A Hippocampal-parietal Network for Reference Frame Coordination.

Abstract

Navigating space and forming memories based on spatial experience are crucial for survival, including storing memories in an allocentric (map-like) framework and conversion into egocentric (body-centered) action. The hippocampus and parietal cortex (PC) comprise a network for coordinating these reference frames, though the mechanism remains unclear. We used a task requiring remembering previous spatial locations to make correct future action and observed that hippocampus can encode the allocentric place, while PC encodes upcoming actions and relays this to hippocampus. Transformation from location to action unfolds gradually, with 'Came From' signals diminishing and future action representations strengthening. PC sometimes encodes previous spatial locations in a route-based reference frame and conveys this to hippocampus. The signal for the future location appears first in PC, and then in hippocampus, in the form of an egocentric direction of future goal locations, suggesting egocentric encoding recently observed in hippocampus may originate in PC (or another "upstream" structure). Bidirectional signaling suggests a coordinated mechanism for integrating allocentric, route-centered, and egocentric spatial reference frames at the network level during navigation.Significance Statement Our study has broad implications for understanding how the brain coordinates and integrates different spatial reference frames. Our data suggests rats can alternate between multiple neural strategies within the same task. In addition, we find out that similar signals are present in both the hippocampus and the PC but at different times, providing novel insights into the mechanisms underlying spatial navigation and memory. It reveals an intricate system involving an extended brain network that includes the hippocampus, PC, and structures anatomically 'in-between'. The bidirectional signaling suggests this brain network truly operates as a network and not a unidirectional circuit. These findings suggest a focus on brain networks (and not just single regions) is critical for understanding transformations. These processes are fundamental for spatial cognition and related disorders and even for solving problems that may use similar neural machinery, such as building abstract representations from egocentric views, as occurs with object invariance.