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PubMed1989

[Electrophysiological monitoring of the brainstem function in impending brain death--serial changes of blink reflex and brainstem auditory evoked potential].

Serial changes of EEG, BR and BAEP recordings were obtained over a period of two days on two patients who had suffered massive cerebral hemorrhage while their clinical condition evolved from coma with evidence of preserved cerebral and brainstem functions to a state meeting the criteria of brain death. As clinical evidence of deteriorating brainstem function became apparent in case 1, first wave IV and V components of BAEP disappeared while waves I to III were normal. Finally, when clinical criteria of brain death were fulfilled, the BAEP response was restricted to wave I with small amplitude to stimulation of left ear only. These serial changes were likely consistent with gradual dissolution of brainstem function in a rostrocaudal direction. By contrast, in case 2, the BAEP response was restricted to waves I and II and was stationary in the whole process of impending brain death in no association with some preservation of cerebral and brainstem function. The changes of BAEP was not parallel to the progressive deterioration of EEG and BR. After meeting clinical criteria of brain death, complete abolition of waves II and I was sequential in that order, and then Babinski sign besides withdrawal and deep tendon reflexes may revive in the extremities. Monitoring of serial electrophysiological changes is helpful in the course of impending brain death to determine whether revival of Babinski sign is due to recovery of cerebral-brainstem dysfunction or due to establishment of spinal autonomy.

Aged↗
PubMed1985

State-changes in the brain viewed as linear steady-states and non-linear transitions between steady-states.

Preceding papers concern a linear theory of electrocortical waves and their regulation by brain-stem neurones, in conditions of steady-state. The present paper reconsiders the theory, and generalizes beyond the effects of the fibre systems so far studied. Relaxation and unification of the assumptions upon which the initial model was based is undertaken. It is shown that the generalised model may render state changes within the brain accessible to systematic description, using the EEG as dependent variable. It is proposed that a multitude of stable states are possible within the brain, each characterised by a set of damping parameters for separate linear resonant modes. Within each stable state, the set of sums of resonant modes characterises a sub-space of the total state-space. Transition between stable regions can occur with either perturbation by external signals, or by internal controls. Tentative consideration is given to the role of plastic changes leading to adaptive learning as an attribute of a system of this type.

Cerebral Cortex↗
PubMed2005

Sleep EEG evidence of sex differences in adolescent brain maturation.

STUDY OBJECTIVES: The steep decline in slow-wave (delta) electroencephalogram (EEG) intensity across adolescence is a prominent feature of late brain maturation. As a first step in determining whether the adolescent delta decline is similar in both sexes, we compared cross-sectional sleep EEG data from 9- and 12-year-old boys and girls. DESIGN: All-night EEG recordings, 6 months apart, were conducted on each subject. SETTING: EEG was recorded in the subjects' homes. PARTICIPANTS: Thirty-two 9-year-olds and 38 12-year-olds are enrolled in a 4-year longitudinal study of adolescent sleep. There are equal numbers of each sex in both age cohorts. INTERVENTIONS: N/A. MEASUREMENTS: Using ambulatory recorders, EEG was recorded in the subjects' homes on their normal sleep schedule. For each of the 2 semi-annual recording periods, data from the 10 subjects from each age-sex group with the cleanest (fewest artifacts) signals were selected for crosssectional comparisons of visual scoring and EEG variables. All artifact-free 20-second non-rapid eye movement epochs were analyzed with power spectral and period-amplitude analysis. RESULTS: In the 12-year-old cohort, delta power per minute was 37% higher in boys than girls. The 9-year-old cohort showed no sex difference. A second recording 6 months later produced similar results. CONCLUSION: These cross-sectional data indicate that girls begin the steep adolescent decline in slow-wave EEG earlier than boys. We hypothesize that this reflects an earlier onset of adolescent synaptic pruning in females.

Adolescent↗
PubMed1982

The auditory brain stem response in five vertebrate classes.

In representative elasmobranchs, osteichthyans, amphibians, reptiles and birds, average evoked potentials in response to acoustic clicks and tone bursts were recorded intracranially, but outside the brain, or extracranially. Controls against artifacts and tests after transections show that these potentials conform to criteria for auditory brain stem responses (ABRs). Brief waves in a 10-15 msec sequence originate successively in the eighth nerve, medulla and midbrain; there is little contribution to the latter waves from the lower levels. This response pattern appears to be consistent within each species and is similar to that extensively studied in mammals. Some of its features are remarkably alike in all the vertebrate classes tested, implying a generality in the existence of a subset of auditory neurons at several brain levels that are highly synchronous in activity, even after several synapses, and geometrically oriented to add their macroscopic, open, dipole fields. The intensity, repetition rate and the power spectrum of the click stimuli have little effect on the ABR pattern, except when the peak energy is in the low frequency range. In the range below ca. 700 Hz frequency content has a considerable effect; lower frequencies broaden certain waves. Cooling has marked and differential effects on component processes. Reversing click phase, e.g. from initial compression to initial rarefaction, can show no effect or any of several effects, depending on the species. Tone bursts evoke onset ABRs and in some cases after a transitional period a sustained frequency following response. The ABR resembles a click evoked potential even when stimulus rise time is slow. Background tones of particular frequency are most efficient in masking click evoked ABRs; white noise is less efficient. The ABR should be useful in neuroethology since it can be studied without invading the brain. It can tell that the brain is sensitive to a sound. In an immobilized animal it can be recorded in a single sweep, or it can be averaged from an awake tethered animal. It shows good sensitivity and at least some correspondence with behavioral measures of hearing.

Acoustic Stimulation↗
PubMed2003

The wave packet: an action potential for the 21st century.

Sensing and perceiving involve enormous numbers of widely distributed dendritic and action potentials in cortex, before, during and after stimulus arrival but with differing spatiotemporal patterns. Stimulus-activated receptors drive cortical neurons directly (olfactory) or indirectly through thalamocortical relays. The driven activity induces hemisphere-wide, self-organized patterns of neural activity called wave packets. Three levels of brain function are hypothesized to mediate transition from sensation and perception. Microscopic activity expressed by action potentials is sensory. Macroscopic activity of the whole forebrain expressed by behavior is perceptual. Mesoscopic activity bridges the gap by the formation of wave packets. They form when sensory input destabilizes the primary receiving areas by local state transitions. The sensory-driven action potentials condense into mesoscopic wave packets like molecules forming raindrops from vapor. The condensation disks sustain 2D spatial patterns of phase and amplitude of carrier waves in the beta and gamma EEG. The AM patterns correlate not with features but with the context and value of sensory stimuli for the subjects, in a word, their meaning. The wave packets from all sensory areas are broadly transmitted through the forebrain. They induce the formation of macroscopic patterns that coalesce like scintillating pools over much and perhaps all of each hemisphere. The prediction is made for clinical testing that wave packets are precursor to states of awareness. They are not by themselves accessible to experience, as may be the macroscopic states initiated by global state transitions.

Cerebral Cortex↗
PubMed2005

Application of magnetoencephalography in epilepsy patients with widespread spike or slow-wave activity.

PURPOSE: To examine whether magnetoencephalography (MEG) can be used to determine patterns of brain activity underlying widespread paroxysms of epilepsy patients, thereby extending the applicability of MEG to a larger population of epilepsy patients. METHODS: We studied two children with symptomatic localization-related epilepsy. Case 1 had widespread spikes in EEG with an operation scar from a resection of a brain tumor; Case 2 had hemispheric slow-wave activity in EEG with sensory auras. MEG was collected with a 204-channel helmet-shaped sensor array. Dynamic statistical parametric maps (dSPMs) were constructed to estimate the cortical distribution of interictal discharges for these patients. Equivalent current dipoles (ECDs) also were calculated for comparison with the results of dSPM. RESULTS: In case 1 with widespread spikes, dSPM presented the major activity at the vicinity of the operation scar in the left frontal lobe at the peak of the spikes, and some activities were detected in the left temporal lobe just before the peak in some spikes. In case 2 with hemispheric slow waves, the most active area was located in the left parietal lobe, and additional activity was seen at the ipsilateral temporal and frontal lobes in dSPM. The source estimates correlated well with the ictal manifestation and interictal single-photon emission computed tomography (SPECT) findings for this patient. In comparison with the results of ECDs, ECDs could not express a prior activity at the left temporal lobe in case 1 and did not model well the MEG data in case 2. CONCLUSIONS: We suggest that by means of dSPM, MEG is useful for presurgical evaluation of patients, not only with localized epileptiform activity, but also with widespread spikes or slow waves, because it requires no selections of channels and no time-point selection.

Adolescent↗
PubMed2005

B(1) destructive interferences and spatial phase patterns at 7 T with a head transceiver array coil.

RF behavior in the human head becomes complex at ultrahigh magnetic fields. A bright center and a weak periphery are observed in images obtained with volume coils, while surface coils provide strong signal in the periphery. Intensity patterns reported with volume coils are often loosely referred to as "dielectric resonances," while modeling studies ascribe them to superposition of traveling waves greatly dampened in lossy brain tissues, raising questions regarding the usage of this term. Here we address this question experimentally, taking full advantage of a transceiver coil array that was used in volume transmit mode, multiple receiver mode, or single transmit surface coil mode. We demonstrate with an appropriately conductive sphere phantom that destructive interferences are responsible for a weak B(1) in the periphery, without a significant standing wave pattern. The relative spatial phase of receive and transmit B(1) proved remarkably similar for the different coil elements, although with opposite rotational direction. Additional simulation data closely matched our phantom results. In the human brain the phase patterns were more complex but still exhibited similarities between coil elements. Our results suggest that measuring spatial B(1) phase could help, within an MR session, to perform RF shimming in order to obtain more homogeneous B(1) in user-defined areas of the brain.

Algorithms↗
PubMed2006

Epilepsy surgery in a patient with Lennox-Gastaut syndrome and cortical dysplasia.

Lennox-Gastaut syndrome (LGS) is classified as a generalized epilepsy, and is often intractable to antiepileptic drugs. Although corpus callosotomy may sometimes control drop attacks, curative epilepsy surgery is rarely possible in LGS. We report, here, a patient with LGS and focal cortical dysplasia, who became seizure-free after epilepsy surgery. The patient was a 24-month-old boy without perinatal insult in whom seizures began 7 days after birth and who experienced development delay. Brain magnetic resonance imaging (MRI) showed focal cortical lesion with calcification in the right frontal area. At age 13 months, his seizure type changed from tonic seizures to head drops (atonic types) and atypical absence seizures. His interictal electroencephalogram (EEG) showed generalized slow spike and wave discharges, and he was diagnosed with LGS. His seizures were intractable to medical treatment, and a ketogenic diet was not effective. He was evaluated prior to surgery by long-term video-EEG monitoring, which detected many seizures consisted of a sudden onset of falling attacks (atonic type) intermittently followed by atypical absence seizures with diffuse slow wave bursts followed by slow spike and wave discharges in ictal EEG, brain positron emission tomography (PET) and MRI. A right frontal lesionectomy with intra-operative electrocorticography (EcoG) was performed. From the time of lesionectomy to the present, the patient has been seizure free and has been developing normally. Our results suggest that focal resective surgery should be considered in patients with LGS and focal epileptic lesions.

Anticonvulsants↗
PubMed1989

Somnogenic activity of O-acetylated and dimeric muramyl peptides.

Slow-wave sleep-promoting factors in brain and urine were identified as muramyl peptides (MPs), the building blocks of bacterial cell wall peptidoglycan. In this study, structural variations of MPs that occur naturally in bacterial peptidoglycan were investigated for somnogenic activity. Monomeric and dimeric MPs were isolated and purified from Neisseria gonorrhoeae and Actinomadura sp. strain R39. The structures of these MPs were verified by fast atom bombardment mass spectroscopy and tandem mass spectroscopy. After intracerebroventricular administration of MPs, electroencephalograms and brain temperatures of rabbits were recorded for 6 h and were analyzed to determine durations of slow-wave sleep, rapid-eye-movement sleep, and wakefulness. The 6-O acetylation of muramic acid enhanced the somnogenic effects of certain monomeric MPs relative to their non-O-acetylated (but otherwise identical) counterparts. Two monomeric MPs containing an unsubstituted amide (i.e., Iso-Gln) were inactive, thus confirming previous results showing that amidation of a variety of MPs can block somnogenic activity. Two peptide-cross-linked MP dimers tested had no effect on slow-wave sleep, although a third peptide-cross-linked MP containing a 1,6-anhydro muramyl end on one of its monomeric subunits, a structure that enhances somnogenic potency of un-cross-linked monomers, was somnogenic. Two dimers connected by glycosidic bonds and containing an Iso-Gln moiety were inactive. Two other glycosidically linked dimers that also contained an Iso-Gln moiety, but were of lower molecular weight, were somnogenic. In summary, 6-O acetylation of muramic acid in somnogenic MPs enhances activity, and as a class, peptide-linked dimeric MPs tend to be less active than their constituent monomers.

Acetylation↗
PubMed1980

Frequency-specific RSA-like hippocampal patterns elicited by septal, hypothalamic, and brain stem electrical stimulation.

Hippocampal electrographic patterns comprised of specific frequencies of slow waves electrographically similar to the waves comprising normal hippocampal rhythmical slow activity (RSA, theta) may be generated by appropriate electrical stimulation of specific septal, hypothalamic, and brain stem sites. The waves elicited from some but not all sites are further similar to normal RSA patterns in that they may be differentiated into atropine-sensitive (immobility-related) and atropine-resistant (movement-related) types by the same criteria used to define atropine-sensitive and atropine-resistant RSA. The high degree of behavioral, pharmacological, and electrographic similarity between the electrically elicited hippocampal activity and normal hippocampal RSA would seem to warrant further use of the present technique in the investigation of hippocampal function.

Animals↗
PubMed1996

Effect of continuous-wave and amplitude-modulated 2.45 GHz microwave radiation on the liver and brain aminoacyl-transfer RNA synthetases of in utero exposed mice.

Investigations have been carried out concerning the effects of microwave (MW) exposure on the aminoacyl-transfer ribonucleic acid (tRNA) synthetase of the progeny of females that were exposed during their entire period of gestation (19 days). The changes caused by continuous-wave (CW) and amplitude-modulated (AM) MW radiation have been compared. CFLP mice were exposed to MW radiation for 100 min each day in an anechoic room. The MW frequency was 2.45 GHz, and the amplitude modulation had a 50 Hz rectangular waveform (on/off ratio, 50/50%). The average power density exposure was 3 mW/cm2, and the whole body specific absorption rate (SAR) was 4.23 +/- 0.63 W/kg. The weight and mortality of the progeny were followed until postnatal day 24. Aminoacyl-tRNA synthetase enzymes and tRNA from the brains and livers of the offspring (461 exposed, 487 control) were isolated. The aminoacyl-tRNA synthetase activities were determined. The postnatal increase of body weight and organ weight was not influenced by the prenatal MW radiation. The activity of enzyme isolated from the brain showed a significant decrease after CW MW exposure, but the changes were not significant after 50 Hz AM MW exposure. The activity of the enzyme isolated from liver increased under CW and 50 Hz modulated MW.

Amino Acyl-tRNA Synthetases↗
PubMed1979

A functional measure of brain activity: brain stem transmission time.

Surface-recorded auditory nerve and brain stem responses are being used routinely for diagnostic purposes in man. When interest is in auditory diagnosis, the electric response threshold is of primary importance. However, when used in neurological diagnosis, the wave form of the response is important. As a measure of one aspect of response wave form, this paper suggests the use of brain stem transmission time (BTT), defined as the time interval between the first earlobe-negative wave (response of the auditory nerve--the 'input' to the brain stem) and the earlobe-positive wave from the region of the inferior colliculus (the 'output' of the brain stem). The paper shows that BTT is longest in neonates, approaches adult values at the age of about 3 years, is relatively independent of click intensity, conductive hearing loss (middle ear lesion), click rate (except for high rates) and click frequency (filtered clicks). The finding that in a given age group, BTT is generally independent of most stimulus conditions, makes it a useful functional test of brain stem activity.

Adolescent↗
PubMed1990

[Facioscapulohumeral muscular dystrophy (FSH) and hearing loss].

It has been reported that cochlea is the lesion of hearing loss in FSH. However, the details of this lesion are not yet sufficiently known. We performed detailed audiologic studies to examine hearing loss in FSH. We experienced 2 cases of FSH associated with hearing loss. Case 1 was a girl aged 5 years, and case 2 a boy aged 15 years. Clinical findings, EMG and muscle biopsy gave a diagnosis of FSH in both cases. Hearing loss was evaluated by pure tone audiography, speech audiography, tympanometry, stapedial reflex, auditory brain stem response and electrocochleography. In case 1, pure tone audiograms revealed high tone hearing loss without an A-B gap. On speech audiography, the maximum articulation score was 100% and proved normal. The tympanogram was type A. Stapedial reflex was normal bilaterally. The threshold of the 5th wave increased markedly on auditory brain stem response. On electrocochleography, the H-curve of the input-output function curves of action potential was recorded, but the L-curve was absent. There were no complaints of hearing loss in case 2, but pure tone audiograms revealed high-tone hearing loss without an A-B gap. The tympanogram was type A. Stapedial reflex was normal bilaterally. On auditory brain stem response, threshold was increased and latency was prolonged when intensity was lowered. The electrocochleograms were almost normal. It has been reported that, in electrocochleography, the L-curve represents the function of the outer hair cells and the H-curve that of the inner hair cells. The electrocochleograms in case 1 showed damage to the outer hair cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Effects of hypothermia on the cat brain-stem auditory evoked response.

Effects of systemic hypothermia on the brain-stem auditory evoked responses (BAERs) in 4 pentobarbital anesthetized adult cats placed on total cardiopulmonary bypass were investigated. Hypothermia was achieved by slowly cooling the bypass blood through a heat exchanger. Serial BAERs were recorded at 2 min intervals as brain temperature was lowered from 37 to 22 degrees C and then rewarmed over a 1-2 h period. Temperatures were recorded from the brain, esophagus and rectum. Three effects were produced by controlled systemic hypothermia. First, latencies of each component wave (I-V) of the BAER increased exponentially as brain temperature was lowered to 19 degrees C. Latencies of earlier waves (I-III) increased less than those of the later waves (IV-V). Arrhenius plots of inverse latency (rate) versus reciprocal of the absolute temperature generated a family of straight lines of similar slope for each of the 5 component waves of the BAER. The activation energy for each of the 5 BAER waves was derived from the slope of the Arrhenius plot. The mean and standard deviation of the activation energy of all 5 waves was 9.7 +/- 0.5 kcal/mole degree C. The fact that the activation energy was similar for each BAER component wave (I-V) indicated that the increase in latencies for all 5 waves was governed by the same rate-limiting, temperature-dependent process(es). Second, the rise time and duration of each of the component waves of the BAER increased with decreasing temperature. Third, wave amplitudes increased from 37 to 32 degrees C in a quasiparabolic relation and then, decreased at approximately a linear rate. The BAER wave form completely disappeared below 20.3 degrees C. Slow rewarming of the brain to its initial temperature restored the BAER component waves to their original latencies and amplitudes.

Animals↗
PubMed1989

Somnogenic activities of synthetic lipid A.

Bacterial infections and various immune response modifiers, including endotoxin and its lipid A moiety, alter sleep duration. The purpose of this study is to amplify our understanding of lipid A structure-somnogenic-pyrogenic activity relationships. Four synthetic disaccharide analogs of lipid A (LA-15-PP, LA-15-PH, LA-16-PH, and LA-18-PP) and a biosynthetic monosaccharide analog of lipid A (lipid X) were tested in rabbits for their effects on slow-wave sleep, rapid-eye-movement sleep, electroencephalographic slow-wave (0.5- to 4.0-Hz) amplitudes, and brain-colonic temperatures. Substances were injected intravenously and intracerebroventricularly. Compound LA-15-PP was the most potent; it significantly increased slow-wave sleep, delta electroencephalographic amplitudes, and brain-colonic temperatures while reducing rapid-eye-movement sleep. Compound LA-15-PH (monophosphoryl analog of LA-15-PP) induced effects similar to those of LA-15-PP, although the responses were weaker. Compound LA-18-PP induced increases in slow-wave sleep and delta amplitudes only after high doses, whereas compound LA-16-PH was devoid of these activities at the doses tested. Intracerebroventricular, but not intravenous, injections of lipid X induced small but significant increases in both slow-wave sleep and rapid-eye-movement sleep without affecting delta amplitudes or brain-colonic temperatures. These data suggest that the somnogenic actions of these lipid A analogs depend on the acylation or phosphorylation pattern and backbone structures of the molecules. Their soporific activities parallel their relative behaviors in other biological assays.

Animals↗
PubMed2003

Radio-wave exposure of the human head: analytical study based on a versatile eccentric spheres model including a brain core and a pair of eyeballs.

A versatile eccentric-spheres model of the human head is used in this paper to investigate radio-wave absorption. Numerical results, obtained by use of an exact analytical solution, are presented for the total, percentage, and gram-specific absorption. Interest is mainly in the brain and in the eyes of an adult or an infant head. Our model comprises a host sphere and several spherical inclusions, all concentrically stratified with respect to their own center. Any number of inclusions and any number of concentric layers for the host sphere and each one of the inclusions can be considered. Excitation is provided either by a plane-wave or by a nearby electric dipole. The analytical solution is obtained by use of the indirect-mode matching method. The theory of this paper and the accompanying computer code constitute a versatile tool for analytical studies of cellular-phone interactions with the human head. Specific absorption rate maps in a horizontal cross section of the head model manifest the existence of hot spots in the eyes and near the center of the brain.

Adult↗
PubMed1976

Click evoked eighth nerve and brain stem responses (electrocochleogram)--experimental observations in the cat.

The origin of waves two to five occurring in the first 10 milliseconds after repetitive click stimuli is not definitely established. Published studies have suggested that waves two and three are derived from the cochlear nucleus and superior olivary complex respectively and that waves four and five are generated by the inferior colliculus. Our studies of the effect of chronic brain stem lesions in the cat do not support this hypothesis of specific localization, but reveal that a more general reduction in amplitude, and at times prolongation in latency, occurs with lesions in the pons and lower midbrain and that wave one amplitude is also diminished with brain stem lesions.

Animals↗