Waveform analysis of frontal midline theta rhythm during short-term memory tasks based on EEG measurement

Conditions that require continuous attention in the performance of various mental tasks like a serial addition, video game, and spatial navigation often evoke frontal midline theta (Fm theta) rhythm in electroencephalogram (EEG). In this study, using three-dimensional (3-D) maze tasks for spatial navigation in health subjects, we carried out quantification of Fm theta rhythm with a new method using a combination of time-frequency analysis (wavelet transform, WT) and singular values decomposition (SVD). And we also attempted to clarify relationship between turning points of 3-D maze tasks and Fm theta rhythm with the proposed method. Nine healthy subjects participated in the EEG measurement with 3-D maze tasks. We obtained informed consent from all subjects. The tasks were navigating 3-D mazes with four different turning points (turning points: 7, 9, 11, 13) for 5 min, respectively. We examined the quantification of Fm theta rhythm with two conditions (singular value is over 85% and duration of Fm theta rhythm is longer than 1s), which were defined by the proposed method. It was found that appearance ratio of the Fm theta rhythm increased with changing difficulty (increasing turning points). It is confirmed that the proposed method is useful for quantifying appearance of Fm theta rhythm during spatial navigation.