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The olfactory system:

Olfactory perception is initiated upon the recognition of odorants by a large repertoire of receptors in the sensory epithelium. Neurons expressing a given receptor are randomly distributed within zones of the epithelium but project with precision to two spatially invariant glomeruli in the olfactory bulb. Thus, odor is represented in a topographic map of activated glomeruli. This map in the bulb is transformed in the representations in higher olfactory centers. For instance, the piriform cortex appears to discard the map, as it receives distributed input from seemingly random sets of glomeruli in the olfactory bulb, and this structure has been implicated in learned associations. In contrast, the cortical amygdala receives topographically organized input from the olfactory bulb, and in recent work we have demonstrated that the neurons in this pathway mediate innate behaviors.





The Cortical amygdala mediates innate behaviors:

Anatomic tracing experiments had implicated the cortical amygdala in genetically determined behaviors. We used optogentic experiments to directly determine if the cortical amygdala is involved in innate odor-driven behavior. Indeed, we found that the stereotyped circuits from the olfactory bulb to the cortical amygdala are required for innate aversive and appetitive responses to odor. Moreover, we identified and manipulated the activity of these neurons by exploiting the promoter of the activity-dependent gene, arc, to express channelrhodopsin in neurons of the cortical amygdala activated by odors that elicit innate behaviors. Optical activation of these neurons leads to appropriate behaviors that recapitulate the responses to odors. Together these data demonstrate that the cortical amygdala contains distinct neurons that are necessary and sufficient for the generation of innate, odor-driven behaviors (Root et al., Nature 2014).  Moreover, we have observed that neurons mediating aversive and appetitive behaviors have distinct projections to downstream targets.  The identification of neural circuits that elicit innate behaviors provides a foundation for dissecting sites of plasticity to afford behavioral flexibility.


We are using 2-photon endoscopic imaging to probe neuronal activity in deep brain structures. This is accomplished by implanting GRIN (Graded Refractive Index) lens above brain regions of interest that express the calcium indicator GCaMP. The movie below shows odor- evoked calcium activity in a region of the cortical amygdala.