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At least 703 records · Page 39Linked to original sources
PubMed2006

Effects of anesthesia on the responses to cortical spreading depression in the rat brain in vivo.

OBJECTIVES: The aim of this study was to evaluate the effect of cortical spreading depression (CSD) on the metabolic, hemodynamic, electrical and ionic properties during anesthesia as compared with the awake state. METHODS: The mitochondrial NADH redox state, reflected light, direct current (DC) potential, electrocorticography (ECoG), cerebral blood flow (CBF) and volume (CBV), and extracellular K(+) concentrations ([K(+)](e)), were measured continuously and simultaneously in real time using two unique monitoring systems that evaluate brain function. Three consecutive CSD waves were initiated using a KCl solution in both awake and anesthetized rats. RESULTS AND DISCUSSION: CSD caused typical amplitude changes: biphasic waves in reflectance, oxidation cycles in NADH, an increase in CBF, CBV and in [K(+)](e), a negative shift in DC potential and depression in ECoG. Anesthesia by equithesin decreased significantly the baseline levels of CBF and [K(+)](e), showing a reduction in oxygen supply and demand. After anesthesia, CSD significantly decreased [K(+)](e) and NADH oxidation cycles, indicating a reduction in oxygen demand and in oxygen balance, respectively. Furthermore, anesthesia reduced CSD wave frequencies by slowing the recovery period, showing a decline in energy production during brain activation, or by changing electrophysiological properties of the tissue. No changes were found in the propagation rate and in the initiation period of CSD, which may indicate that equithesin does not block CSD initiation. In addition, we found that the whole cerebral cortex reacts homogenously to CSD and that equithesin may reduce oxygen demand and energy production, which may have a protective effect on the brain exposed to pathophysiological conditions.

Anesthetics↗
PubMed1997

Evaluation of neurologic function in Gulf War veterans. A blinded case-control study.

OBJECTIVE: To determine whether Gulf War-related illnesses are associated with central or peripheral nervous system dysfunction. DESIGN: Nested case-control study. PARTICIPANTS: Twenty-three veterans with factor analysis-derived syndromes (the cases), 10 well veterans deployed to the Gulf War (the deployed controls), and 10 well veterans not deployed to the Gulf War (the nondeployed controls). METHOD: With investigators blinded to group identities, participants underwent objective neurophysiological, audiovestibular, neuroradiological, neuropsychological, and blood tests. MAIN OUTCOME MEASURES: Evidence of neurologic dysfunction. RESULTS: Compared with the 20 controls, the 23 cases had significantly more neuropsychological evidence of brain dysfunction on the Halstead Impairment Index (P=.01), greater interside asymmetry of the wave I to wave III interpeak latency of brain stem auditory evoked potentials (P=.02), greater interocular asymmetry of nystagmic velocity on rotational testing, increased asymmetry of saccadic velocity (P=.04), more prolonged interpeak latency of the lumbar-to-cerebral peaks on posterior tibial somatosensory evoked potentials (on right side, P=.03, and on the left side, P=.005), and diminished nystagmic velocity after caloric stimulation bilaterally (P values range from .02 to .04). Cases (n=5) with syndrome 1 ("impaired cognition") were the most impaired on brain stem auditory evoked potentials (P=.005); those (n=13) with syndrome 2 ("confusion-ataxia") were the most impaired on the Halstead Impairment Index (P=.006), rotational testing (P=.01), asymmetry of saccadic velocity (P=.03), and somatosensory evoked potentials (P< or =.01); and those (n=5) with syndrome 3 ("arthro-myo-neuropathy") were the most impaired on caloric stimulation (P< or =.01). CONCLUSIONS: The 3 factor-derived syndromes identified among Gulf War veterans appear to represent variants of a generalized injury to the nervous system.

Adult↗
PubMed2026

Co-Use of Some Substances Associated With Higher Doses in Adolescents: Findings From the Adolescent Brain Cognitive Development Study.

PURPOSE: Adolescence is a critical developmental period marked by heightened vulnerability to initiating substance use, with long-term implications for health and behavior. Nicotine, alcohol, and cannabis are the most commonly used substances among adolescents. Their use often co-occurs but few studies have described or quantified the patterns and doses of substance co-use in this vulnerable population. METHODS: We used data from six waves of the Adolescent Brain Cognitive Development study. Substance use was measured through a web-based timeline followback interview, and outcomes are operationalized into substance use quantity (in standard units), single use, and co-use (use of two substances on the same day) of alcohol, cannabis, and nicotine. Group differences of average dose in standard units between single use and co-use for each substance class were analyzed using linear mixed-effects modeling in years 4-6. RESULTS: The average dose of nicotine was significantly higher when co-used with alcohol (4.32; 95% confidence interval [CI]: 2.55-6.09; p < .001) or when co-used with cannabis (4.41; 95% CI: 2.76-6.05; p < .001) in year 6; nicotine trends were similar in years four and five. In year 6, the average dose of alcohol was higher when co-used with cannabis (1.87; 95% CI: 0.37-3.36; p = .004) or co-used with nicotine (1.64; 95% CI: 0.06-3.22; p = .03) compared to single use of alcohol. The average dose of cannabis was not significantly different when used singularly or co-used with either alcohol or nicotine in our study years. DISCUSSION: During adolescence, the co-use of substances (namely alcohol and nicotine) may lead to higher average doses compared to single-substance use.

Humans↗
PubMed2000

Rapid-eye-movement sleep involves the memory-conversion circuits in a brain model.

People can remember the content of a dream in rapid eye movement (REM) sleep but cannot do so in slow-wave sleep. According to a brain model, memory is stored in encoding synapses as presynaptic axonal 'on-off' patterns and modulating synapses help encoding synapses convert short-term memory into long-term memory. These lead to the hypothesis that REM sleep involves modulating synapses of the memory-conversion circuits including the anterior nuclei and dorsomedial nuclei of the thalamus. Cortical neurons get more rest in slow-wave sleep than in REM sleep. The locus coeruleus, raphe nuclei, and tuberomammillary nuclei get more rest during REM sleep when these nuclei cease to fire. The paralyses of peripheral muscles during REM sleep and cataplexy, and cessation of chorea, athetosis, hemiballismus, and parkinsonism tremor during sleep may result from spinal cord inhibition by the gigantocellular nuclei and raphe nuclei at the reticular formation. Sleep and wake relate to the light-dark cycle on the Earth. Were the light-dark cycle 50 hours a day, the human circadian clock might be around 50 hours. With increasing use of artificial light to keep people awake at night, it may affect the circadian rhythm and firing rate of neurons, the presynaptic axonal 'on-off' patterns as content of consciousness, and the mood.

Brain↗
PubMed1994

Effects of shock waves on the mouse fetus.

Extracorporeal shock wave lithotripsy is contraindicated during pregnancy because its effects on the fetus remain to be ascertained. The purpose of this study was to elucidate the effects of shock waves on fetuses at various stages of pregnancy. Pregnant mice received 100, 250, or 500 shock waves on 8, 10, 12, 14, and 16 days postcoitum. The effect on fetal survival rate and weight was minimal in the early stages of pregnancy. In the later stages of pregnancy, however, the number of viable fetuses decreased in proportion to an increasing number of shock waves, and almost no viable fetuses were found in the group treated with 500 shock waves. Fusion and necrosis were found in many dead fetuses. Histological examination of the fetuses, which was obtained immediately after the shock wave treatment, revealed hemorrhages in the brain, lungs and subcutaneous tissue. This study indicated that shock waves lead to fetal damage and death in the late stage of pregnancy in mice.

Animals↗
PubMed1997

Management of vestibular schwannomas (acoustic neuromas): the value of neurophysiology for intraoperative monitoring of auditory function in 200 cases.

OBJECTIVE: The present study investigated the significance of the presence or absence of auditory brain stem response (ABR) Waves I, III, and V as functional representatives of the cochlea, the nucleus cochlearis, and the colliculus inferior, respectively, and attempted to identify the microsurgical maneuvers that were especially likely to cause isolated or combined component losses and subsequent hearing losses. METHODS: Based on the previously described ABR classification system, 201 patients with preserved Waves I, III, and V or Waves I and V were investigated for the peak latencies and amplitudes of the waves at 15 defined microsurgical stages. Analysis was performed with respect to the presence or absence of ABR components during specific microsurgical actions and the related danger of deafness. RESULTS: Temporary or permanent losses of Waves V, I, and III occurred with 21, 27, and 29% of surgical actions, respectively, leading to deafness in 65 to 78% of the patients. Wave III disappearance was identified as the earliest and most sensitive sign. Wave V loss was usually preceded by disappearances of Waves I and III. During the most dangerous actions (drilling, pulling downward, medially, or laterally, and direct nerve manipulation), special attention ws paid to deterioration of Wave-III and then Wave I; if impairment was seen, intermittent breaks or changes in the type or site of microsurgical action were used to enable wave recovery. Acute, simultaneous, and permanent loss of all waves occurred in 27.5% of postoperatively deaf patients, whereas stepwise wave deterioration and losses occurred in 72.5%. CONCLUSION: Useful (in-time) recognition of significant waveform changes is possible and enables a change of microsurgical maneuvers to favor ABR recovery.

Audiometry, Pure-Tone↗
PubMed1984

Brain stem potentials evoked by binaural click stimuli with differences in interaural time and intensity.

Auditory-evoked brain stem potentials were recorded from 12 adults with normal hearing using click stimuli with differences in interaural time and intensity. Almost independent superimposed Jewett V peaks were produced, whose latency and amplitude depended on the parameters of the stimulus applied to either ear. This indicates that separate binaural information for the evaluation of sound source direction is still available at the brain stem level where wave V originates. We demonstrate that the normal nonlinear latency/intensity function may be responsible for the subjective compensation of time and intensity differences, since the well-known trading functions show similar intensity-dependent gradients.

Adult↗
PubMed2003

Neuroprotection assessment by topographic electroencephalographic analysis: effects of a sodium channel blocker to reduce polymorphic delta activity following ischaemic brain injury in rats.

The spatiotemporal electroencephalogram (EEG) pathology associated with brain injury was studied using high-resolution, 10-electrode cortical EEG mapping in a rat model of middle cerebral artery occlusion (MCAo). Using this model we evaluated the ability of the novel sodium channel blocker and neuroprotective agent RS100642 to resolve injury-induced EEG abnormalities as a measure of neurophysiological recovery from brain injury. The middle cerebral artery (MCA) was occluded for 1 h during which a dramatic loss of EEG power was measured over the injured cortex with near complete recovery upon reperfusion of blood to the MCA region in all rats. The resultant progression of the MCAo/reperfusion injury (6-72 h) included the appearance of diffuse polymorphic delta activity (PDA), as visually indicated by the presence of high-amplitude slow-waves recorded from both brain hemispheres. PDA was associated with large increases in EEG power, particularly evident in outer 'peri-infarct' regions of the ipsilateral parietal cortex as visualized using topographic EEG mapping. Post-injury treatment with RS100642 (1.0 mg/kg, i.v.) significantly reduced the PDA activity and attenuated the increase in EEG power throughout the course of the injury. These effects were associated with a reduction in brain infarct volume and improved neurological function. These methods of EEG analysis may be helpful tools to evaluate the physiological recovery of the brain from injury in humans following treatment with an experimental neuroprotective compound.

Animals↗
PubMed2001

A combined study of tumor-related brain lesions using MEG and proton MR spectroscopic imaging.

The purpose of this study is to localize, in cases of brain tumors, pathological magnetic brain activities and to analyze metabolic alterations in functionally abnormal lesions using magnetoencephalography (MEG) and proton magnetic resonance spectroscopic imaging (1H MRSI). The study focused on 10 healthy volunteers and seven patients with common brain tumors, namely astrocytic tumor and meningioma. In spontaneous MEG, the pathological brain activities (slow, fast waves and spikes) were localized using a single equivalent dipole model. After the results of MEG and 1H MRSI were superimposed onto the corresponding MR images, the signal intensities of spectroscopically visible metabolites were analyzed in the regions where the dipoles of the pathological activities were concentrated. Increased slow wave activity was observed in four cases and fast wave or spike activity was significantly increased in one case. These pathological activities were localized in surrounding regions of the bulk of tumors, where mild reduction of N-acetyl aspartate (NAA) and slight accumulation of lactate (Lac) consistently existed. Preserved cortical areas, which are indicated by residual NAA, might be able to generate pathological magnetic activities under lactic acidosis. Such areas could be understood as a border zone between normal and seriously damaged brain tissue by tumors or associated brain edema. This combined technique with the different modalities gives insight into functional as well as metabolic aspects of pathological brain conditions.

Adult↗
PubMed1999

Neurophysiological support of consciousness during waking and sleep.

The aim of this review was to try to establish the current neurophysiological knowledge capable of explaining the differences of mental functioning during the different stages of sleep and waking. The analysis focused on the cortical state. Waking is characterized by electrophysiological activities (low voltage and gamma range EEG field patterns, unitary activities) and cerebral blood flow reflecting an activated state. On the contrary, neurochemical influences are marked by inhibitory afferent processes since dopamine, noradrenaline, serotonin and histamine tend, for the most part, to inhibit cortical neurons by diffuse release at the level of varicosities. During slow wave sleep, all these brain stem influences sustaining the cortical state decrease and transiently disappear just prior to onset of REM sleep. During REM sleep, pontine and mesopontine ascending activating influences invade the cortex in their turn while neurochemical inhibitory influences disappear with the exception of dopaminergic ones. We hypothesize that the activating influences acting on the cortex allow the latter to function, just as petrol makes an engine run, but that the diffuse inhibitory influences somehow regulate cortex functioning. Therefore, it is understandable that, during waking, mental activity is reflective and rational, and that psychological content is less intense during slow wave sleep. During REM sleep, the activated and mostly disinhibited state might induce the characteristic dream activity which appear to be rather ill-considered and illogical. Persistent dopaminergic input combined with the absence of noradrenergic input may induce psychological activities somewhat similar to those related to psychotic syndromes. Deactivation of part of the prefrontal cortex could contribute to this unusual mental activity.

Animals↗
PubMed1987

[EEG topographic changes of brain abscesses in children].

EEG topography was investigated before and after surgical treatment in 4 patients with brain abscess aged from 5 to 13 years. According to the recording technique designed by Matsuoka and Ueno, the recorded EEG for each 5 seconds was analyzed to obtain square roots of power spectra for each band of delta (2-3.8 Hz), theta (4-7.8 Hz) and alpha (8-12.8 Hz) which were then added for the 60-seconds duration of each trial. After that, numerical matrix presenting the topographic distribution of spectral energy of each band were constructed and displayed as color images. In addition, the EEG topographies of brain abscesses were compared with the CT scans simultaneously obtained. In all of four cases before surgical treatment of the brain abscess, the location of the focal delta wave on the EEG topography was more closely related to the site of brain abscess comparing with its correlation between the location of the delta focus on the conventional EEG and the site of brain abscess. In contrast, as for the theta wave, there was no prominent correlation to the site of the brain abscess. In the early stage of 10-15 days after aspiration of the brain abscess, the most characteristic change of the EEG topography was an approximately 25% reduction of the maximum equivalent voltage of delta band with associated disappearance of the sharply located focal delta wave being noted before aspiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

[Electroencephalographic changes during experimental plateau waves].

The present study was designed to induce plateau waves by electrical stimulation of the brain stem and examine the changes in EEG during the plateau waves. Experiments were carried out on 10 adult mongrel dogs which were slightly anesthetized, immobilized and artificially respired. Electroencephalogram (EEG), intracranial pressure (ICP), systemic blood pressure (SBP) and cerebral perfusion pressure were simultaneously recorded on the electromagnetic tape after transorbital puncture of the intracavernous internal carotid artery. EEGs were recorded from cortical electrodes, and were analyzed by a frequency analysis. At the stage of increased ICP, the mesencephalic reticular formation was stimulated. Stimulation parameters, i.e., intensity, duration and frequency, were 0.1 mA, 1 msec and 40 - 50 Hz, respectively. The total duration of each period was 5 seconds. Spontaneous plateau waves occurred in 2 dogs associated with subarachnoid hemorrhage, subdural hematoma and intraventricular hemorrhage. Plateau waves were induced by electrical stimulation in the mesencephalic reticular formation in one of two dogs with spontaneous plateau waves. Twenty-one repetitions of electrical stimulation induced ten plateau waves. Two plateau waves were induced during slow EEG associated with desynchronization of EEG. Eight plateau waves were induced during fast EEG activity with no changes in EEG before and after the stimulation. In addition, plateau waves occurred immediately after short duration (5 seconds) of electrical stimulation. It seems that CBV increases during plateau waves are due to rapidly occurring neurogenic vasodilatation of cerebral vessels, later augmented by increases in cerebral metabolism. In conclusion, plateau waves are produced in a rigid condition within the cranial cavity by stimulation of the brainstem reticular formation which influences cortical activation and cerebral vasodilatation.

Animals↗
PubMed1984

Intracranial recording of short latency somatosensory evoked potentials in man: identification of origin of each component.

In normal subjects the short latency SEPs generally consisted of 3 positive waves (P9, P11, P14) and a succeeding negative wave (N20). To determine the origins of these waves we have made intracranial records from 17 patients, which suggest the following results. P9 originates in stimulated median nerve peripheral to the dorsal roots such as brachial plexus, P11 in the dorsal column of the cervical cord, P14 in the cuneate nucleus and medial lemniscal pathway, and N20 in the cerebral cortex. On the basis of intracranial and intraspinal records, the onset of P11 indicates the arrival of the afferent volley at the cord entry and the peak latency of P11 its arrival time at the C1-2 level dorsal column. The onset latency of P14 indicates the onset of postsynaptic events in cuneate nucleus neurons and the peak latency of P14 arrival at the midbrain. From the ventral surface of the brain-stem 3 positive waves (P'9, P'11, P'14) like the initial positive components of the scalp short latency SEPs (P9, P11, P14) were recorded. The amplitude of P'14 was large compared to that of P14. The peak latencies of P'14 recorded at the medulla and the pons were shorter than that of P14 by 0.7-0.8 msec and 0.2-0.5 msec, respectively. The peak latency of P'14 at the midbrain was almost the same as that of P14. By measuring the distance between the recording electrodes in the brain-stem and the peak latency difference of P'14, the fastest lemniscal conduction velocity was estimated as 56 m/sec.

Adult↗
PubMed1988

[Characteristics of slow electrical potentials in healthy subjects and in patients with various forms of neuroses].

The shapes of the slow brain potentials--conditioned negative wave (CNW) and postimperative negative wave (PNW)--were compared in normal and neurotic subjects. Instruction-directed performance was used to investigate the physiological mechanisms of neuroses and to develop the diagnostic psychophysiologic tests with simultaneous recording of the slow potentials. These were evaluated by calculation of asymmetry and power amplification coefficients for CNW and PNW while more and more complicated instructions were given.

Acoustic Stimulation↗
PubMed1998

Somnogenic and pyrogenic effects of interleukin-1beta and lipopolysaccharide in intact and vagotomized rats.

The vagus nerve appears to serve a role in mediating peripheral immunologic influences on CNS processes. Previous work demonstrates that subdiaphragmatic vagotomy prevents or attenuates many of the behavioral and physiological responses to exogenous interleukin-1 (IL-1) or lipopolysaccharide (LPS). We determined whether the somnogenic effects of IL-1 and LPS were altered in vagotomized rats, and whether the effects of vagotomy on IL-1- and LPS-induced alterations in sleep would vary as a function of circadian phase. The data indicate that vagotomy does not influence the normal circadian patterns of sleep and wakefulness in untreated rats, or modify the pyrogenic or somnogenic effects of intracerebroventricular administration of IL-1. However, in unchallenged animals vagotomy reduces basal brain temperatures, increases delta wave amplitudes during slow-wave sleep (SWS), and induces a reduced rate of weight gain, gastric distension, and adrenal hypoplasia. Vagotomy attenuates the febrile effects of IL-1 during both light and dark phases, attenuated IL-1-induced sleep enhancement during the dark phase, and attenuated IL-1-induced increases in delta wave amplitudes within SWS during the light period. In LPS-treated rats, vagotomy attenuates the febrile and SWS responses to LPS after administration at light onset, but not after administration at dark onset. These results indicate that subdiaphragmatic vagotomy attenuates several of the somnogenic and pyrogenic effects of IL-1beta and LPS, although the effectiveness of the vagal transection in modulating these responses is influenced by circadian factors.

Animals↗
PubMed2005

Do 'auditory processing' tests measure auditory processing in the elderly?

OBJECTIVE: To examine the associations between measures of auditory processing and measures of auditory or cognitive function in elderly listeners with impaired hearing. DESIGN: Multiple measures of auditory processing, auditory function, and cognitive function were obtained and linear, multiple-regression analyses were conducted to examine the relations between these sets of variables. In particular, four measures of auditory processing were obtained from each of 213 elderly participants. Measures of auditory processing included duration discrimination for a 1000-Hz pure tone, temporal-order discrimination for mid-frequency pure tones, dichotic syllable identification, and recognition of 45% time-compressed monosyllables. Each participant also completed additional measures of auditory function, including pure-tone thresholds, auditory brain stem responses for each ear and at two presentation rates (11.1 and 71.1 clicks per second), and performance-intensity functions for monosyllabic words (PI-PB rollover). Finally, three measures of cognitive function, all from the Wechsler Adult Intelligence Scale-Revised, were obtained from the 213 participants. RESULTS: For three of the four measures of auditory processing examined in this study (duration discrimination, temporal-order discrimination, and dichotic CV identification), a measure of cognitive function (IQ) and age were the two primary predictors of individual differences in performance. For these three measures of auditory processing, 11 to 14% of the total variance could be accounted for by the predictor variables. For the remaining measure of auditory processing (recognition of time-compressed monosyllables), 56% of the total variance could be accounted for by a set of four predictor variables, but most of this variance (54% of the total variance) was associated with individual differences in hearing loss. When hearing loss was removed as a predictor for this measure of auditory processing, 14% of the total variance was explained by four variables: age, IQ, and two measures derived from auditory brain stem response wave-V latency. CONCLUSIONS: Performance on the battery of auditory processing measures by elderly hearing-impaired listeners was systematically related to individual differences in cognitive function rather than auditory function, especially for stimuli not affected by peripheral hearing loss. However, much of the variance in auditory processing performance remained unaccounted for by any of the predictor variables examined in this study.

Aged↗
PubMed2005

Quantitative magnetization transfer by trains of radio frequency pulses in human brain: extension of a free evolution model to continuous-wave-like conditions.

A theoretical model of free evolution between repeated magnetic transfer (MT) pulses was extended to continuous-wave (CW)-like conditions showing that only the repetitive "direct" saturation of bulk water changes the transient and stationary behavior. The influence of the pulse repetition period (PR) on progressive saturation was studied in cortical gray matter (GM) and central white matter (WM) under conditions of short periods of free evolution and strong macromolecular saturation. Interpulse delays of 3 ms were achieved in vivo on a 1.5-T MR system with bell-shaped MT pulses of 12-ms duration and nominal flip angles of up to 1440 degrees and single-shot readout by a stimulated echo acquisition mode localization sequence. The frequency offset was chosen between 1 and 3 kHz to avoid excessive direct saturation. The stationary MT ratio (MTR) followed an inverse linear PR dependence, showing a consistent partial saturation of about 90% at zero PR for both WM and GM. Comparison to a relaxation-matched liquid indicated the presence of MT, but not necessarily of direct saturation. The transient behavior indicated considerable direct saturation, but this could also be explained by MT. These inconsistencies showed that the intervals of time evolution in our experiments were too long to be modeled by CW-like conditions. Free evolution takes place during the whole PR rather than during the interpulse delay only. Quantification using the rates of free evolution theory yielded the saturations and rate constants necessary to explain the observed behavior. The theory of rapid CW-like pulsing provides an upper limit for the rate of progressive saturation. This limit is approached at PR below an estimated value of 5 ms. The phenomenological PR dependence of the steady-state MTR may indicate that MT exceeded the direct saturation. Unlike to an idealized CW experiment, the extrapolated value at zero PR is subject to direct effects and not a physically meaningful constant.

Adult↗