Although the present findings implicate an important role for the hippocampus in the memory disruptive effects of the chief psychoactive component of marijuana and other cannabinoids, the involvement of CB1 receptors in other brain regions on learning and memory cannot be excluded. For instance, cannabinoids are known to disrupt synaptic plasticity in several brain regions (Iversen 2003). In particular, Δ9-THC infused into the prefrontal cortex impaired memory in a radial arm maze procedure that incorporated a 1 h delay (Silva de Melo, et al 2005), but not in the standard radial arm maze task (Egashira, et al 2002). Thus, the demands of the task are likely to determine the neural substrates underlying marijuana-induced memory impairment.
