Multi-Source Interference Task (MSIT) is frequent‑ ly used in fMRI research to robustly activate the cin‑ gulo‑fronto‑parietal attention network (CFP). MSIT contains two stimuli conditions: Easy, spatially con‑ gruent with no flanker distractors (EC), and Hard, with multi‑source interference, i.e. incongruent locations and flanker distractors (HI). In order to gradually in‑ crease MSIT difficulty and possibly observe progress‑ ing engagement of CFP network, we expanded it with two intermediate conditions: Easy with Incongruent (EI) digit locations (introduced for the first time); and Hard, with flanker distractors but Congruent digit loca‑ tions (HC). We used high‑density EEG (128 active elec‑ trodes) to study the dynamics of brain activity during MSIT+. Pilot EEG and behavioral (reaction times, RT) data were acquired from six participants. Gradual in‑ crease of RT was observed between four MSIT+ condi‑ tions, with flanker‑interference requiring more time than spatial incongruence. Power spectral analysis us‑ ing Welch method performed on z‑scored EEG data re‑ vealed significantly larger theta (4‑8 Hz) power in both incongruent versus congruent conditions, with the largest theta power observed for the most demanding HI trials. Inverse results were found for alpha power (8‑13 Hz), which was stronger in both congruent condi‑ tions in contrast to incongruent ones (highest alpha in easiest EC trials). Spectral analyses were repeated for electrode clusters: Frontal, Central, Parietal, Occipital, Posterior Temporal Left and Right, and Anterior Tem‑ poral Left and Right. Significant differences were also found for alpha and theta power: the strongest theta power was observed for Frontal cluster followed by Occipital electrodes. For alpha power, the strongest re‑ sults were found for Occipital and Frontal clusters. Our results are in line with earlier EEG MSIT literature and with established theory of midline frontal theta being a neural signature of anterior cingulate cortex activa‑ tion during conflict processing with its occurrence and power related to increasing task difficulty. Observed suppression of alpha in the more demanding conditions also corroborates the earlier proposal that alpha power seems to be inversely related to increased atten‑ tion demand. Observed discrepancies between behav‑ ioral and EEG results requires further study. Supported by National Science Centre, Poland, UMO‑2016/20/W/ NZ4/00354.
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