Temporal evolution of alpha and beta bands during visual spatial attention

Wavelet analysis of the EEG during the neurocognitive evaluation of invalidly cued targets

In a spatial central cueing paradigm, positions in the horizontal meridian were cued to evaluate the neurocognitive processing of validly (V) and invalidly cued (I) targets. ERPs were obtained from 20 EEG channel recordings. Complex Morlet wavelets were applied for computing event-related spectral power (ERSP) modulations and inter-trial phase coherence (ITC). P3a and P3b responses were increased in a statistically significant manner in I targets with regard to V targets. This increase seems to be generated only by phase resetting without enhancement of spectral power. Comparing ERSP modulations between I and V target trials we found a major effect centred in the alpha range. The following results were obtained for invalid condition in relation to valid condition: 6-12Hz ERSP decrease topographically widespread over the scalp, starting around 450 ms and peaking around 650 ms; 10-14Hz ERSP increase peaking around 200 ms at fronto-central electrodes; and 10-14Hz ERSP decrease occurring from 400 to 600 ms at posterior electrodes. Therefore, the invalidity effect indeed produces salient changes in the stimulus related and ongoing neuronal activity leading to a brain state of comparative higher activity both excitatory and inhibitory with respect to the validly cued target processing.

A novel ANCOVA design for analysis of MEG data with application to a visual attention study

Statistical inference from MEG-based distributed activation maps is well suited to the general linear modeling framework, a standard approach to the analysis of fMRI and PET neuroimaging studies. However, there are important differences from the other neuroimaging modalities related to how observations are created and fitted in GLM models, as well as how subsequent statistical inference is performed. In this paper, we demonstrate how MEG oscillatory components can be analyzed in this framework based on a custom ANCOVA model that takes into account baseline and inter-hemispheric effects, rather than a simpler ANOVA design. We present the methodology using as an example an MEG study of visual spatial attention, since the model design depends on the specific experiment and neuroscience hypotheses being tested. However, the techniques presented here can be readily adapted to accommodate other experimental paradigms. We create statistics that estimate the temporal evolution of attention effects on alpha power in several cortical regions. We present evidence for direction-specific attention effects on alpha activity in occipital and parietal regions and demonstrate the sub-second timing of these effects in each region. The results support a mechanism for anticipatory attentional deployment that dynamically modulates the local alpha synchrony in a network of parietal control and occipital sensory regions.

Abnormal ERPs and high frequency bands power in multiple sclerosis

Event-related potentials (ERPs) and power spectral density (PSD) were registered during an auditory-oddball paradigm in 11 MS patients. These patients showed a decrease in the amplitude of P2 and N2 components and a delayed P3 latency compared to control subjects suggesting that the attentional orienting mechanism in the auditory modality is affected in MS. The PSD analysis showed that MS patients exhibited an increased power in beta and gamma bands. The combined analysis of frequency and time domain suggested diverse phenomena that occurred in the MS patient group related with the EEG background or the motivational status.

What happens in between? Human oscillatory brain activity related to crossmodal spatial cueing

Previous studies investigated the effects of crossmodal spatial attention by comparing the responses to validly versus invalidly cued target stimuli. Dynamics of cortical rhythms in the time interval between cue and target might contribute to cue effects on performance. Here, we studied the influence of spatial attention on ongoing oscillatory brain activity in the interval between cue and target onset. In a first experiment, subjects underwent periods of tactile stimulation (cue) followed by visual stimulation (target) in a spatial cueing task as well as tactile stimulation as a control. In a second experiment, cue validity was modified to be 50%, 75%, or else 25%, to separate effects of exogenous shifts of attention caused by tactile stimuli from that of endogenous shifts. Tactile stimuli produced: 1) a stronger lateralization of the sensorimotor beta-rhythm rebound (15–22 Hz) after tactile stimuli serving as cues versus not serving as cues; 2) a suppression of the occipital alpha-rhythm (7–13 Hz) appearing only in the cueing task (this suppression was stronger contralateral to the endogenously attended side and was predictive of behavioral success); 3) an increase of prefrontal gamma-activity (25–35 Hz) specifically in the cueing task. We measured cue-related modulations of cortical rhythms which may accompany crossmodal spatial attention, expectation or decision, and therefore contribute to cue validity effects. The clearly lateralized alpha suppression after tactile cues in our data indicates its dependence on endogenous rather than exogenous shifts of visuo-spatial attention following a cue independent of its modality.

Preliminary report of familial clustering of EEG measures in ADHD

The purpose of the present study is to examine the familiality of electroencephalographic (EEG) measures among affected sibling pairs with Attention-Deficit Hyperactivity Disorder (ADHD). EEG was recorded during baseline (eyes open and eyes closed) and cognitive activation conditions on a sample of 58 children with ADHD (27 multiplex families), ages 6-18. EEG power in three frequency bands: theta (4-7 Hz), alpha (8-12 Hz) and beta (12-20 Hz) was tested for sibling correlation, familial co-segregation and association with behavioral task performance on a sustained attention task. Sibling correlation for EEG measures was moderate during baseline conditions and significantly higher for the cognitive activation condition. Familial clustering of frontal and parietal alpha power was evident, but only during the cognitive activation condition. Theta and alpha power correlated significantly with CPT response variability and omission errors, respectively. Cognitive task performance did not exhibit familial clustering in our sample. EEG measures (i.e., alpha power) recorded during cognitive activation is a strongly familial trait in ADHD and may be a putative endophenotype for ADHD.

Effects of temporal context and temporal expectancy on neural activity in inferior temporal cortex

Timing is critical. The same event can mean different things at different times and some events are more likely to occur at one time than another. We used a cued visual classification task to evaluate how changes in temporal context affect neural responses in inferior temporal cortex, an extrastriate visual area known to be involved in object processing. On each trial a first image cued a temporal delay before a second target image appeared. The animal's task was to classify the second image by pressing one of two buttons previously associated with that target. All images were used as both cues and targets. Whether an image cued a delay time or signaled a button press depended entirely upon whether it was the first or second picture in a trial. This paradigm allowed us to compare inferior temporal cortex neural activity to the same image subdivided by temporal context and expectation. Neuronal spiking was more robust and visually evoked local field potentials (LFP's) larger for target presentations than for cue presentations. On invalidly cued trials, when targets appeared unexpectedly early, the magnitude of the evoked LFP was reduced and delayed and neuronal spiking was attenuated. Spike field coherence increased in the beta-gamma frequency range for expected targets. In conclusion, different neural responses in higher order ventral visual cortex may occur for the same visual image based on manipulations of temporal attention.

Alpha reduction and event-related potentials, theta and gamma increase linked to letter selection

We examined evoked and induced modulations in theta, alpha and gamma oscillations, and also the P2 and late positive component of event-related potentials, during a visual discrimination task with target and nontarget letters. Results for target letters showed a decrease in the amplitude of alpha-band (10-11 Hz) activity and an increase in theta (4-7 Hz) and gamma (40-44 Hz) activities around 350 ms after stimulation. P2 and late positive component presented a higher amplitude to target than to repeated nontarget letters. Alpha reduction was inversely related to theta and late positive component increase. Moreover, gamma oscillation amplitude was directly related to theta amplitude. The findings suggest the importance of occipitoparietal alpha reduction for the development of task-related neuronal activity.

The human EEG--physiological and clinical studies

The present review summarizes the research in EEG performed by our group during the last 5 years. Our studies have been focussed on two areas: studies of variability and correlations in the oscillations during resting conditions of normal subjects, and the abnormalities related to type 1 diabetes. Recordings in normal subjects showed that also under standardized conditions with regular cycles of closed and open eyes, there is a temporal variability of the spectral components in EEG that necessitates samples>124 s in order to achieve estimates of alpha power with a coefficient of variation<0.1 in all recording channels (brain regions). The temporal variability in alpha and beta power demonstrates long-range temporal correlations, i.e., periods of large power (alpha or beta) are more likely to be followed by large power, and vice versa. The long-range temporal correlations were reproducible, especially during the closed-eyes condition, stronger in males than females, and not age dependent. In patients with type 1 diabetes, the alpha and beta power components were both decreased with similar nadirs in the posterior temporal regions, and the slow spectral components were increased in the frontal regions. The cognitive function was presently not studied but in a group of adolescents with diabetes we found a correlation between the presence of slow activity and the number of hypoglycaemic episodes. The loss of alpha and beta power was highly correlated which initiated a study of the normal alpha-beta correlation. A significant 1:2 phase synchronization was present between alpha and beta oscillations with a phase lag of about pi/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggested that they are generated by a common mechanism.

Interindividual variability in EEG correlates of attention and limits of functional mapping

In this study, we analyzed the EEG oscillatory activity induced during a simple visual task, in search of spectral correlate(s) of attention. This task has been previously analyzed by conventional event-related potential (ERP) computation, and Slow Potentials (SPs) were seen to be highly variable across subjects in topography and generators [Basile LF, Brunetti EP, Pereira JF Jr, Ballester G, Amaro E Jr, Anghinah R, Ribeiro P, Piedade R, Gattaz WF. (2006) Complex slow potential generators in a simplified attention paradigm. Int J Psychophysiol. 61(2):149-57]. We obtained 124-channel EEG recordings from 12 individuals and computed latency-corrected peak averaging in oscillatory bursts. We used current-density reconstruction to model the generators of attention-related activity that would not be seen in ERPs, which are restricted to stimulus-locked activity. We intended to compare a possibly found spectral correlate of attention, in topographic variability, with stimulus-related activity. The main results were (1) the detection of two bands of attention-induced beta range oscillations (around 25 and 21 Hz), whose scalp topography and current density cortical distribution were complex multi-focal, and highly variable across subjects (topographic dispersion significantly higher than sensory-related visual theta induced band-power), including prefrontal and posterior cortical areas. Most interesting, however, was the observation that (2) the generators of task-induced oscillations are largely the same individual-specific sets of cortical areas active during the pre-stimulus baseline. We concluded that attention-related electrical cortical activity is highly individual-specific, and possibly, to a great extent already established during mere resting wakefulness. We discuss the critical implications of those results, in combination with results from other methods that present individual data, to functional mapping of cortical association areas.

Brain oscillations differentiate the picture of one's own grandmother

The present report introduces, as a first study, the concept and methods of oscillatory brain dynamics to analyze well-known (familiar) and unfamiliar face processing in the 800 ms following a face presentation. We analyzed event-related oscillations in young, healthy subjects (N=26) by using three types of stimulation: (1) a simple light signal, (2) the picture of the face of an anonymous elderly lady and (3) the picture of the subjects' own grandmother. We found a number of significant peak to peak amplitude measures in all frequency bands in the time period of 0-500 ms, allowing a differentiation between perception of the subjects' own grandmother, the unknown elderly face and the light stimulation. The results showed increased event-related oscillatory responses elicited by the unknown face compared to the known grandmother a) in the theta responses (4-8 Hz) at T(6) (46%), b) in the gamma (28-48 Hz) responses at C(z) (22%) and C(3) (38%) and c) in the beta responses at F(4) (46%), C(z) (47%) and P(3) (105%). In contrast, the subjects' own grandmother elicited 20% increased fast theta (6-8 Hz) oscillations at F(4) compared to the unknown face. Delta responses dissociated face from simple light processing, as reflected in the observation of approx. 50% higher amplitudes at the occipital compared to the frontal locations during face perception. We conclude that the described multiple brain oscillations clearly differentiate the known and unknown faces with varied degrees of selective-responsiveness in a short time window between 0 and 800 ms. Furthermore, the results are in conceptual accordance with the "selectively distributed processing" hypothesis.

Varieties of attention in neutral trials: linking RT to ERPs and EEG frequencies

It is often assumed that when a neutral cue is presented in a spatial cueing task, attention remains at fixation until target onset. We hypothesized that variance in nonspatial attention and switches of attention toward target locations can account for variance in reaction times of neutral trials. Lateralized event-related potentials (ERPs) and changes in electroencephalogram (EEG) frequency bands served as predictor variables in a single-trial logistic regression analysis to predict the direction of spatial attention in cued and neutral trials. The contingent negative variation (CNV) and non-lateralized changes in the alpha band served as markers of nonspatial attention. The direction of attention in cued trials was reliably predicted from single-trial lateralized ERP components. In neutral trials, only evidence for nonspatial attention was found, indicated by increases in the CNV and decreases in alpha preceding targets to which responses were relatively fast.

Opposite dependencies on visual motion coherence in human area MT+ and early visual cortex

In order to understand the relationship between brain activity and visual motion perception, knowledge of the cortical areas participating in signal processing alone is insufficient. Rather knowledge on how responses vary with the characteristics of visual motion is necessary. In this study, we measured whole brain activity using magnetoencephalography in humans discriminating the global motion direction of a random dot kinematogram whose strength was systematically varied by the percentage of coherently moving dot elements. Spectral analysis revealed 2 components correlating with motion coherence. A first component in the low-frequency domain ( approximately 3 Hz), linearly increasing with motion coherence, could be attributed to visual cortex including human area middle temporal (MT) +. A second component oscillating in the alpha frequency range and emerging after stimulus offset showed the inverse dependence on motion coherence and arose from early visual cortex. Based on these results, we first of all conclude that motion coherence is reflected in the population response of human extrastriate cortex. Second, we suggest that the occipital alpha activity represents a gating mechanism protecting visual motion integration in later cortical areas from disturbing upcoming signals.

Location of brain rhythms and their modulation by preparatory attention estimated by current density

To test the hypothesis that there is a functional modulation of conventional EEG bands associated with preparatory attention, putative changes in the spontaneous brain rhythms and their associated cerebral sources were addressed. The goals of the present report were, first, to find the brain areas with maximal rhythmic activity before warning and imperative stimuli in a classic contingent negative variation (CNV) paradigm, and, second, to study the modulation of the EEG rhythms of these areas during the preparatory attention interval which precedes the S2 (imperative) stimulus. Trial by trial LORETA analysis found similar brain rhythm generators during both pre-S1 and pre-S2 intervals. Each theta, alpha and beta traditional EEG rhythm originates in several anatomically distinct brain structures. Preparatory attention is associated with a decrease in power in alpha (right and left occipital and temporal areas) and low-beta (left frontal, bilateral occipital and middle frontal areas) EEG bands. In these structures power changes associated with preparatory attention modulated either a dominant or a non-dominant oscillatory band, suggesting that non-dominant rhythms of a cerebral area have some functional relevance. Our results imply distributed regional sources for brain rhythms and support the view that during preparatory attention there is a modulation of the brain sources generating alpha and beta brain rhythms. Moreover, the proposed combined approach makes it possible to explore the definition of a given brain area not only anatomically, but also by the frequency content and the functional reactivity of the electrical rhythms that it generates.

A shift of visual spatial attention is selectively associated with human EEG alpha activity

Event-related potentials and ongoing oscillatory electroencephalogram (EEG) activity were measured while subjects performed a cued visual spatial attention task. They were instructed to shift their attention to either the left or right visual hemifield according to a cue, which could be valid or invalid. Thereafter, a peripheral target had to be evaluated. At posterior parietal brain areas early components of the event-related potential (P1 and N1) were higher when the cue had been valid compared with invalid. An anticipatory attention effect was found in EEG alpha magnitude at parieto-occipital electrode sites. Starting 200 ms before target onset alpha amplitudes were significantly stronger suppressed at sites contralateral to the attended visual hemifield than ipsilateral to it. In addition, phase coupling between prefrontal and posterior parietal electrode sites was calculated. It was found that prefrontal cortex shows stronger phase coupling with posterior sites that are contralateral to the attended hemifield than ipsilateral sites. The results suggest that a shift of attention selectively modulates excitability of the contralateral posterior parietal cortex and that this posterior modulation of alpha activity is controlled by prefrontal regions.

Brain oscillatory responses to an auditory-verbal working memory task in mild cognitive impairment and Alzheimer's disease

We report preliminary findings on EEG oscillatory correlates of working memory in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Event-related desynchronization (ERD) and synchronization (ERS) of the 1-20 Hz EEG frequencies were studied using wavelet transforms in elderly controls, MCI patients and mild probable AD patients performing an auditory-verbal Sternberg memory task. Behaviourally, the AD patients made more errors than the controls and the MCI group. Statistically significant differences during the encoding of the memory set were found between the controls and the MCI group, such that the latter group showed ERD in the approximately 10-20 Hz frequencies. The findings may reflect different, compensatory encoding strategies in MCI. During retrieval, the most obvious differences were observed between the controls and the AD group: the ERD in the approximately 7-17 Hz frequencies was absent in the AD group particularly in anterior and left temporal electrode locations. This finding might indicate that AD is associated with deficient lexical-semantic processing during the retrieval phase in working memory tasks. Future studies with larger patient groups are needed to establish the diagnostic value of ERD/ERS patterns in MCI and AD.

The effects of memory load and stimulus relevance on the EEG during a visual selective memory search task: an ERP and ERD/ERS study

OBJECTIVE

Psychophysiological correlates of selective attention and working memory were investigated in a group of 18 healthy children using a visually presented selective memory search task.

METHODS

Subjects had to memorize one (load1) or 3 (load3) letters (memory set) and search for these among a recognition set consisting of 4 letters only if the letters appeared in the correct (relevant) color. Event-related potentials (ERPs) as well as alpha and theta event-related synchronization and desynchronization (ERD/ERS) were derived from the EEG that was recorded during the task.

RESULTS

In the ERP to the memory set, a prolonged load-related positivity was found. In response to the recognition set, effects of relevance were manifested in an early frontal positivity and a later frontal negativity. Effects of load were found in a search-related negativity within the attended category and a suppression of the P3-amplitude. Theta ERS was most pronounced for the most difficult task condition during the recognition set, whereas alpha ERD showed a load-effect only during memorization.

CONCLUSIONS

The manipulation of stimulus relevance and memory load affected both ERP components and ERD/ERS.

SIGNIFICANCE

The present paradigm may supply a useful method for studying processes of selective attention and working memory and can be used to examine group differences between healthy controls and children showing psychopathology.

Validating the efficacy of neurofeedback for optimising performance

The field of neurofeedback training has largely proceeded without validation. Here we review our studies directed at validating SMR, beta and alpha-theta protocols for improving attention, memory, mood and music and dance performance in healthy participants. Important benefits were demonstrable with cognitive and neurophysiological measures which were predicted on the basis of regression models of learning. These are initial steps in providing a much needed scientific basis to neurofeedback, but much remains to be done.

Long-range EEG phase synchronization during an arithmetic task indexes a coherent cortical network simultaneously measured by fMRI

An open question lies in whether or not distributed activities in the distant brain regions are integrated into a coherent ensemble for cognitive information processing. Long-range phase synchronization is often observed by scalp EEG measurements during cognitive tasks and is considered to provide a possible neural principle for the functional integration of distributed neural activities. Synchronization could be reflected at the neuron firing level or at the local field potential and could appear in the scalp EEG under certain conditions on neural spatial and temporal coherence. To examine if phase synchronization is concerned with the integration of distant regions, we proposed a method to extract brain activities associated with task-dependent phase synchronization by combining simultaneous fMRI and EEG. By applying this method in a mental arithmetic task, we found a dominant task-dependent increase of phase synchronization around 14 Hz (in beta frequency) across bilateral parietal sites that were associated with both negative and positive BOLD responses. Functional connectivity analyses of these regions demonstrated that an increase in hemispheric beta synchronization was associated with a linking between the cross-hemispheric regions (left angular gyrus and right superior parietal gyrus) and also among the anterior-posterior regions (right dorsolateral prefrontal cortex, putamen, and right superior temporal gyrus). These findings indicate that the positive BOLD regions (dorsolateral prefrontal cortex and superior parietal lobule) are linked with other negative BOLD regions. We also discussed the possible importance of beta synchronization in the formation of a working memory network.

Amplitude and phase relationship between alpha and beta oscillations in the human electroencephalogram

The relationship between the electro-encephalographic (EEG) alpha and beta oscillations in the resting condition was investigated in the study. EEGs were recorded in 33 subjects, and alpha (7.5-12.5 Hz) and beta (15-25 Hz) oscillations were extracted with the use of a modified wavelet transform. Power, peak frequency and phase synchronisation were evaluated for both types of oscillation. The average beta-alpha peak frequency ratio was about 1.9-2.0 for all electrode derivations. The peak frequency of beta activity was within 70-90 % of the 95 % confidence interval of twice the alpha frequency. A significant (p < 0.05) linear regression was found between beta and alpha power in all derivations in 32 subjects, with the slope of the regression line being approximately 0.3. There was no significant difference in the slope of the line in different electrode locations, although the power correlation was strongest in the occipital locations where alpha and beta oscillations had the largest power. A significant 1:2 phase synchronisation was present between the alpha and beta oscillations, with a phase lag of about pi/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggests that they are generated by a common mechanism. Power and phase relationships were weaker, suggesting that these properties can be modulated by additional mechanisms as well as be influenced by noise. A careful distinction between alpha-dependent and alpha-independent beta activity should be considered when making statements about the possible significance of genuine beta activity in different neurophysiological mechanisms.

Effect of fixation tasks on multifocal visual evoked potentials

PURPOSE

This study investigated the effects of cognitive influence on the multifocal visual evoked potential (mVEP) at different levels of eccentricity. Three different foveal fixation conditions were utilized involving varying levels of task complexity. A more complex visual fixation task has been known to suppress peripheral signals in subjective testing.

METHODS

Twenty normal subjects had monocular mVEPs recorded using the AccuMap objective perimeter. This allowed simultaneous stimulation of 58 segments of the visual field to an eccentricity of 24 degrees. The mVEP was recorded using three different fixation conditions in random order. During task 1 the subject passively viewed the central fixation area. For task 2 alternating numbers were displayed within the fixation area; the subject on viewing the number '3' in the central fixation area indicated recognition by pressing a button. Throughout task 3, numbers were displayed as in task 2. The subject had the cognitive task of summating all the numbers.

RESULTS

Analysis revealed that the increased attention and concentration demanded by tasks 2 and 3 in comparison with task 1 resulted in significantly enhanced central amplitudes of 9.41% (Mann-Whitney P = 0.0002) and 13.45% (P = 0.0002), respectively. These amplitudes became reduced in the periphery and approached those of task 1, resulting in no significant difference between the three tasks. Latencies demonstrated no significant difference between each task nor at any eccentricity (P > 0.05). As the complexity of each task increased the amount of alpha rhythm was significantly reduced.

CONCLUSIONS

Our findings indicate that task 1 required a minimal demand of cognition and was associated with the greatest amount of alpha rhythm. It was also the most difficult to perform because of loss of interest. The other two tasks required a greater demand of higher order cognitive skills resulting in significantly enhanced amplitudes centrally and the attenuation of alpha rhythm. Therefore, amplitudes are increased around the area of attention.

The influence of methylphenidate on the power spectrum of ADHD children - an MEG study

BACKGROUND

The present study was dedicated to investigate the influence of Methylphenidate (MPH) on cortical processing of children who were diagnosed with different subtypes of Attention Deficit Hyperactivity Disorder (ADHD). As all of the previous studies investigating power differences in different frequency bands have been using EEG, mostly with a relatively small number of electrodes our aim was to obtain new aspects using high density magnetoencephalography (MEG).

METHODS

35 children (6 female, 29 male) participated in this study. Mean age was 11.7 years (+/- 1.92 years). 17 children were diagnosed of having an Attention-Deficit/Hyperactivity Disorder of the combined type (ADHDcom, DSM IV code 314.01); the other 18 were diagnosed for ADHD of the predominantly inattentive type (ADHDin, DSM IV code 314.0). We measured the MEG during a 5 minute resting period with a 148-channel magnetometer system (MAGNES 2500 WH, 4D Neuroimaging, San Diego, USA). Power values were averaged for 5 bands: Delta (D, 1.5-3.5 Hz), Theta (T, 3.5-7.5 Hz), Alpha (A, 7.5-12.5 Hz), Beta (B, 12.5-25 Hz) and Global (GL, 1.5-25 Hz).). Additionally, attention was measured behaviourally using the D2 test of attention with and without medication.

RESULTS

The global power of the frequency band from 1.5 to 25 Hz increased with MPH. Relative Theta was found to be higher in the left hemisphere after administration of MPH than before. A positive correlation was found between D2 test improvement and MPH-induced power changes in the Theta band over the left frontal region. A linear regression was computed and confirmed that the larger the improvement in D2 test performance, the larger the increase in Theta after MPH application.

CONCLUSION

Main effects induced by medication were found in frontal regions. Theta band activity increased over the left hemisphere after MPH application. This finding contradicts EEG results of several groups who found lower levels of Theta power after MPH application. As relative Theta correlates with D2 test improvement we conclude that MEG provide complementary and therefore important new insights to ADHD.

Synchronous neural oscillations and cognitive processes

The central problem for cognitive neuroscience is to describe how cognitive processes arise from brain processes. This review summarizes the recent evidence that synchronous neural oscillations reveal much about the origin and nature of cognitive processes such as memory, attention and consciousness. Memory processes are most closely related to theta and gamma rhythms, whereas attention seems closely associated with alpha and gamma rhythms. Conscious awareness may arise from synchronous neural oscillations occurring globally throughout the brain rather than from the locally synchronous oscillations that occur when a sensory area encodes a stimulus. These associations between the dynamics of the brain and cognitive processes indicate progress towards a unified theory of brain and cognition.

Attention-driven discrete sampling of motion perception

In movies or on TV, a wheel can seem to rotate backwards, due to the temporal subsampling inherent in the recording process (the wagon wheel illusion). Surprisingly, this effect has also been reported under continuous light, suggesting that our visual system, too, might sample motion in discrete "snapshots." Recently, these results and their interpretation have been challenged. Here, we investigate the continuous wagon wheel illusion as a form of bistable percept. We observe a strong temporal frequency dependence: the illusion is maximal at alternation rates around 10 Hz but shows no spatial frequency dependence. We introduce an objective method, based on unbalanced counterphase gratings, for measuring this phenomenon and demonstrate that the effect critically depends on attention: the continuous wagon wheel illusion was almost abolished in the absence of focused attention. A motion-energy model, coupled with attention-dependent temporal subsampling of the perceptual stream at rates between 10 and 20 Hz, can quantitatively account for the observed data.

Beta oscillations in face recognition

This report presents an analysis of the brain's beta oscillations in face recognition. We performed experiments on 26 subjects with a strategy consisting of two types of stimulations: (1) the picture of an elder anonymous lady (unknown face) and (2) the picture of the subject's own grandmother (known face). The subjects were healthy, young people between the ages of 15-32 years. Data were analyzed by means of amplitude frequency characteristics and digital filtering. Our results show the significant role of beta response in face recognition and the differentiation of known and unknown faces. Furthermore, this report supports our former view that the presentation of grandmother face evokes selectively distributed multiple oscillations in the brain. Together with the scope of other frequencies (e.g., delta, theta, and alpha), this method can serve as a tool for research studies or clinical studies in memory and cognition.

EEG Correlates of Methylphenidate Response in ADHD: Association With Cognitive and Behavioral Measures

The authors examined the association between EEG correlates of medication response and concomitant cognitive and behavioral changes among children with attention-deficit hyperactivity disorder (ADHD). Subjects were 36 children with ADHD, aged 8 to 12 years. EEG activity was recorded from nine active electrodes during placebo and medication conditions. Medication administration resulted in increased alpha activity in central and parietal regions during both the baseline and cognitive activation conditions. Children who were medication responders exhibited increased frontal beta activity whereas nonresponders showed decreased beta activity in the same region. Increased frontal beta activity was significantly correlated with medication-related improvement in performance on Conners'Continuous Performance Test and parent behavior ratings in attention and hyperactivity. Decreased right frontal theta activity was associated with improvements in parent-rated attention, but not in CPT performance. Stimulant medication increases beta activity in children with ADHD, particularly in frontal regions. Increased cortical arousal and activation in the frontal cortex is strongly associated with sustained attention and response inhibition and with parent-rated attention and hyperactivity/impulsivity.

Effects of diazepam and zolpidem on EEG beta frequencies are behavior-specific in rats

A pharmacological dissociation of the relation between electroencephalographic (EEG) activity and behavior has been described for the benzodiazepines. While a decrease in high frequency EEG activity is associated with a decrease in arousal in drug-free conditions, sedative benzodiazepines increase beta activity. Non-benzodiazepine GABA(A) receptor modulators can increase beta activity as well. To further study the relationship between rat behavior and EEG under GABA(A) receptor modulation, EEG effects of diazepam (2.5 mg/kg) and zolpidem (2.5 mg/kg) were studied during different behaviors. Both drugs modulate the GABA(A) receptor, albeit that zolpidem shows alpha(1) subunit selectivity while diazepam is non-selective. A detailed analysis of rat open field behavior was made with a distinction of 25 behavioral elements. The EEG was segmented according to each behavioral element and a corresponding power spectrum calculated. Both diazepam and zolpidem increased EEG beta frequencies, characteristic for the benzodiazepines. However, the beta and gamma increase was specific for active behavior and not for inactivity. Interestingly, diazepam and zolpidem seemed to amplify, rather than dissociate, the relation between behavior and the EEG. It is hypothesized that the large increase in beta-3/gamma activity caused by diazepam and zolpidem is a compensatory mechanism that allows for behavioral activation, despite pharmacologically induced sedation.

Analysis of state-dependent transitions in frequency and long-distance coordination in a model oscillatory cortical circuit

Changes in behavioral state are typically accompanied by changes in the frequency and spatial coordination of rhythmic activity in the neocortex. In this article, we analyze the effects of neuromodulation on ionic conductances in an oscillating cortical circuit model. The model consists of synaptically-coupled excitatory and inhibitory neurons and supports rhythmic activity in the alpha, beta, and gamma ranges. We find that the effects of neuromodulation on ionic conductances are, by themselves, sufficient to induce transitions between synchronous gamma and beta rhythms and asynchronous alpha rhythms. Moreover, these changes are consistent with changes in behavioral state, with the rhythm transitioning from the slower alpha to the faster gamma and beta as arousal increases. We also observe that it is the same set of underlying intrinsic and network mechanisms that appear to be simultaneously responsible for both the observed transitions between the rhythm types and between their synchronization properties. Spike time response curves (STRCs) are used to study the relationship between the transitions in rhythm and the underlying biophysics.

Functional effects of the DAT1 polymorphism on EEG measures in ADHD

OBJECTIVE

This paper examines whether dopamine transporter gene (DAT1) allele status mediates medication-related change in cognitive and neurophysiological measures among children with attention-deficiency/hyperactivity disorder (ADHD).

METHOD

A single 10-mg dose of methylphenidate was given in a double-blind, placebo-controlled fashion to children with ADHD who were seen for cognitive testing and EEG recording. Buccal samples were obtained and genotyped for the DAT1 polymorphism.

RESULTS

DAT1 allele status was associated with performance on a sustained attention task and medication-related EEG changes. Compared with those with one or more copies of the DAT1 9-repeat allele (9R), children with two copies of the 10-repeat allele (10R) exhibited poorer performance on the vigilance task. In addition, children with 10R exhibited medication-related EEG changes of increased central and parietal beta power, decreased right frontal theta power, and lower theta/beta ratios; 9R carriers showed the opposite pattern.

CONCLUSIONS

The data suggest that the DAT1 polymorphism mediates medication-related changes in cortical activity among children with ADHD.

Propagation of repetitive alpha waves over the scalp in relation to subjective preferences for a flickering light

Paired-comparison tests were performed to examine subjective preferences for a flickering light. Electroencephalograms were then recorded from seven electrodes (10-20 system) during presentations of the most and least preferred flickering-light conditions. As a way of investigating the flow of alpha waves on the scalp over both the left and right hemispheres in relation to subjective preference, the alpha waves were analyzed by means of the cross-correlation function (CCF). The maximum value of the CCF, /phi(tau)/(max), between the alpha waves measured at different electrodes and its delay time, tau(m), were analyzed. Results show that the most preferred flickering light has a significant larger /phi(tau)/(max) than the least preferred flickering light, and that /phi(tau)/(max) decreases with increasing distance between comparison (O(1) or O(2)) and test electrodes. On the other hand, the delay time of the maximum value of the CCF, tau(m), increases with the distance between comparison and test electrodes.