Neural oscillatory responses have been attributed to various cognitive processes in the literature. Delta responses are considered to mediate signal detection and decision-making (Basar and others 1999), while theta rhythms have been attributed with attention, recognition memory, and episodic retrieval (Basar and others 2001; Klimesch and others 2001). The theta component of the P3 response may be of particular relevance in relation to the interaction of cholinergic and glutamatergic systems in light of recent neurophysiological data acquired from experiments on rat brains. For example, cholinergic agonists induced oscillations in the delta, and theta frequency range in the rat hippocampal (Fellous and Sejnowski 2000) and neocortical (Lukatch and MacIver 1997) slices. Recently, a human study using a 3-T proton magnetic resonance spectroscopy (1H-MRS) and EEG theta activity during an auditory target detection paradigm demonstrated a robust relationship between hippocampal glutamate concentration and frontal theta activity during stimulus processing (Gallinat and others 2006). The results suggest a functional coupling between the frontal cortex and hippocampal region during stimulus processing and support the idea of the hippocampus as a neural rhythm generator driven
