FROM EXPLORATION TO REST: MEDIAL ENTORHINAL CORTEX NEURONS INTEGRATE SPATIAL AND OBJECT INFORMATION

Memory formation and spatial navigation critically rely on the medial entorhinal cortex (MEC). Extensive in vivo electrophysiological studies in freely moving animals have identified not only spatially modulated neurons in the MEC, but also object-vector cells and fast-spiking object-tuned interneurons. Although object-vector cells encode the distance and direction of objects relative to the animal, the mechanisms by which MEC neurons represent object position and identity are still poorly understood. In this study, we investigated whether MEC neurons encode object presence, object location, and object identity, and how such encoding is modulated by environmental context. Using in vivo electrophysiology, neuronal activity was recorded from the MEC of freely moving mice across multiple experimental protocols in which objects varied in configuration and shape within open-field environments. Neuronal activity was also recorded during rest sessions to assess object-related representations outside of active exploration. Our results show that both putative excitatory neurons and fast-spiking interneurons in the MEC convey object-related information. A subpopulation of object-tuned neurons exhibited spatially localized firing fields associated with specific object positions. Notably, increased neuronal firing was also observed during rest sessions when objects were present, indicating that object-related activity is not restricted to exploratory behavior. Together, these findings demonstrate that MEC neurons integrate spatial and object-related information across diverse object configurations and behavioral states. This expanded coding repertoire supports a broader role for the MEC in episodic memory through the representation of complex and dynamic environmental features.