Unilateral vibrissae stimulation during waking induces interhemispheric EEG asymmetry during subsequent sleep in the rat

To test the theory that sleep is a regional, use-dependent process, rats were subjected to unilateral sensory stimulation during waking. This was achieved by cutting the whiskers on one side, in order to reduce the sensory input to the contralateral cortex. The animals were kept awake for 6 h in an enriched environment to activate the cortex contralateral to the intact side. Whiskers are known to be represented in the barrel field of the contralateral somatosensory cortex and their stimulation during exploratory behavior results in a specific activation of the projection area. In the 6 h recovery period following sleep deprivation, spectral power of the nonrapid eye-movement (NREM) sleep EEG in the 0.75-6.0 Hz range exhibited an interhemispheric shift towards the cortex that was contralateral to the intact whiskers. The results support the theory that sleep has a regional, use-dependent facet.     

Interhemispheric sleep EEG asymmetry in the rat is enhanced by sleep deprivation

Vigilance state-related topographic variations of electroencephalographic (EEG) activity have been reported in humans and animals. To investigate their possible functional significance, the cortical EEG of the rat was recorded from frontal and parietal derivations in both hemispheres. Records were obtained for a 24-h baseline day, 6-h sleep deprivation (SD), and subsequent 18-h recovery. During the baseline 12-h light period, the main sleep period of the rat, low-frequency (<7.0 Hz) power in the non-rapid eye-movement (NREM) sleep EEG declined progressively. Left-hemispheric predominance of low-frequency power at the parietal derivations was observed at the beginning of the light period when sleep pressure is high due to preceding spontaneous waking. The left-hemispheric dominance changed to a right-hemispheric dominance in the course of the 12-h rest-phase when sleep pressure dissipated. During recovery from SD, both low-frequency power and parietal left-hemispheric predominance were enhanced. The increase in low-frequency power in NREM sleep observed after SD at the frontal site was larger than at the parietal site. However, frontally no interhemispheric differences were present. In REM sleep, power in the theta band (5.25-8.0 Hz) exhibited a right-hemispheric predominance. In contrast to NREM sleep, the hemispheric asymmetry showed no trend during baseline and was not affected by SD. Use-dependent local changes may underlie the regional differences in the low-frequency NREM sleep EEG within and between hemispheres. The different interhemispheric asymmetries in NREM and REM sleep suggest that the two sleep states may subserve different functions in the brain.     

Interhemispheric EEG asymmetry in patients with insomnia during nocturnal sleep

Sleep EEG was recorded and analyzed in patients with neurotic insomnia. It was found that interhemispheric asymmetry in the same individual can vary during sleep from right-hemispheric to left-hemispheric. Interhemispheric EEG asymmetry is closely related to the stage of sleep. The development of left-hemisphere or right-hemisphere asymmetry is mainly determined by activity of the right hemisphere. The development of interhemispheric asymmetry during wakefulness, stages 1 and 2 sleep, and delta sleep is mediated by common mechanisms. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 2, pp. 157–160, February, 2006     

Interhemispheric asymmetry of human sleep EEG in response to selective slow-wave sleep deprivation

Recent evidence suggests that the human sleep electroencephalogram (EEG) shows regional differences over both the sagittal and coronal planes. In the present study, in a group of 10 right-handers, the authors investigated the presence of hemispheric asymmetries in the homeostatic regulation of human sleep EEG power during and after selective slow-wave sleep (SWS) deprivation. The SWS deprivation was slightly more effective over the right hemisphere, but the left hemisphere showed a markedly larger increase of EEG power in the 1.00-24.75 Hz range during recovery-night non-REM sleep, and a larger increase of EEG power during both deprivation-night and recovery-night REM sleep. These results support the greater need for sleep recuperative processes of the left hemisphere, suggesting that local sleep regulation processes may also act during REM sleep.     

Regional differences in cortical electroencephalogram (EEG) slow wave activity and interhemispheric EEG asymmetry in the fur seal

Slow wave sleep (SWS) in the northern fur seal (Callorhinus ursinus) is characterized by a highly expressed interhemispheric electroencephalogram (EEG) asymmetry, called ‘unihemispheric’ or ‘asymmetrical’ SWS. The aim of this study was to examine the regional differences in slow wave activity (SWA; power in the range of 1.2–4.0 Hz) within one hemisphere and differences in the degree of interhemispheric EEG asymmetry within this species. Three seals were implanted with 10 EEG electrodes, positioned bilaterally (five in each hemisphere) over the frontal, occipital and parietal cortex. The expression of interhemispheric SWA asymmetry between symmetrical monopolar recordings was estimated based on the asymmetry index [AI = (L?R)/(L+R), where L and R are the power in the left and right hemispheres, respectively]. Our findings indicate an anterior–posterior gradient in SWA during asymmetrical SWS in fur seals, which is opposite to that described for other mammals, including humans, with a larger SWA recorded in the parietal and occipital cortex. Interhemispheric EEG asymmetry in fur seals was recorded across the entire dorsal cerebral cortex, including sensory (visual and somatosensory), motor and associative (parietal or suprasylvian) cortical areas. The expression of asymmetry was greatest in occipital–lateral and parietal derivations and smallest in frontal–medial derivations. Regardless of regional differences in SWA, the majority (90%) of SWS episodes with interhemispheric EEG asymmetry meet the criteria for ‘unihemispheric SWS’ (one hemisphere is asleep while the other is awake). The remaining episodes can be described as episodes of bilateral SWS with a local activation in one cerebral hemisphere.     

Modification of EEG asymmetry induced by auditory biofeedback loop during REM sleep in man

Several studies have emphasized the relationship between (1) rapid eye movement sleep (REM sleep) and learning, and (2) between REM sleep and asymmetry in EEG activity. Since we have shown that obtaining operant conditioned responses via auditory biofeedback during REM sleep is feasible, we demonstrate here that REM contingent auditory stimulations (white noise stimulation or interruption of a continuous white noise stimulation) lead to differential changes in phasic and tonic components of REM sleep. Whereas during baseline nights a relative right activation is found in the medium bands of EEG frequencies, our procedure seems to induce a systematic interhemispheric change during experimental nights. A new approach to the information processing hypothesis during REM sleep is proposed in terms of functional lateralized modifications of the EEG.     

NREM sleep with low-voltage EEG in the rat

NREM sleep in the rat has traditionally been defined by electroencephalographic (EEG) amplitudes above those of wakefulness (W) and paradoxical sleep (PS); we refer to this high-amplitude NREM sleep as "HS." We have found that approximately 5% of total time is occupied by episodes in which EEG amplitude is low, distinguishing it from HS; theta amplitude is low, distinguishing it from PS; and electromyographic (EMG) amplitude is low, distinguishing it from W. We have called these low-EEG, low-theta, low-EMG episodes "low-amplitude sleep" (LS). Three studies are done to elucidate additional characteristics of LS. Polygraphically scored 30-s epochs were matched with independent classifications of rat behavior as W, NREM, or PS; 87% of polygraphically scored LS epochs were matched with NREM sleep behavior. Response thresholds to noxious stimuli were lowest in W, intermediate and similar in LS and HS, and highest in PS. The incidence of PGO-type (ponto-geniculo-occipital) waves in W, HS, and LS were all very low in comparison with rates in PS. Thus, LS and HS exhibited similarly quiescent spontaneous behavior, similar intermediate response thresholds, and similar low rates of PGO-type activity. Accordingly, we have proposed that LS, along with HS, is an NREM sleep stage.     

EEG alpha power and alpha power asymmetry in sleep and wakefulness.

Asymmetry of waking electroencephalography (EEG) alpha power in frontal regions has been correlated with waking emotional reactivity and the emotional content of dream reports. Little is known regarding alpha asymmetry during sleep. The present study was performed to compare alpha power and alpha power asymmetry in various brain regions across states of sleep and wakefulness. Waking and sleep EEG were recorded in a group of patients undergoing polysomnographic evaluation for possible sleep disorders. Alpha EEG asymmetry in frontal and temporal regions was significantly correlated in waking versus sleep, particularly during rapid eye movement (REM) sleep. These results suggest that patterns of frontal alpha asymmetry are stable across sleep and waking and may be related to emotional reactivity during dreaming. During sleep, alpha power was highest during slow-wave sleep and lowest during REM sleep. Implications of these data for understanding the functional significance of alpha power during waking and sleeping are considered.     

Sexual dimorphism of the interhemispheric asymmetry dynamics during the processing of the transcallosal signal

The characteristics of the dynamics of the functional interhemispheric asymmetry (FIAs) of the transcallosal influences in male and female rats were compared in this study through an analysis of the amplitude-temporal parameters of the homotopic transcallosal responses (TCR) in the course of their multiple topographical pickup from the dorsolateral surface of the cortex of both hemispheres in the time interval of the realization of the components of the responses. Two principal types of patterns of hemispheric dominance have been distinguished. The first type was described in accordance with the rule of the right-left-right shift of FIAs; the second type was described in accordance with the rule of its left-right-left shift. The changes in the FIAs of the temporal parameters of the positive components and the amplitude parameters of the positive and negative fluctuations were characterized by the identical type of dynamics in rats of both sexes. The dynamics of the FIAs of the temporal parameters of the negative components unfolded in accordance with the first type in the females, but in accordance with the second type in the males. The dominance of the investigated zones of the cortex of the right hemisphere was expressed more markedly in the females at the initial and terminal stages of the processing of transcallosal information. The phases of the dominance of the left hemisphere, by contrast, were identified and detected in a relatively larger territory of the neocortex examined in the males by comparison with the females. The results obtained suggest the relatively greater participation of the cortex of the right hemisphere in the females, but of the left hemisphere in the males during the processing of a transcallosal signal. Laboratory of the Neurobiology of Behavior, Biological Scientific-Research Institute of the State University, Saint Petersburg. Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 80, No. 12, pp. 21–33, December, 1994.     

Topographic mapping of EEG during sleep

Summary Topographic aspects of all night sleep EEG were investigated in 10 healthy volunteers (age 20–35 years). EEG brain maps showed an increase of delta power from stage 1 to 4, a decrease of alpha power most pronounced parieto-occipitally and a slowing of the dominant alpha frequency. Differences of EEG power in different sleep stages (as compared to wakefulness) are displayed topographically. Analysis of the course of stage 2 showed an increase of delta power and a decrease of theta power in the first sections of the night, and an increase of beta power later in the night.     

Prolonged effects of 24-h total sleep deprivation on sleep and sleep EEG in the rat

Long-term effects of 24-h sleep deprivation (SD) on sleep and sleep EEG were analyzed in male rats during 4 recovery days (Rec). An increase of total sleep time and non-rapid eye-movement (NREM) sleep was present during Rec 1-4, and of REM sleep in Rec 1 and in the dark periods of Rec 2 and 3. After the initial increase of slow-wave activity (SWA, mean EEG power density in the 0.75-4.0 Hz range) in NREM sleep, SWA declined below baseline until Rec 3. Sleep continuity was increased in Rec 1. The persistent effects of SD which are probably due to homeostatic and circadian facets of sleep regulation, must be taken into account in the design of SD studies.     

Functional regional asymmetry in intrahemisphere coherencein the EEG during conditioning in dogs

The individual characteristics of regional interhemisphere relationships were studied during acquisition of a food-related conditioned reflex in dogs. Electrical activity was recorded from symmetrical anterior (frontal and motor) and posterior (auditory and visual) areas of the brain. Comparison of averaged intrahemisphere EEG coherence values in the left and right hemispheres of the brain revealed individual features of regional interhemisphere relationships. In dogs with the strong type of nervous system, higher levels of EEG coherence in the anterior areas of the cerebral cortex were seen in the left hemisphere, while coherence in the posterior areas was greater in the right hemisphere. The opposite pattern was seen in animals with the weak type of nervous system. Thus, the spatial organization of cortical electrical activity differed in the associative and projection areas. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 56, No. 1, January–February, 2006, pp. 56–64.     

The asymmetry of interhemispheric interaction in reverse-stroop task

The purpose of the present study was to examine the effect of interference on interhemispheric interaction in the reverse-stroop task. In two experiments, color-word in black ink and color-patch in red or blue ink were briefly presented to a bilateral visual-field (BVF). The participants were asked to identify the color word, ignoring the color patch. In Experiment 1, color-words written in kanji character were used as target ([Chinese character: see test] or [Chinese character: see test]). In Experiment 2, color-words written in kana character were used as target ([Chinese characters: see test] or [Chinese characters: see test]). The result in Experiment I showed that the size of the interference effect was invariant irrespective of the visual-field of the target. On the contrary, in Experiment 2, the interference effect was larger in the condition where the kana color-word was presented to left visual-field (LVF) than to right visual-field (RVF). These results suggested that the interference effect would be modulated by the dominant hemisphere for processing the target.     

Changes of interhemispheric hippocampal responses during conditioning in the awake rat

Summary The responses of the hippocampus of the awake rat to stimulation of one of its afferent pathways were measured during classical conditioning. It was found that when the contralateral hippocampus is stimulated concurrently with the presentation of a conditioned stimulus preceding either food or an aversive shock, a late (30–40 msec) negative component in the averaged evoked response can be recorded. This late component was absent when the interhemispheric stimulation was applied prior to presentation of a conditioned stimulus or when the rat was satiated or pretreated with drugs which interfere with noradrenergic or serotonergic neurotransmission. It is suggested that classical conditioning changes neurotransmission in certain pathways in the brain and that the monoamines are involved in mediation of this change.     

A method for the diagnosis of interhemispheric brain asymmetry

Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 76, No. 11, pp. 1632–1636, November, 1990.     

Electroencephalogram asymmetry and spectral power during sleep in the northern fur seal

The fur seal (Callorhinus ursinus), a member of the Pinniped family, displays a highly expressed electroencephalogram (EEG) asymmetry during slow wave sleep (SWS), which is comparable with the unihemispheric sleep in cetaceans. In this study, we investigated the EEG asymmetry in the fur seal using spectral analysis. Four young (2-3 years old) seals were implanted with EEG electrodes for polygraphic sleep recording. In each animal, EEG spectral power in the frequency range of 1.2-16 Hz was computed in symmetrical cortical recordings over two consecutive nights. The degree of EEG asymmetry was measured by using the asymmetry index [AI = (L - R)/(L + R), where L and R are the spectral powers in the left and right hemispheres, respectively]. In fur seals, EEG asymmetry, as measured by the percent of 20-s epochs with absolute AI > 0.3 and >0.6, was expressed in the entire frequency range (1.2-16 Hz). The asymmetry was significantly greater during SWS (25.6-44.2% of all SWS epochs had an absolute AI > 0.3 and 2.1-12.2% of all epochs had AI > 0.6) than during quiet waking (11.0-20.3% and 0-1.9% of all waking epochs, respectively) and REM sleep (4.2-8.9% of all REM sleep epochs and no epochs, respectively). EEG asymmetry was recorded during both low- and high-voltage SWS, and was maximal in the range of 1.2-4 and 12-16 Hz. As shown in this study, the degree of EEG asymmetry and the frequency range in which it is expressed during SWS in fur seals are profoundly different from those of terrestrial mammals and birds.