Success of the test task performance by students with different spectral α-rhythm characteristics in the baseline electroencephalogram

The subjects were divided into two groups according to the α₁ and α₂ spectral powers in the occipital derivations of the EEG recorded in the initial state with their eyes closed. Group I included subjects whose α₁-rhythm spectral power (7–10 Hz) was more than 70% of the total α-rhythm band power. Group II included subjects whose α₂-rhythm spectral power (10–13 Hz) was more than 70% of the total α-rhythm band power. It was established that, in the tasks requiring prediction of the subsequent result (memorizing a certain sequence of signals and its subsequent reproduction on the monitor screen), group I subjects differed from group II subjects in fewer sequence errors and a greater number of accurate predictions. In group II subjects, a decrease in the ϑ-band spectral power in the EEG of the central and frontal cortical areas was observed compared to the baseline. Therefore, the EEG ϑ-rhythm power at the memorizing stage was lower in them than in group II subjects. The results suggest that the baseline characteristics of ϑ-activity can be regarded as prognostic criteria of similar types of activity.     

Time-frequency analysis of the electrocortical activity during maturation using wavelet transform

In this study, we introduce the wavelet transform (WT) as a method for characterizing the maturational changes in electrocortical activity in 24 fetal lambs ranging from 110–144 days gestation (term 145 days). The WT, based on multiresolution signal decomposition, is free of assumptions regarding the characteristics of the signal. The approximation of the electrocortical activity at resolutions varying from 2^j+1 to 2^j can be extracted by decomposing the signal on a wavelet orthonormal basis of L ²(R). We performed multiresolution decomposition for four sets of parameters D _2j, where −1<j<−4. The four series WT represent the detail signal bandwidths: (1) 16–32 Hz, (2) 8–16 Hz, (3) 4–8 Hz, (4) 2–4 Hz. The data were divided into three groups according to gestational age: 110–122 days (early), 123–135 days (middle), and 136–144 days (late). In the early group, the power was highest in the fourth signal bandwidth, with relatively low power in the other bands. Increase in gestational age was characterized by increased power in all four bandwidths. Comparison of the cumulative distribution function of the power in the four wavelet bands confirmed the presence of two statistically different patterns in all three age groups. These two patterns correspond to the visually identified patterns of HVSA (high-voltage slow activity) and LVFA (low-voltage fast activity). The earliest development change occurred in HVSA, with progressive increase in power in the 2–8 Hz band. Later changes occurred in LVFA, with a significant increase in power in the 16–32 Hz band. The same database was also analyzed by the short-term Fourier transform (STFT) method, the most common time-frequency analysis method. Comparison of the results clearly show that the WT provided much better time-frequency resolution than the STFT method and was superior in demonstrating maturational changes in electrocortical activity. Received: 7 July 1993/Accepted in revised form: 15 November 1993     

Topographic analysis of dimension estimates of EEG and filtered rhythms in epileptic patients with complex partial seizures

Nonlinear dynamic properties were analyzed on the EEG and filtered rhythms recorded from healthy subjects and epileptic patients with complex partial seizures. Estimates of correlation dimensions of control EEG, interictal EEG and ictal EEG were calculated. The values were demonstrated on topograms. The delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz) and gamma (30–40 Hz) components were obtained and considered as signals from the cortex. Corresponding surrogate data was produced. Firstly, the influence of sampling parameters on the calculation was tested. The dimension estimates of the signals from the frontal, temporal, parietal and occipital regions were computed and compared with the results of surrogate data. In the control subjects, the estimates between the EEG and surrogate data did not differ (P > 0.05). The interictal EEG from the frontal region and occipital region, as well as its theta component from the frontal region, and temporal region, showed obviously low dimensions (P < 0.01). The ictal EEG exhibited significantly low-dimension estimates across the scalp. All filtered rhythms from the temporal region yielded lower results than those of the surrogate data (P < 0.01). The dimension estimates of the EEG and filtered components markedly changed when the neurological state varied. For each neurological state, the dimension estimates were not uniform among the EEG and frequency components. The signal with a different frequency range and in a different neurological state showed a different dimension estimate. Furthermore, the theta and alpha components demonstrated the same estimates not only within each neurological state, but also among the different states. These results indicate that the theta and alpha components may be caused by similar dynamic processes. We conclude that the brain function underlying the ictal EEG has a simple mechanism. Several heterogeneous dynamic systems play important roles in the generation of EEG. Received: 10 December 1999 / Accepted in revised form: 8 May 2000     

Long-term Exposure of Variable Dietary Protein-to-Carbohydrate Ratio: Effect on Brain Regional Glutamatergic Activity with Age

Glutamatergic activity of hypothalamus and hippocampus of young (3 months) male albino rats having normal diet [protein (20%)–carbohydrate (68%)] was increased with the increase of age. Long-term (60 consecutive days) feeding of low protein (8%)–high carbohydrate (80%) diet (LP–HC) increased glutamatergic activity in these brain regions of young rats and decreased that in aged (18 months). On the contrary, supplementation of high protein (50%)–low carbohydrate (38%) diet (HP–LC) under similar condition decreased glutamatergic activity in those brain regions of young and increased that in aged brain regions. Thus, prolonged exposure of LP–HC diet may damage young brain; whereas, HP–LC diet under similar condition causes excitotoxicity to aged brain. Therefore, considering the present scenario in relation to metabolism and receptor activity of glutamatergic system, it may be suggested that long-term consumption of LP–HC and HP–LC diets modulate the brain regional glutamatergic activity reversibly with age.     

Dynamic characteristics of the human resonance EEG responses to rhythmic photostimulation

The development of the resonance EEG responses of the left and right occipital areas was studied in right-handed men during prolonged (12 or 120 s) rhythmic, photostimulation with the intensity of 0.7 J and frequencies of 6, 10, and 16 Hz. Analysis of the EEG fine spectral structure was applied to compare the accumulated baseline EEG spectra and EEG spectra during photostimulation, to observe the dynamics of the short-term spectra and to detect power changes in the EEG narrow spectral band sharply coincident with the stimulation frequency. The more pronounced EEG responses to photostimulation were observed in subjects with the initially low EEG baseline, α-rhythm. Two-minute flash trains produced a substantial increase in the EEG power within the stimulation frequency with superposed oscillatory processes with different periods. These fluctuations are considered a reflection of intricate interaction between the adaptive and resonance EEG responses to the presented intermittent stimulation. Under 12-s stimulation the resonance EEG responses are steadily recorded within the first 3 s of stimulation and immediately after the flash cessation EEG power at the stimulation frequency returns to the initial level. The resonance EEG responses were more pronounced in the right hemisphere than in the left one, especially, at the stimulation frequencies of 6 and 16 Hz. With increasing the stimulation frequency, the maximum of resonance EEG responses was reached earlier. Under the stimulation frequency of 6 Hz, the maximal response was recorded 9–12 s after the beginning of flashes, at the frequencies of 10 and 16 Hz, it was recorded within 3–6 and 3 s, respectively.     

Animal model of Alzheimer’s disease: characteristics of EEG and memory

We studied the effects of aggregated amyloid β-peptide Aβ_25–35 on spatial memory and the spectral-correlational characteristics of EEG of both the dorsal hippocampus and the frontal cortex both in adult and aged rats at the early stage of Aβ_25–35 action. Spatial memory was characterized using a novel cognitive test. A decrease in low-frequency theta band oscillations in the dorsal hippocampus and the frontal cortex was observed. The mean coefficient of EEG cross-correlation between these structures was significantly reduced at the early stage of Aβ_25–35 action both in adult and aged rats. In addition, we found that one month after Aβ_25–35 injection spatial memory was impaired. These results suggest that the decrease in low-frequency theta band oscillations and the weakening of binding between the dorsal hippocampus and the frontal cortex under the action of Aβ_25–35 may be an underlying cause of the typical memory breakdown associated with the Alzheimer’s disease.     

Baseline EEG gamma activity and induced responses to facial stimuli during the formation of a visual cognitive set

The power spectra of cortical potentials of baseline activity during interstimulus intervals (4 s; Fourier transform in the frequency band of 1–60 Hz) and short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15–60 Hz band) were assessed during the study of the visual cognitive set to facial expression. Significant differences between groups of subjects with different set plasticities were observed only at the set-testing stage. Estimation of short-term (0.8 s) induced responses of wavelet spectra in the group with the plastic set revealed an increase in the power (compared to the power of background activity) of the γ₂ band (41–60 Hz) in the temporal, central and occipital areas of the left hemisphere, whereas in the group with the rigid set these power spectra decreased. At the same time, the power in the γ₁ band (21–40 Hz) was significantly lower (at the same level with the rigid form), indicating the discrete nature and functional selectivity in the γ frequency band.     

Brain amines and neocortical EEG in young and aged rats

1. Frontal and parieto-occipital electroencephalography (EEG) of young (4 months-old) and aged (17 and 22 months-old) Wistar rats were analyzed, both during movement and during waking immobility. 2. The levels of monoamines, serotonin and their metabolites were measured from the frontal cortex, parieto-occipital cortex, hippocampus, brainstem and midbrain. 3. In aged rats, as compared to young rats, the most apparent changes of the quantitative EEG spectrum were the decreased amplitude of alpha (5-10 Hz) and beta (10-20 Hz) frequency bands in the frontal and parieto-occipital cortices during both movement and waking immobility behavior (p less than 0.05). 4. The levels of dopamine (DA), homovanillinic acid (HVA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) or the ratios of 5-HT/5-HIAA and DA/HVA did not differ between young and aged rats in any brain region studied, with the exceptions of brainstem DA and parieto-occipital 5-HIAA, which were elevated in aged rats (p less than 0.05). 5. In the frontal cortex, hippocampus and midbrain, noradrenaline (NA) levels of aged rats were slightly increased as compared to young rats (p less than 0.05). 6. NA levels of the parieto-occipital cortex and brainstem did not change during aging. 7. Furthermore, there were no clear correlations between the decreased amplitude of the quantitative EEG spectrum and monoamine or serotonin concentrations, or the ratios of 5-HT/5-HIAA and DA/HVA in the cerebral cortex of aging Wistar rat.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electroencephalograms of patients with initial signs of depression: Independent component analysis

Independent component analysis (ICA) of 19-channel background EEG was performed in 111 patients with the early signs of depressive disorders and in 526 healthy subjects. The power spectra of the independent components were compared in the depressive patients and in healthy subjects at the eyes closed and eyes opened states. Statistically significant differences between the groups were detected in three frequency bands: θ (4–7.5 Hz), α (7.5–14 Hz), and β (14–20 Hz). Increased θ and α activities in parietal and occipital derivations of depressive patients may have been caused by a reduced cortical activity in the projection of these derivation. Diffuse enhancement of the β activity may be correlated with anxiety symptoms that are pronounced in the clinical picture of depressive disorders at early stages of the disease. ICA used to compare quantitative EEG parameters in different groups of patients and in healthy persons makes it possible to localize the differences more accurately than the traditional analysis of EEG spectra.     

EEG correlates of individual differences in performance efficiency of students during examination stress

Performance of cognitive tests and EEG spectral power were evaluated in 39 students aged from 19-21 years in two conditions: during common educational process and immediately before examination (stress condition). Before examination, the performance was better in subjects with low level of spectral density in the delta band (in the occipital, parietal, central and frontal cortical areas) and high level of the alpha-rhythm spectral density in all the cortical areas, A decrease in performance scores before examination was correlated with an increase in the delta activity (in the right frontal and temporal cortical areas) and rise of the anxiety level (tested by Spielberger).     

Emotionality and spatio-temporal organization of momentary EEG potentials

With the aim to reveal features of the neocortical spatiotemporal organization of potentials characteristic of different genetically predetermined emotional levels, momentary values of EEG potentials were analyzed in inbred rats of MR and MNRA strains. A topogram was described by a basic parameter such as its general level (the mean of momentary values of potentials derived from 24 symmetrical electrodes bilaterally implanted into the brain cortex) and a similarity coefficient (correlation between the set of its momentary values and that of a standard topogram). The general level and similarity coefficient values were calculated for a series of successive topograms individually for the right and left hemisphere. Also, right- and left-side power spectra of these series were calculated. In rats of MR strain, significant (p < 0.05) peaks in the general level and similarity coefficient spectra were observed in the delta (2.0 Hz), teta (6.5 Hz) and alpha (9 Hz) frequency bands. In this strain, the general level power was higher at the right side, and the similarity coefficient power displayed the left-side dominance. In rats of MNRA strain, peaks in the delta(2.0 Hz) band coinsided in the general level and similarity coefficient spectra, whereas, independently, the general level spectra had peaks in the theta band (7.0 Hz), and similarity coefficient had peaks at frequencies 3.0, 4.5, and 6.0 Hz. The left-side general level spectral power was higher than the right-side general level spectral power in the delta and lower in the high-frequency theta bands. The similarity coefficient power displayed the left-side dominance for the peaks in the delta (2.0 Hz) and theta (3.0 Hz) bands, and it displayed the right-side dominance for the peaks in the theta (4.5 Hz) band. The specific features of the cortical spatiotemporal organization of potentials revealed in rats of MR and MNRA strains suggest different modes of functioning of at least two systems, reticulo-thalamo-corticaland hippocampo-cortical.     

Induction of emotional states by reading aloud texts with various emotional valences and changes in the EEG power in the β and γ frequency bands

The EEG power in the β₁, β₂, and γ frequency bands during reading according to the method of “self-regulatory utterance” was compared in subjects reading aloud emotionally neutral business texts related to an unknown field of activity, fiction texts with clear positive or negative valences or personally important autobiographic texts with similar emotional valences. Two groups of subjects participated in the study: students training to be actors (N = 22) and students with other specializations (N = 23). We observed higher values of the EEG power in the γ (30–40 Hz) and β₂ (18.5–29.5 Hz) frequency bands when comparing the states during reading of emotionally positive and emotionally negative fiction texts and personally important texts. These data are similar to our previous studies with the use of techniques that apply internal induction of positive or negative emotions without speech, in different groups of subjects. Internal induction of positive emotions was associated with an increase in the EEG power in these bands compared to the performance of an emotionally neutral task, whereas induction of negative emotions resulted in a decrease in the EEG power.     

Modifications of EEG Related to Directed Perception and Analysis of Olfactory Information in Humans

We recorded EEG in adult volunteers in the course of perception of smells of plant essential oils under conditions of directed attention. It was found that perception of olfactory information, even in the case of mild intensity of the smells inducing no aversive effects, correlates with noticeable changes in the EEG characteristics mostly typical of the reaction of nonspecific EEG activation induced by sensory stimulation and manifested in a decrease in the spectral power, SP, of low-frequency EEG components (6–10 Hz)). In addition, the SP of relatively high-frequency EEG components (11–25 Hz) increased; this effect was most pronounced in the occipital regions of the neocortex. Perception of the smells of essential oils was also accompanied by increases in the coherence of EEG oscillations, most intense in the β2 range (20–25 Hz). Such modifications were maximum in the left temporal/parietal region; this is interpreted as an indication of the special role of these cortical areas in the processes of interaction between the neocortical part of the olfactory analyzer and the respective structures of other analyzer systems. It is hypothesized that such interaction is necessary for the formation of a semantic image of the analyzed stimuli. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 70–78, January–February, 2009.     

食物奖赏和渴求行为相关的大鼠左侧眶额叶皮质Delta频段脑电活动(英文）

眶额叶皮质与中脑边缘多巴胺奖赏系统有着复杂的相互纤维联系。先前的研究探讨了药物成瘾过程中眶额叶皮质的脑电活动。在本实验中,将探讨食物奖赏和渴求过程中该皮质的脑电活动。实验采用了两个环境:对照环境和食物刺激相关的环境。首先,训练大鼠在食物刺激相关的环境中吃巧克力花生豆,而后在该环境中设置两种不同的刺激方式:能看到和闻到但不能吃到(渴求实验),或者仍旧可以吃到巧克力花生豆(奖赏实验);同时进行左侧眶额叶皮质的脑电记录。结果发现,在食物刺激相关的环境中大鼠 Delta 频段(2-4 Hz)的脑电活动与食物刺激显著相关,此外,与在对照环境中相比,其相对功率在食物渴求时下降而在食物奖赏时升高。本实验表明,食物相关的奖励可以改变大鼠眶额叶皮质的脑电活动,而且,Delta 频段的脑电活动能够作为监测该奖励的一个指标。     

High Resolution Topography of Age-Related Changes in Non-Rapid Eye Movement Sleep Electroencephalography

Sleeping brain activity reflects brain anatomy and physiology. The aim of this study was to use high density (256 channel) electroencephalography (EEG) during sleep to characterize topographic changes in sleep EEG power across normal aging, with high spatial resolution. Sleep was evaluated in 92 healthy adults aged 18–65 years old using full polysomnography and high density EEG. After artifact removal, spectral power density was calculated for standard frequency bands for all channels, averaged across the NREM periods of the first 3 sleep cycles. To quantify topographic changes with age, maps were generated of the Pearson’s coefficient of the correlation between power and age at each electrode. Significant correlations were determined by statistical non-parametric mapping. Absolute slow wave power declined significantly with increasing age across the entire scalp, whereas declines in theta and sigma power were significant only in frontal regions. Power in fast spindle frequencies declined significantly with increasing age frontally, whereas absolute power of slow spindle frequencies showed no significant change with age. When EEG power was normalized across the scalp, a left centro-parietal region showed significantly less age-related decline in power than the rest of the scalp. This partial preservation was particularly significant in the slow wave and sigma bands. The effect of age on sleep EEG varies substantially by region and frequency band. This non-uniformity should inform the design of future investigations of aging and sleep. This study provides normative data on the effect of age on sleep EEG topography, and provides a basis from which to explore the mechanisms of normal aging as well as neurodegenerative disorders for which age is a risk factor.     

Sleep changes induced by lipopolysaccharide in the rat are influenced by age

In mammals, aging is associated with immune senescense. To examine whether the sleep changes occurring during immune challenge are affected by age, we assessed sleep alterations induced by the administration of lipopolysaccharide (LPS) in young and middle-aged rats. During vehicle, the middle-aged rats exhibited less pre-rapid eye movement sleep (pre-REMS) as well as REMS, due to a smaller number and shorter duration of REMS episodes, than young rats. LPS elevated body temperature, increased non-REMS, and suppressed both pre-REMS and REMS in the young as well as in the middle-aged rats. However, in the young animals, LPS significantly enhanced slow-wave activity in the electroencephalogram (EEG) within non-REMS, reflecting an increase in sleep intensity. In contrast, LPS attenuated EEG power in most frequency bands in the older animals. This finding indicates age-related changes in the modulation of sleep by LPS.     

Transitions from Wakefulness to Sleep at Different Times of Day: Old vs. Young Subjects

In order to assess age effects upon the daytime level of alertness, both subjective and objective measures of alertness were obtained in 19 healthy elderly males (mean age 65 years) and 19 healthy young males (mean age 21 years). Subjects were recorded during a Multiple Sleep Latency Test (MSLT), administered at 5 different times of day (9 a.m., 12 a.m., 3 p.m., 6 p.m., 9 p.m.). Before each test, subjects filled out an alertness questionnaire. During the entire 20 minutes of each test electroencephalographic (EEG) recordings were made and transformed into 40 averaged spectra, one for each 30 s epoch. For the delta, theta, alpha, sigma and beta bands of the EEG 6 consecutive values were averaged to obtain 1 value per 3 minutes. On the basis of the visually guided detection of the first spindle, sleep onset was determined. The elderly subjects obtained a higher overall level of subjective alertness than the young subjects. No age effect was observed for sleep latency, which followed a U-shaped diurnal trend. Overall, the mean relative EEG energy values followed a diurnal trend that was the reverse of that for sleep latency. The mean relative delta EEG energy gradually increased, and the mean relative alpha EEG energy gradually decreased across the MSLT. For the young subjects the respective ranges of variation of these EEG bands were very similar, while for the elderly subjects the range of variation of the alpha values was less than half of that for the delta band. Apparently, alpha EEG activity during the wake-sleep transition does not simply covary with delta EEG activity. Moreover, age appears to have a significant effect upon the dynamics of alpha EEG activity during the wake-sleep transition.     

Spectral and coherence EEG analysis of rats differing in the level of seizure readiness

The resting EEGs of several brain structures (motor and visual cortex, caudate nucleus and intralaminar thalamic nuclei) were submitted to spectral and coherence computer analyses in two rat strains. Genetically predisposed to convulsive state KM rats were shown to differ from nonpredisposed Wistar rats in EEG spectral properties. KM rats EEG pattern was characterized by increase of low frequencies (1-2 Hz) power and decrease of faster activity (5-12 Hz) power in cortical spectrograms as well as by decrease of caudate nucleus EEG absolute power. The coherence value between cortical or subcortical structures at below 4 Hz was intensified in KM rats. Reinforcement of cortical auto-oscillating properties manifested by ECoG synchronization in cortical-thalamic resonance interaction as well as weakening of striatal inhibitory system may constitute neurophysiological mechanisms of enhanced convulsive readiness. The probable role of mediator imbalance in these mechanisms is discussed.     

State-dependent effects of light-dark cycle on somatosensory and visual cortex EEG in rats

Somatosensory (SSctx) and visual cortex (Vctx) EEG were evaluated in rats under a 12:12-h light-dark (LD) cycle and under constant light (LL) or constant dark (DD) in each sleep or wake state. Under LD conditions during light period, relative Vctx EEG slow-wave activity (SWA) was higher than that of the SSctx, whereas during dark period, relative Vctx EEG SWA was lower than in the SSctx. These effects were state specific, occurring only during non-rapid eye movement sleep (NREMS). Under LL conditions, the duration of REMS and NREMS during the period that would have been dark if the LD cycle had continued (subjective dark period) was greater than under LD conditions. DD conditions had little effect on the duration of NREMS and REMS. SSctx and Vctx EEG SWA were suppressed by LL during the subjective dark period; however, the degree of Vctx SWA suppression was smaller than that of the SSctx. DD conditions during the subjective light period enhanced SSctx SWA, whereas Vctx SWA was suppressed. Under LL conditions during the subjective dark period, Vctx EEG power was higher than that of the SSctx across a broad frequency range during NREMS, REMS, and wakefulness. During DD, SSctx EEG power during NREMS was higher than that of the Vctx in the delta wave band, whereas SSctx power during REMS and wakefulness was higher than that of the Vctx in frequencies higher than 8 Hz. We concluded that the SSctx and Vctx EEGs are differentially affected by light during subsequent sleep. Results provide support for the notion that regional sleep intensity is dependent on prior regional afferent input.     

Age-associated deficit of mitochondrial oxidative phosphorylation in skeletal muscle: Role of carnitine and lipoic acid

Mitochondrial damage has implicated a major contributor for ageing process. In the present study, we measured mitochondrial membrane swelling, mitochondrial respiration (state 3 and 4) by using oxygen electrode in skeletal muscle of young (3–4 months old) and aged rats (above 24 months old) with supplementation of l-carnitine and dl-α-lipoic acid. Our results shows that the mitochondrial membrane swelling and state 4 respiration were increased more in skeletal muscle mitochondria of aged rats than in young control rats, whereas the state 3 respiration, respiratory control ratio (RCR) and ADP:O ratio decreased more in aged rats than in young rats. After supplementation of carnitine and lipoic acid to aged rats for 30 days, the state 3 respiration and RCR were increased, whereas the state 4 and mitochondrial membrane swelling were decreased to near normal rats. From our results, we conclude that combined supplementation of carnitine and lipoic acids to aged rats increases the skeletal muscle mitochondrial respiration, thereby increasing the level of ATP. (Mol Cell Biochem xxx: 83–89, 2005)