Whether for finding food, avoiding predators or choosing a mate, the sense of smell is critical for the existence of many creatures.
We humans, able to distinguish over 10,000 scents, utilize our sense of smell for a multitude of activities from enjoying the aroma of freshly brewed coffee to deciding whom not to sit next to on the bus.
Scientists are now beginning to understand how the nose and brain process the complex information that gives rise to the perception of smell.
Studies from insects and mammals have demonstrated that the first cells in the smell pathway, called olfactory receptor neurons, appear to have a receptor for only one particular odor.
Cells with the same odorant receptors send projections to the same target region in the brain. This arrangement forms a kind of odor map in the brain so that a certain smell will activate a very specific region of the brain.
Two groups of scientists from Columbia and Stanford Universities, led by Dr. Richard Axel and Dr. Liqun Luo, respectively, have taken the research one step further and examined how the odor map is represented in regions that lie even deeper in the brain.
Their research examining how information is relayed from primary to secondary brain regions via the next cells in the pathway is presented in today's issue of Cell.
Both groups performed studies using fruit flies and pointed out that the cellular organization of smell is similar in insects and mammals.
By using techniques that allowed them to visualize the processes of single cells, the scientists were able to follow the projections of distinct cells between the primary brain regions and a secondary region.
They found that spatial information was also conserved at this level. Second order cells from a particular location projected to a specific part of the higher brain region, thereby translating the spatial odor map to deeper regions of the brain where more complex processing of the signal occurs.
However, unlike the strict point-to-point projections observed in the first leg of the pathway, individual projections of the second order cells overlapped each other.
This observation spurred speculation that higher order processing may require an eventual convergence of the inputs. Both sets of researchers conclude that interpretation of olfactory information likely relies at least in part on spatial information.
[Contact: Dr. Richard Axel, Dr. Liqun Luo]