Frontal theta event-related synchronization: comparison of directed attention and working memory load effects

Event-related potentials and changes of brain rhythm oscillations during working memory activation in patients with first-episode psychosis

BACKGROUND

Earlier contributions have documented significant changes in sensory, attention-related endogenous event-related potential (ERP) components and θ band oscillatory responses during working memory activation in patients with schizophrenia. In patients with first-episode psychosis, such studies are still scarce and mostly focused on auditory sensory processing. The present study aimed to explore whether subtle deficits of cortical activation are present in these patients before the decline of working memory performance.

METHODS

We assessed exogenous and endogenous ERPs and frontal θ event-related synchronization (ERS) in patients with first-episode psychosis and healthy controls who successfully performed an adapted 2-back working memory task, including 2 visual n-backworking memory tasks as well as oddball detection and passive fixation tasks.

RESULTS

We included 15 patients with first-episode psychosis and 18 controls in this study. Compared with controls, patients with first-episode psychosis displayed increased latencies of early visual ERPs and phasic θ ERS culmination peak in all conditions. However, they also showed a rapid recruitment of working memory-related neural generators, even in pure attention tasks, as indicated by the decreased N200 latency and increased amplitude of sustained θ ERS in detection compared with controls.

LIMITATIONS

Owing to the limited sample size, no distinction was made between patients with first-episode psychosis with positive and negative symptoms. Although we controlled for the global load of neuroleptics, medication effect cannot be totally ruled out.

CONCLUSION

The present findings support the concept of a blunted electroencephalographic response in patients with first-episode psychosis who recruit the maximum neural generators in simple attention conditions without being able to modulate their brain activation with increased complexity of working memory tasks.

Spatial and temporal EEG dynamics of dual-task driving performance

Background

Driver distraction is a significant cause of traffic accidents. The aim of this study is to investigate Electroencephalography (EEG) dynamics in relation to distraction during driving. To study human cognition under a specific driving task, simulated real driving using virtual reality (VR)-based simulation and designed dual-task events are built, which include unexpected car deviations and mathematics questions.

Methods

We designed five cases with different stimulus onset asynchrony (SOA) to investigate the distraction effects between the deviations and equations. The EEG channel signals are first converted into separated brain sources by independent component analysis (ICA). Then, event-related spectral perturbation (ERSP) changes of the EEG power spectrum are used to evaluate brain dynamics in time-frequency domains.

Results

Power increases in the theta and beta bands are observed in relation with distraction effects in the frontal cortex. In the motor area, alpha and beta power suppressions are also observed. All of the above results are consistently observed across 15 subjects. Additionally, further analysis demonstrates that response time and multiple cortical EEG power both changed significantly with different SOA.

Conclusions

This study suggests that theta power increases in the frontal area is related to driver distraction and represents the strength of distraction in real-life situations.

Decreased delta event-related synchronization in patients with early vascular dementia

Electroencephalogram (EEG) activity, recorded while performing an "odd ball" detection task, was compared between patients with early vascular dementia (VD), healthy young controls and healthy elderly controls performing the same task. The data were analyzed using the event-related synchronization/desynchronization (ERS/ERD) method. VD patients, compared with controls, showed decreased ERS effects in the delta frequency band (0.5-3.5Hz) of EEG after the target stimulus appeared in frontal, central and parietal regions. Similarly, elderly controls also showed a decreased ERS compared with young controls only in central and parietal regions. As part of this analysis, we introduce a novel quantitative index, the Event-related Energy Change Progression (EECP), which provides a reliable measure that distinguishes these groups and thereby provides a promising marker for early diagnosis of VD.

Brain oscillatory 4-30 Hz electroencephalogram responses in adolescents during a visual memory task

Brain oscillatory responses of the 4-30 Hz electroencephalogram frequencies were assessed in 12 adolescents (mean age 14 years) during a visual N-back task with four memory load conditions (0-back, 1-back, 2-back, and 3-back). Theta frequency range (approximately 4-6 Hz) responses were elicited in all memory load conditions. The magnitude and duration of alpha frequency range (approximately 8-12 Hz) responses varied as a function of memory load. Beta frequency range (approximately 15-20 Hz) responses were modulated by both task difficulty and cognitive strategy. The differences between the memory load conditions were most prominent between the 0-back and 1-back conditions in the approximately 10 and 20 Hz electroencephalogram frequencies. Dynamic alpha and beta rhythm brain oscillatory responses are related to the cognitive processes in adolescence.

Induced theta oscillations as biomarkers for alcoholism

OBJECTIVE

Studies have suggested that non-phase-locked event-related oscillations (ERO) in target stimulus processing might provide biomarkers of alcoholism. This study investigates the discriminatory power of non-phase-locked oscillations in a group of long-term abstinent alcoholics (LTAAs) and non-alcoholic controls (NACs).

METHODS

EEGs were recorded from 48 LTAAs and 48 age and gender comparable NACs during rest with eyes open (EO) and during the performance of a three-condition visual target detection task. The data were analyzed to extract resting power, ERP amplitude and non-phase-locked ERO power measures. Data were analyzed using MANCOVA to determine the discriminatory power of induced theta ERO vs. resting theta power vs. P300 ERP measures in differentiating the LTAA and NAC groups.

RESULTS

Both groups showed significantly more theta power in the pre-stimulus reference period of the task vs. the resting EO condition. The resting theta power did not discriminate the groups, while the LTAAs showed significantly less pre-stimulus theta power vs. the NACs. The LTAAs showed a significantly larger theta event-related synchronization (ERS) to the target stimulus vs. the NACs, even after accounting for pre-stimulus theta power levels. ERS to non-target stimuli showed smaller induced oscillations vs. target stimuli with no group differences. Alcohol use variables, a family history of alcohol problems, and the duration of alcohol abstinence were not associated with any theta power measures.

CONCLUSIONS

While reference theta power in the task and induced theta oscillations to target stimuli both discriminate LTAAs and NACs, induced theta oscillations better discriminate the groups. Induced theta power measures are also more powerful and independent group discriminators than the P3b amplitude.

SIGNIFICANCE

Induced frontal theta oscillations promise to provide biomarkers of alcoholism that complement the well-established P300 ERP discriminators.

Human frontal midline theta and its synchronization to gamma during a verbal delayed match to sample task

The involvement of oscillatory activity, especially at theta and gamma frequency, in human working memory has been reported frequently. A salient pattern during working memory is electroencephalographic frontal midline theta activity which has been suggested to reflect monitoring functions in order to deal with a task. In general, theta activity has been credited with integrative functions of distributed activity. In the present study, we focused on electroencephalographic power analyses and cross-frequency phase synchronization in order to test whether frontal midline theta activity is linked to more locally generated gamma oscillations during the performance of a verbal delayed match to sample task. The task consisted of two different conditions where subjects either had to reorganize three consonant letters in alphabetical order (manipulation condition) or where they merely had to retain the three consonant letters (retention condition). Results revealed higher frontal midline theta activity for the manipulation of maintained stimulus material compared to pure retention of stimulus material. Interestingly, power differences between conditions were most pronounced during the second half of the delay period. Cross-frequency phase synchronization between frontal midline theta activity and distributed gamma activity, on the other hand, was predominant during the first half of the delay period and was stronger for manipulation compared to retention. We suggest that coupling of frontal midline theta to gamma activity reflects monitoring functions on the temporal segregation of memory items, whereas higher frontal midline theta power in the second half of the delay period might be associated with rehearsal processes. Rehearsal processes in the manipulation condition are likely more pronounced, because rehearsal of a new letter string in a limited time window requires higher mental effort compared to pure retention where rehearsal processes may already start at the beginning of the delay period.

Brain oscillatory responses during the different stages of an auditory memory search task in children

We assessed brain oscillatory responses of the 4-30 Hz electroencephalographic frequency bands in children (mean age 13 years) during the different stages of an auditory memory search, namely the encoding of four words and recognition of the positive and negative probe words. In children, theta (approximately 4-6 Hz) electroencephalographic responses during recognition were of greater magnitude than those during encoding and alpha (approximately 8-12 Hz) event-related synchronization responses during encoding increased with increasing memory load. During recognition, greater magnitude alpha and beta (>12 Hz) event-related desynchronization responses were observed during the presentation of the positive probe as compared with the negative. Complex patterns of theta, alpha and beta frequency brain oscillatory responses during auditory information processing are present already in children of age approximately 13 years.

Dissociation of sustained attention from central executive functions: local activity and interregional connectivity in the theta range

Human brain oscillatory activity was analysed in the electroencephalographic theta frequency range (4-7 Hz) while subjects executed complex sequential finger movements with varying task difficulty and memory load. Local frontal-midline theta activity was associated with the general level of cognitive demand, with the highest amplitudes in the most demanding condition. Using low-resolution electromagnetic tomography analysis (LORETA), this theta activity was localized in the anterior cingulate gyrus including the cingulate motor area. These results suggest that local theta activity in the anterior cingulate gyrus represents correlates of an attentional system that allocate cognitive resources. In addition, interregional connectivity in the theta frequency range was modulated by memory-related executive functions independently of task difficulty. Connectivity analyses revealed a more distributed long-range network including frontal and parietal cortices during execution of novel compared with well-trained finger movement sequences. Thus, these results are compatible with a model in which theta long-range coupling indicates integration of sensory information into executive control components of complex motor behaviour.