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Results for “Brain waves”

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At least 973 records · Page 54Linked to original sources

PubMed1990

[Somatosensory evoked potentials in patients with hypoxic coma--correlation with neurologic prognosis].

Somatosensory evoked potentials to median nerve stimulations were recorded in 21 patients with hypoxic coma within 24 hours from the onset. According to the neurologic prognosis, the patients were classified into 4 groups, such as I, complete recovery (5 patients), II, partial recovery (3 patients), III, vegetable state (8 patients), IV, brain death (5 patients). Measurements performed include central conduction time (N13-N20 interpeak latency) and amplitude ratio between N20 and P25. As N20 and P25 disappeared in 3 of 8 vegetable patients and all of brain death patients, disappearance of these waves indicates poor neurologic prognosis. Central conduction time showed no significant difference. Amplitude ratio between N20 and P25 (P25/N20) revealed significant decrease in vegetative patients for normal control subjects, complete recovery and partial recovery patients (p less than 0.05). Measurement of this ratio in early phase is useful to predict neurologic outcome in patients with hypoxic coma.

Adolescent↗

PubMed2026

Assessing the effects of non-invasive transcranial electrical stimulation (tACS and tDCS) on electrophysiological sleep parameters - a systematic review.

Transcranial electrical stimulation (tES), including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), is considered a safe method to modulate cortical activity and endogenous brain oscillations. Given the therapeutic potential of tES across various clinical conditions and the central role of sleep in restoration and memory consolidation, numerous studies have investigated its effects on sleep and sleep-related parameters, yielding inconsistent results. This systematic review provides an up-to-date synthesis of 51 studies assessing the impact of tES on objectively measured electrophysiological sleep outcomes in both healthy individuals and clinical populations. The reviewed studies demonstrate heterogeneous effects, reflecting substantial variability in study designs. Nonetheless, consistent trends emerge, including reduced NREM1 and increases in total sleep time, NREM2, and NREM3 following tES. Moreover, slow-oscillatory tES increased slow-wave power during sleep. Here we show that tES, particularly slow-oscillatory tES, may positively influence sleep architecture and continuity by modulating endogenous brain oscillations. However, due to heterogeneous stimulation protocols, inconsistent findings, the limited number of significant effects and substantial risk of bias the current evidence remains inconclusive. Well-designed, large-scale trials targeting specific sleep outcomes are needed to clarify the therapeutic potential of tES.

Humans↗

PubMed1991

Intracranial pressure waves and intracranial hypertension in rats with ischemic fulminant hepatic failure.

Brain edema and intracranial hypertension are a major cause of death in fulminant hepatic failure. We have shown that brain water measured in rats after hepatic devascularization (portacaval anastomosis followed in 24 to 48 hr by ligation of the hepatic artery) increases with the progression of encephalopathy. In this study, we examined whether intracranial hypertension develops in this model of fulminant hepatic failure. Using a fiberoptic pressure transducer, intracranial pressure rose from 3.3 +/- 1.1 mm Hg to 23.7 +/- 2.7 mm Hg (mean +/- S.E.M.) by the time the corneal reflex was lost; intracranial pressure was unchanged in control rats. Immediately after ligation of the hepatic artery, intracranial pressure was normal and remained stable until the last hours of the experiment, when it progressively rose, suggesting a loss of intracranial compliance. In addition, sudden and short episodes of marked increases in intracranial pressure (greater than 50 mm Hg) not related to seizure activity markedly decreased cerebral perfusion pressure. Internal carotid artery blood flow, an indirect measure of cerebral perfusion, decreased 29% +/- 12% by the end of the experiment. The time elapsed from ligation of the hepatic artery until loss of the corneal reflex (range 340 to 940 min) was related to the change in cerebral perfusion pressure, suggesting that an increase in systemic arterial pressure at the time of the initial rise in intracranial pressure may result in an increased length of survival. In this animal model, widely used to study the pathogenesis of hepatic encephalopathy, intracranial hypertension invariably appears in the terminal phase of the course. The development of intracranial pressure waves may be an indication that brain herniation is imminent.

Animals↗

PubMedDate not supplied

[Validation of the use of the CO2 laser in operations on the brain].

It is reported that the CO2-laser can be used in operations on the brain. Information is given on the response of the brain structures to irradiation with a wave length of 10.6 microns. The optimal regimens of the device operation were elaborated depending on the concrete object of the various stages of the surgical intervention. The medical laser device Skal'pel'-1 was used in the clinic in 109 operations. The low traumatization of such operations and the favourable course of the postoperative period are pointed out.

Animals↗

PubMedDate not supplied

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%).

Adult↗

PubMedDate not supplied

Cocaine and pseudococaine: comparative effects on electrical after-discharge in the limbic system of cats.

The effects of cocaine and its dextroisomer pseudococaine on electrical after-discharge (AD) evoked by electrical stimulation of the hippocampus or amygdala were studied in cats with electrodes implanted in the brain. Intravenous injection of cocaine (2.0 to 4.0 mg/kg doses) produced a suppressive effect on the AD while producing low-voltage fast waves (LVFWs) in the electrical activities of the brain (EEG) associated with behavioral excitation. In contrast, pseudococaine at the same dose as cocaine failed to show a significant suppressive effect on the AD except at high doses (5.0 mg/kg). Pseudococaine produced high-voltage slow waves (HVSWs) in the EEG associated with behavioral depression. A linear dose-response relationship was observed for the suppressive effect of cocaine on the AD. The results suggested that the limbic system may be involved as a primary site of action of cocaine in the central nervous system (CNS).

Amygdala↗

PubMed1989

Abnormal brain-stem function (brain-stem auditory evoked response) correlates with acoustic cry features in term infants with hyperbilirubinemia.

We hypothesized that changes in brain-stem auditory evoked responses related to bilirubin would be associated with changes in cry because of the anatomic proximity in the brain stem of cranial nerves 8 (auditory) and 9 to 12 (vagal complex, which controls cry). Brain-stem auditory evoked responses and computerized cry analysis were used to study the concurrent effects of moderate hyperbilirubinemia on auditory function and cry. Fifty term infants were divided equally into two groups on the basis of serum bilirubin concentrations: low (less than 8 mg/dl; 136) mumol/L and moderate (10 to 20 mg/dl, 170 to 342 mumol/L). Forty-three infants had successful tracings of brain-stem auditory evoked responses recorded with a Cadwell model 5200A evoked response unit during two successive trials, and a cry recording of each infant was analyzed by computer. The moderate serum bilirubin group had an increase in percent cry phonation (p less than 0.02) and an increase in the variability of the first formant (p less than 0.04) in comparison with the low serum bilirubin group. Serum bilirubin values correlated positively with brain-stem conduction time (r = 0.36, p less than 0.01), percent phonation (r = 0.42, p less than 0.004), and variability of the first formant (r = 0.39, p less than 0.02). Percent phonation, the voiced component produced by increased neural control, correlated with the interpeak of waves latencies I to III (r = 0.32, p less than 0.03) and brain-stem conduction time (wave I to V) (r = 0.35, p less than 0.01). We conclude that hyperbilirubinemia affects adjoining areas of the brain stem that control hearing and cry production.

Brain Stem↗

PubMed1975

Electrocardiographic findings in brain death; description and presumed mechanism.

Electrocardiogram changes and pharmacologic responses were studied in 28 cases of brain death. Cardiac activity in this condition is possibly determined by the dynamic balance between the depressant action of hypothermia and the stimulating action of the sympathetic nervous system (without any vagal or central influence). The electrocardiographic alterations are the results of this dual influence, and are probably characteristic of this condition. In the initial stage of brain death the ECG shows J waves in the terminal part of the QRS, prolongation of the QT interval and the ST-T changes; in the advanced stages, progressive showing of the heart rate and the depolarization and repolarization processes are observed (manifested by gradual accentuation of the findings mentioned above); in the terminal stage dynamic electrocardiographic changes (among them, progressive depression of sinus activity, atrial fibrillation, atrioventricular and intraventricular conduction disturbances and severe ST-T changes) appear. It is possible that additional factors, like metabolic changes and possible myocardial damage in some instances, may have some influence on the electrocardiographic pattern. Final conclusions cannot be drawn from these preliminary observations. The atropine test was found to be an efficient and simple diagnostic aid in cases of brain death.

Adolescent↗

PubMed1987

Study of the constant wave form of ML-AEP in humans.

Wave forms of ML-AEP were studied in 21 healthy subjects and in 4 cases with well localized lesions in the brain. In order to obtain and define the constant wave form we used 5 mg of diazepam in these subjects. In awake state (before administration of diazepam) two types of muscle activity were observed. Postauricular muscle reflex (PMR), which follows high amplitude Na, Pa and Nb potentials, decreases its amplitude and seems to disappear when No and Po come out in light sleep (after administration of diazepam). The other type of muscle activity is derived from facial and other extracranial muscles associated with face or neck movements and deforms wave form in which we are unable to identify each component. These muscle activities cause the variability of wave form in awake state. In light sleep, wave forms were classified as follows: A, includes all components of ML-AEP; B, no Nb component; C, no No and Po components. The most constant waves are Na and Pa potentials and No, Po are variable in appearance. Sequential recordings from awake to light sleep suggested that No, Po are the remnants of PMR in light sleep. Studies of ML-AEP in 4 cases revealed attenuated or absent Na, Pa and Nb potentials. No and Po are variable in appearance in these cases in spite of different locations of lesions in the brain. These studies seemed to support the idea that No and Po are remnants of PMR in light sleep and the constant wave form of ML-AEP consists of Na, Pa and Nb potentials.

Adolescent↗

PubMed1989

The recording of brain evoked potentials resulting from intra-articular focused ultrasonic stimulation: a new experimental model for investigating joint pain in humans.

Pain was induced in the proximal interphalangeal joint of the index finger in human volunteers using a high powered focused ultrasonic generator. Eighty, 100 ms pulses were applied during each test. This test was repeated at hourly intervals for a period of 5 h. A brain evoked potential with a characteristic wave form was recorded, resulting from the application of these stimuli. A computerised visual analogue scale system was used to measure subject's perception of the painfulness of each stimulus. A significant correlation was found between evoked potential amplitude and mean visual analogue scale score. There was some variation in evoked potential amplitude and mean visual analogue scale score as a result of repeated application of the test but this was not significant over the 5 h time period.

Adult↗

PubMed1992

The relationship between short-term memory capacity and EEG power spectral density.

Multiplying memory span by mental speed, we obtain the information entropy of short-term memory capacity, which is rate-limiting for cognitive functions and corresponds with EEG power spectral density. The number of EEG harmonics (n = 1, 2,..., 9) is identical with memory span, and the eigenvalues of the EEG impulse response are represented by the zero-crossings up to the convolved fundamental, the P300. In analogy to quantum mechanics the brain seems to be an ideal detector simply measuring the energy of wave forms. No matter what the stimulus is and how the brain behaves, the metric of signal and memory can always be understood as a superposition of n pi states of different energy and their eigenvalues.

Brain↗

PubMed2004

Hemodynamic observations on a yogic breathing technique claimed to help eliminate and prevent heart attacks: a pilot study.

OBJECTIVE: This pilot study investigated the hemodynamics of a yogic breathing technique claimed "to help eliminate and prevent heart attacks due to abnormal electrical events to the heart," and to generally "enhance performance of the central nervous system (CNS) and to help eliminate the effects of traumatic shock and stress to the CNS." DESIGN: Parameters for (4) subjects were recorded during a preexercise resting period, a 31-minute exercise period, and a postexercise resting period. SETTINGS/LOCATION: Parameters for subjects were recorded in a laboratory at the University of California, San Diego. SUBJECTS: Parameters for 3 males (ages 44, 45, 67) and 1 female (age 41) were recorded. One (1) subject (male age 45) had extensive training in this technique. INTERVENTIONS: This yogic technique is a 1 breath per minute (BPM) respiratory exercise with slow inspiration for 20 seconds, breath retention for 20 seconds, and slow expiration for 20 seconds, for 31 consecutive minutes. OUTCOME MEASURES: Fourteen beat-to-beat parameters were measured noninvasively and calculated for body surface area to yield: stroke index (SI), heart rate (HR), cardiac index, end diastolic index, peak flow, ejection fraction, thoracic fluid index, index of contractility, ejection ratio, systolic time ratio, acceleration index, and systolic, diastolic, and mean arterial pressures (MAPs). Left stroke work index (LSWI) and stroke systemic vascular resistance index (SSVRI) were calculated. RESULTS: We report on SI, HR, MAP, LSWI, and SSVRI and how they can help to describe hemodynamicstate changes. This technique induces dramatic shifts in all hemodynamic variables during the 1 BPM exercise and can produce unique changes in the postexercise resting period after long-term practice that appears to have a unique effect on the brain stem cardiorespiratory center regulating the Mayer wave (0.1-0.01 Hz) patterns of the cardiovascular system. CONCLUSIONS: Preclinical studies are warranted to examine the possible long-term effects of this technique that appear to reset a cardiorespiratory brain-stem pacemaker. We postulate that this effect may be the basis for the purported yogic health claim.

Adult↗

PubMed1988

Evoked potentials in basilar artery thrombosis: correlation with clinical and angiographic findings.

In 28 patients with vertebro-basilar or basilar artery thrombosis brain-stem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs) have been recorded. Visual evoked potentials (VEPs) were recorded in 7 of these 28 patients. In 24 patients the diagnosis was angiographically proven and in 4 patients Doppler sonography and computerized tomography suggested this diagnosis. The BAEP and SEP findings were correlated to clinical and angiographical signs. BAEPs could be classified into 6 different patterns. In more than half of the patients different BAEP patterns from the two ears could be found. A pathological IV/V complex was most often found in comatose patients and in patients with a basilar artery occlusion distal to the anterior inferior cerebellar artery. Prolonged interpeak latency of I-III was mainly found in alert or drowsy patients with caudal occlusions. The frequent occurrence of a BAEP with only wave I preserved, or with no waves preserved, in patients with brain-stem functions suggests that BAEPs are not useful in the diagnosis of brain death when basilar artery thrombosis is suspected. SEPs were either absent bilaterally or else severely altered on one side in all comatose patients. In alert patients, including those with 'locked-in' syndrome, SEPs were never absent bilaterally. Increased N13-N20 interpeak latency was an uncommon finding in this series. There was no correlation between the SEP and the angiographically proven location of the occlusion. In the 'locked-in' syndrome both SEP and BAEP findings were non-uniform. Normal SEPs were sometimes found in combination with severely altered BAEPs, suggesting partial deafferentation. Since basilar artery thrombosis is now a treatable condition, early diagnosis and documentation of functional deficits moves into a more important clinical area than heretofore.

Adult↗

PubMed1983

Prognostic value of brainstem auditory evoked potentials in neonates.

The clinical outcome in 74 children at risk for audiologic or neurologic sequelae of a variety of perinatal insults was correlated with brainstem auditory evoked potentials (BAEPs) in the newborn period. No constant relationship was found between BAEP findings and later hearing status in preterm infants or in infants with severe brain damage. However, persistent patterns of wave I abnormality correctly predicted the presence and type of hearing loss in other infants. Central BAEP abnormalities recorded in preterm infants or in infants who had just suffered anoxia had little predictive value. The abnormalities had greater prognostic value when there was a delay between acute injury and testing. Prognostic errors could be minimized in this population by obtaining repeated recordings at least one month post term and after injury from infants who showed BAEP abnormalities in the neonatal period.

Brain Stem↗

PubMed1998

Changes in brain barbiturate concentration in brain-dead rabbits.

Pentobarbital concentration was evaluated in the brain tissues of brain-dead rabbits. Pentobarbital was infused into the vein of Japanese white male rabbits at 60 mg/kg/h until an isoelectric EEG of the cortex was reached. Brain death was induced by inflation of a balloon catheter placed in the subdural space. The diagnosis of brain death was confirmed by a flat line ABR wave. A significant increase in heart rate, intracranial pressure, and mean arterial pressure, was observed following brain death induction. These parameters returned to below basal values within 60 mm. Immediately after, and at 6 h and 24 h after brain death, each group of rabbits was sacrificed by phenobarbital overdose, and brains were then removed for determination of pentobarbital concentration in the brain tissue. Blood pentobarbital disappeared about 18 h after brain death was induced. Although the brain pentobarbital concentration slightly decreased over time, a high concentration of pentobarbital remained in the brain 24 h after brain death was induced.

Animals↗

PubMed2005

Grouping of brain rhythms in corticothalamic systems.

Different brain rhythms, with both low-frequency and fast-frequency, are grouped within complex wave-sequences. Instead of dissecting various frequency bands of the major oscillations that characterize the brain electrical activity during states of vigilance, it is conceptually more rewarding to analyze their coalescence, which is due to neuronal interactions in corticothalamic systems. This concept of unified brain rhythms does not only include low-frequency sleep oscillations but also fast (beta and gamma) activities that are not exclusively confined to brain-activated states, since they also occur during slow-wave sleep. The major factor behind this coalescence is the cortically generated slow oscillation that, through corticocortical and corticothalamic drives, is effective in grouping other brain rhythms. The experimental evidence for unified oscillations derived from simultaneous intracellular recordings of cortical and thalamic neurons in vivo, while recent studies in humans using global methods provided congruent results of grouping different types of slow and fast oscillatory activities. Far from being epiphenomena, spontaneous brain rhythms have an important role in synaptic plasticity. The role of slow-wave sleep oscillation in consolidating memory traces acquired during wakefulness is being explored in both experimental animals and human subjects. Highly synchronized sleep oscillations may develop into seizures that are generated intracortically and lead to inhibition of thalamocortical neurons, via activation of thalamic reticular neurons, which may explain the obliteration of signals from the external world and unconsciousness during some paroxysmal states.

Animals↗

PubMed2005

Ultrasound contrast agents for brain perfusion imaging and ischemic stroke therapy.

Stroke is one of the major causes of death and disabilities in industrialized countries. Ultrasound imaging is a largely wide spread bedside technique that is easily accessible and valuable in case of emergency but suffers from the fact that the ultrasound wave has to cross the skull for brain imaging. However, ultrasound contrast agents and new contrast-specific imaging modalities have helped to improve the diagnostic quality of transcranial ultrasonography. This review article surveys and discusses the current state of microbubbles technology and the use of contrast-enhanced transcranial ultrasound for the assessment of brain perfusion. Future aspects and expectations in contrast agent functionality, such as targeting and drug or gene delivery, acceleration of thrombolysis, and imaging technology, are also discussed.

Brain↗

PubMed1991

Human auditory system response to pulsed radiofrequency energy in RF coils for magnetic resonance at 2.4 to 170 MHz.

The threshold conditions for an auditory perception of pulsed radiofrequency (RF) energy absorption in the human head have been studied on six volunteers with RF coils for magnetic resonance (MR) imaging. For homogeneous RF exposure with MR head coils in the 2.4- to 170-MHz range and pulse widths 3 microseconds less than or equal to Tp less than 100 microseconds, the auditory thresholds were observed at 16 +/- 4 mJ pulse energy. Localized RF exposure with optimized surface coils positioned flush with the ear lowers the auditory threshold to only 3 +/- 0.6 mJ. The hearing threshold of RF pulses with Tp greater than 200 microseconds occurs at more or less constant peak power levels of typically 150 +/- 50 W for head coils and as low as 20 W for surface coils. The results from this study confirm theoretical predictions from a thermoelastic expansion model and compare well with reported thresholds from near field antenna measurements at 425 to 3000 MHz. Details of the threshold dependence on RF pulse length reveal primary sites of RF to acoustic energy conversion at the mastoid and temporal bone region and the outer layer of the brain from where thermoelastically generated pressure transients excite audible pressure waves at the resonance modes of the skull around 1.7 kHz and of the brain around 11 kHz. If not masked by usually dominating noise from switched gradients, the conditions for hearing RF pulses, as applied to head coils in MR studies with flip angle alpha at main field B0, is given by Tp/ms less than or equal to 0.4 (alpha/pi)B0/[T]. At peak power levels up to 15 kW presently available in clinical MR systems, there is no evidence known for detrimental health effects arising from the RF auditory phenomenon which is a secondary cause associated with primary RF to thermal energy conversion in body tissues. To avoid the RF-evoked sound pressure levels in the head rising above the discomfort threshold at 110 dB SPL, an upper limit of 30 kW applied peak pulse power is suggested for head coils and 6 kW for surface coils.

Auditory Perception↗