“…The theta rhythm (4–12 Hz) is prominent oscillations recorded in the hippocampus and surrounding limbic structures during exploration and REM sleep (Vanderwolf, 1969 ; Bland, 1986 ; Buzsáki, 2002 ). Theta oscillations have also been registered in the neocortex where they are particularly pronounced in the frontal midline (Klimesch et al, 1997 ; Kahana et al, 1999 ; Jensen and Tesche, 2002 ; Canolty et al, 2006 ; Guderian et al, 2009 ), and in the subcortical areas (Paré et al, 2002 ; Magill et al, 2006 ; Nerad and McNaughton, 2006 ; DeCoteau et al, 2007 ; Kabanova et al, 2011 ). The theta rhythm is important in the formation and retrieval of episodic and spatial memory (Hasselmo, 2005 ).…”