High-precision mapping reveals the structure of odor coding in the human brain

Area of Science:

• Neuroscience
• Olfactory neuroscience
• Sensory perception

Background:

• Odor perception is subjective, with neural activity patterns in olfactory cortices not fully mapped to individual percepts.
• Understanding the neural basis of idiosyncratic odor perception is crucial for olfactory research.

Purpose of the Study:

• To investigate the neural coding scheme of idiosyncratic odor perception.
• To determine how olfactory cortices represent fine-grained versus coarse odor percepts.
• To explore the role of the orbitofrontal cortex (OFC) and piriform cortex (PirC) in subjective odor experience.

Main Methods:

• Collected neuroimaging (functional magnetic resonance imaging) responses to 160 odors from 3 subjects.
• Developed perceptual encoding models to predict olfactory responses.
• Analyzed activity patterns in the orbitofrontal cortex (OFC), piriform cortex (PirC), and amygdala.

Main Results:

• Orbitofrontal cortex (OFC) activity represents fine-grained odor identity more than coarse percepts, unlike the piriform cortex (PirC) and amygdala.
• Encoding models successfully predicted olfactory responses to novel odors.
• Perceptual space dimensionality increases from PirC to OFC, with higher-order dimensions being idiosyncratic across subjects.

Conclusions:

• Subjective olfactory percepts are primarily represented in the orbitofrontal cortex (OFC).
• Encoding of lower-order odor dimensions is consistent across individuals, while higher-order dimensions are unique.
• Findings offer new insights into cortical mechanisms of odor coding and subjective experience.