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PubMedDate not supplied

Simultaneous response of brain electrical activity (EEG) and cerebral circulation (REG) to microwave exposure in rats.

The correlations between physiological modalities in microwave field-activated systemic or localized regulatory mechanisms with changes in the central nervous system (CNS) seem not to be identical. These problems are important because of the increased number of radiating appliances, e.g. portable radios and mobile telephones. In two series of experiments on anaesthetized rats (N = 40) (i) before and after 10 min, whole body exposures to 2.45 GHz CW microwaves, and (ii) during 30 min exposures to 4 GHz amplitude modulated (AM, 16 Hz) microwaves, the effects on the CNS were observed simultaneously with those on the cardiovascular system by quantitative polygraphic measurement. In acute experiments on rats, electroencephalograms (EEG), rheoencephalograms (REG) as an index of cerebral blood flow (CBF), brain tissue DC impedance and temperature and ECG were recorded simultaneously. The total power of EEG spectra increased after whole body 30 mW/cm2 2.45 GHz CW exposure for 10 min. No changes occurred at 10 mW/cm2. The CBF increased after 10 mW/cm2 exposure. The power of EEG delta (0.5-4 Hz) waves was increased by thermal level of brain localized 4 GHz CW exposure at 42 mW/g specific absorption rate (SAR) simultaneously with the REG amplitude as an index of cerebral blood flow. Amplitude modulation at 16 Hz and 8.4 mW/g SAR was associated with increased power of EEG beta (14.5-30 Hz) waves but changes in the CBF were not observed. CW radiation at 8.4 mW/g increased the cerebral blood flow, but did not change EEG spectra.

Animals↗
PubMed1975

Raised intracranial pressure and cerebral blood flow. 5. Effects of episodic intracranial pressure waves in primates.

The effects of episodic waves of intracranial pressure on cerebral blood flow were studied in primates. Six pressure waves each of 20 minutes' duration and ranging from 50 to 100 mmHg in magnitude were induced in baboons, at intervals of 30 minutes, in an attempt to simulate clinical plateau waves. With pressure waves up to 75 mmHg, cerebral blood flow remained at control levels despite falling cerebral perfusion pressures. Between the initial pressure waves a marked hyperaemia developed, with cerebral blood flow increasing by as much as 100%, and this appeared to be a means whereby adequate flow was maintained during pressure waves. Later pressure waves, up to 100 mmHg, eventually reduced blood flow below control levels, although moderately high flows were maintained during periods of very low perfusion pressure. Brain metabolism was affected by eht episodic pressure waves, although no consistent change was seen.

Acetoacetates↗
PubMed1984

Absent auditory brain stem response: peripheral hearing loss or brain stem dysfunction?

Interpretation of auditory brain stem response (ABR) findings can be problematic in cases where waves III and V are absent. Such findings can be attributed to profound hearing loss, brain stem neuropathology, or both. Over a 3-year period, 48 patients with no known brain stem damage and on whom audiologic data were available were found to have no response by ABR or absent waves III and V. Severe to profound hearing loss was documented in 38 cases, audiometric data were equivocal in 3 cases, and 7 patients showed pure tone sensitivity ranging from normal hearing to moderate impairment. Thus 15% had better hearing sensitivity than might have been expected from their ABR findings. Each of these patients also exhibited abnormal acoustic reflex findings. We report the electrophysiological (ABR, MLR, acoustic reflex), medical (history, neurological, EEG, CT scan) and behavioral (audiometric, speech and language, learning disabilities, psychological) data which characterize this group of patients.

Acoustic Impedance Tests↗
PubMed1986

The depression of the auditory nerve-brain-stem evoked response in hypoxaemia--mechanism and site of effect.

During severe hypoxaemia in the cat the ABR was depressed in 2 different patterns: if mean arterial blood pressure (MAP) was maintained then all other evoked potentials (EPs--somatosensory and visual) remained. If MAP was not maintained, all of these EPs were depressed. This study sought to document these different patterns of ABR depression and to ascertain their mechanisms. When MAP fell, the ABR loss began with the later waves and progressed to the earlier waves. These are signs of a central brain lesion. The hypoxaemia, detrimental to normal function of the cardiovascular system, leads to depression of MAP, to a fall in cerebral perfusion pressure and blood flow, to cerebral ischaemia and ABR loss. On the other hand, when MAP was maintained, severe hypoxaemia was accompanied by a depression of all of the ABR waves at the same time. The cochlear microphonic potential was also simultaneously depressed. These are signs of a peripheral, cochlear effect similar to the demonstrated depression of the positive endocochlear resting potential of the scala media and of the cochlear microphonic potential during hypoxaemia. This leads to interference with the cochlear transduction mechanism so that all of the auditory evoked potentials, including the ABR, are simultaneously depressed. These results lead to the suggestion that the ABR abnormalities seen in patients who suffered a hypoxic (anoxic) insult or an ischaemic episode (prolonged interpeak latencies, loss of later waves and finally all waves absent or only the first wave remaining) is always due to ischaemia even when the initial insult was hypoxic.

Animals↗
PubMed1982

Trigeminal evoked potentials in the cat.

Electrical stimulation of the infraorbital nerve in the cat resulted in a series of far-field evoked potentials at the vertex. The wave form of these potentials is similar to the auditory brain stem evoked response and the somatosensory far-field response; it is multicomponent, the amplitudes of individual components are of the order of 1 microV, and the latencies are all less than 4 msec. The anatomical origins of these evoked potentials were investigated. The results indicated that contributions due to the afferent trigeminal nerve, the principal sensory nucleus, and the spinal trigeminal nucleus are involved.

Animals↗
PubMed2005

Reduced sustained brain activity during processing of positive emotional stimuli in major depression.

BACKGROUND: This study examines the directionality and temporal specificity of brain activity during sustained processing of emotional stimuli in individuals with current major depressive disorder (MDD) and nondepressed control participants. METHODS: Slow wave (SW) components of the event-related brain potential (ERP) were recorded from 16 control participants and 15 participants with MDD during a working memory task. During the task, individuals were shown a positive, neutral, or negative word and were asked to maintain it in memory for 5 sec. Participants then saw a letter and had to decide whether it was a part of the previously presented word. The ERP components were measured from nine scalp sites (F3, Fz, F4, C3, Cz, C4, P3, Pz, P4) during the encoding of emotional words. RESULTS: Compared with control individuals, MDD participants exhibited decreased brain responses to positive relative to negative or neutral stimuli. This decrease in brain activity during processing of positive information was evident across all sites and SW components. CONCLUSIONS: Our findings suggest that cognitive deficits in MDD may stem from diminished brain responses during processing of positive information and may not be associated with an augmented response to negative stimuli.

Acoustic Stimulation↗
PubMedDate not supplied

Slow-wave sleep induced in cats by extremely small amounts of synthetic and pineal vasotocin injected into the third ventricle of the brain.

A single injection of 10(-6) pg synthetic arginine vasotocin (AVT), corresponding to about 600 molecules AVT, into the third ventricle of unanesthetized cats, induced slow-wave sleep 5 min after the injection. An equivalent amount, of a partially purified pineal AVT injected into the third ventricle, produced the same effects. After incubation with trypsin, pineal AVT completely lost its ability to induce slow-wave sleep. The slow-wave sleep induced by 10(-6) pg synthetic AVT injected intraventricularly could be matched by 1 microgram synthetic AVT injected intraperitoneally. Neither synthetic arginine vasopressin, nor synthetic oxytocin, injected intraventricularly in the amount of 10(-6) pg, was able to induce slow-wave sleep. Whereas in the control animals injected with pineal AVT after incubation with trypsin, or in the control animals injected with vasopressin or oxytocin, the paradoxical sleep averaged 21.9--22.8% of the sleep time, during a total recording time of 5 hr, in the cats injected with synthetic or pineal AVT, the paradoxical sleep was completely suppressed.

Animals↗
PubMed1983

Differential effects of benzodiazepines on EEG activity and hypnogenic mechanisms of the brain stem in cats.

The effects of quazepam, flurazepam and diazepam (0.12-1 mg/kg i.v.) on cortical electroencephalogram (EEG) and EEG power spectra were studied in cats with lesioning at various levels of the brain stem (encéphale isolé, midpontine pretrigeminal and cerveau isolé preparations). In the encéphale isoleé, quazepam produced slow waves, spindles and power increases in the 0.5-14 Hz range. Flurazepam produced similar EEG activity but alternated with fast frequency rhythms (8-14 Hz) of moderate amplitude. Diazepam produced spindles superimposed on a continuous fast frequency background while the slow waves were not observed. In the midpointine cats, quazepam modified the desynchronized EEG only at the higher doses. It enhanced the fast rhythms (10-14 Hz) observed in controls. Flurazepam produced similar effects but to a great extent. EEG effects of diazepam were similar to those observed in the encéphale isolé. Thus, the midpontine transection precluded the appearance of the slow wave synchronization. None of the benzodiazepines affected the synchronized EEG of the cerveau isolé. It is suggested that quazepam and, at least in part, flurazepam may induce EEG synchronization and slow wave sleep by influencing hypnogenic mechanisms of the lower brain stem. Fast EEG patterns produced by diazepam and partially by flurazepam seemed unrelated to the sleep-inducing mechanisms while the activating mesencephalic system appeared to be involved.

Animals↗
PubMed1991

Plateau-wave phenomenon (I). Correlation between the appearance of plateau waves and CSF circulation in patients with intracranial hypertension.

Plateau waves, as described by Lundberg (1960), can often be observed in patients with increased intracranial pressure (ICP) resulting from brain tumours, benign intracranial hypertension and other causes. The clinical significance of the waves, however, is still debated. In this study, the ICP was recorded continuously, the size of the ventricular system was evaluated using computerized tomography (CT), the cerebrospinal fluid (CSF) flow was studied using isotope cisternography, and the absorptive capacity of the CSF was determined by measuring the conductance to CSF outflow, in 94 patients with increased ICP. All patients who received continuous ICP monitorings had a basic ICP level of more than 200 mmHg, and these patients were assigned to two groups on the basis of the presence or absence of the plateau waves in the ICP recordings: group I comprising 17 patients without plateau waves but with a high ICP resulting from subarachnoid haemorrhage or hypertensive intracerebral haemorrhage, within 5 days after the start of bleeding; and group II consisting of 77 patients with both plateau waves and a high ICP resulting from brain tumours, meningitis carcinomatosa, benign intracranial hypertension, superior sagittal sinus thrombosis and communicating hydrocephalus. The isotope cisternography and conductance to CSF outflow studies showed that there was neither a delay in CSF circulation nor an impairment of CSF absorption in the group 1 patients and these patients showed no ventricular dilatation on CT, whereas there was a marked sluggishness in the CSF flow and a severe defect in the CSF absorption capacities of the group II patients irrespective of the presence or absence of ventricular dilatation on CT. The present observations indicate that patients with a plateau-wave phenomenon have a marked impairment of CSF absorption and CSF flow. We suggest that the phenomenon is an important sign indicating an impairment of CSF absorption capacities.

Adult↗
PubMed1985

Regional cerebral glucose metabolism in man during wakefulness, sleep, and dreaming.

Regional cerebral glucose metabolism was measured by positron emission tomography in 4 healthy male volunteers, both during wakefulness and sleep, using the 2-deoxy-D-[2-18F]glucose method. While 3 of the subjects did not report dreaming and, during sleep stages I-IV of variable duration, exhibited a non-selective decrease in metabolic rates averaging 12.6 +/- 4.73% (mean +/- S.D.) for the entire brain, the fourth volunteer who experienced an extended nightmare during his sleep examination showed a generalized increase in cerebral glucose utilization ranging from 2.1% in lentiform nucleus to 30.0% in the superior frontal cortex, with a weighted whole brain average of 16.4%. These findings suggest that energy metabolism in the human brain is generally depressed during slow-wave sleep as opposed to a--possibly differential--activation during dreaming.

Adult↗
PubMed1994

Transcranial Doppler and brain death diagnosis.

OBJECTIVES: a) To examine the clinical utility of transcranial Doppler and continuous-wave Doppler in monitoring nonsurgical patients with severe intracranial disease until intracranial circulatory arrest and brain death; and b) to investigate if hemodynamic phenomena that occur under such conditions are correlated to specific transcranial Doppler and continuous-wave Doppler waveforms. DESIGN: Prospective, observational study. SETTING: Medical intensive care unit (ICU) in a city hospital. PATIENTS: Thirty-seven consecutive patients with Glasgow Coma Scores of < 7. MEASUREMENTS AND MAIN RESULTS: Transcranial Doppler examination was conducted transtemporally on the left- and right-middle cerebral artery four times daily. In all patients, transcranial Doppler waveforms exhibited high resistance profiles with low, zero, and then reversed diastolic flow velocity. Only three waveform patterns, consisting of diastolic reverse flow without diastolic forward flow, brief systolic forward flow, and undetectable flow in the middle cerebral artery were registered in the 22 brain-dead patients, but in none of the other comatose patients. CONCLUSION: Transcranial Doppler offers a noninvasive method to document deterioration of cerebral perfusion pressure and in the future could be included in protocols for brain death diagnosis.

Adolescent↗
PubMedDate not supplied

Comparison of auditory brain stem response latency norms for premature infants.

Two investigations were conducted in an attempt to devise an improved set of auditory brain stem response (ABR) latency norms for premature infants. The first study utilized the responses of 130 infants to develop conventional ABR wave V latency norms for different conceptual ages. In addition, three sets of alternative norms were devised which utilized both waves III and V and used ABR interwave intervals as measures of brain stem maturation. A second study examined how well each of the four sets of latency norms predicted the ABR latencies of an additional group of 131 normal-hearing infants. The results of this second study demonstrated that norms utilizing wave III and the I-III interwave interval as an indicator of brain stem maturation were more sensitive than conventional norms, which provide expected wave V latencies for different conceptual ages.

Audiometry, Evoked Response↗
PubMed1972

Organotypic bioelectric activity in cultured reaggregates of dissociated rodent brain cells.

Complex repetitive-spike or slow-wave discharges can be evoked, and can also occur spontaneously, in small clusters of neurons which reaggregate in vitro after dissociation of cerebral cortex, brainstem, or spinal cord from the fetal mouse. Even after random dispersion in culture, these cells still form functional synaptic networks with bioelectric discharge patterns and pharmacologic sensitivities characteristic of the organ (that is, organotypic).

Animals↗
PubMed1987

[Interpretation of paroxysmal slow activity--"subcortical signs"--in the electroencephalography of adults].

Slow paroxysmal EEG activity, also referred to as "subcortical signs", offers an indication of impaired subcortico-cortical functional interaction that may be set off as a result of intracranial processes of a wide range of localisation. For this reason, the occurrence of this EEG pattern should not be taken to indicate a primary localisation in the range of the medical subcortical structures, nor does its absence imply any improbability of extensive lesions in the region. Taking into consideration the form and frequency of the waves during paroxysms and their local distribution, even this aspecific pattern yields more information for the clinical diagnosis. In particular, generalised paroxysms from monomorphic delta waves are usually associated with an existing primary or secondary brain illness, and would suggest the need for further diagnostic clarification. In interpreting the slow-wave groups restricted to the temporal regions, frequently counted among the "subcortical signs", the wave frequency and the patient's age must be taken into account. In the second half of life they frequently occur unaccompanied by any pathological process.

Adult↗
PubMed1998

Subdiaphragmatic vagotomy does not block sleep deprivation-induced sleep in rats.

Cytokines, such as interleukin-1beta (IL-1beta), are involved in physiological sleep regulation and in the sleep responses to sleep deprivation. Sleep deprivation increases systemic cytokine levels and recent evidence suggests that cytokine-to-brain communication occurs via the vagus nerve. Furthermore, the vagus nerve plays a role in sleep responses elicited by feeding and vagal activity affects electroencephalographic (EEG) activity. Thus, this study examined sleep-wake activity and brain temperature (Tbr) responses to sleep deprivation in subdiaphragmatically vagotomized and sham-operated rats. In control rats, 6 h of total sleep deprivation significantly increased nonrapid eye movement sleep (NREMS), rapid eye movement sleep (REMS), and electroencephalographic slow-wave activity during nonrapid eye movement sleep. Brain temperature was significantly increased during the 6 h of sleep deprivation and decreased following sleep deprivation. Vagotomy had no significant effects on any of these variables. These results indicate that the subdiaphragmatic vagus nerve is not critical in the sleep and thermoregulatory responses after 6 h of sleep deprivation. Together with other data, the current results suggest that central pools of interleukin-1 are important in moderate sleep deprivation-induced sleep responses and that vagotomy does not disrupt the ability to increase sleep using a well-known sleep-inducing stimulus likely mediated by brain cytokines.

Animals↗
PubMed1986

[Intracranial pressure irregularities in experimental subarachnoid hemorrhage].

The intracranial pressure (ICP) irregularities, i.e., pressure waves, were studied in dogs with experimental subarachnoid hemorrhage. Animals were lightly anesthetised, immobilised with panchronium bromide and respirated artificially. Subarachnoid infusion of hemolysed red blood cells was used to induce intracranial hypertension. Recordings of both systemic blood pressure (SBP) and ICP were undertaken continuously. After the infusion of hemolysed blood the ICP increased gradually and reached to 50 mmHg or more at the terminal stage. The pressure waves were classified into two types, i.e., the fast waves and the slow waves. The fast waves had a duration of 10-30 seconds, being accompanied by a marked increase of the SBP. The slow waves gradually increased their frequency and the duration, when the ICP increased more than 20 mmHg or more resembling plateau-like waves. Postmorten examination showed hemogenic meningitis at the base of the brain, especially the medulla oblongata. The results suggest that studies of the slow waves is of value for analyzing plateau waves.

Animals↗
PubMed2006

Generalized epilepsy and classic spike-wave discharges with unilateral thalamic lesions.

BACKGROUND: Idiopathic generalized epilepsy (IGE) is a heterogeneous condition with a predominantly genetic origin. Clinical hallmarks of IGE syndromes include generalized spike and wave discharges and normal results on brain imaging. OBJECTIVE: To describe 2 patients with clinical presentations compatible with IGE but whose imaging studies revealed unilateral thalamic lesions. DESIGN: Case reports. SETTING: University-affiliated hospitals. PATIENTS: Two 21-year-old patients (1 man and 1 woman). MAIN OUTCOME MEASURES: Magnetic resonance imaging findings. RESULTS: Magnetic resonance imaging unexpectedly revealed unilateral thalamic lesions. CONCLUSIONS: We recommend doing magnetic resonance imaging studies in patients with IGE, especially in refractory or atypical cases. In rare cases, clinical features compatible with IGE may be associated with structural thalamic or other lesions.

Adult↗