INTRODUCTION: Information processing and stimuli filtering mechanisms are dispersed over many networks engaged in different processes and located all over the brain. In the present study, we examined neural correlates of attention-related working memory during the repeated modified delay match‑to‑sample test (DMTS). AIM(S): To find the most effective analytical method for assessment of attention related activity to be used in neurofeedback training. METHOD(S): In order to identify neuronal activity underlying state of increased attention, we used a DMTS test amended by control trials that did not require the engagement of attention and memory. These additional trials allowed us to compare the impact of attended versus passive conditions on electrical brain activity. We examined 14 subjects in 3 sessions performed within 10‑20 days. EEG was collected with 21 electrodes in the 10‑20 system. For each electrode channel and trial in selected time windows, we analyzed power in consecutive frequency bands (<40 Hz) and signal complexity measures, including sample entropy, Shannon entropy, and Higuchi fractal dimension (HFD). RESULTS: The results averaged over the whole group showed significant differences between EEG signals recorded during attentional and control trials on several electrodes. However, at the level of individual subjects, the selection of signals with such differences varied between subjects and applied methods. The most prominent effect of attention was observed in a window extracted from the 5-sec period of stimulus expectation and information retention, not accompanied by sample of the object. With repetition of DMTS sessions, the effect of differentiation of attentional and controls trials has been also emphasized in all analyzed measures. CONCLUSIONS: The results indicated the importance of the individual subject and session analysis and relevance of applying signal complexity methods to support spectral analysis in a further application.
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