RCA2.ii: Physiological Studies in Manipulated Environment

When an animal invents a new solution to a dynamic locomotion problem, it must integrate sensory perception with higher level cognitive representations in order to envisage new locomotor paradigms. To discover high level representations for environmental interaction, and observe how they allow innovation, we propose to examine neurophysiological encoding of spatial navigation during challenging locomotor behaviors in freely behaving animals. We focus on studies of grid cells (Hafting et al, 2005), place cells (O'Keefe, 1976), and other spatial signals in the brain as these animals creatively solve problems in 3D environments. Our studies focus on the grid cells of the Medial Entorhinal Cortex (MEC), egocentric (i.e. "self-based") spatial encoding of external places in the Lateral Entorhinal Cortex (LEC), and place cells of the hippocampus. The MEC is thought to provide a signal of the organism’s current location in an allocentric spatial framework. This signal is primarily derived through a path integration computation, with input from visual landmarks providing a calibration and error-correction signal. New data suggest that the LEC may provide a complementary spatial signal, based on an animal’s egocentric bearing relative to salient, external landmarks or reference points (Wang et al, 2018). Thus, these two systems interact to provide the hippocampus with a self-motion-based signal of the rat’s current location in an allocentric (i.e. "world-centered") coordinate frame along with a signal about the location of salient landmarks and other points external to the organism, based on an egocentric coding representation. Place cells of the hippocampus integrate these two inputs and create context-dependent representations of the animal’s current location, planned trajectories and remembered past sequences of experience. These representations are transmitted to downstream brain regions that make action decision and control motor patterns based in part on the context-dependent memory signals provided by the hippocampus.