Neural correlates of individual performance differences in resolving perceptual conflict

Attentional mechanisms are a crucial prerequisite to organize behavior. Most situations may be characterized by a 'competition' between salient, but irrelevant stimuli and less salient, relevant stimuli. In such situations top-down and bottom-up mechanisms interact with each other. In the present fMRI study, we examined how interindividual differences in resolving situations of perceptual conflict are reflected in brain networks mediating attentional selection. Doing so, we employed a change detection task in which subjects had to detect luminance changes in the presence and absence of competing distractors. The results show that good performers presented increased activation in the orbitofrontal cortex (BA 11), anterior cingulate (BA 25), inferior parietal lobule (BA 40) and visual areas V2 and V3 but decreased activation in BA 39. This suggests that areas mediating top-down attentional control are stronger activated in this group. Increased activity in visual areas reflects distinct neuronal enhancement relating to selective attentional mechanisms in order to solve the perceptual conflict. Opposed to good performers, brain areas activated by poor performers comprised the left inferior parietal lobule (BA 39) and fronto-parietal and visual regions were continuously deactivated, suggesting that poor performers perceive stronger conflict than good performers. Moreover, the suppression of neural activation in visual areas might indicate a strategy of poor performers to inhibit the processing of the irrelevant non-target feature. These results indicate that high sensitivity in perceptual areas and increased attentional control led to less conflict in stimulus processing and consequently to higher performance in competitive attentional selection.     

EEG correlates for efficiency of the nonverbal creative performance (drawing)

This work was aimed at a search for EEG corellates of efficiency of nonverbal creative performance. Standardized Torrens technique which makes it possible to quantitatively assess creativity was used. The EEG records were performed before and during test performance, EEG parameters were compared to Torrens scores on three scales: flexibility, originality and efficiency. Absolute values of spatial synchronization, coherence and spectral power both in the baseline and during the performance were calculated. Changes in these parameters were traced during the transition from the state of quiet wakefulness to creative performance. The narrow-band analysis of coherence and spectral power allowed the number and orientation of processes associated with creativity scales to be assessed. The absence of substantial EEG changes during the test performance is indicative of the steady, nondynamical functional state of the brain.     

Functional-anatomic correlates of individual differences in memory

Memory abilities differ greatly across individuals. To explore a source of these differences, we characterized the varied strategies people adopt during unconstrained encoding. Participants intentionally encoded object pairs during functional MRI. Principal components analysis applied to a strategy questionnaire revealed that participants variably used four main strategies to aid learning. Individuals' use of verbal elaboration and visual inspection strategies independently correlated with their memory performance. Verbal elaboration correlated with activity in a network of regions that included prefrontal regions associated with controlled verbal processing, while visual inspection correlated with activity in a network of regions that included an extrastriate region associated with object processing. Activity in regions associated with use of these strategies was also correlated with memory performance. This study reveals functional-anatomic correlates of verbal and perceptual strategies that are variably used by individuals during encoding. These strategies engage distinct brain regions and may separately influence memory performance.     

Physiological correlates of individual differences in decision-making time during purposeful mental activity in humans

EEG correlates of individual differences in decision-making time were studied in subjects performing the task of memorizing and subsequently reproducing, on a monitor screen, a sequence of signals. Forty-six students were volunteers in the study, carried out with the use of an original computer-aided technique. Pioneering data on the individual specificity of physiological processes underlying human mental activity were obtained. Individual differences in EEG characteristics related to differences in the temporal parameters of the decision-making stage were found. In a situation directly preceding the activity, subjects characterized by a short decision-making time exhibited higher powers of the Δ (in the occipital, parietal, and central cortical areas) and θ-(in both the central and the right frontal and temporal areas) EEG rhythms. The subjects with a short decision-making time differed from those with a long decision-making time in a higher power of the θ rhythm in the right temporal area during memorization and an increased θ rhythm power in the frontal areas during reproduction of a signal sequence.     

Electroencephalographic correlates of individual features of the mental efficiency of adolescents

Evident correlations of spatial-temporal organization of the electrical brain activity with individual features of the mental working capacity were revealed in juveniles by the methods of analysis of spectra power density and of coherence function of rhythmic EEG components. EEG in juveniles with a low working mental capacity is characterized by hypersynchroneity, monofrequency, low reactivity of alpha-rhythm and high level of generalized spatial synchronization. Juveniles with high level of mental working capacity are characterized by regional specificity of the main EEG rhythm, the presence of the local dynamic foci of interconnected activity. It is suggested that the correlation of mechanisms of controlled local and non-specific generalized cortical activity is one of the main factors, determining the individual specificity of mental ability.     

EEG correlates of attentional load during multiple object tracking

While human subjects tracked a subset of ten identical, randomly-moving objects, event-related potentials (ERPs) were evoked at parieto-occipital sites by task-irrelevant flashes that were superimposed on either tracked (Target) or non-tracked (Distractor) objects. With ERPs as markers of attention, we investigated how allocation of attention varied with tracking load, that is, with the number of objects that were tracked. Flashes on Target discs elicited stronger ERPs than did flashes on Distractor discs; ERP amplitude (0-250 ms) decreased monotonically as load increased from two to three to four (of ten) discs. Amplitude decreased more rapidly for Target discs than Distractor discs. As a result, with increasing tracking loads, the difference between ERPs to Targets and Distractors diminished. This change in ERP amplitudes with load accords well with behavioral performance, suggesting that successful tracking depends upon the relationship between the neural signals associated with attended and non-attended objects.     

Context-dependent EEG spectral characteristics during performance of tasks

Spatial and frequency EEG characteristics of two groups of healthy adult subjects were examined in two series of experiments, which differed in conditions of the second cognitive task in a trial. The first task was the same in the two series: subjects had to evaluate size relationship between two closely spaced circles. The second task successively presented in trials of the first series consisted in the recognition of words/pseudowords, and in the second series, subjects had to localize a target letter in a matrix. It was assumed that the cognitive performance in the first series predominantly involved the ventral visual system, whereas during task performance in the second series, predominant involvement of the ventral and dorsal visual systems alternated. Multichannel EEG fragments recorded prior to the presentation of the task pairs were analyzed. Analysis of variance of the EEG spectral power revealed the generalized significant effect of the factor of the second task in the pair for delta band and lower beta subband, the power being higher in the first series. Factor brain hemisphere had a significant effect for the alpha band in the occipital area, the spectral power being lower in the left hemisphere for both experimental series. The task x hemisphere interaction was significant in the temporal cortical areas for the EEG power in alpha2 band, i.e., the predominant involvement of the ventral visual system was associated with stronger asymmetry of alpha2 rhythm and lower spectral power in this band in the left temporal area. Thus, the character of the forthcoming cognitive activity was shown to be reflected in spatio-frequency characteristics of the preceding EEG.     

EEG correlates of social creativity

EEG correlates of social creativity defined as ability to originally and flexibly interpret social significant situations were studied. It was found that the alpha2 and gamma2 rhythms are specific bands which make it possible to tell the difference between social creativity and control task. Solving socially significant problems in experimental conditions is accompanied by an increase in the power of the delta and gamma2 bands and desynchronization in the alpha2 band less pronounced in divergent tasks than during the interpretation of convergent visual stimuli.     

Spectral EEG characteristics in students with different anxiety profile during tests

EEG spectral power was calculated in 39 students at the age of 19-21 years in two experimental conditions: during the common educational process and immediately before an examination (stress condition). During the education process, in subjects with high anxiety (tested by Spielberger) the relative spectral power of the delta activity was higher than in the other group in the occipital, parietal, central, and right frontal brain areas, whereas the power of the EEG alpha in these areas was lower. Before examination tests, in subjects with high activity the delta power bilaterally increased in the temporal areas, whereas in subjects with low anxiety there was a decrease in the alpha rhythm power, especially in the right frontal area. In stress condition, the relative power of the delta activity in both occipital and temporal, right parietal and central areas was higher in subjects with low anxiety, whereas their alpha power was lower in both frontal and in occipital, parietal, and temporal areas of the left hemisphere.     

Intra-genomic variation in Symbiodinium correlates negatively with photosynthetic efficiency and coral host performance

Coral Reefs - Reef-building corals are nutritionally dependent on the symbiotic alga Symbiodinium and may therefore select for high-performing symbiont lineages. However, the effects of fine-scale...     

The influence of examination stress on psychophysiological characteristics and heart rate in students

With the aim to assess the influence of pre-examination psychoemotional stress on the level of centralization of the heart rate control, mathematical analysis of ECG of students was performed in normal condition (a common day of academic semester), before, and after an examination. The ECG was recorded and processed with the help of IBM-486 PC. R-R cardiointevalograms were processed by the method of variational pulsometry after Baevsky. Common quantitative heart rate indices were studied. The level of anxiety of students was assessed by Spilberger, and subjective estimations of general condition, activity and mood were obtained from the respective questionnaire. Three types of heart rate reactions on the examination stress were revealed. The reactions depended on the individual typological characteristics and the state of autonomic nervous system.     

EEG spatial organization during intense hyperventilation (cyclic breathing): II. EEG correlates of psychovisceral phenomena

EEG correlates of two main effects of long-term hyperventilation (cyclic breathing similar to rebirthing), namely, psychotic manifestations and sensations in internal organs, are considered. Standard EEGs of 44 subjects were recorded and subsequently treated by multiparametric methods. It was shown that, in the case of psychotic phenomena (hallucinations, visual and auditory images, different scenes, virtual travels, out-of-body experiences, etc.), the changes in the spatial organization of bioelectric potentials as compared with the baseline have different patterns than in the case of sensations in internal organs. The changes are observed in the frontal regions of the cortex: a decrease in spatial synchronization (linear processes) during an increase in spatial disarray (nonlinear processes) of bioelectric potentials and the intensifying of high-frequency β activity. If sensations in internal organs appear, a decrease in the above parameters was observed in the right hemisphere and in posterior cortical areas. The data are discussed from the viewpoint of qualitative specificity of changes in functional states during an altered state of consciousness with manifestations of different psychovisceral phenomena.     

Development of sleep during monotonous stimulation as related to individual differences

This study was designed to examine whether the sleep-promoting effect of monotonous stimulation depends on individual differences in strength of the nervous system, as was suggested by Pavlov. Sixty male subjects were divided into three groups, depending on their score on the "strength of excitation" scale of the Strelau Temperament Inventory. Within each group, subjects were randomly assigned to be exposed to either a) a sequence of tones or b) "no tones" (i.e., a quiet room). Dependent variables were latencies to Sleep Stage 1 (SOL 1) and Sleep Stage 2 (SOL 2). The main effects of stimulation and strength of the nervous system were not statistically significant. However, there was a significant interaction between stimulation and strength for both dependent variables. "Weak" subjects tended to fall asleep more rapidly during monotonous stimulation, whereas the reverse was true of "strong" subjects. The results suggest that individual differences might play an important role in the development of sleep during monotonous stimulation.