Spatiotemporal Dynamics of High-Gamma Activities during a 3-Stimulus Visual Oddball Task

Although many studies have investigated the neural basis of top-down and bottom-up attention, it still requires refinement in both temporal and spatial terms. We used magnetoencephalography to investigate the spatiotemporal dynamics of high-gamma (52–100 Hz) activities during top-down and bottom-up visual attentional processes, aiming to extend the findings from functional magnetic resonance imaging and event-related potential studies. Fourteen participants performed a 3-stimulus visual oddball task, in which both infrequent non-target and target stimuli were presented. We identified high-gamma event-related synchronization in the left middle frontal gyrus, the left intraparietal sulcus, the left thalamus, and the visual areas in different time windows for the target and non-target conditions. We also found elevated imaginary coherence between the left intraparietal sulcus and the right middle frontal gyrus in the high-gamma band from 300 to 400 ms in the target condition, and between the left thalamus and the left middle frontal gyrus in theta band from 150 to 450 ms. In addition, the strength of high-gamma imaginary coherence between the left middle frontal gyrus and left intraparietal sulcus, between the left middle frontal gyrus and the right middle frontal gyrus, and the high-gamma power in the left thalamus predicted inter-subject variation in target detection response time. This source-level electrophysiological evidence enriches our understanding of bi-directional attention processes: stimulus-driven bottom-up attention orientation to a salient, but irrelevant stimulus; and top-down allocation of attentional resources to stimulus evaluation.     

Hemispheric interactions during a search of original verbal associations: EEG coherence in creative men and women

A hemispheric interaction during verbal creative thinking was studied by the analysis of EEG coherence in the band of 4-30 Hz. 18 males and 21 females (right-handed university students) participaited in the experiments. Independently of gender, the performance of Remote Associates Task was accompanied by an increase in coherence in the theta1 and beta2 frequency bands as compared to the states of rest and the letter-fluency and simple associate's tasks. Successful search for original word associates as compared to generation of standard words was accompanied by a local increase in the interhemispheric coherence of the beta2 rhythm mostly in the parietotemporal cortex. In creative men, the increase in the hemispheric interaction efficient for a search for original words was focused in the frontal and temporal loci of the right hemisphere and in the left occipital locus, whereas in creative women the increase in coherence was observed in the left frontal and temporal regions. Creative men differed from non-creative ones by higher inter- and intrahemispheric coherence and were similar to women in the level of hemispheric interaction. The cortical distribution of foci of interhemispheric coherence reactivity indicates that the cortical organization of verbal functions depends on both sex and creativity of men and women.     

Representation of Cognitive Reappraisal Goals in Frontal Gamma Oscillations

Recently, numerous efforts have been made to understand the neural mechanisms underlying cognitive regulation of emotion, such as cognitive reappraisal. Many studies have reported that cognitive control of emotion induces increases in neural activity of the control system, including the prefrontal cortex and the dorsal anterior cingulate cortex, and increases or decreases (depending upon the regulation goal) in neural activity of the appraisal system, including the amygdala and the insula. It has been hypothesized that information about regulation goals needs to be processed through interactions between the control and appraisal systems in order to support cognitive reappraisal. However, how this information is represented in the dynamics of cortical activity remains largely unknown. To address this, we investigated temporal changes in gamma band activity (35–55 Hz) in human electroencephalograms during a cognitive reappraisal task that was comprised of three reappraisal goals: to decease, maintain, or increase emotional responses modulated by affect-laden pictures. We examined how the characteristics of gamma oscillations, such as spectral power and large-scale phase synchronization, represented cognitive reappraisal goals. We found that left frontal gamma power decreased, was sustained, or increased when the participants suppressed, maintained, or amplified their emotions, respectively. This change in left frontal gamma power appeared during an interval of 1926 to 2453 ms after stimulus onset. We also found that the number of phase-synchronized pairs of gamma oscillations over the entire brain increased when participants regulated their emotions compared to when they maintained their emotions. These results suggest that left frontal gamma power may reflect cortical representation of emotional states modulated by cognitive reappraisal goals and gamma phase synchronization across whole brain regions may reflect emotional regulatory efforts to achieve these goals. Our study may provide the basis for an electroencephalogram-based neurofeedback system for the cognitive regulation of emotion.     

EEG study of the functional organization of the right and left hemisphere during solution of verbal and spatial problems

In adult healthy right-handed subjects, the expression and degree of synchronization of the EEG alpha-range rhythmic components in different areas of the right and left hemispheres, were studied in a state of quiet wakefulness and during solving of verbal and spatial tasks presented in the visual field. The EEG of quiet wakefulness was characterized by different distribution of the alpha-range rhythmic components in the right and left hemispheres; in the right hemisphere low frequencies (7.5-10.5 c/s) were more expressed and more coherent; in the left one--the high frequencies (10.5-13.5 c/s). The solving of tasks was accompanied--along with a decrease of the whole alpha-range power spectra both in the right and the left hemispheres--by a local increase of synchronization of certain components of this range; the increase was specific to the hemisphere and the kind of task. The increase of synchronization of low-frequency components was observed in the right hemisphere during solving of the spatial task and that of the high-frequency components was noticed in the left hemisphere during solving of the verbal task. On the basis of the data on hemispheric specificity of electric activity synchronization of the alpha-rhythm, a suggestion is made about a different character of the functional integration of the structures of the right and left hemispheres in the process of solving of spatial and verbal tasks.     

Dynamics of the gamma-band power of induced EEG responses to facial stimuli with increased visual working memory load

The dynamics of power of short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15-60 Hz band) were assessed in the study of the visual cognitive set under conditions of different loads on working memory in two groups of subjects. Subjects of the first group had to react only to facial stimuli (n = 29), whereas the second group solved an additional task loading the working memory (they had to find a target stimulus in a matrix of letters, n = 35). We estimated wavelet spectra in the occipital, temporal, central and frontal areas of both hemispheres. In both groups of subjects with the plastic form of set, the power level in the gamma2 band (41-60 Hz) was significantly higher than in subject with the rigid form. In group A at the set-testing stage, the largest increase in the gamma2 band was related to the central areas of the left hemisphere. In more complex situation (group ), the increase in power in the gamma2 and gamma1 (21-40 Hz) bands was observed in the occipital and temporal areas of both hemispheres. At the same time, the EEG power of the central areas in these gamma bands was significantly lower. In the frontal areas there were no significant differences in the dynamics of power between the subjects of both groups.     

Distributed neural systems for the generation of visual images

Visual perception of houses, faces, and chairs evoke differential responses in ventral temporal cortex. Using fMRI, we compared activations evoked by perception and imagery of these object categories. We found content-related activation during imagery in extrastriate cortex, but this activity was restricted to small subsets of the regions that showed category-related activation during perception. Within ventral temporal cortex, activation during imagery evoked stronger responses on the left whereas perception evoked stronger responses on the right. Additionally, visual imagery evoked activity in parietal and frontal cortex, but this activity was not content related. These results suggest that content-related activation during imagery in visual extrastriate cortex may be implemented by "top-down" mechanisms in parietal and frontal cortex that mediate the retrieval of face and object representations from long-term memory and their maintenance through visual imagery.     

Topographic analysis of auditory event-related potentials associated with acoustic and semantic processing

The topography of auditory event-related potentials (ERPs) was examined during 3 kinds of tasks: selection of a specified real word or nonsense syllable from a list; simple detection of each of the same stimuli without discrimination; and classification of a set of words according to a specified semantic category. The potentials that were associated with the additional processing required by the discriminative tasks were disclosed by subtracting the wave forms obtained in the detection condition from those obtained during discriminative performance. Difference wave forms were also derived between the semantic classification and verbal discriminative ERP to delineate the changes associated with the extraction of word meaning.The topography of the ERP associated with stimulus detection was comparable to that found in previous studies of evoked potentials to non-speech stimuli. This distribution was consistent with 2 cortical generators, one within the supratemporal plane and the other on the lateral surface of the superior temporal gyrus. When discriminative performance was required on the basis of acoustic stimulus properties, the topography of the difference wave form that reflected this discriminative processing extended more posteriorly over temporal cortex. Semantic processing elicited a further posterior extension of ERP components by 330 msec after stimulus onset, as well as longer latency potentials that were not present in the verbal selection task. These differences imply that a more extensive portion of language cortex is engaged in semantic classification than in verbal identification.     

任务转换的多脑区作用机制：来自ERP的证据

采用＂任务转换＂实验范式,以数字、汉字的归类为任务,探究预知和未预知条件下任务转换的ERPs.实验中被试先后完成2个连续的任务,任务序列为重复（AA,BB,……）或转换（AB,BA,……）.结果发现,在预知条件下,转换序列的先行任务数/词比重复序列的先行任务数/词、转换序列的后继任务数/词比重复序列的后继任务数/词都产生一个更为负走向的波,在中央区（CZ）差异波为D-N320.而未预知条件下,仅转换序列后继任务数/词比重复序列后继任务数/词产生一个更为负走向的波,中央区差异波为D-N320.对差异波溯源分析发现,内源性准备源于左侧颞区（Left BA20）;外源性调节在预知条件下源于右侧顶区（Right BA19）,而未预知条件下源于左侧额区（Left BA47）和右侧额区（Right BA10）.结果表明,任务转换本质是认知冲突过程,对应的脑电成分为D-N320.在预知条件下任务转换先后单独由颞区和顶区负责,预知准备使得任务转换在低级皮层区完成,而未预知条件下任务转换在更广的高级皮层区完成,同时激活左侧额区和右侧额区,且外源性调节对应的脑区在预知条件和未预知条件下是分离的.     

Frontal cortical afferents facilitate striatal nitric oxide transmission in vivo via a NMDA receptor and neuronal NOS-dependent mechanism

Striatal nitric oxide (NO) signaling plays a critical role in modulating neural processing and motor behavior. Nitrergic interneurons receive synaptic inputs from corticostriatal neurons and are activated via ionotropic glutamate receptor stimulation. However, the afferent regulation of NO signaling is poorly characterized. The role of frontal cortical afferents in regulating NO transmission was assessed in anesthetized rats using amperometric microsensor measurements of NO efflux and local field potential recordings. Low frequency (3 Hz) electrical stimulation of the ipsilateral cortex did not consistently evoke detectable changes in striatal NO efflux. In contrast, train stimulation (30 Hz) of frontal cortical afferents facilitated NO efflux in a stimulus intensity-dependent manner. Nitric oxide efflux evoked by train stimulation was transient, reproducible over time, and attenuated by systemic administration of either the NMDA receptor antagonist MK-801 or the neuronal NO synthase inhibitors 7-nitroindazole and NG-propyl-L-arginine. The interaction between NO efflux evoked via train stimulation and local striatal neuron activity was assessed using dual microsensor and local field potential recordings carried out concurrently in the contralateral and ipsilateral striatum, respectively. Systemic administration of the non-specific NO synthase inhibitor methylene blue attenuated both evoked NO efflux and the peak oscillation frequency (within the delta band) of local field potentials recorded immediately after train stimulation. Taken together, these observations indicate that feed-forward activation of neuronal NO signaling by phasic activation of frontal cortical afferents facilitates the synchronization of glutamate driven oscillations in striatal neurons. Thus, NO signaling may act to amplify coherent corticostriatal transmission and synchronize striatal output.     

The mapping of brain biopotentials during the solving of a verbal task]

Reverse averaging of cortical potentials from the moment of the motor response followed the verbal task solving (anagram riddle) revealed some brain potentials correlations with the process of a decision making. In the case of task solving the negative frontal wave with the latency 900-400 ms from the motor response was recorded. Intracortical interaction mapping of this potential showed the regular patterns of cortical functional connections in different frequency ranges (alpha, beta). Successful solving of the task was characterized with predominant interaction foci topography in the frontal and left-temporal cortical areas in alpha band and parietal zones in beta. The absence of the task solution was characterized with the parieto-occipital interaction foci in alpha band and their frontal localization in beta.     

Motivation effect on power changes in the brain biopotentials in the figurative and verbal creativity tasks

Effect of extrinsic motivation stimulating the most original problem solving during verbal and figurative divergent thinking was studied by EEG mapping. The righthanded university students (27 males and 26 females) participated in the experiments. An instruction "to create the most original solution" as compared to condition with an instruction "to create any solution" induced an increase in the baseline power of the alpha 1 and alpha 2 rhythms most pronounced in the posterior cortex. Task-related desynchronization of the alpha rhythms was higher but the beta-2 synchronization was lower after the former than after the latter instruction. Differences in the asymmetry of the alpha 1 and alpha 2 rhythms in the parietal and temporal regions of hemispheres suggested the right hemisphere dominance in intrinsic alertness and evoked activation related to divergent thinking. The findings were common and gender-independent in both figurative and verbal tasks suggesting a generalized influence of extrinsic motivation on creative activity.     

Functional asymmetry of the frontal cortex and lateral hypothalamus of cats during food instrumental conditioning

The synchronism and latency of auditory evoked potentials (EP) recorded in symmetric points of the frontal cortex and lateral hypothalamus of cats were measured at different stages of instrumental food conditioning and after the urgent transition to 30% reinforcement. Correlation coefficients between EPs in the cortex and hypothalamus were high (with left-side dominance) at the beginning of the experiments, when food motivation was high, and during the whole experiments in cases of high-probability of conditioned performance. Analysis of early positive P55-80 EP component showed that at all conditioning stages the peak latency of this component was shorter in the left cortical areas than in symmetrical points, whereas in the hypothalamus the shorter latency at the left side was observed at the stage of unstable conditioned reflex, and at the stage of stable reflex the latency of the studied component was shorter at the right side. During transition to 30% reinforcement, the latency was also shorter in the right hypothalamus. It is suggested that the high left-side correlation between the hypothalamus and cortex was associated with motivational and motor component of behavior rather than reflected the emotional stress induced by transition to another stereotype of food reinforcement (30%).     

A Shared Neural Substrate for Mentalizing and the Affective Component of Sentence Comprehension

Using event-related fMRI in a sample of 42 healthy participants, we compared the cerebral activity maps obtained when classifying spoken sentences based on the mental content of the main character (belief, deception or empathy) or on the emotional tonality of the sentence (happiness, anger or sadness). To control for the effects of different syntactic constructions (such as embedded clauses in belief sentences), we subtracted from each map the BOLD activations obtained during plausibility judgments on structurally matching sentences, devoid of emotions or ToM. The obtained theory of mind (ToM) and emotional speech comprehension networks overlapped in the bilateral temporo-parietal junction, posterior cingulate cortex, right anterior temporal lobe, dorsomedial prefrontal cortex and in the left inferior frontal sulcus. These regions form a ToM network, which contributes to the emotional component of spoken sentence comprehension. Compared with the ToM task, in which the sentences were enounced on a neutral tone, the emotional sentence classification task, in which the sentences were play-acted, was associated with a greater activity in the bilateral superior temporal sulcus, in line with the presence of emotional prosody. Besides, the ventromedial prefrontal cortex was more active during emotional than ToM sentence processing. This region may link mental state representations with verbal and prosodic emotional cues. Compared with emotional sentence classification, ToM was associated with greater activity in the caudate nucleus, paracingulate cortex, and superior frontal and parietal regions, in line with behavioral data showing that ToM sentence comprehension was a more demanding task.     

Frequency-spatial organization of brain electrical activity in creative verbal thinking: role of the gender factor

Gender differences in EEG patterns associated with verbal creativity were studied by EEG mapping. The EEGs of 18 males and 21 females (right-handed university students) were recorded during a performance of Remote Associates Task (RAT) compared with the letter-fluency and simple associate's tasks. Gender differences were found in a factor structure of the indices of verbal thinking and a score of generating words was greater in women than men. No significant gender differences in originality of associations were revealed, however, gender-related differences in the EEG-patterns were found at the final and initial stages of RAT. In men, the beta2-power was increased in both hemispheres at the beginning of test. To the end of testing, the power of oscillations in the beta2 band increased only in the central part of the cortex. In women, the beta2-power was increased to a greater extent in the right than in the left hemisphere at the initial stage of task performance, whereas the final stage was characterized by a relative decrease in beta-activity in parietotemporal cortical regions and increase in the left prefrontal region. It is suggested that the verbal creative thinking in men is based mostly on "insight" strategy whereas women additionally involve the "intellectual" strategy.     

Complex Visual Search in Children and Adolescents: Effects of Age and Performance on fMRI Activation

Complex visuospatial processing relies on distributed neural networks involving occipital, parietal and frontal brain regions. Effects of physiological maturation (during normal brain development) and proficiency on tasks requiring complex visuospatial processing have not yet been studied extensively, as they are almost invariably interrelated. We therefore aimed at dissociating the effects of age and performance on functional MRI (fMRI) activation in a complex visual search task. In our cross-sectional study, healthy children and adolescents (n = 43, 19 females, 7-17 years) performed a complex visual search task during fMRI. Resulting activation was analysed with regard to the differential effects of age and performance. Our results are compatible with an increase in the neural network''s efficacy with age: within occipital and parietal cortex, the core regions of the visual exploration network, activation increased with age, and more so in the right than in the left hemisphere. Further, activation outside the visual search network decreased with age, mainly in left inferior frontal, middle temporal, and inferior parietal cortex. High-performers had stronger activation in right superior parietal cortex, suggesting a more mature visual search network. We could not see effects of age or performance in frontal cortex. Our results show that effects of physiological maturation and effects of performance, while usually intertwined, can be successfully disentangled and investigated using fMRI in children and adolescents.     

An fMRI Study of Grammatical Morpheme Processing Associated with Nouns and Verbs in Chinese

This study examined whether the degree of complexity of a grammatical component in a language would impact on its representation in the brain through identifying the neural correlates of grammatical morpheme processing associated with nouns and verbs in Chinese. In particular, the processing of Chinese nominal classifiers and verbal aspect markers were investigated in a sentence completion task and a grammaticality judgment task to look for converging evidence. The Chinese language constitutes a special case because it has no inflectional morphology per se and a larger classifier than aspect marker inventory, contrary to the pattern of greater verbal than nominal paradigmatic complexity in most European languages. The functional imaging results showed BA47 and left supplementary motor area and superior medial frontal gyrus more strongly activated for classifier processing, and the left posterior middle temporal gyrus more responsive to aspect marker processing. We attributed the activation in the left prefrontal cortex to greater processing complexity during classifier selection, analogous to the accounts put forth for European languages, and the left posterior middle temporal gyrus to more demanding verb semantic processing. The overall findings significantly contribute to cross-linguistic observations of neural substrates underlying processing of grammatical morphemes from an analytic and a classifier language, and thereby deepen our understanding of neurobiology of human language.     

Influence of connection type on phase synchrony: analysis of a neural mass model

Empirical studies have demonstrated synchronized frontal and parietal electrophysiological signals at 22-34?Hz during a conjunctive visual search task and at 36-56?Hz during a pop-out visual search task. Bidirectional (conjunctive) versus unidirectional (pop-out) information transfer between neuronal populations is hypothesized to underly this difference in synchronization frequency. This study modeled the influence of connection type (i.e., unidirectional vs. bidirectional) on phase synchrony between two neural populations using a neural mass model. Phase-locking values (PLVs) were used as the measure of synchrony between populations. Consistent with the connectivity hypothesis, the model revealed greater PLVs at 22-34?Hz when the two populations were connected bidirectionally than unidirectionally, but greater PLVs at 34-52?Hz when connected unidirectionally than bidirectionally. The model suggests that inter-population connectivity also changes with bottom-up versus top-down control of attention.     

Functional Changes in the Human Auditory Cortex in Ageing

Hearing loss, presbycusis, is one of the most common sensory declines in the ageing population. Presbycusis is characterised by a deterioration in the processing of temporal sound features as well as a decline in speech perception, thus indicating a possible central component. With the aim to explore the central component of presbycusis, we studied the function of the auditory cortex by functional MRI in two groups of elderly subjects (>65 years) and compared the results with young subjects (<lt;30 years). The elderly group with expressed presbycusis (EP) differed from the elderly group with mild presbycusis (MP) in hearing thresholds measured by pure tone audiometry, presence and amplitudes of transient otoacoustic emissions (TEOAE) and distortion-product oto-acoustic emissions (DPOAE), as well as in speech-understanding under noisy conditions. Acoustically evoked activity (pink noise centered around 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, 8 kHz), recorded by BOLD fMRI from an area centered on Heschl’s gyrus, was used to determine age-related changes at the level of the auditory cortex. The fMRI showed only minimal activation in response to the 8 kHz stimulation, despite the fact that all subjects heard the stimulus. Both elderly groups showed greater activation in response to acoustical stimuli in the temporal lobes in comparison with young subjects. In addition, activation in the right temporal lobe was more expressed than in the left temporal lobe in both elderly groups, whereas in the young control subjects (YC) leftward lateralization was present. No statistically significant differences in activation of the auditory cortex were found between the MP and EP groups. The greater extent of cortical activation in elderly subjects in comparison with young subjects, with an asymmetry towards the right side, may serve as a compensatory mechanism for the impaired processing of auditory information appearing as a consequence of ageing.     

Temporal Features of Spike Trains in the Moth Antennal Lobe Revealed by a Comparative Time-Frequency Analysis

The discrimination of complex sensory stimuli in a noisy environment is an immense computational task. Sensory systems often encode stimulus features in a spatiotemporal fashion through the complex firing patterns of individual neurons. To identify these temporal features, we have developed an analysis that allows the comparison of statistically significant features of spike trains localized over multiple scales of time-frequency resolution. Our approach provides an original way to utilize the discrete wavelet transform to process instantaneous rate functions derived from spike trains, and select relevant wavelet coefficients through statistical analysis. Our method uncovered localized features within olfactory projection neuron (PN) responses in the moth antennal lobe coding for the presence of an odor mixture and the concentration of single component odorants, but not for compound identities. We found that odor mixtures evoked earlier responses in biphasic response type PNs compared to single components, which led to differences in the instantaneous firing rate functions with their signal power spread across multiple frequency bands (ranging from 0 to 45.71 Hz) during a time window immediately preceding behavioral response latencies observed in insects. Odor concentrations were coded in excited response type PNs both in low frequency band differences (2.86 to 5.71 Hz) during the stimulus and in the odor trace after stimulus offset in low (0 to 2.86 Hz) and high (22.86 to 45.71 Hz) frequency bands. These high frequency differences in both types of PNs could have particular relevance for recruiting cellular activity in higher brain centers such as mushroom body Kenyon cells. In contrast, neurons in the specialized pheromone-responsive area of the moth antennal lobe exhibited few stimulus-dependent differences in temporal response features. These results provide interesting insights on early insect olfactory processing and introduce a novel comparative approach for spike train analysis applicable to a variety of neuronal data sets.     

Electroencephalographic Correlates of Brain States during Verbal Learning: II. Characteristics of EEG Spatial Synchronization

Spatial EEG synchronization was studied using mean EEG coherences in 57 subjects in a resting state with the eyes open, during memorization of verbal bilingual semantic pairs (Latin and Russian), and during retrieval (monitoring) of the learned information. Statistical comparison of the EEG spectral power in the frequency bands θ, α ₁, α₂, β₁, β₂, and γ showed that induction of the states of memorization and retrieval of the verbal information resulted in multiple significant increases in the mean coherence (spatial synchronization) as compared to the state of rest. These increases were significantly higher in the state of retrieval than in the state of memorization. Such changes simultaneously occurred in different frequency bands and over the entire cortex. The highest relative augmentations of coherence with the highest significance estimates were observed in long-distance derivation pairs involving the temporal areas or combining the anterofrontal and frontal derivations with the parietal and occipital ones. The results are discussed in combination with data obtained in the same study for changes in EEG local synchronization and reported earlier. The intense rearrangements of the bioelectrical activity of the cortex may be determined both by the effect of cognitively specific mechanisms of encoding-decoding of information in the memory system and by a cognitively nonspecific modulating system of the brain.