all the remaining output units to zero activity. Two network architectures, differing only in the hidden unit layer, with 40 and 16 hidden units, respectively, were trained by using standard back-propagation. Several trials from different starting points were performed for each architecture. The best network, found after 60 epochs (3,000 presentations), was able to correctly identify 17 of 20 cases (85%) from a set of test cases that were independent from the training set.

Evaluation Studies as Topic↗
PubMed2003

Localization of fast MEG waves in patients with brain tumors and epilepsy.

It was investigated if single dipole analysis of spontaneous fast waves (>8 Hz) can be used to determine the location of the epileptic focus. Automatic dipole analysis was applied to MEG data of 25 patients with intracranial tumors and epilepsy. The frequency range of 8-50 Hz was divided into standard EEG bands. MEG results were overlaid on the MRI scans of the patients. Dipoles describing fast wave fields were located in the parietal/occipital cortex, and not at tumor border zones. In the cases that the dipoles were lateralized there was no clear preference to be located ipsi or contralateral to the tumor. However the generators of epileptic activity in these patients are thought to be located in the border areas of the tumors. Therefore it seems unlikely that the dipole locations describing fast waves are related to the epileptic zones in patients with brain tumors and epilepsy. A remarkable finding is that lateralized dipoles tend to be located in the right hemisphere and not in the left hemisphere. This appears to reflect an asymmetry of possibly normal background activity.

Adult↗
PubMed1988

Microwave-induced thermoelastic pressure wave propagation in the cat brain.

This paper presents direct measurements of acoustic pressure wave propagation in cat brains irradiated with pulsed 2.45-GHz microwaves. Short rectangular microwave pulses (2 microseconds, 15 kW peak power) were applied singly through a direct-contact applicator located at the occipital pole of a cat's head. Acoustic pressure waves were detected by using a small hydrophone transducer, which was inserted stereotaxically into the brain of an anesthetized animal through a matrix of holes drilled on the skull. The measurements clearly indicate that pulsed microwaves induce acoustic pressure waves which propagate with an acoustic wave velocity of 1523 m/s.

Acoustics↗
PubMedDate not supplied

Effect of hyperthermia on brain auditory evoked potentials in the conscious sheep.

To assess the effect of hyperthermia on brain function of conscious sheep, auditory evoked potentials (AEPs) were studied. Auditory brain-stem potentials (BAEPs) and mid-latency potentials (MLPs) to monaural rarefaction click stimuli were recorded as the potential difference between midline skull screws and mastoid electrodes. Hyperthermia was induced by a combined passive heat and work stress in a climatic chamber. Brain temperature was monitored with a thermistor in the parietal lobe. Hyperthermia resulted in a progressive decrease in the absolute latencies of the BAEPs up to the time of heat-induced collapse. There was a similar decrease in the latencies of MLPs up to a brain temperature of 42.0 degrees C +/- 0.3 degrees C (mean +/- S.D.), while there was prolongation of latencies at higher brain temperatures. The wave form of the BAEPs (I-V) persisted up to the time of heat-induced collapse. In contrast those of MLPs showed reproducible changes in the form of flattening or splitting of the Pa wave at a brain temperature of 41.8 degrees C +/- 0.7 degrees C, reversible with cooling. That temperature was also associated with behavioural changes reversible with cooling. A complete loss of the MLP waves occurred at a brain temperature of 42.9 degrees C +/- 0.6 degrees C which was not reversed with whole body cooling and immediately preceded the heat-induced collapse. This study demonstrates that hyperthermia in the conscious sheep produces potentially damaging effects on the central nervous system once a critical brain temperature (41.8 degrees C +/- 7.0 degrees C) is exceeded and that the MLPs are more sensitive indicators of this damage than BAEPs.

Animals↗
PubMed1976

Body position and cerebrospinal fluid pressure. Part 1: clinical studies on the effect of rapid postural changes.

Cerebrospinal fluid (CSF) pressure was recorded in 149 patients and arterial blood pressure (BP) in 11 patients while moving between lateral and sitting positions. Rapid tilting initiated waves in BP and CSF filling pressure. The postural CSF pressure wave manifested itself either as a transient or as a stationary wave similar to a plateau wave. When patients sat up, transient waves had amplitudes up to 550 and stationary waves up to 1000 mm H2O. When they lay down, transient waves had amplitudes up to 800 mm H2O. Stationary waves were found only among patients with elevated intracranial pressure and a diseased brain. The waves were mainly caused by changes in cerebral blood volume probably reflecting the postural BP wave and brain autoregulation. Most patients with stationary and large transient waves also manifested clinical symptoms. These symptoms were aggravated when a craniospinal block developed in the sitting position, and were reduced or avoided when the tilting was performed slowly over 2 to 3 minutes.

Blood Pressure↗