Human cortical responses during one-bit short term memory. A high-resolution EEG study on delayed choice reaction time tasks.

Objective: We investigated whether a very simple short-term memory (STM) demand induces a visible change of EEG rhythms over the two hemispheres. Methods: High-resolution EEG was obtained in young adults during two delayed choice reaction time tasks. In the STM condition, a simple cue stimulus (one bit) was memorized along a brief delay period (3.5–5.5 s). The task was visuo-spatial in nature. Results: In the control (NSTM) condition, the cue stimulus remained available along the delay period. Compared to the control condition, the theta power (4–6 Hz) decreased in left frontal and bilateral parietal areas (delay period). Furthermore, low alpha power (6–8 Hz) decreased in bilateral frontal and left parietal areas, while high alpha power (10–12 Hz) decreased in the left fronto-parietal areas. Conclusions: The decrease of the alpha power is as an expression of the efficient information transfer within thalamo-cortical pathways. The significance of the study stands in the fact that even a very simple STM task (only one bit to be memorized) revealed changes in frontoparietal theta and alpha rhythms.