Our personal internal preferences while making decisions are usually consistent. Recent psychological studies, however, show observable variability of internal criteria occurs by random noise. The neural correlates of said random noise - an instance of ‘psychological noise’ – yet remain unclear. Combining simulation, behavioral, and neural approaches, our study investigated the psychological and neural correlates of such random noise in our internal criteria during decision making. We applied well-established decision-making tasks which relied on either internal criteria - occupation choice task as internally-guided decision making (IDM) - or external criteria - salary judgment task as externally-guided decision making (EDM). Subjects underwent EEG for resting state and task-evoked activity during IDM and EDM. We measured resting state long-range temporal correlation (LRTC) in the alpha frequency range as the index of neuronal noise. Based on our simulation, we identified a measure of psychological noise (as distinguished from true preference change) in IDM. The main finding shows that the indices for psychological noise are directly related to frontocentral LRTC in the alpha range. Higher degrees of frontocentral LRTC, which index lower neuronal noise, were related to lower degrees of psychological noise during IDM. This was not found during EDM. Resting state LRTC was also related to task-evoked activity, such as conflict-related negativity, during IDM only. Taken together, our data demonstrate, for the first time, the direct relationship between neuronal noise in the brain's intrinsic activity and psychological noise in the internal criteria of our decision making.
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