Another IBioBA contribution to scientific knowledge: The Neural Circuits group has just published a research paper in the journal PNAS describing the functioning of neurons involved in memory and olfaction.
Have you ever wondered how the brain interprets a smell? It is not only a matter of “smelling” a scent, but also of understanding the context in which we perceive it: a smell can be pleasant or unpleasant depending on the place where we are or the memory it generates. This phenomenon occurs in the piriform cortex, a brain region that receives olfactory information and is also influenced by other types of signals. On this subject, the journal PNAS published a research work of the laboratory led by Antonia Marin Burgin, which seeks to unravel the mechanism by which external signals are integrated in the piriform cortex to build a perception of odor in context.
Despite the amount of knowledge accumulated on how the brain works, there is still much to be unveiled. And in this mission is the Neural Circuits group, which a few months ago, published another paper in the journal Nature Communications in which they found that the olfactory cortex doesn’t only process odors, but also receives other types of information. Now the question was where does this ‘extra information’ it receives come from?
In other words, it is not just a matter of “smelling” a smell, but of understanding its context: is that coffee smell coming from the bar around the corner, or from the office kitchen? To understand how this odor-context linkage happens, during her PhD, Olivia Pedroncini set out to study the connection between two parts of the brain: the piriform cortex (PCx), -the brain’s central hub for odor processing-, and the lateral entorhinal cortex (LEC), known to play a crucial role in processing the spatial location of objects and in the formation and consolidation of memories.
“Our hypothesis was that since there are projections from the LEC to the piriform cortex, those projections could be providing the spatial information that is detected in the piriform cortex”, explains Pendroncini, first author of the paper. What they found is that the LEC does indeed send signals to the piriform cortex, and that this influences the way odors are perceived. So, the two cortices, together, are the ones that would complete the perception: such odor comes from such place.
“This complements previous work and gives us clues to understand where these external signals come from to the piriform cortex. This paper shows us that the piriform cortex can integrate not only olfactory data, but also contextual information”, says Marin Burgin.
This work is also important because understanding the mechanisms of neural circuits in the vertebrate brain helps us to understand alternative and efficient ways that nature found to process information. This area of knowledge has important implications as it impacts new developments that can be applied to artificial intelligence (AI).
About the techniques
The team, which also includes researcher Noel Federman, relied mainly on electrophysiology and optogenetic techniques in the mouse brain. Using this tool, which allows neurons to be activated with light, they directed a special type of light-sensitive protein to neurons in the LEC. They then stimulated them and observed how different cells in the piriform cortex reacted: “What we saw is that LEC projections influence the piriform cortex heterogeneously, activating some neurons and suppressing others”, says Marin Burgin. In other words, they do not affect all neurons in the same way: they selectively activate a specific group called parvalbumin (PV) interneurons, which, when activated, “silence” the recurrent activity of the piriform cortex circuit, that is, they reduce the activity that is not directly related to odor perception.
“This tells us that when there is information coming from the LEC, the circuit responds more to olfactory afferent information and less to recurrent activity. In other words, activation of the LEC helps to integrate contextual information with sensory information, allowing for a richer representation of olfactory objects in the piriform cortex”, says Pedroncini.
“These results help us understand how the broader representations of sensory stimuli are assembled at the level of the cortex, which are not limited to representing the characteristics of the sensory stimulus alone, but also encompass contextual signals”, adds the scientist, who is currently a postdoctoral fellow at the Francis Crick Institute in London. “And this would somehow explain the mechanism by which the circuit can also respond to contextual signals, in this case to signals coming from the LEC”, says Noel Federman. This mechanism, which integrates contextual cues, is key to giving our perceptions meaning in everyday life.