NMDA receptor dependent functions of hippocampal networks in spatial navigation and memory formation

In this work, we studied neural patterns of activity in the CA 1 region of the hippocampus of the mouse, when different strategies are used. Different input areas support CA 1, depending on the type of navigation: when the animal uses sensory (such as environmental cues) and non-sensory (self-motion) information to guide behavior (place navigation), the entorhinal cortex plays a crucial role, while if the animal executes a sequence of body movements (sequence navigation), CA3 area supports CA1 activity. Our findings show that network oscillations in the gamma range allow CA 1 to tune to one or the other input area, according to the strategy being employed: low gamma oscillations (20-45 Hz) are predominant during the use of a sequence-navigation strategy, while high gamma oscillations (55-90 Hz) prevail during place-navigation. We further show that the NMDA receptors in region CA 1 shape network oscillations: by monitoring knock-out mice lacking this receptor in CA 1, we report that its role is particularly important during sequence navigation, as shown by the impaired behavior and affected neural activity during this type of navigation. KO mice show a lower resolution of spatial representation and our research indicates that this is a consequence of variability across trials and that single-trial properties of CA 1 neuronal activity is largely intact. This work offers new insight into how CA 1, assisted by NMDA receptors, integrates different sources of information and how it uses different frequency channels to communicate with different brain areas