PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Brain waves”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed2006

Characterization of cerebrovascular reactivity after craniectomy for acute brain injury.

Analysis of slow waves in arterial blood pressure (ABP) and intracranial pressure (ICP) has been used as an index to describe cerebrovascular pressure-reactivity. It has been previously demonstrated that the pressure-reactivity index (PRx) can be used to reflect global cerebrovascular reactivity with changes in ABP. A positive PRx signifies a positive association between ABP and ICP, indicating a non-reactive vascular bed, while a negative PRx is reflective of intact cerebral autoregulation, where ABP waves provoke inversely correlated waves in ICP. To date, there has been no characterization of pressure-reactivity following decompressive craniectomy. In this prospective observational study, 33 patients who underwent surgery for acute brain injury with mass lesions for which the bone flap was left out were studied. The PRx was calculated as a moving correlation coefficient between 30 consecutive samples of values of ICP and ABP averaged for a period of 10 s. The time profiles of mean PRx values at 6-hourly intervals were analysed and compared with that in seven patients treated by medical therapy alone. The initial mean PRx 6 h after surgery was positive, indicative of disturbed pressure-reactivity. With time, PRx trended towards a more negative value, suggestive of an improving cerebrovascular autoregulatory reserve. The mean PRx 24 h after surgery was 0.28 (+/-0.26), while the mean PRx 72 h after surgery was 0.15 (+/-0.25) (p = 0.012). In contrast, the mean PRx in patients that were not decompressed did not change significantly with time (p = 0.357). Surgery in acute brain injury for which the bone flap is left out in anticipation of raised intracranial pressure in the postoperative period leads to an improved PRx as compared with controls. Craniectomy in this situation may have a contribution to the restoration of disturbed cerebrovascular pressure-reactivity.

Adult↗
PubMedDate not supplied

Noninvasive detection of functional brain activity with near-infrared diffusing-wave spectroscopy.

We use near-infrared dynamic multiple scattering of light [diffusing-wave spectroscopy (DWS)] to detect the activation of the somato-motor cortex in 11 right-handed volunteers performing a finger opposition task separately with their right and left hands. Temporal autocorrelation functions g(1)(r,tau) of the scattered light field are measured during 100-s periods of motor task alternating with 100-s resting baseline periods. From an analysis of the experimental data with an analytical theory for g(1)(r,tau) from a three-layer geometry with optical and dynamical heterogeneity representing scalp, skull, and cortex, we obtain quantitative estimates of the diffusion coefficient in cortical regions. Consistent with earlier results, the measured cortical diffusion coefficient is found to be increased during the motor task, with a strong contralateral and a weaker ipsilateral increase consistent with the known brain hemispheric asymmetry for right-handed subjects. Our results support the interpretation of the increase of the cortical diffusion coefficient during finger opposition being due to the functional increase in cortical blood flow rate related to vasodilation.

Adult↗
PubMed1987

Auditory brain stem responses from human adults and infants: wave V tuning curves.

Decrement in ABR wave V amplitude was measured in the presence of simultaneous tonal maskers. Probe stimuli were 1.0, 4.0, and 8.0-kHz third-octave-filtered clicks. Adults and 3-month-old infants served as subjects. The resultant amplitude-decrement functions for each tonal masker were fit with regression lines. The sound pressure level (SPL) required to reduce wave V to 50% of the unmasked probe amplitude was plotted for each masker to develop tuning curves. The tuning curves were quantified by calculations of tip-to-tail difference, Q 10, and SPL at maximum masker frequency (MMF). Tuning curves for adult and infant subjects were similar for the 1.0-kHz probe. For the high-frequency probes (4.0 and 8.0 kHz), smaller tip-to-tail differences and lower Q 10 values were observed for the infant subjects. Ranges of MMF level were similar across adult and infant subjects. For the 8.0-kHz probe, tuning curves from infant subjects consistently showed maximum masker frequencies which were lower than the probe.

Acoustics↗
PubMed1983

Validity of Doppler measurements of anterior cerebral artery blood flow velocity: correlation with brain blood flow in piglets.

Continuous wave Doppler ultrasonography through the anterior fontanel has recently been used to assess changes in cerebral blood flow in human neonates. There has been controversy concerning whether measurements of Doppler blood flow velocity indeed correlate with brain blood flow. An in vivo correlation was performed between brain blood flow as measured by the microsphere method and Doppler flow velocity measurements of the cerebral arteries via an artificial fontanel in young piglets. The peak systolic velocity (r = .76, P less than .001), end diastolic velocity (r = .72, P less than .001) and area under the velocity curve (r = .86, P less than .001) all showed significant positive correlations with brain blood flow. The pulsatility index did not correlate with brain blood flow. Although continuous wave Doppler flow velocity measurements of the anterior cerebral artery cannot quantitatively assess cerebral blood flow, this methodology can be used to correlate changes in cerebral blood flow and provide a meaningful trend analysis following physiologic or pharmacologic perturbation of the cerebral circulation.

Animals↗
PubMed1979

Acute intracranial hypertension and auditory brain-stem responses. Part 2: The effects of brain-stem movement on the auditory brain-stem responses due to transtentorial herniation.

Movement of the upper brain stem (inferior colliculus) was correlated with the alterations in the amplitude of wave V of the auditory brain-stem responses (BER's) during supratentorial brain compression in cats. In vivo observation of the brain stem and postmortem inspection show that suppression of the amplitude of BER wave V reflects the extent of caudal displacement of the inferior colliculus. Marked suppression of the amplitude of BER wave V (approximately 30% of control) correlates with the beginning of transtentorial herniation, and complete suppression of the wave V indicates complete transtentorial herniation of the brain-stem and supratentorial structures. The BER wave V is thought to be a sensitive index of caudal movement of the upper brain stem due to transtentorial herniation.

Animals↗
PubMed1963

PULMONARY EDEMA AS A CONSEQUENCE OF HYPOTHALAMIC LESIONS IN RATS.

Rats were observed for the incidence of pulmonary edema after the placement of hypothalamic lesions by radio frequency thermocoagulation or d-c electrolysis. In the animals with electrolytic lesions, 31 percent died with pulmonary edema and marked signs were observed in another 20 percent. Moderate transient signs appeared in only 3.7 percent of the animals with radio-frequency lesions, and there were no deaths attributable to this syndrome in this group. These results suggest that this syndrome is an irritative consequence of the electrolytic lesion process rather than a "release" phenomenon.

Animals↗
PubMed1989

[Parkinson disease and cognitive evoked potentials].

Long latency auditory evoked potentials were recorded in 50 patients with Parkinson's disease, some case were also investigated by the Rapid Evaluation of Cognitive Functions test (RECF) and Trail Making A test (TMA). Latencies of P2, N2 and P300 waves were longer in the parkinsonian group than in a control group matched for age. Latencies of N2 and P300 waves were correlated significantly with scores for RECF and TMA presumed to be sensitive to organic brain lesions. On the other hand no significant correlation was found between RECF and P1 and P2 latencies. In addition, correlation was lacking between Verbal Automatism test scores, presumed to be resistant to organic brain lesions, and P300 wave latencies. Cognitive evoked potential (CEP) latency increases with age in normal subjects. In the parkinsonian group the coefficient of correlation between these two factors was lower but still significant. The parkinsonian patients with dementia as defined by DSM III criteria, or an RECF score of less than 46, showed longer N2 and P300 latencies but no significant difference in N1 and P2 latencies. In contrast, comparison of P300 and N2 wave latencies in depressed and non-depressed parkinsonian patients failed to show any significant difference. The bilateral akinetic forms had marked lengthening of P300 wave latencies and a lower TMA score. Neither the duration of the disease, type of treatment, duration of L-Dopa therapy significantly influenced the latency of cognitive event-related potentials.

Age Factors↗
PubMed1998

[The activity of neurons of the thalamus and brain cortex hemispheres during EEG complexes "slow wave-spindle wave" in rabbits].

Neurons of the medial thalamus and some cortical neurons revealed the same activity upon the spindle wave as upon the slow wave. The membrane potential was changing in a similar way. The data obtained suggests that the slow wave mechanism is analogous to the mechanism of the spindle waves, whereas the rhythm of complexes occurrence or their common with the "spontaneous" sleep spindles rhythm, are determined by a different mechanism.

Animals↗
PubMed1992

Brainstem auditory evoked potentials in familial dysautonomia.

The brainstem function of eight children with familial dysautonomia was investigated by brainstem auditory evoked potentials and compared with that of age-matched healthy control children. All median latencies of waves III and V in the study group were significantly higher than those of the control children. Brain transmission times of waves I-III and I-V were significantly prolonged in the study group compared with the control group. These results provide additional objective support for the assumption that the brainstem function of children with familial dysautonomia is affected by this disease.

Adolescent↗
PubMed1992

The early development of neurosonology: III. Pulsatile echoencephalography and Doppler techniques.

From the earliest days of echoencephalography, it was noted that echoes from intracerebral interfaces showed systolic pulsations both in amplitude and range. Recordings of larger pulsations in range could also be obtained from the walls of intracranial arteries. It was hoped that clinical information might be obtained from recording and measuring these pulsations. Since it was easier to build equipment that recorded pulsations in amplitude, most work was confined to the recording of amplitude pulsations. However, such recordings of both amplitude and range pulsations usually used range gates in order to isolate the echo of interest and movement of the echoes within the gates introduced artefact in the recordings. Such artefact was more easily identified in recordings of range rather than amplitude. None of these types of recordings resulted in the development of a clinically useful examination in either the living or dying patient. However, the recordings of range fluctuations were able to demonstrate the presence of Traube-Hering waves in the blood vessels of the brain, thus suggesting that these vessels received an autonomic innervation in addition to their chemical sensitivity. Such range recordings also showed that, as a result of the increase in cerebral volume with the arrival of each systolic pulse wave, the brain moved centripetally to compress the cerebral ventricles and downwards to compress the basal cisterns and venous sinuses. The volume increase in the brain was accomodated by displacing cerebrospinal fluid and venous blood outside the rigid skull. When such a venting mechanism was over-taxed, as may result from increased intracranial pressure, it was postulated that the systolic pulse pressure wave, which could no longer be adequately attenuated by the compensatory venting of blood and cerebrospinal fluid outside the rigid skull, gave rise to shock waves which damaged the periventricular ependymal interface and the underlying brain with the production of progressive hydrocephalus. The development of ultrasonic Doppler techniques was quite a different matter and led to a number of clinically useful examinations as the technology became increasingly developed. The Doppler frequency shifts were displayed in various forms culminating in the display of their whole spectrum. Directional displays added further information and the ability to use short pulses enabled the Doppler shift and velocity of blood flowing in small regions of blood vessels to be recorded. Two-dimensional displays of the Doppler frequencies present in blood flowing in vessels were developed concurrently with duplex techniques which made B-mode displays of the blood vessel of interest in a tomogram of the surrounding tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Behavioral changes correlated with brain-stem auditory evoked responses in term infants with moderate hyperbilirubinemia.

The purpose of this study was to test the hypotheses that newborn infants with moderate serum bilirubin concentrations have depressed Brazelton scores and increased brain-stem conduction time and that serum bilirubin levels correlate with Brazelton behavior scores and brain-stem auditory evoked response changes. Fifty term infants who were enrolled into either a low serum bilirubin group (less than 8 mg/dl) or a moderate serum bilirubin group (10 to 20 mg/dl) were tested with the Brazelton Neonatal Behavioral Assessment Scale and a brain-stem auditory evoked response test. Partial correlation analysis controlling for phototherapy revealed that increased bilirubin concentration correlated negatively with the Brazelton orientation and with state range clusters and individual Brazelton test items that involve auditory processing. Increased bilirubin concentration correlated with an increased latency of brain-stem auditory evoked response wave 4, 5. An increased interpeak 1-5 (brain-stem conduction time) correlated with the decreased animate visual and auditory item. We conclude that moderate hyperbilirubinemia in term infants affects both infant behavior, as measured by specific components of the Brazelton test, and brain-stem conduction time, as measured by the brain-stem auditory evoked response test.

Arousal↗
PubMed2000

Brain stem auditory evoked fields in response to clicks.

Magnetoencephalographic correlates of brain stem auditory evoked potentials (BAEP) have been identified by applying the model of a current dipole with invariant location and orientation (fixed dipole) to data recorded with a 37-channel first-order gradiometer system. In all three subjects studied, the dominating wave of the recorded brain stem auditory evoked field (BAEF) coincided exactly with wave V in the contralateral BAEP (maximal field amplitude of the order of 2-3 fT). In one subject, also a wave preceding wave V was observed, which was associated with basically the same spatial pattern as wave V itself, but had an opposite polarity. The study suggests that the supplementary information provided by BAEF measurements could be decisive for a better understanding of human auditory evoked brain stem activity.

Acoustic Stimulation↗
PubMed1988

[The auditory evoked potentials of the brain stem in the guinea pig].

The examination of the standard waves' amplitude and latency of the brain stem auditory evoked response (BAEP) was performed in 20 guinea pigs (males and females, weighing 250 to 300 g). According with the relative loudness of stimuli (90, 70, 50, 30, 10 dB SPL), the latency of BAEP waves was larger (t1 = 0.2 msec), but the conductance time between P1 to P5 was constant (3.1 to 3.6 msec). The highest wave of BAEP was P2 with an amplitude: 90 dB SPL, U = 6.5 +/- 1.2 microV; 70 dB SPL, U = 4.3 +/- 1.0 microV; 50 dB SPL, U = 3.5 +/- 0.6 microV; 30 dB SPL, U = 2.0 +/- 0.4 microV.

Acoustic Stimulation↗
PubMed1991

Predictability of human EEG: a dynamical approach.

The electroencephalogram recordings from human scalp are analysed in the framework of recent methods of nonlinear dynamics. Three stages of brain activity are considered: the alpha waves (eyes closed), the deep sleep (stage four) and the Creutzfeld-Jakob coma. Two dynamical parameters of the attractors are evaluated. These are the Lyapunov exponents, which measure the divergence or convergence of trajectories in phase space and the Kolmogorov or metric entropy, whose inverse gives the mean predicting time of a given EEG signal. In all the stages considered, the results reveal the presence of at least two positive Lyapunov exponents, which are the footprints of chaos. This number increases to three positive exponents in the case of alpha waves, indicating that although for very short episodes the alpha waves seem extremely coherent, the variability of the brain increases markedly over larger periods of activity. The degree of entropy/chaos increases from coma to deep sleep and then to alpha waves. The large predicting time observed for deep sleep suggests that these waves are related to a slow rate of information processing. The predicting time of the alpha waves is much smaller, indicating a rapid loss of information. Finally, with the help of the Lyapunov exponents, the attractor's dimensions are evaluated using two different conjectures and compared to values obtained previously by the Grassberger-Procaccia algorithm.

Brain↗
PubMed2002

Effect of ambient temperature on brain temperature and sleep-wakefulness in medial preoptic area lesioned rats.

The changes in brain temperature and sleep-wakefulness were studied in rats during their exposure to different ambient temperatures of 18 degrees C, 24 degrees C and 30 degrees C, before and after N-methyl D-aspartic acid lesion of the medial preoptic area. The medial preoptic area lesion produced a decrease in sleep, and increase in brain temperature except at 30 degrees C. Increase and decrease in brain temperature with slow wave sleep and paradoxical sleep respectively, were observed both in normal and lesioned rats. Sleep-wakefulness and brain temperature cycle durations were increased and their frequencies decreased at higher ambient temperature in normal rats. After the medial preoptic area lesion, sleep-wakefulness cycle duration was decreased and frequency increased at 30 degrees C. There was no significant change in brain temperature cycles at higher ambient temperature in lesioned rats. The medial preoptic area, in normal rats, possibly interlinks the neuronal circuits involved in regulating brain temperature and sleep-wakefulness cycles. The medial preoptic area is essential for increasing the sleep-wakefulness cycle duration with higher ambient temperature. The possible contribution of the increased brain temperature variation in producing sleep-wakefulness changes cannot be ruled out. The results of the study show that this area may serve as a fine tuning mechanism which helps to interlink the sleep-wakefulness with the thermoregulation.

Analysis of Variance↗