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Functional role of neuronal spontaneous activity for sensory processing

Periodic Reporting for period 1 - Spontaneous activity (Functional role of neuronal spontaneous activity for sensory processing)

Reporting period: 2018-09-01 to 2020-08-31

The brain is always spontaneously active even in the absence of explicit stimuli coming from the outside world. What is the meaning of such activity? While it is now accepted that spontaneous activity does not simply represent “noise” in the brain, its functional role remains elusive. In particular, it remains unclear whether changes in the population activity of cortical neurons can affect performances in tasks that require discriminating a feature of a stimulus, for example, the frequency (low/high) of a sound. In this project we aimed at answering this intriguing question.
Answering this question is of paramount importance for many reasons. First, it would solve a long-studied mystery in neuroscience. Second, it would provide indications of how altered spontaneous activity, for example in diseases such as Schizophrenia, may functionally affect brain function. Third, understanding the causal role of spontaneous activity on behavioral performances may lead to potentially innovative technological avenues to boost human performances.
The objective of this study is to implement cutting-edge behavioral, electrophysiological and computational techniques to elucidate the functional role of spontaneous neuronal activity for the decision making process. To achieve this goal, we aim at creating expectations about upcoming sensory stimuli in head-fixed mice and test whether such expectation may affect behavior and could be modulated optogenetically. Furthermore, we want to understand the neuronal basis of how expectation can affect behavioral responses.
Since the beginning of the project:
1) I developed multiple tasks in head-fixed mice to study the possible effects of expectation on behavioral performances.
2) I developed the analysis tools necessary to study in detail the behavior of the mice we trained.
3) I set up a pipeline to acquire and process videos while recording neuronal activity in behaving mice.
4) I developed all the analysis to process the neuronal data.
5) The tools that I developed turned out to be of more general use and were also applied to a project that examined the effect of optogenetics-induced serotonin release on pupil size.
6) I presented my results at multiple international conferences, I wrote and published a manuscript and currently working on two other papers.
1) I found that the behavior of head-fixed mice is consistent with a normative model that assumes sensory, modeling and control limitations. This finding helps refining the way we think about the study of decision making in head-fixed mice.
2) I found that desynchronized spontaneous activity is beneficial for behavioral performance in a discrimination taks but only after error trials. This finding may shed light on the role of cortical activity in the decision making process.
3) As a parallel project I also found, for the first time, that optogenetics-induced release of serotonin can modulate pupil size in mice. This finding helps re-thinking about the effects of neuromodulators on internal states such as arousal.