Theta-band phase locking of orbitofrontal neurons during reward expectancy

Area of Science:

• Neuroscience
• Computational Neuroscience
• Behavioral Neuroscience

Background:

• The orbitofrontal cortex (OFC) is crucial for coding reward expectancy.
• Previous models focused on average neuronal firing rates for reward prediction.
• The role of precise spike timing and neural oscillations in OFC reward coding is less understood.

Purpose of the Study:

• To investigate the temporal structure of neural coding in the OFC during olfactory discrimination learning.
• To determine if neuronal phase locking to local field potential oscillations predicts reward outcome.
• To examine how learning and reversal of associations affect this temporal coding.

Main Methods:

• Multineuron and local field potential recordings in the rat OFC during olfactory discrimination tasks.
• Analysis of neuronal firing rates and phase locking to theta oscillations.
• Correlation of neural activity with behavioral measures of outcome expectancy (licking responses).

Main Results:

• After associative learning, OFC neurons phase locked to theta oscillations in anticipation of reward.
• This phase locking diminished upon reversal of learned associations and reappeared after relearning.
• The strength of theta-band phase locking robustly tracked behavioral learning dynamics and outcome expectancy.

Conclusions:

• Neuronal phase locking to theta oscillations in the OFC is a dynamic code for reward expectancy.
• This temporal coding mechanism may facilitate inter-areal communication of value signals in reinforcement learning.
• Spike timing relative to oscillations provides a richer representation of outcome expectancy than firing rates alone.