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

Abstract

Early studies showed that long-term encoding and retrieval of new information is associated with modulation of the theta rhythm. More recently, changes in theta power amplitude over frontal electrode sites were reported during working memory, yet their relative significance in regard to attentional and memory processes remains unclear. Event-related synchronisation responses in the 4-7.5 Hz theta EEG frequency band was studied in 12 normal subjects performing four different tasks: two working memory tasks in which load varied from one (1-back task) to two (2-back task) items, an oddball detection (attention) task and a passive fixation task. A phasic theta increase was observed following stimulus apparition on all electrode sites within each task, with longer culmination peak and maximal amplitude over frontal electrodes. Frontal theta event-related synchronization (ERS) was of higher amplitude in the 1-back, 2-back and detection tasks as compared to the passive fixation task. Additionally, the detection task elicited a larger frontal and central theta ERS than the 2-back task. By analyzing theta ERS characteristics in various experimental conditions, the present study reveals that early phasic theta response over frontal regions primarily reflects the activation of neural networks involved in allocation of attention related to target stimuli rather than working memory processes.

Predicting term-relevance from brain signals

“…An essential aspect of electroencephalography (EEG) is that different types of oscillations, from the very slow theta (4-8 Hz) to the higher gamma (80 Hz), have been associated with various psychological functions. For example, alpha activity has been related to attentiveness [3], theta activity to attention [22], and alpha desynchronisation with semantic memory performance [15]. Possibly, decisions regarding relevance or irrelevance, through acts of motor imagery [21] and motor control [38], would trigger activity in the beta frequency.…”

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

“…20,21 As for ERPs, the sustained θ ERS was assessed in a time period defined by the time lag (500-1600 ms) after subtraction of 150 ms (15% of the total sustained θ) corresponding to rise and fall time.…”

“…18,19 In particular, a frontal θ power increase in initial phases of encoding with demanding attentional tasks followed by a late sustained oscillatory activity for higher working memory load was also described during n-back activation. 20,21 Whereas the phasic θ synchron ization supports the activation of neural networks involved in allocation of attention, 20,21 the later sustained power appears related to item retention and active maintenance for further task requirements. 22 Previous contributions documented the presence of early changes in sensory ERPs, 23,24 attention-related endogenous ERPs 25,26 and θ band oscillatory responses 24,27 during working memory activation in patients with chronic schizophrenia.…”

“…As expected, a frontal phasic θ increase was observed in both groups within 500 ms poststimulus, reflecting the encoding of the first visual stimulus that is usually followed by a habituation in the subsequent stimuli. 21,24,40 Although the amplitude of this EEG component was preserved in patients with firstepisode psychosis, they exhibited a general delay of phasic θ culmination peak independent of the task, suggesting the presence of early deficits in the integration of the incoming visual information for further cognitive process. Supporting this idea, an inability to respond to the first stimulus with an increase in evoked θ activity and to habituate to the second stimulus was described in a visual n-back working memory paradigm 24,27 and an auditory sensory modality [41][42][43] in patients with schizophrenia.…”

Individual Differences in Working Memory Performance: «overload» Effect

“…А у «низкопродуктивных» испытуемых после достижения максимальной активации тета-ритма при запоминании 5-буквенных ком-бинаций в алфавитном порядке наблюдалось резкое падение активности тета-ритма при попытке запомнить 7-буквенные сочетания. Таким обра-зом, динамика активации среднелобного тета-ритма и связанной с ним anterior cingulate cortex (ACC) при решении задач средней степени слож-ности лежит в пределах существующих представлений о росте тета-ак-тивности по мере увеличения нагрузки на РП [9,14,19,25,27,28]. Одна-ко наиболее трудные задания провоцировали перестройку активности те-та-ритма, ранее не наблюдаемую в других исследованиях.…”