Organization of the cortical bioelectric activity at different stages of a relaxation session

The dynamics of electroencephalographic (EEG) parameters in adults were studied during active relaxation (which involved simple psychological techniques) and passive relaxation (without using any techniques). The experiment included four stages: background 1, active relaxation, passive relaxation, and background 2. During the experiment, the EEG was recorded in the occipital, parietal-temporal-occipital, central, and frontal regions of both hemispheres of the brain. Comparative analysis of the dynamics of EEG parameters during changing experimental conditions was performed in the frequency range from 5 to 40 Hz divided into ten frequency subranges. It was possible to establish the general pattern in the dynamics of EEG parameters at different relaxation stages, as well as differences in system-level brain performance in the active and passive relaxation states.     

EEG spectral characteristics at different stages of the unconscious visual set in two motivation conditions

Multichannel EEG were recorded in young healthy subjects in two series of experiments during formation, actualization, and extinction of the visual unconscious set to the perception of unequal circles under conditions of increased motivation of subjects to the result of their performance. In the first series of experiments, subjects were promised to be rewarded (a small money price) for each correct response (the "general" rise of motivation). In the second series, subjects were promised to be rewarded for correct responses only in cases when one of the circles was larger than the other one (the "directed" rise of motivation). The dynamics of the EEG spectral power derived under these two conditions was compared with similar indices obtained earlier during formation of the same set without any special motivation of subjects (control). In all experimental conditions, before the presentation of the stimuli the EEG power in the alpha range was higher in subjects with the stable set. The dynamics of changes in the alpha power at set stages was principally similar in all conditions. In all the experimental conditions, in subjects with unstable set the EEG power in the delta range was highest at the stage of set actualization. The most pronounced generalized changes in the EEG power in the theta-range during the "general" rise of motivation in subjects with stable and unstable forms of set and greater variability of the reaction time to the probe stimulus suggest that the task performance under these conditions required greater tension than under conditions of the "directed" rise of motivation.     

Orientation sensitivity at different stages of object processing: evidence from repetition priming and naming

Background

An ongoing debate in the object recognition literature centers on whether the shape representations used in recognition are coded in an orientation-dependent or orientation-invariant manner. In this study, we asked whether the nature of the object representation (orientation-dependent vs orientation-invariant) depends on the information-processing stages tapped by the task.

Methodology/ Findings

We employed a repetition priming paradigm in which briefly presented masked objects (primes) were followed by an upright target object which had to be named as rapidly as possible. The primes were presented for variable durations (ranging from 16 to 350 ms) and in various image-plane orientations (from 0° to 180°, in 30° steps). Significant priming was obtained for prime durations above 70 ms, but not for prime durations of 16 ms and 47 ms, and did not vary as a function of prime orientation. In contrast, naming the same objects that served as primes resulted in orientation-dependent reaction time costs.

Conclusions/Significance

These results suggest that initial processing of object identity is mediated by orientation-independent information and that orientation costs in performance arise when objects are consolidated in visual short-term memory in order to be reported.     

Correlation of EEG asymmetry and hypnotic susceptibility

Hypnosis research of the last decades confirmed that some cortical regions show characteristic modification of spontaneous brain electrical activity as a function of hypnotic responsiveness. Using FFT spectrum of 16 channel EEG recording, it was demonstrated that in highly susceptible subjects the right parieto-temporal region show more electric power than the left one while the low susceptibles have left side predominance or equilibrated power in all derivations. If a specific (Ericksonian) indirect hypnosis induction was administered, the same right side preponderance could be recorded in low susceptibles, too. On the basis of these results we can confirm the importance of the right parieto-temporal associative area in the alteration of consciousness characterizing hypnotic state.     

Changes in components of the auditory long-latency evoked potentials at different stages of the slow-wave sleep

In accordance with the present views, during sleep, analysis of external stimuli continues at the subconscious level, because the need to estimate the biological significance of external stimuli in order to maintain a flexible contact of a sleeping subject with the environment persists during sleep. It is known that new components of the auditory evoked potentials (AEP) appear as sleep deepens. However, the common procedure of analysis of event-related potentials averaged for a group of subjects has some drawbacks because of the interindividual variability of the event-related potentials. Therefore, an additional analysis of the interindividual variability of the AEP shape and component structure can simplify the detection of individual components of group-averaged AEP at different stages of the slow-wave sleep. The AEPs were recorded in healthy volunteers (n = 26) during falling asleep in the evening from eight EEG derivations (F3, F4, C3, C4, P3, P4, O1, O2) in reference to a linked mastoid electrode. Computer-generated sound stimuli (50 ms-pulses with the frequency of 1000 Hz, 60 dB HL) were presented binaurally through earphones with interstimulus intervals of 20-40 s. Selective summation of AEPs for all the subjects was performed for each stage of the slow-wave sleep individually for each of the eight derivations. It was shown that the account made for interindividual variability of the AEP shape facilitated the identification of individual components of the group-averaged AEP typical of wakefulness (P1, N1, P300) and those which appeared during sleep onset and at different stages of the slow-wave sleep (P2, N350, P450, N550, N900).     

Spatial synchronization of cortical electrical activity at different stages of visual set in preschool children

Changes in the alpha-rhythm synchronization were revealed at different stages of cognitive visual set in 5- to 7-year-old children. We found a clear-cut correlation of these changes with set plasticity. In children with a plastic set, the EEG synchronization between the frontal and other brain regions substantially increased in the period of set-shifting (the actualization stage). At the set extinction stage, after set-shifting has already taken place, the EEG-synchronization becomes minimal. On the contrary, in children who formed a rigid set, EEG coherence considerably increases at the set extinction stage. This finding suggests that the rigid set still affects the cognitive activity even after (judging from oral reports) the set shift has been completed. The age-related differences in cognitive set formation clearly correlate with the time course of the EEG synchronization between the frontal and other brain regions. We think that the ability to form a plastic visual set depends on the frontal cortex maturation, which occurs at the age of 6-7 years, and its age-related effect on the brain cognitive functions.     

Shortening of the photoperiod affects sleep distribution, EEG and cortical temperature in the Djungarian hamster

To asses the influence of photoperiod on sleep regulation EEG, EMG, and cortical temperature were continuously recorded for two baseline days and after 4 h sleep deprivation in Djungarian hamsters (Phodopus sungorus) adapted to a short photoperiod (light dark 816). Comparison to previous data collected in a long photoperiod (lightdark 168) showed several major effects of photoperiod: 1. A prominent change in the 24-h distribution, duration and number of vigilance state episodes, whereas the total amount of sleep and waking was unchanged; 2. Cortical temperature was 0.7°C lower in the short photoperiod; 3. There was a significant negative correlation between cortical temperature and the frequency of REM sleep episodes; and 4. Absolute EEG power density showed a marked reduction in the short photoperiod. After sleep deprivation EEG slow-wave activity (mean power density 0.75–4.0 Hz) in NREM sleep showed a remarkably similar increase in both photoperiods demonstrating the robustness of the homeostatic regulation of sleep. Cortical temperature remained above baseline values after sleep deprivation in the short photoperiod whereas a negative rebound was present in the long photoperiod. Our results support the hypothesis that cortical temperature has a strong influence on REM sleep propensity and indicate the possibility of an optimum cortical temperature for recovery sleep after sleep deprivation. The lower EEG power density in the short photoperiod may contribute to energy conservation.Abbreviations LP long photoperiod - NREM non-rapid-eye-movement - REM rapid-eye-movement - SCN suprachiasmatic nucleus - SD sleep deprivation - SP short photoperiod - SWA slow-wave activity - T _CRT cortical temperature     

Sustained attention performance during sleep deprivation: evidence of state instability

Nathaniel Kleitman was the first to observe that sleep deprivation in humans did not eliminate the ability to perform neurobehavioral functions, but it did make it difficult to maintain stable performance for more than a few minutes. To investigate variability in performance as a function of sleep deprivation, n = 13 subjects were tested every 2 hours on a 10-minute, sustained-attention, psychomotor vigilance task (PVT) throughout 88 hours of total sleep deprivation (TSD condition), and compared to a control group of n = 15 subjects who were permitted a 2-hour nap every 12 hours (NAP condition) throughout the 88-hour period. PVT reaction time means and standard deviations increased markedly among subjects and within each individual subject in the TSD condition relative to the NAP condition. TSD subjects also had increasingly greater performance variability as a function of time on task after 18 hours of wakefulness. During sleep deprivation, variability in PVT performance reflected a combination of normal timely responses, errors of omission (i.e., lapses), and errors of commission (i.e., responding when no stimulus was present). Errors of omission and errors of commission were highly intercorrelated across deprivation in the TSD condition (r = 0.85, p = 0.0001), suggesting that performance instability is more likely to include compensatory effort than a lack of motivation. The marked increases in PVT performance variability as sleep loss continued supports the "state instability" hypothesis, which posits that performance during sleep deprivation is increasingly variable due to the influence of sleep initiating mechanisms on the endogenous capacity to maintain attention and alertness, thereby creating an unstable state that fluctuates within seconds and that cannot be characterized as either fully awake or asleep.     

Functional neuroanatomy of the hypnotic state

The neural mechanisms underlying hypnosis and especially the modulation of pain perception by hypnosis remain obscure. Using PET we first described the distribution of regional cerebral blood flow during the hypnotic state. Hypnosis relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in "normal alertness". The hypnotic state was related to the activation of a widespread set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal and anterior cingulate cortices. This pattern of activation shares some similarities with mental imagery, from which it mainly differs by the relative deactivation of precuneus. Second, we looked at the anti-nociceptive effects of hypnosis. Compared to the resting state, hypnosis reduced pain perception by approximately 50%. The hypnosis-induced reduction of affective and sensory responses to noxious thermal stimulation were modulated by the activity in the midcingulate cortex (area 24a'). Finally, we assessed changes in cerebral functional connectivity related to hypnosis. Compared to normal alertness (i.e., rest and mental imagery), the hypnotic state, significantly enhanced the functional modulation between midcingulate cortex and a large neural network involved in sensory, affective, cognitive and behavioral aspects of nociception. These findings show that not only pharmacological but also psychological strategies for pain control can modulate the cerebral network involved in noxious perception.     

Characteristics of the functional state of rat tracheal and bronchial smooth muscle at different stages of alveolitis

In isolated tracheal smooth muscle preparations in normal rats and in rats with experimental fibrotic alveolitis, responses to electrical field stimulation of nervous and muscle fibers were studied. At stimulation of muscles or nerves of tracheal preparations without intramural ganglia in rats with acute alveolitis, parameters of smooth muscle contractions did not practically differ from those in normal rats. In rats with fibrotic alveolitis the amplitude and rate of muscle contraction decreased, while the response latent period (LP) increased. At stimulation of preganglionic nerve fibers of the tracheal preparations with intramural ganglia in rats with acute alveolitis, the value and rate of smooth muscle contraction decreased, while the response LP increased. After transition into chronic phase of the disease (fibrotic alveolitis), a partial restoration of the response parameters took place. In rats with acute alveolitis, the repeated stimulation of the nerve fibers led to an increase of amplitude and a decrease of rate of tracheal smooth muscle contractions. In rats with fibrotic alveolitis, the repeated stimulation caused a decrease of amplitude and rate of contractions and an increase of the response LP.     

Growth forms of Leymus chinesis (Poaceae) at the different developmental stages of the natural population

The manner in which the density of Leymus chinensis increases from a single plant to a dominant population can be understood by tracing the development of a population from early to late stages. Parent shoot density, above‐ground dry weight, spike density, heading rate and spike dry weight, density of spreading shoots (buds/daughter shoots in apical/axillary rhizomes) and clumping shoots (buds/daughter shoots in axillary parent shoots), and young rhizome length and weight were investigated in the same quadrats for a low density/early stage (LE) population and a high density/late stage (HL) population. Clonal growth (buds/daughter shoots formation) and sexual reproduction (spikes formation) increased while rhizome storage (young rhizome weight) decreased during the transition from LE to HL. In a LE population an outward occupation strategy was employed, with a high proportion of spreading shoots. As the population density gradually increased until HL, an inward consolidation strategy increasing shoot amount in previously occupied areas, was adopted. This was characterized by a high proportion of clumping shoots. Interestingly, the trade‐off between spreading and clumping shoots can be adjusted by the duration of young rhizome elongation during a growth season. In other words, compared with a HL population, a LE population shortened the duration of young rhizome elongation during the growth season, which resulted in more time for the production of axillary spreading shoots along the rhizomes, and high amounts and proportions of total spreading shoots. The special growth patterns, that is, trade‐offs among growth forms, allow L. chinensis to establish dominant populations throughout the eastern Eurasian Steppe.