PubMed Health⌕ Search

Biomedical subjects

Vadim V Nikulin

Publications and source records attributed to Vadim V Nikulin.

11 recordsLinked to original sources
PubMed2005

Effects of alcohol on spontaneous neuronal oscillations: a combined magnetoencephalography and electroencephalography study.

Electroencephalography (EEG) and magnetoencephalography (MEG) can detect different aspects of alcohol effects on auditory processing measured with event-related potentials and magnetic fields. The present study aimed to detect alcohol-induced changes in spontaneous neuronal oscillations with combined EEG and MEG techniques. The effects of alcohol on spontaneous neuronal rhythms were studied in 12 healthy subjects after 0.8 g/kg alcohol or juice in a double-blind, placebo-controlled, cross-over design using simultaneous high-resolution MEG and EEG in eyes-open and eyes-closed conditions. The data were analyzed with a power spectral density analysis. MEG recording showed that alcohol significantly increased the relative power of alpha rhythm (8-10 Hz) and reduced the relative power of beta activity (17-25 Hz) in both left and right hemispheres, but only in the eyes-closed condition. These effects did not depend on gender. No analogous statistically significant changes were observed in EEG rhythms. However, the power of alpha and beta rhythms was positively correlated in MEG and EEG recordings, indicating that MEG and EEG reflect similar processes. A distinct sensitivity of MEG and EEG to the sources of cortical oscillations, a better signal-to-noise ratio of MEG, as well as strong spatial blurring of potentials in EEG are most likely the reasons for the observed differences in the effects of alcohol on spontaneous oscillations as detected with two methods.

Adult↗
PubMed2005

Functional links between motor and language systems.

Transcranial magnetic stimulation (TMS) was applied to motor areas in the left language-dominant hemisphere while right-handed human subjects made lexical decisions on words related to actions. Response times to words referring to leg actions (e.g. kick) were compared with those to words referring to movements involving the arms and hands (e.g. pick). TMS of hand and leg areas influenced the processing of arm and leg words differentially, as documented by a significant interaction of the factors Stimulation site and Word category. Arm area TMS led to faster arm than leg word responses and the reverse effect, faster lexical decisions on leg than arm words, was present when TMS was applied to leg areas. TMS-related differences between word categories were not seen in control conditions, when TMS was applied to hand and leg areas in the right hemisphere and during sham stimulation. Our results show that the left hemispheric cortical systems for language and action are linked to each other in a category-specific manner and that activation in motor and premotor areas can influence the processing of specific kinds of words semantically related to arm or leg actions. By demonstrating specific functional links between action and language systems during lexical processing, these results call into question modular theories of language and motor functions and provide evidence that the two systems interact in the processing of meaningful information about language and action.

Adult↗
PubMed2004

Prestimulus oscillations enhance psychophysical performance in humans.

The presence of various ongoing oscillations in the brain is correlated with behavioral states such as restful wakefulness or drowsiness. However, even when subjects aim to maintain a high level of vigilance, ongoing oscillations exhibit large amplitude variability on time scales of hundreds of milliseconds to seconds, suggesting that the functional state of local cortical networks is continuously changing. How this volatility of ongoing oscillations influences the perception of sensory stimuli has remained essentially unknown. We investigated the relationship between prestimulus neuronal oscillations and the subjects' ability to consciously perceive and react to somatosensory stimuli near the threshold of detection. We show that, for prestimulus oscillations at approximately 10, 20, and 40 Hz detected over the sensorimotor cortex, intermediate amplitudes were associated with the highest probability of conscious detection and the shortest reaction times. In contrast, for 10 and 20 Hz prestimulus oscillations detected over the parietal region, the largest amplitudes were associated with the best performance. Our data indicate that the prestimulus oscillatory activity detected over sensorimotor and parietal cortices has a profound effect on the processing of weak stimuli. Furthermore, the results suggest that ongoing oscillations in sensory cortices may optimize the processing of sensory stimuli with the same mechanism as noise sources in intrinsic stochastic resonance.

Adult↗
PubMed2004

Time course and variability of power in different frequency bands of EEG during resting conditions.

The aim of the present study was to evaluate the variability of EEG power spectrum data, considering the time course of the EEG spectrum in resting conditions, and the relationship between the spectral parameters and the length of the analyzed segments. Recordings were performed in 57 normal subjects, with a protocol consisting of regular cycles with open eyes (5 s) followed by closed eyes (55 s) repeated during 10 min. Towards the end of the recording there was a decrease in the alpha and beta power and an increase in the delta and theta power. The coefficient of variation (CV) for the power of 4 s epochs was in the range 0.49-0.67 (delta), 0.53-0.58 (theta), 0.58-0.76 (alpha), 0.37-0.49 (beta) and 0.09-0.12 for the alpha peak frequency. CV decreased with the increase of the sample size, being inversely proportional to the square root of the sample size. Increasing the recording length from 40 to 400 s increased CV by 36% (alpha), 41% (beta), 29% (delta) and 35% (theta), while the standard error of the mean decreased by 55-60%. It is concluded that the power estimates of the EEG activity are heavily dependent on the length of the analyzed segments, and the way they are selected. This observation is particularly relevant for clinical and drug studies where short recordings are often used, thus significantly biasing the estimation of the EEG parameters. The present data provide an estimate on the minimal length of EEG required for a given level of variability.

Adult↗
PubMed2004

Long-range temporal correlations in alpha and beta oscillations: effect of arousal level and test-retest reliability.

OBJECTIVE: The aim of the present study was to evaluate test-retest reliability and condition sensitivity of long-range temporal correlations in the amplitude dynamics of electroencephalographic alpha and beta oscillations. METHODS: Twelve normal subjects were measured two times with a test-retest interval of several days. Open- and closed-eyes conditions were used, representing different levels of arousal. The amplitude of the alpha and beta oscillations was extracted with bandpass filtering and the Hilbert transform. The long-range temporal correlations were quantified with detrended fluctuation analysis. RESULTS: The amplitude dynamics of the alpha and beta oscillations demonstrated power-law long-range temporal correlations lasting for tens of seconds. These correlations were degraded in the open- compared to the closed-eyes condition. Test-retest statistics demonstrated that the long-range temporal correlations had significant reliability, which was greatest in the closed-eyes condition. CONCLUSIONS: The presence of long-range temporal correlations indicates that the amplitude of neuronal oscillations at a given time is dependent on the amplitude at times as remote in the past as tens of seconds. The reliability of long-range temporal correlations suggests that the mechanisms generating the amplitude fluctuations are not perturbed over several days. The systematic changes in the scaling exponents at different levels of arousal indicate that these changes occur on many time scales (5-80 s) as a result of modifications in the intrinsic dynamics of the neuronal oscillations. SIGNIFICANCE: This study demonstrates that the dynamics of spontaneous neuronal oscillations possess long-range temporal correlations with properties suitable for functional and clinical studies.

Adult↗
PubMed2004

Stimulus-induced change in long-range temporal correlations and scaling behaviour of sensorimotor oscillations.

The human brain spontaneously generates large-scale network oscillations at around 10 and 20 Hz. The amplitude envelope of these oscillations fluctuates intermittently and was recently reported to exhibit power-law decay of the autocorrelation for hundreds of seconds. This indicates that the underlying networks are in a dynamic state resembling the self-organized critical state known to exist in many complex systems. Based on the mechanism of how correlations emerge in these systems, we hypothesized that the physiological basis of long-range power-law correlations is the buildup of a memory of past activity by a continuous modification of the network's functional connectivity by the ongoing oscillations. In this framework, exogenous perturbations of ongoing oscillations would degrade or abolish this dynamic network memory. We investigated the sensitivity of the temporal correlations in sensorimotor 10- and 20-Hz oscillations to median nerve stimulation that is known to have immediate effects on ongoing oscillations. Our results show that the amplitude fluctuations of these oscillations were effectively modulated by the somatosensory stimuli but still exhibited long-range temporal correlations and power-law scaling behaviour. The magnitude of the temporal correlations was, however, attenuated and the power-law exponents were decreased. This implies that the stimuli indeed degraded the network's memory of its past.

Adult↗
PubMed2003

Acute tryptophan depletion does not change somatosensory evoked magnetic fields.

RATIONALE: Serotonin is shown to regulate the activity of primary auditory cortex, but little is known about serotonin modulation of other sensory cortices. METHODS: We investigated somatosensory evoked magnetic fields (SEF) to left median nerve stimulation in eight healthy subjects in a double-blind, controlled, cross-over design study after acute tryptophan depletion (ATD) and control mixture. SEFs were recorded with the whole-head magnetoencephalography 6 h after ingestion of mixtures. The SEF sources and strength were estimated by a least-squares fit of a single equivalent current dipole. RESULTS: ATD decreased the total and free TPR levels by 75 and 48% and control mixture increased them by 98% and 44%. ATD had no effect on the amplitudes or latencies of SEF components. The source locations of the responses were not significantly affected by ATD. CONCLUSION: Serotonin does not affect stimuli processing in the primary somatosensory cortex.

Adult↗
PubMed2003

Modulation of electroencephalographic responses to transcranial magnetic stimulation: evidence for changes in cortical excitability related to movement.

Transcranial magnetic stimulation (TMS) and multichannel electroencephalography (EEG) were used for the investigation of cortical excitability preceding voluntary movement in human subjects. The study showed the practical value of the combined TMS-EEG approach in differentiating between cortical and spinal-cord mechanisms, which is difficult with conventional electromyographic measures alone. TMS induced a pronounced negativity (N100) lasting for 150-200 ms, with the amplitude maximum in the stimulated hemisphere. When TMS was applied just before the onset of the visually triggered movement, N100 was markedly attenuated, although motor evoked potentials (MEPs) became larger. We suggest that the N100 component represents an inhibitory response following TMS. This interpretation is in agreement with intracellular recordings in animals, paired-pulse TMS studies and experiments showing increased premovement excitability on the basis of MEPs. N100 was not affected only by the subsequent movement, but also by the switching from rest to the motor-task condition, which caused a slight attenuation of the N100 component; no changes, however, were found in the amplitude of MEPs, suggesting that modified excitability did not affect the output of the corticospinal pyramidal cells. By contrast to MEPs, N100 was modulated also by the presentation of the visual stimulus alone, i.e. when no movement was required. This attenuation suggests that even in a rest condition visual stimuli have an access to the sensorimotor regions of the cortex, most probably through ascending arousal brain systems.

Adult↗
PubMed2002

Alcohol reduces prefrontal cortical excitability in humans: a combined TMS and EEG study.

The effects of alcohol (0.8 g/kg) on the prefrontal cortex were studied in nine healthy subjects using the technique of transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG). A total of 120 magnetic pulses were delivered with a figure-of-eight coil to the left prefrontal cortex at the rate of 0.4-0.7 Hz. The EEG was recorded simultaneously with 60 scalp electrodes (41 electrodes were used for analysis); the TMS-evoked activation was estimated by the area under the global mean field amplitude (GMFA) time curve. TMS caused changes in EEG activity lasting up to 270 ms poststimulus. Alcohol decreased GMFA at 30-270 ms poststimulus (713+/-303 vs 478+/-142 microV ms; p=0.007). Alcohol-induced differences were most pronounced at anterior electrodes. These results suggest that alcohol reduces the excitability in the prefrontal cortex.

Adult↗
PubMed2002

Visual attention to words in different languages in bilinguals: a magnetoencephalographic study.

We recorded evoked magnetic fields from bilingual subjects while they were visually presented with words. The task was to count words in a target language when most of the words were in another language and there were also nontarget deviants in a third language. Our results indicate that in a multilingual visual environment there is a different need for attention to a nontarget language depending on whether the subject is attending to words in the subject's first (L1) or second (L2) language. When words in L2 are attended to, more effort appears to be devoted to words in the nontarget language than when words in L1 are attended to. In addition, attention to the nontarget language while counting words in L2 does not seem to depend on the age of acquisition of L2.

Adolescent↗