Researchers Reveal Spatial Organization of Olfactory Cortex

The path from sensation to cognition has been an ever-present riddle that neuroscientists are working hard to understand, particularly for the olfactory system. The precise organization behind our noses’ smell-processing system is complex at best, with increasing interest in how certain viral pathogens, such as SARs-CoV-2, induce anosmia in some patients. To learn more about how our noses detect and perceive odors, Cold Spring Harbor Laboratory (CSHL) investigators Florin Albeanu, Alexei Koulakov, and Anthony Zador have created a new, extensive map of the brain’s olfactory circuits. 

“It’s an open question at this point, how exactly we process smell,” says senior author Albeanu. “What are the features in the odor space that the brain is extracting and using to create percepts of olfactory objects? And exactly what are the mechanisms in the brain?” 

Previous studies have failed to find any logical organization among neurons in the olfactory cortex, so for a while, researchers suspected that information was relayed randomly throughout the brain. However, those studies only examined connectivity patterns between a few dozen neurons, while the CSHL team was able to investigate more olfactory-processing neurons than ever before.

This detailed view was due to a new DNA-based brain-mapping technique developed in contributing author Zador’s lab, MAPseq and BARseq. These techniques allowed the team to trace the paths of thousands of olfactory-processing neurons within the brain of a single mouse.

The map charts how sensory information is routed between olfactory-processing regions of the brain, including the olfactory bulb and the piriform cortex. Within that cortex, the team found that neurons towards the front of the brain had different patterns of connectivity than those observed in the back.

“As you move along this axis, you see the neurons’ projection pattern gradually changing in terms of how it broadcasts information into other brain regions,” says contributing author Koulakov. “That is synchronized with the way the olfactory bulb projects to those brain regions, as well as to the same locations within the piriform cortex.”

The pattern of these findings, recently published in the journal Cell, reflects what other neuroscientists have observed in brain regions where neurons’ connections and locations correspond to specific sensory inputs, such as sight and sound. For example, the auditory system has neurons positioned along an axis relative to the sound frequencies we hear. The visual system has neurons positioned in a way in the dorsal and lateral streams (i.e., the “what” and “where” pathways) to convey information about the object’s location, hue, movement, and more.

The team says that this olfactory map could offer information for researchers to tackle “…the last frontier of sensory neuroscience.” This detailed view of olfactory neurons points towards the existence of different neural circuits dedicated to assessing the identity and location of odors. “It puts us and the field in a way, in a very different state of mind,” says Albeanu. “It’s a step toward understanding the nature of olfactory processing.”