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

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.