Local microcircuitry of parasubiculum shows distinct and common features of excitatory and inhibitory connectivity

The parasubiculum is located within the parahippocampal region, where it is thought to be involved in the processing of spatial navigational information. It contains a number of functionally specialised neuron types including grid cells, head direction cells and border cells, and provides input into layer 2 of the medial entorhinal cortex where grid cells are abundantly located. The local circuitry within the parasubiculum remains so far undefined but may provide clues as to the emergence of spatially tuned firing properties of neurons in this region. We used simultaneous patch-clamp recordings to determine the connectivity rates between the three major groups of neurons found in the parasubiculum. We find high rates of interconnectivity between the pyramidal class and interneurons, as well as features of pyramid to pyramid interactions indicative of a non-random network. The microcircuit that we uncover shares both similarities and divergences to those from other parahippocampal regions also involved in spatial navigation