Spontaneous electrical activity of the rat cerebral cortex during microwave irradiation

A study was made of changes in spontaneous electrical activity of rat brain cortex induced by a single exposure to microwave radiation (electromagnetic fields of 0.1, 1.0, 10, and 35 mW/cm2). The animals were exposed in anechoic chambers to continuous waves at 2450 MHz in conditions of continuous generation. The data obtained indicate that the EEG parameters change under the effect of microwave radiation. The technique applied permits to study the occurrence and development of the CNS reactions to microwave radiation at the time of action of the factor.     

Hemispheric asymmetries in cortical electrical activity during sleep. I

The hypothesis of a predominance of the right hemisphere in stage REM as compared to NREM has been tested through a spectral analysis of the EEG recorded from left (T3) and right (T4) temporal sites in 5 young healthy right-handed male subjects. Variations in the asymmetry coefficient R - L/R + L in different sleep stages have been analyzed by one way ANOVAs and Sheffé's tests. The hypothesis of a progressive increase in left hemisphere activity throughout different REM cycles as one approaches final awakenings have been investigated by comparing variations in the asymmetry coefficient for epochs of REM and stage 2 NREM sampled in different phases of the REM cycle. EEG results do not support either the hypothesized stage dependent or cycle dependent variation in EEG activity during sleep. We question whether variations in EEG amplitude and synchronization can be used as indices of hemispheric asymmetries during sleep.     

Masseter EMG activity during sleep and sleep bruxism

The masseter muscle is involved in the complex and coordinated oromotor behaviors such as mastication during wakefulness. The masseter electromyographic (EMG) activity decreases but does not disappear completely during sleep: the EMG activity is generally of low level and inhomogeneous for the duration, amplitude and intervals. The decreased excitability of the masseter motoneurons can be determined by neural substrates for NREM and REM sleep. The masseter EMG activity is increased in association with the level of arousal fluctuations within either sleep state. In addition, there are some motor events such as REM twitches, swallowing and rhythmic masticatory muscle activity (RMMA), whose generation might involve the additional activation of specific neural circuits. Sleep bruxism (SB) is characterized by exaggerated occurrence of RMMA. In SB, the rhythmic activation of the masseter muscle can reflect the rhythmic motor inputs to motoneurons through, at least in part, common neural circuits for generating masticatory rhythm under the facilitatory influences of transient arousals. However, it remains elusive as to which neural circuits determine the genesis of sleep bruxism. Based on the available knowledge on the masseter EMG activity during sleep, this review presents that the variety of the masseter EMG phenotypes during sleep can result from the combinations of the quantitative, spatial and temporal neural factors eventually sending net facilitatory inputs to trigeminal motoneurons under sleep regulatory systems.     

Background cerebral electrical activity in healthy mental aging

EEG power mapping in the frequency bands from Δ to γ₂ was used to study the changes in the background cerebral activity during “successful” cognitive aging, with the cognitive ability preserved, in subjects engaged in complex occupational activities. The sample consisted of an older age group (OAG) of 32 subjects (14 men and 18 women with a mean age of 65.1 ± 1.18 years) and a younger age group (YAG) of 33 subjects (18 men and 15 women with a mean age of 22.1 ± 0.38 years). The mean power of the slow (Δ, θ, and α₂) rhythms decrease with age, and that of the fast (β and γ) rhythms increase with age. The heterogeneity of the power parameters recorded at different sites was decreased in the OAG compared to the YAG. The centro-lateral power gradient was smoothed in the frequency bands from Δ- to β₂-, and both the centro-lateral and fronto-parietal power gradients and interhemispheric differences, in the α- and β₁ bands in the OAG. The results suggest that the observed age-related changes are prerequisites for the involvement of compensatory mechanisms, which may be related to both mobilization of larger resources ensuring cognitive activity and reorganization of cortical networks in the areas prone to age-related physiological changes.     

Effect of artemether on pentobarbitone sleep and electrical activity in rats

Artemether (AM), a highly effective treatment for multidrug-resistant malaria and a component of artemisinin combination therapy, has been associated with some neurotoxicity following repeated high doses. This study was aimed at investigating the effect of AM on pentobarbitone sleep and electrical activities in rats. Wistar rats received AM i.p. at 3 dose levels: 1.5, 7.5, and 15 mg/kg, whereas control rats received 0.2 mL of the vehicle (3% v/v Tween 80). AM administered 20 min before pentobarbitone had no significant effect on the onset and duration of sleep. However, after a 7-day pretreatment, AM dose-dependently prolonged pentobarbitone sleep, as did chloramphenicol. Electroencephalogram and electromyogram recordings 20 min after pretreatment showed that AM (15 mg/kg) exhibited inhibitory activity similar to chlorpromazine as opposed to the excitatory effect of amphetamine. When pretreated for 7 days, rats receiving 1.5 mg/kg AM also showed inhibitory activity of the cortical centres, whereas desynchronization of the optic tectum and reticular formation was observed in rats pretreated with 7.5 and 15 mg/kg AM. The present data suggest that although the therapeutic equivalent dose of 1.5 mg/kg AM had no appreciable effects on pentobarbitone sleep but caused reduced electrical activity in rats, higher doses have more profound effects on both indices.