Induced Synchronization of the Alpha Rhythm During the Pauses Between Visual Stimuli with Different Levels of Cognitive Set Plasticity

Abstract

Studies using models of cognitive sets (the Uznadze paradigm) for simple nonverbal visual stimuli or an emotionally negative facial expression have identified features of the dynamics of electrical oscillations in the range of the α rhythm in the cerebral cortex at specified periods of time between warning and target stimuli [4] or between target and trigger stimuli [3]. Both cases recorded the long-known rhythm desynchronization reaction in response to presentation of the first stimulus in the pair, but produced the first evidence that the middle part of the pause, conversely, involved synchronization, which then decreased notably or changed to desynchronization before presentation of the second stimulus in the pair. Working on the basis of current concepts, we regarded these changes in α activity over the 8-or 9-sec interstimulus time interval as induced reactions evoked by top-down spikes coming from the internal representation of time intervals between the acting stimuli formed in the prefrontal cortex during the training process [6,[10][11][12][13]18].α rhythm power in humans is known to be linked with the function of selective attention and to reflect its activity [7,8,15,19]. Thus, desynchronization of the α rhythm is regarded as an indicator of increased functional activity in the corresponding area of the cortex, its readiness to undertake some particular type of cortical activity, and as an indicator of "covert attention" [20] or "expectant attention" [16,17]. On the other hand, we regard the α-activity synchronization in the midpart of the interstimulus pause seen Studies in healthy adults (n = 35) using a model of a set to recognition of an angry facial expression showed that increases in loading on working memory by extending the duration of the time interval between the target (a facial image) and trigger (a spot of light) stimuli to 16 sec did not lead to any significant slowing of the switching from the old set to the new. Differences were seen between the group of subjects in whom set switching was accompanied by distorted perception of the emotional facial expression and the "no errors" group in the extents of the induced synchronization of the α rhythm during the interstimulus period. Synchronization was more marked in this latter group. The dynamics of changes in the α rhythm showed that selective attention was modulated during sequential cognitive acts, this being apparent at the bioelectrical level as changes in the extent of induced synchronization/desynchronization of α-range potentials. The proposed "inhibitory control" mechanism provides flexibility for cognitive processes by suppressing the influences of irrelevant factors on cortical processes during interstimulus pauses. We believe that this "protective" mechanism can explain the minor effect of increased loading on working memory in the present studies.

Human neurophysiological markers of high anxiety level during preparation for visual recognition

“…Alternatively, decreased theta-rhythm in high-anxiety subjects might be linked directly to the anxious state [60]. Accordingly, the lateral prefrontal cortex where in high-anxiety subjects the alphaand theta-rhythm power is relatively low ( Table 2 and Table 3), is associated with explicit emotion regulation and top-down cognitive control [35,61,62], and is disturbed in anxious subjects [23,63]. During the last decade a theory has developed that declares the anxious state is linked with the activity of the so-called behavior inhibition system [11,64].…”

“…It is worth noting that preparation for visual recognition is mainly studied for short time periods (no more than 1 second(s) before stimulus presentation). Longer periods, allowing an estimate of trends in electroencephalogram (EEG) rhythmics changes, have only been used in single studies of healthy subjects [35].…”

“…during 1 s EEG fragments immediately before stimulus presentation. In the current study, several extra conditions were analysed, including: listening to instruction, operative rest (the period between listening to instruction and the beginning of task performance), while the preparation for recognition period was increased to 4 s. In studies on healthy subjects conducted in our laboratory, this approach provided new data pertaining to the state of the subject before testing and during the interstimulus intervals of the cognitive task activities [25][26][27][28][29][30][31][32][33][34][35][36]. The presented methods might be of value for patients not capable, due to some pathological or age restriction, of undergoing or completing standard cognitive testing by EEG recording.…”