Theta and gamma rhythmic coding through two spike output modes in the hippocampus during spatial navigation.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Hippocampal CA1 neurons exhibit two main firing modes: single spikes and stereotyped bursts.
• The dynamic switching between these modes and their distinct information coding remain poorly understood.

Purpose of the Study:

• To investigate how individual hippocampal CA1 neurons switch between single spiking and bursting modes.
• To determine if these distinct spiking outputs carry different information during spatial navigation.

Main Methods:

• Extracellular recordings in freely moving rats during spatial navigation.
• In vivo cellular voltage imaging and optogenetics in awake mice.
• Biophysical modeling of neuronal intrinsic properties.

Main Results:

• Spike bursts preferentially correlate with theta rhythms (3-12 Hz) and encode position via theta phase precession upon entering a place field.
• Single spikes show additional coupling to gamma rhythms (30-100 Hz), particularly when exiting a place field.
• Biophysical models indicate intracellular properties can explain frequency-dependent spike coding.

Conclusions:

• Hippocampal neurons dynamically regulate burst and single spike generation based on network and intracellular frequency dynamics.
• Distinct spiking modes likely perform specialized computations supporting spatial behavior and memory.
• This frequency-dependent coding provides a mechanism for nuanced information processing in the hippocampus.