Earlier studies of the olfactory cortex by Buck's group indicated that in contrast to the straightforward mapping of inputs from odorant receptors onto the glomeruli, however, the mapping of odorant receptor inputs onto the olfactory cortex was quite complex.
"We had found that inputs from one type of odorant receptor are targeted to several loose clusters of neurons at specific locations in the cortex, " said Buck. In sharp contrast to the olfactory bulb, where signals from different receptors are segregated, inputs from different odorant receptors overlap extensively in the cortex. Moreover, individual cortical neurons are likely to get inputs from many different odorant receptors."
Buck's group previously showed that each odorant is recognized by a combination of receptors, and that each receptor can recognize multiple odorants. "So, the odorant receptor family is being used combinatorially," she said. "Just like letters of the alphabet are used in different combinations to form different words, the odorant receptors are used in different combinations to detect different odorants and encode their unique identities."
In the new studies, Buck and her colleagues sought further information about how the brain translates these combinatorial receptor codes into distinctive odor perceptions. Because of the complex patterns of receptor inputs in the cortex, it was impossible to predict how odors might be represented in this structure. They therefore decided to investigate the patterns of activity that were triggered by a range of odorant