This is what the office smells like, so the kitchen …: What is the connection of olfactory impressions with places that shape our perception and that of many animals? A study on rats now shows that in a certain nerve network in the olfactory center an olfactory-spatial map is created that the animals use to orientate themselves. This basic principle probably also shapes human perception, say the researchers.
As is well known, our orientation and memories of certain places are based primarily on visual impressions. But as everyone knows from personal experience, olfactory associations can also be strongly pronounced: a scent, stench or a special aroma can even transport us mentally to a certain place. In addition, according to a phrase, we sometimes “follow our nose”. It is well known that this plays a much more important role in some animal species: “They use smells for spatial navigation and memory, which enables them to find valuable resources such as food,” says Cindy Poo from the Champalimaud Center for the Unknown in Lisbon. “We wanted to understand the neural basis of these behaviors, so we used rats to study how the brain combines olfactory and spatial information,” says the scientist.
On the trail of olfactory-spatial associations
It was previously known that neurons in the hippocampus of the brain function as “place cells”: They become active in specific locations in an environment. Together they code entire areas – a spatial map is created in the brain. This discovery in rats was even honored with the Nobel Prize in 2014. The neural effects in the hippocampus are so pronounced that scientists can use certain activity patterns to determine where an animal is in a spatial system. As part of their study, Poo and her colleagues have now investigated the suspicion that similar effects also occur in the olfactory center of the brain, the olfactory cortex – in connection with olfactory impressions. “We suspected that this region of the brain can do more than just identify different smells,” says Poo.
To gain insights, the researchers carried out experiments with rats in a labyrinth system: “There they learned to associate certain smells and rewards with special places,” explained Poo. While the animals were solving corresponding tasks, the scientists looked into their brains, as it were. For this purpose, the rats had previously been inserted into small implants that recorded the activity of the neurons in part of the olfactory cortex. “By recording the electrical signals sent out by hundreds of individual neurons in this area of the brain, we were able to decipher what certain neurons were doing. For example, whether they became active when the animal smelled a certain smell, or if it was in a certain place in the maze, ”explains senior author Zachary Mainen.
Odor neurons encode spatial maps
As the researchers report, they discovered a population of neurons in the olfactory cortex that apparently react in a similar way to the hippocampal place cells: They become active at a specific location in the labyrinth – they form a neural map of the system. However, the nerve complex mainly covers the relevant points in the labyrinth – where the animals perceived the smells and received rewards. “We found that some of the neurons responded to the smell, some to the location, and some to varying degrees to both types of information. All of these different neurons are in turn mixed up and probably also connected to one another. It therefore stands to reason that the activation of olfactory-space associations occurs through activities within this network, ”says Poo.
But do we also create memories in this way that associate special smells with certain places? “Humans rely more on visual landmarks than smells, but it’s likely that the principles by which we remember where we’ve been and where we’re going are very similar,” says Mainen. “Our study can thus contribute to a fundamental understanding of how the senses are used for navigation and memory,” says the scientist.
Source: Champalimaud Center for the Unknown, specialist article: Nature, doi: 10.1038 / s41586-021-04242-3