a set of brain regions that exhibit resting state synchronized low frequency oscillations. The default mode network is impaired in addiction and it has been suggested that the altered resting state functional connectivity may underlie the heightened sensitivity to drug related cues and weakened cognitive control that is a hallmark of addiction [8]. Moreover, the hippocampus, together with the amygdala and the frontal cortex, sends projections to the nucleus accumbens that plays a critical role in the acute reinforcing effects of drugs [4], [9]. Hippocampal function is determined by the balance between excitatory pyramidal cell firing and their modulation by GABA-containing interneurons. Alcohol alters this balance and indeed the hippocampus has been implicated in the development of alcohol tolerance [10], [11]. GABAergic inhibition and hippocampal theta oscillations are both critical for synaptic plasticity and learning behaviors [12]. Cocaine depresses the GABA current of hippocampal neurons [13].
