Single-trial characterization of frontal theta and parietal alpha oscillatory episodes during spatial navigation in humans.

Theoretical proposals and empirical findings both highlight the relevance of theta brain oscillations in human spatial navigation. However, whilst the general assumption is that the relevant theta band activity is purely oscillatory, most empirical studies fail to disentangle oscillatory episodes from wide band activity. In addition, experimental approaches often rely on averaged activity across trials and subjects, disregarding moment-to-moment fluctuations in theta activity, contingent on key aspects of the task. Here, we used novel oscillation detection approaches to investigate the dynamics of theta and alpha episodes in human subjects performing a spatial navigation task in a virtual reality environment, resolved at single-trial level. The results suggest that bouts of frontal theta oscillatory activity are related to task difficulty and access to previously encoded information, across different timescales. Parietal alpha episodes, instead, seem to anticipate successful navigational decisions and could be related to shifts in internal attention.