Recurrent circuits within medial entorhinal cortex superficial layers support grid cell firing

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Specialized cells in the medial entorhinal cortex (mEC), including speed cells, head direction (HD) cells, and grid cells, are crucial for spatial navigation.
• The precise contribution of local circuits within the mEC to these spatial computations remains incompletely understood.

Purpose of the Study:

• To investigate the dependency of mEC spatial cell activity on local circuits.
• To differentiate the network properties of sharply tuned HD cells from those of broadly tuned HD cells, speed cells, and grid cells.

Main Methods:

• Neuronal activity was recorded in layers II and III of the mEC.
• Optogenetic perturbation was used to selectively inhibit locally projecting layer II pyramidal cells.

Main Results:

• Sharply tuned HD cells showed weak responses to perturbation, suggesting they are part of a separate network.
• Speed cells, broadly tuned HD cells, and grid cells exhibited transient excitatory and inhibitory responses.
• Grid cell accuracy transiently decreased during feedback inhibition, recovering as firing rates normalized, indicating rapid updates from afferent inputs.

Conclusions:

• Sharp HD cells are likely embedded in a distinct mEC sub-network compared to broad HD cells, speed cells, and grid cells.
• Grid cell tuning is dependent on local processing and is rapidly modulated by head direction, speed, and other inputs to the mEC.