Progress report:
Aim1: As a first step for testing the idea that cortical feedback projections introduce context specificity to olfactory bulb odor responses, we developed a novel behavioral task for mice. In this task mice are trained to detect target odors from background mixtures, but importantly the target odor is cued on each trial. The cue defines the context as the same odor mixture can have different behavioral meanings depending on the cue it followed. We now have mice performing this task and at the same time we record the activity of neurons in the olfactory bulb using 32 chronically implanted electrodes. We are now in the position to test whether odor responses are indeed context dependent in the olfactory bulb.
Additionally, to analyze how background mixtures affect behavioral decisions in mice, we generated a model of mouse behavior using the drift-diffusion decision making framework. We showed that the addition of background odors acts like increased noise rather than reduced signal. These findings were published in Plos Computation Biology.
Aim 2: To analyze the signals that are projected form the olfactory cortex to the olfactory bulb, we record neural activity in the olfactory cortex with 32 chronically implanted electrodes. We use optogenetic tagging to identify neurons that send feedback axons to the olfactory bulb. We have expanded this aim to include a comparison between mice at different states – anesthetized, passive awake, and behaving. Some of the findings in this aim have been published in Frontiers in Systems Neuroscience.
We also tested to what extent cortical activity and mouse performance in the tasks mentioned above depend on an intact olfactory bulb. To this end we analyzed a mouse model with severe olfactory bulb degeneration. To our great surprise, these mice (with as little as 5% remaining of the olfactory bulb) could solve the task and their cortical activity was very similar to normal mice. These findings were recently published in Current Biology.
