Genetic tracing reveals a stereotyped sensory map in the olfactory cortex

The olfactory system translates myriad chemical structures into diverse odo ur perceptions. To gain insight into how this is accomplished, we prepared mice that coexpressed a transneuronal tracer with only one of about 1,000 d ifferent odorant receptors. The tracer travelled from nasal neurons express ing that receptor to the olfactory bulb and then to the olfactory cortex, a llowing visualization of cortical neurons that receive input from a particu lar odorant receptor. These studies revealed a stereotyped sensory map in t he olfactory cortex in which signals from a particular receptor are targete d to specific clusters of neurons. Inputs from different receptors overlap spatially and could be combined in single neurons, potentially allowing for an integration of the components of an odorant's combinatorial receptor co de. Signals from the same receptor are targeted to multiple olfactory corti cal areas, permitting the parallel, and perhaps differential, processing of inputs from a single receptor before delivery to the neocortex and limbic system.