Phase precession of grid cells in a network model without external pacemaker.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Cognitive Science

Background:

• Rodent brains utilize both firing rate and spike timing of medial entorhinal cortex neurons for spatial encoding.
• Grid fields, arranged hexagonally, represent the rate code, while theta oscillations accompany these fields.
• Phase precession, where spike phase decreases with distance, indicates spike timing's role in spatial coding.

Purpose of the Study:

• To present a computational model resolving the paradox of how pacemaker neurons (entorhinal cortex stellate cells) exhibit phase precession relative to self-generated oscillations.
• To explain the coexistence of rate and timing codes for spatial representation in the medial entorhinal cortex.

Main Methods:

• Development of a computational model simulating entorhinal cortex stellate cell activity.
• Analysis of network dynamics, including direct excitatory and indirect inhibitory coupling between stellate cells.
• Simulation of h-current modulation for adjusting phase precession.

Main Results:

• Model simulations demonstrate that connections between stellate cells synchronize small cell groups, enabling population oscillations during grid field activity.
• These population oscillations are accompanied by theta phase precession, consistent with experimental observations.
• The model suggests that modulation of h-currents can tune phase precession to running speed.

Conclusions:

• The study resolves the paradox of phase precession in putative pacemaker neurons within the medial entorhinal cortex.
• Recurrent network self-organization naturally explains the coexistence of rate and timing codes for spatial information.
• The findings provide a mechanistic explanation for neural coding underlying spatial navigation.