Frontal midline theta and cross-frequency coupling during short term memory and resting state.

This paper aims to establish how frontal midline theta and theta-gamma coupling are altered by memory load as well as by recall performance during a verbal digit span task using an open EEG dataset. Traditional behavioral scores, as well as new measure were used, as the recall accuracy as a function of the order of the digits followed a sigmoid curve. The new behavioral score was strongly correlated with traditional measures. The EEG results show that neither the resting state theta nor the theta during the digit span task is predictive of the task performance. However, there was a strong positive correlation between cognitive load and theta power as well as a negative correlation between cognitive load and theta peak frequency during the task. These results are in line with earlier studies indicating that frontal midline theta is modulated by cognitive load rather than memory performance. Furthermore, there was an increased alpha-beta cross frequency coupling during resting state but that was not correlated with the performance of the upcoming memory task. During the task the cross-frequency coupling was minimal, and it did not correlate with memory performance nor with task load, that raises the possibility that EEG is not sensitive enough for cross-frequency coupling measures.