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Cortical feedback in figure background segregation of odors.

Periodic Reporting for period 2 - COFBMIX (Cortical feedback in figure background segregation of odors.)

Periodo di rendicontazione: 2019-10-01 al 2021-03-31

What is the problem/issue being addressed?
When performing a sensory-guided behavioral task, we typically utilize mechanisms of attention that make sure that our brains process important information adequately. These mechanisms are flexible and allow us to switch our attention to different types of information depending on what is important at the moment. A daily example of such mechanisms is our ability to listen to one person in a cocktail party while ignoring all others. However, we can quickly shift our attention to another person if he calls our name.

Why is it important for society?
While attention is heavily involved in sensory processing, the underlying mechanisms are not well understood. Understanding the mechanisms responsible for attention may provide a basis for treating individuals with attention deficits.

What are the overall objectives?
One prominent hypothesis for stimulus specific attention is that central brain areas send information to more peripheral sensory brain areas and modify neuronal representations there to fit current behavioral demands. Our project aims to test this hypothesis in the rodent olfactory system. We proposed that when trying to detect specific odors against rich backgrounds, olfactory cortex sends information about the identity of the target odors to the olfactory bulb via feedback projections. The hypothesis is that these feedback projections introduce context specificity to olfactory bulb odor representations.
Our aims were:
1. To determine how the representation of odor information in the olfactory bulb (the first brain region the analyses odor information), is modulated by behavioral goals and by feedback projections.
2. To determine the signals conveyed by feedback projections from the olfactory cortex to the olfactory bulb.
3. To determine the relationship between feedforward sensory inputs and feedback inputs in the olfactory bulb. That is to investigate how the olfactory bulb integrates the information from the nose with the information from the cortex.
In the first half of the project we have significantly advanced in fulfilling aims 1 and 2, and have not reached aim 3 yet.

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.

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 as a preprint and submitted for publication in a journal.
The novel task we've developed is one of the most complex sensory-guided behavioral tasks in rodents. In combination with chronic multi-electrode recordings, these experiments provide data that has not been available beforehand. I expect that by the end of the project we will have an extensive understanding of how behavioral context affects sensory representations in the most peripheral olfactory brain region. These data will enable testing of our proposed hypothesis for attention mechanisms in the olfactory system.