Transient and Persistent Representations of Odor Value in Prefrontal Cortex.

Area of Science:

• Neuroscience
• Olfactory system
• Learning and memory

Background:

• Odor representation in the piriform cortex is unstructured and gains behavioral relevance through learning.
• Understanding how olfactory information is processed and represented in downstream brain regions during associative learning is crucial.

Purpose of the Study:

• To investigate the neural representation of odors in the piriform cortex, orbitofrontal cortex (OFC), and medial prefrontal cortex (mPFC) during olfactory associative learning in mice.
• To elucidate the sequential processing and consolidation of learned appetitive olfactory associations.

Main Methods:

• Two-photon imaging was employed to monitor neuronal activity in the piriform cortex, OFC, and mPFC.
• Mice were trained to associate odors with specific outcomes (conditioned stimuli, CS+ and CS-).
• Optogenetic silencing was used to determine the functional roles of the OFC and mPFC in memory consolidation.

Main Results:

• Odor responses in the piriform cortex remained largely unchanged during learning.
• In the OFC, a subset of neurons developed robust responses to CS+ odors post-learning, modulated by internal state and task context.
• Persistent representations of both CS+ and CS- odors emerged in the mPFC, while OFC responses diminished with extended training.

Conclusions:

• The OFC and mPFC, but not the piriform cortex, undergo significant changes in odor representation during associative learning.
• Direct projections from the piriform to the OFC can be harnessed to drive learned olfactory behavior.
• The OFC and mPFC function sequentially to consolidate learned appetitive olfactory associations, with the OFC involved in initial learning and the mPFC in persistent representation.