Anterior Olfactory Cortices Differentially Transform Bottom-Up Odor Signals to Produce Inverse Top-Down Outputs.

Area of Science:

• Neuroscience
• Olfactory System Research
• Sensory Coding

Background:

• Odor information processing involves hierarchical pathways from the main olfactory bulb (MOB) to downstream olfactory cortices and the striatum.
• Different brain regions possess unique cellular structures and connectivity, potentially leading to varied odor coding patterns.
• Understanding region-specific olfactory processing is crucial for deciphering how distinct odor percepts are generated.

Purpose of the Study:

• To investigate region-specific response features, tuning, and decoding of single-unit populations in the olfactory system.
• To compare olfactory coding across the MOB, anterior olfactory nucleus (AON), anterior piriform cortex (aPC), and olfactory tubercle (OT) using closely related aldehydes.
• To elucidate how different olfactory regions contribute to the representation and perception of chemical similarity.

Main Methods:

• Recorded single-unit population responses to identical odors across MOB, AON, aPC, and OT in awake male mice.
• Focused on chemically similar yet perceptually distinct aldehydes to probe fine-grained odor discrimination.
• Analyzed response timing, odor selectivity, and decoding accuracy to identify region-specific encoding strategies.

Main Results:

• The MOB demonstrated the highest aldehyde decoding accuracy and was the sole region encoding chemical similarity.
• The MOB exhibited a greater proportion of inhibited responses and narrowly tuned, time-specific odor-excited responses.
• The AON and aPC showed distinct response profiles, with the AON favoring excitation and the aPC having a significant fraction of inhibited responses.
• Differential outputs to the MOB were observed: AON terminals were activated, while aPC terminals were inhibited by aldehydes, a pattern consistent across complex odors.

Conclusions:

• Olfactory processing regions exhibit specialized encoding features, contributing to diverse odor representations.
• The AON and aPC display distinct local computations, resulting in opposing net outputs to the MOB.
• These findings highlight the complex, region-specific processing within the olfactory system that underlies odor perception.