Electrophysiological studies of the claustrum of rat demonstrate functional connections with the limbic system (dentate gyrus, hippocampus) via the entorhinal cortex. The pathways show reciprocal connectivity, a degree of topological organization and the capacity for a long-term response potentiation in the claustral projection to entorhinal cortex. The hypothesis that claustrum acts to functionally link neocortical regions with components of the limbic system is considered.