 The theta mode appears during states of active, alert behavior (especially locomotion), and also during REM (dreaming) sleep.In the theta mode, the EEG is dominated by large regular waves with a frequency range of 6 to 9 Hz, and the main groups of hippocampal neurons (pyramidal cells and granule cells) show sparse population activity, which means that in any short time interval, the great majority of cells are silent, while the small remaining fraction fire at relatively high rates, up to 50 spikes in one second for the most active of them.An active cell typically stays active for half a second to a few seconds.