Given the importance of the hippocampus in spatial memory (Ferbinteanu and McDonald 2001; Ferbinteanu, et al 2003) and its high density of CB1 receptors (Herkenham, et al 1991; Matsuda, et al 1993), it is not surprising that this brain region plays an integral role in the disruptive effects of marijuana on memory. Consistent with this hypothesis, systemic administration of Δ9-THC or WIN55,212-2 reliably impairs performance in delayed-match-to-sample (DMTS) and delayed-non-match-to-sample (DNTS) tasks, accompanied with decreases in hippocampal cell firing during the sample phases of the task (Hampson and Deadwyler 1999; 2000; Heyser, et al 1993). In addition, WIN 55212-2 reduced encoding in the hippocampus that was required to perform long-delay trials in a DNTS task (Deadwyler, et al 2007). Other supporting evidence came from studies examining the effects of intracerebral administration of cannabinoids on learning and memory. In particular, intrahippocampal infusions of CP-55,940, Δ9-THC, or WIN 55,212-2 were found to disrupt performance in radial arm maze, t-maze delayed alternation, passive avoidance, and place recognition memory tasks (Egashira, et al 2002; Lichtman, et al 1995; Mishima, et al 2001; Suenaga and
