Theta power in the EEG of humans during ongoing processing in a haptic object recognition task

Dynamic changes in spectral theta power (TP) in the EEG over frontal regions were reported previously during the processing of visually presented spatial and verbal tasks [Cereb. Cortex, 7 (1997) 374-385]. Lower TP was found at the beginning compared to the end of processing. In order to test another modality, we examined theta power during the exploration of haptic stimuli with different complexity. A linear correlation between theta power and mean exploration time (as a measure of stimulus complexity) was found at the end of exploration but not at its beginning. These data are in line with our hypothesis since one could expect minimal load of working memory independent of stimulus complexity at the beginning of exploration whereas working memory would have integrated the stimuli of differing complexity into a perceptual model at the end of exploration.     

EEG synchronization likelihood in mild cognitive impairment and Alzheimer's disease during a working memory task.

OBJECTIVE: Synchronization likelihood analysis of resting state EEG has shown that cognitive dysfunction in Alzheimer's disease (AD) and its precursor mild cognitive impairment (MCI) are associated with a loss of functional connectivity in high (upper alpha and beta) frequency bands. Working memory tasks are known to change functional connectivity, but it is unknown whether this increases the differences between AD, MCI and healthy controls. Our objective was to investigate the behavior of synchronization likelihood of multichannel EEG in AD, MCI and cognitively healthy controls, both at rest and during a working memory task. METHODS: EEGs (200 Hz sample frequency, 21 channels, average reference) were recorded at rest as well as during a visual working memory task in 14 patients with AD according to the NINCDS-ADRDA criteria (mean age 76.4; SD 13.6), 11 patients with MCI according to the criteria of Petersen (mean age 78.4; SD 6.4) and 14 with subjective memory complaints but no demonstrable memory disturbance (mean age 61.6; SD 26.6). The synchronization likelihood was computed over 19 channels, comparing each channel with all the other channels for the 0.5-4, 4-8, 8-10, 10-12, 12-30, 30-50 Hz frequency bands. RESULTS: The synchronization likelihood was significantly decreased in the upper alpha (10-12) and beta (12-30) bands in AD compared to persons with subjective memory complaints. The working memory task scores strongly correlated with Mini-Mental State Examination scores. During the working memory task the synchronization likelihood was significantly higher in MCI compared to the control subjects in the lower alpha band (8-10 Hz). CONCLUSIONS: Decrease of beta band synchronization occurs in mild AD, both in a resting condition and during a working memory task. SIGNIFICANCE: Decrease of beta band synchronization in mild AD is a robust finding. The present study confirms our findings in a different cohort of patients, using alternative frequency bands. The diagnostic value of the synchronization likelihood in AD and MCI needs to be further established.     

Accordance between EEG alpha power and dual task performance for different visual cognitive tasks.

Evidence from clinical and experimental studies suggests that the left hemisphere is preferentially engaged in language processing and mathematical-analytic tasks while the right is involved with spatial relations and synthetic tasks. The purpose of the present study was to investigate accordance between dual task paradigm (effects of concurrent cognitive tasks on right- and left-hand finger tapping frequency) and EEG alpha power changes, which are used to conduct research in lateralization of cognitive function. Subjects performed reading, face recognition and line orientation tasks. First, the EEG was recorded during the tasks and, after six months, the dual task was carried out using the same cognitive tasks. Statistical analysis yielded no significant main effect for the hemispheres, performing hand and three cognitive tasks separately for the dual task and the EEG alpha power changes. However, significant correlation between the two methods was found, indicating the left parietal activation for the reading task, the right temporal activation for the line orientation task, and both hemispheric activation for the face recognition task. Results first suggest a significant accordance between dual task performance and EEG alpha asymmetry studies.     

Verbal-manual interactions during dual task performance: An EEG study

Everyday situations regularly require the performance of more than one task at the same time, such as walking and conversing. Here, a dual task approach was adopted for evaluating changes in neural activity associated with a motor assignment. To this end, participants performed a self-paced motor (tapping) task in a unimanual and bimanual context along with a verbal (counting) task. Neural dynamics was assessed by means of EEG coherence in the beta frequency band (13-30 Hz) and included intrahemispheric, interhemispheric and midline connectivity profiles. Results showed that coherence intensified across the motor network during dual tasking for unimanual tapping, which permitted to preserve performance. For bimanual tapping, strengthening of functional connectivity was not observed for interhemispheric and midline regions, which associated with a degradation of coordinative output. The latter underlines the significance of these communication pathways for bimanual behaviour. Overall, the findings indicate that dynamic modulation of functional connectivity patterns provides a substrate for preserving behaviour in effortful circumstances such as dual tasking.     

Event-related prolongation of induced EEG rhythmicities in experiments with a cognitive task.

Since we consider evoked potentials (EPs) and event-related potentials (ERPs) as an ensemble of induced rhythmicities we investigated "sensory" evoked potentials (EPs) and "cognitive" event-related potentials (ERPs) with respect to their frequency components (around 5 Hz and around 10 Hz). "Sensory" EP sessions consisted in standard EP measurements with tone bursts of 2000 Hz frequency. Prior to the subsequent "cognitive" sessions, the subjects were instructed to expect frequent 2000 Hz tones and rare 1950 Hz tones, the rare tones thus being difficult to detect. A further instruction was to count the number of the "rare" stimuli. Not a single tone of different frequency, however, was presented. The single trials were then analyzed with respect to their 5 Hz and 10 Hz components. Time-locking was investigated using a modified single sweep wave identification (SSWI) method. Depending on features of the prestimulus EEG, it was observed that theta (4-7 Hz) and alpha (7-13 Hz) responses were prolonged in the case of "cognitive" sessions. We believe that the prolonged endogenous ERP components are induced rhythmicities triggered by additional information processing, when a high degree of uncertainty has to be resolved during our experimental conditions. For the analysis and visualization of these phenomena, the combination of digital filtering and SSWI showed relevant advantages in comparison to other methods.     

The effects of arithmetic task difficulty and performance level on EEG alpha asymmetry

The effects of arithmetic task difficulty and performance level on ratio measures of parietal alpha asymmetry were evaluated. Sixteen subjects were given 14 visually presented problems varying in difficulty according to Thomas, Q. Jl exp. Psychol. 15, 173-191, 1963. When the mean latencies for these problems were compared, problem data were averaged across four distinctly different levels. As difficulty increased from low to moderate levels (levels 1 to 2 to 3), relative left-hemisphere activation significantly increased, but as difficulty increased to higher levels, alpha asymmetry tended to decrease. Changes in both hemispheres were responsible for this difficulty effect on ratio values and these changes appeared to be independent of strategy effects. When subjects were categorized according to performance (solution latency), the high performance group exhibited greater relative left hemisphere activation, more significant baseline-task asymmetry differences, and greater bilateral activation from baseline levels than the low performance group. Correlations between EEG measures and performance were generally nonsignificant, although task asymmetry was found to be related to performance latency on tasks of moderate difficulty.     

Linear and non-linear EEG analysis of adolescents with attention-deficit/hyperactivity disorder during a cognitive task

Objective

We aimed to investigate whether electroencephalograph (EEG) dynamics differ in adolescents with attention-deficit/hyperactivity disorder (ADHD) compared with healthy subjects during the performance of a cognitive task.

Methods

We recorded EEGs from 19 scalp electrodes in 11 adolescent boys with ADHD and 12 age-matched healthy boys while the subjects were at rest and during a continuous performance test (CPT). The approximate entropy (ApEn), a non-linear information-theoretic measure, was calculated to quantify the complexity of the EEGs.

Results

The mean ApEn of the ADHD patients was significantly lower than the healthy subjects over the right frontal regions (Fp2 and F8) during the performance of the cognitive task, but not at rest. The spectral analysis showed significant differences between the two groups in the P3 and T4 regions at rest and the Fp2 and F8 regions during task performance.

Conclusions

The differences in EEG complexity between the two groups suggest that cortical information processing is altered in ADHD adolescents, and thus their levels of cortical activation may be insufficient to meet the cognitive requirements of attention-demanding tasks.

Significance

This study suggests that a non-linear measure such as ApEn is useful for investigating neural dysfunctions in adolescents with ADHD.     

Interhemispheric correlation of EEG activity during successful and unsuccessful cognitive performance

EEG activity of eight male volunteers was monopolarly recorded at P3 and P4 during an initial baseline and during performance of three series of cognitive tasks: one verbal, one spatial and one "mixed" demanding verbal and spatial processing. Interhemispheric correlation of the EEG activity was compared among tasks and between successful and unsuccessful trials. There was a significant main effect for success or failure of cognitive processing with increased interhemispheric correlation during unsuccessful trials regardless of their nature. There was no main effect for tasks. Interhemispheric correlation proved to be sensitive to success or failure in information processing.     

Short-term learning of a visually guided power-grip task is associated with dynamic changes in EEG oscillatory activity.

OBJECTIVE: Performing a motor task after a period of training has been associated with reduced cortical activity and changes in oscillatory brain activity. Little is known about whether learning also affects the neural network associated with motor preparation and post movement processes. Here we investigate how short-term motor learning affects oscillatory brain activity during the preparation, execution, and post-movement stage of a force-feedback task. METHODS: Participants performed a visually guided power-grip tracking task. EEG was recorded from 64 scalp electrodes. Power and coherence data for the early and late stages of the task were compared. RESULTS: Performance improved with practice. During the preparation for the task alpha power was reduced for late experimental blocks. A movement execution-related decrease in beta power was attenuated with increasing task practice. A post-movement increase in alpha and lower beta activity was observed that decreased with learning. Coherence analysis revealed changes in cortico-cortical coupling with regard to the stage of the visuomotor task and with regard to learning. Learning was variably associated with increased coherence between contralateral and/or ipsilateral frontal and parietal, fronto-central, and occipital brain regions. CONCLUSIONS: Practice of a visuomotor power-grip task is associated with various changes in the activity of a widespread cortical network. These changes might promote visuomotor learning. SIGNIFICANCE: This study provides important new evidence for and sheds new light on the complex nature of the brain processes underlying visuomotor integration and short-term learning.     

Instantaneous EEG coherence analysis during the Stroop task.

OBJECTIVE: In the present study the Stroop effect is analyzed by means of EEG coherence analysis in addition to traditional analysis of behavioral data (reaction time) and ERP analysis. Data from 10 normal subjects are examined. METHODS: In particular, a special dynamic approach for a continuous coherence estimation is applied to investigate the procedural evolution of functional cortical relationships during the Stroop task. RESULTS: The frequency band of 13-20 Hz is found to be sensitive to the discrimination between the congruent and the incongruent task conditions on the basis of instantaneous coherence analysis. The magnitude of coherence values within the time interval of late potentials and the maximal coherence values are used to assess the strength of interaction between distinct areas of the cortex. Higher coherences are observed within the left frontal and left parietal areas, as well as between them for the incongruent situation in comparison with the congruent situation. Furthermore, the time-points of maximal coherence allows a procedural discrimination between both situations. The peak synchrony described by the time-points of maximal coherence correlates strongly with the reaction times mainly within the frontal area and between fronto-parietal areas in the incongruent case, whereas this correlation is restricted to the right hemisphere in the congruent case.     

Comparable cortical activation with inferior performance in women during a novel cognitive inhibition task

Men are hypothesised to perform better than women at tasks requiring cognitive inhibition. The present study applied whole-brain functional magnetic resonance imaging to investigate the neural correlates of cognitive inhibition using a novel task, requiring detection of numbers decreasing in numerical order, in relation to sex. The study involved 19 young healthy subjects (9 men, 10 women). Behavioural sex differences favouring men were found on the inhibition, but not on the automatization (i.e. detection of numbers increasing in numerical order), condition of the task. Significant areas of activation associated with cognitive inhibition included the right inferior prefrontal and bilateral dorsolateral prefrontal cortices, left inferior and superior parietal lobes, and bilateral temporal regions across men and women. No brain region was significantly differently activated in men and women. Our findings demonstrate that (a) cognitive inhibition is dependent on intact processes within frontal and parietal regions, and (b) women show inferior cognitive inhibition despite of comparable activation to men in relevant regions. Equated behavioural performance may elicit sex differences in brain activation.     

EEG mapping during a visuo-spatial task. Averaged maps and group statistics

Twenty young volunteers (10 men, 10 women), righthanded, students, have been recorded in EEG cartography in different situations. We have compared the quantified EEGs when the subjects were resting, eyes closed and later, eyes opened, looking at a cartoon. The EEGs were quantified by spectral Fourier analysis and submitted to data reduction. Ten spectral parameters were computed, yielding 51 variables allowing computations and drawings of 90 EEG maps. Mean parameters, mean variables, averaged EEG maps have been computed for the entire group, between sub-groups, between hemispheres. Non-parametric permutation Fisher tests have been applied for statistical comparisons and statistical validations of the EEG maps computed between subjects. The activation of EEG tracings produced by the opening of the eyes were caracterized topographically by: mean alpha frequencies increased over temporal and rolandic areas; mean alpha amplitudes in microV divided by a factor 3 for occipital areas but unchanged in topography; mean relative amplitudes divided by a factor 2 but with a topography being more parietal than occipital for the alpha rhythm; a resonance coefficient greater over the left parietal than the right (alpha more regular), whereas it was greater over the right occipital than the left during the resting condition. Statistically for the whole group, the left hemisphere, recorded after the right, is more 'activated' in the eyes closed situation. During visual attention, the left hemisphere is less activated than the right.     

Transitory cognitive impairment in epileptic children during a CPT task.

EEGs and behavioral responses were studied in two sex matched groups of 58 epileptic and 20 healthy children between 8 and 12 years of age, during the execution of a go-no go CPT (X; A-X) task to determine transitory cognitive impairment (TCI) incidence. Paroxysmal discharges were found on 87.9% and 5% of the EEGs in the epileptic and control groups respectively, with no differences related to sex. The predominant EEG findings with respect to paroxysmal discharges were the association of two or more types of paroxysms with frequency higher than 5/minute, an average duration less than 0.5 second and topographical distribution over temporal-parietal-occipital areas without significant interhemispheric differences. TCI was detected in 36.2% of epileptic children. The epileptic group showed significantly higher numbers of behavioral errors and longer reaction times (RTs) in relation to the control group. Analyzing RTs on the two blocks of the task, linear discriminant analysis showed an acceptable classification of TCI incidence between groups.     

Changes in neural complexity of the EEG during a visual oddball task.

OBJECTIVE: Neural complexity (C(N)) was introduced by Tononi et al. in an information-theoretic framework to capture the balance between functional specialisation and integration in the brain. We hypothesised that C(N) should vary during cognitive processing, specifically during an oddball task. METHODS: In 11 normal human subjects, we recorded from groups of EEG electrodes in the frontal (F), central-parietal (CP) and occipito-temporal (OT) regions during a visual oddball reward conditioning task and calculated C(N) in each region. Three types of visual stimulus (abstract shapes, called neutral, reward and penalty) were presented randomly in three blocks of trials. During the first block, subjects did not know the significance of the stimulus shapes. For the subsequent (conditioning) blocks, subjects were informed that whenever they saw reward or penalty patterns, they would win or lose money, respectively. RESULTS: In regions CP and OT, C(N) was significantly larger in reward and penalty trials than in neutral during all blocks. During a trial, significant changes in C(N) occurred around the ERP peaks N1 and P300 and the effects of reward conditioning on C(N) could be distinguished from penalty. CONCLUSIONS: Our findings support the above hypothesis, indicating that C(N) correlates with both the sensory and cognitive components of stimulus processing. SIGNIFICANCE: This study extends the scope of C(N) in the analysis of cognitive processing.     

Attentional processes and cognitive performance during expectancy of painful galvanic stimulations: a high-resolution EEG study

In the present high-resolution electroencephalographic (EEG) study, an omitted-stimulus paradigm induced a strong expectancy for a predictable painful stimulation (nonpainful in the control condition). During the expectancy of pain, concurrent cognitive demands were superimposed. The aim was to investigate the effects on primary sensorimotor and central midline areas of the competition among concurrent attentional processes related to cognition and pain expectancy, as indexed by behavioral performance and EEG data. A main issue was whether cognitive performance decreases, due to a re-allocation of attentional resources on primary sensorimotor and midline areas for the anticipation of pain. Behavioral results showed no differences in the cognitive (working memory) performance during the expectancy of nonpainful versus painful stimulations. In parallel, anticipatory event-related potentials (ERPs) were negligible in line with a low emotional reactivity/alertness as revealed by heart rate deceleration (HRD), skin conductance response (SCR), and low-band (6-10Hz) alpha EEG oscillations. In contrast, high-band alpha EEG oscillations (10-12Hz) over the contralateral primary sensorimotor cortex decreased more during the expectancy of painful compared to nonpainful stimuli, in line with an increased anticipatory preparation of the somatosensory channel. These findings provide further evidence on the fact that attentional processes at the basis of cognition can be defended by the anticipation of pain, at least when the incoming painful stimuli are repetitive and predictable. This happens even if the brain increases preparatory processes of the specific sensory channel to be targeted by the painful stimulus.     

Modulation of oscillatory brain activity and evoked potentials in a repetition priming task in the human EEG

Cortical object representations seem to require the formation of neural cell assemblies. The physiological correlate of cell assembly activity may be seen in synchronized neural activity in the gamma band range. The improvement in perceiving and identifying an object by experience is commonly referred to as repetition priming. One possible neural mechanism for repetition priming is 'repetition suppression' within a cell assembly coding the stimulus. The present electroencephalogram study was designed to investigate oscillatory brain activity when line drawings of concrete objects were repeated either immediately after a first presentation or after intervening a number of different stimuli. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial picture presentation. Repeated presentations of the same picture led to a significant decrease of induced gamma power. Furthermore, repeated presentations of the same object resulted in a decrease in phase synchrony between distant electrode sites. No significant repetition effects were found in the alpha or beta frequency range. The event-related potential (ERP), which was also modulated by priming, showed a different scalp distribution compared with induced GBRs. In addition, ERP repetition effects decayed at larger intervals between initial and repeated presentations, whereas induced GBRs were not modulated as a function of stimulus lag. We concluded that the decrease in amplitude of induced GBRs and the reduction of gamma phase synchrony between pairs of electrodes after repeated picture presentations might be linked to a 'sharpening' mechanism within a cell assembly representing an object.     

EEG and task performance after ACTH4-10 in man.

Effects of the heptapeptide ACTH4-10 (Org OI-63) on EEG, some memory tests, and behavior were examined in 12 normal male volunteers under 30 years of age. An intravenous dose of 60 mg was compared to placebo in a Latin square design. EEG was recorded for 2 h after administration of ACTH4-10 or placebo and was quantified by power spectral density analysis. Drug differences were tested by analyses of variance and covariance. No statistical drug effect was seen on the EEG or behavioral measures. Of the psychological tests, only the digit span test showed a decrease in number of errors with ACTH4-10 (p less than or equal to o.05). These results are consistent with previous studies and suggest that an intravenous bolus of ACTH4-10 has a limited effect on the brain function tested.     

Event-related. EEG desynchronization and synchronization during an auditory memory task

Event-related desynchronization (ERD) and synchronization (ERS) of the lower (8–10 Hz) and upper (10–12 Hz) alpha bands of background EEG were studied in 10 subjects during an auditory memory scanning paradigm. Each experimental trial started with the presentation of a visual warning signal, after which an auditory 4-vowel memory set was presented for memorization. Thereafter the probe, a fifth vowel, was presented and identified by the subject as belonging or not belonging to the memorized set. In 50% of the cases, the probe was among the previously presented memory set. The presentation of the memory set elicited a significant ERS in the both alpha frequency bands. In contrast, the presentation of the probe elicited a significant bilateral ERD in both alpha frequency bands studied. The results suggest that the ERD phenomenon is closely associated with higher cortical processes such as memory functions rather than with auditory stimulus processing per se. Event-related desynchronization provides a potentially valuable tool for studying cortical activity during cognitive processing in the auditory stimulus modality.     

Temporal dynamics of cerebro-cerebellar network recruitment during a cognitive task

Previous investigations have demonstrated that two regions in the right cerebellum, one located superiorly in hemispheral lobule VI/Crus I and another located inferiorly in hemispheral lobule VIIB/VIIIA, are activated during verbal working memory performance. On the basis of functional neuroimaging patterns of activation, as well as known cortico-pontine and ponto-cerebellar projections, the superior region has been hypothesized to contribute to the articulatory control system of working memory whereas the inferior region has been linked to the phonological store. The present study used event-related fMRI and individual estimates of hemodynamic response for both the cerebellum and neocortex to test this model and characterize the task phase specific cerebro-cerebellar activations for a Sternberg verbal working memory task. Results demonstrated that the right superior cerebellum showed the strongest activation during the initial encoding phase of the task, and, consistent with predictions, a similar pattern was observed in left opercular inferior frontal and premotor regions. In contrast, the right inferior cerebellum exhibited the greatest activation during the maintenance phase of the task, and as predicted, corresponded with activation in the left inferior parietal lobule. The significance of the results with respect to cerebro-cerebellar models of verbal working memory and to theoretical accounts of cerebellar involvement in cognition is discussed.