  The grid firing patterns are thought to provide an efficient intrinsic metric
capable of supporting universal spatial metric for mammalian spatial navigation
in all environments. However, whether spatial representations of grid cells in
the entorhinal cortex are determined by local environment cues or form globally
coherent patterns remains undetermined. To explore this underlying mechanism,
here we proposed a possible theoretical explanation to describe connection
between the neural space and the physical environment and transition from a
local anchored to a global coherent representation according to relationship
between grid phase distance between physical distance in the physical
environment, and tested our method based on simultaneous localization and
mapping (SLAM) system on a iRat rodent-sized robot platform in a rat-like maze.
Our robotic exploration experiments show that the grid firing firstly is
determined by local environment cues, and after self-correction with
experience-dependence, the regular, continuous grid firing patterns tessellate
the explored space. Head direction (HD) cells also show global patterns in our
experimental results. Our results support that grid firing patterns do provide
a universal spatial metric for mammalian spatial navigation in complex
environments. The results in this study also provide insights into
experience-dependent interactions between path integrative calculation of
location in the entorhinal cortex and learned associations to the external
sensory cues in the hippocampus, which is likely to be critical understanding
spatial memory, even episodic memory.
