Spatial navigation involves co-ordination between action planning by the prefrontal cortex and spatial representation of the environment in the hippocampus. In this study, when rats performed an alternating arm choice task in a T maze, the coordination of the timing of spikes between neurons in the medial prefrontal cortex (mPFC), the thalamic nucleus reuniens (NR) and the hippocampal CA1 was found to increase; co-ordinated firing between supramammillary nucleus (SUM) and CA1 neurons also increased. Silencing of SUM neurons decreased spike-time coordination in the mPFC-NR-CA1 circuit and impaired representations of the trajectory of travel in NR and CA1, suggesting that SUM modulates the communication of action planning information from the mPFC to downstream targets.