Doctor of Philosophy

dissertationThe brain's medial entorhinal cortex (MEC) plays a key role in spatial navigation, serving as the node between the hippocampus and the rest of the mammalian cortex. In the last 10 years, spatially-modulated "grid" cells in the superficial MEC have been shown to preferentially fire as the animal moves into the apices of a hexagonal grid. Our incomplete understanding of the inhibitory dynamics within the MEC, however, limits our knowledge of how this brain structure executes such spatial navigation functions. Here, we explore various roles that inhibition plays in the superficial MEC and characterize the neuronal population that elicits this inhibition. We find that excitatory stellate cells in the layer 2 MEC exhibit membrane-dependent, nonlinear synaptic integration of inhibitory inputs, amplifying inputs that arrive near their firing threshold and dampening those that arrive closer to rest. Our next study is the first systematic anatomical/electrophysiological characterization of the superficial MEC's inhibitory interneuron population. We find that they are best classified into four clusters with distinct anatomical/electrophysiological profiles. In our last study, we investigated the viability of a novel, inhibition-mediated gamma rhythm model, finding that superficial MEC interneurons can exhibit resonant behaviors that could be key to generating neuronal network oscillations. The work presented here provides valuable groundwork for understanding MEC cortical computation