Direction of SMR and Beta Change with Attention in Adults
AbstractIntroduction. The aim of this study was to clarify the interpretation of sensorymotor rhythm (SMR; 13–15 Hz) and beta (16–20 Hz) changes with respect to attention states. Method. For this purpose, EEG was recorded from 11 participants during (a) a multiple object tracking task (MOT), which required externally directed attention; (b) the retention phase of a visuo-spatial memory task (VSM), which required internally directed attention and avoidance of sensory distraction; and (c) the waiting intervals between trials, which constituted a notask-imposed control condition. The 2 active tasks were consecutively presented at 2 difficulty levels (i.e., easy and hard). Two analyses of variance were conducted on EEG log spectral amplitudes in the alpha (8–12 Hz), SMR, and beta bands from F3, F4, C3, C4 and P3, P4. Results. The first 15 analysis compared the MOT to the VSM by difficulty levels and revealed a significant task effect (p<.0005) but no effect of difficulty. The results showed that externally directed attention (MOT) resulted in lower values than internally directed attention (VSM) in all three bands. The second analysis averaged the difficulty levels together and added the no-task-imposed reference condition. The results again showed a significant task effect that did not interact with site, hemisphere, or, more important, band. Post hoc tests revealed that bothMOT and VSM produced significantly smaller means than the no-task-imposed condition. This pattern of log-amplitude means and the lack of task interaction with any other factor indicate that task-induced attention reduces EEG power in the same proportion across the 3 bands and the 6 channels studied. Conclusions. These results contradict a frequent interpretation concerning the relationship between the brain’s aptitude to increase low beta in neurofeedback programs and improved sustain attention capacities.
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