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How neuronal activity patterns drive behavior: novel all-optical control and monitoring of brain neuronal networks with high spatiotemporal resolution

Periodic Reporting for period 3 - NEURO-PATTERNS (How neuronal activity patterns drive behavior: novel all-optical control and monitoring of brain neuronal networks with high spatiotemporal resolution)

Reporting period: 2018-10-01 to 2020-03-31

When we hear a sound, see an object, or smell an odor, precise spatial and temporal patterns of electrical activity are generated in neuronal networks located in specialized brain areas. This electrical representation of the external stimulus is believed to mediate the perception of the external stimulus. However, what information about the stimulus is encoded in these activity patterns and how this information is used by the brain to drive perceptual behavior remains unclear.
In this project we develop innovative optical technologies for manipulating and monitoring brain circuits with single cell resolution in the intact brain. These novel methods will be used to causally test fundamental questions about how the brain processes sensory information to guide behavior.
This project will provide fundamental information about a key aspect of brain function, i.e. how spatiotemporal patterns of electrical activity in neuronal networks control sensory perception. Understanding these basic processes is the first fundamental step to understand the pathogenesis of brain diseases. Moreover, the knowledge of the cellular and network mechanisms underlying brain function may inspire a new generation of more efficient brain machine interfaces and artificial intelligence devices. Thus this project has the potential to positively impact on the health and technology development of our society.
In this first reporting period (30 months), we purchased and installed the new equipment, we recruited three postdoctoral fellows (Dr. Brondi and Dr. Forli at the IIT and Dr. Cone at the University of Chicago) and we developed the new technology to monitor and manipulate neural activity patterns in the intact mouse brain which was described in Aim 1 of the Description of the Action. As a necessary step towards the development of this technology, we first applied two-photon holographic illumination to map the activity of cortical cells with millisecond temporal resolution and subcellular spatial resolution (Bovetti et al. Sci. Reports 2017) and we validated this approach in GRIN lens-based endoscopes for fast imaging in deep brain regions (Moretti et al. Biom. Optics Express 2016). We then combined holographic scanless imaging of GCaMP6 signals in population of neurons with wide-field single-photon optogenetic stimulation of the inhibitory opsin Archaerhodopsin (Bovetti et al. Sci. Reports 2017). This new experimental approach allowed mapping the response of neuronal circuits in the intact mammalian brain with unprecedented temporal resolution and no stimulation artefacts during inhibitory optogenetic manipulations. More recently, we combined two-photon holography to stimulate neurons expressing blue light-sensitive opsins (ChR2 and GtACR2) with two-photon imaging of the red-shifted indicator jRCaMP1a in the mouse neocortex in vivo. We demonstrated efficient control of neural excitability across cells types and layers with holographic stimulation and improved spatial resolution by opsin somatic targeting. Moreover, we performed simultaneous two-photon imaging of jRCaMP1a and bidirectional two-photon manipulation of cellular activity with negligible effect of the imaging beam on opsin excitation (Forli et al. Cell Reports 2018). Finally, we contributed to develop the conceptual framework for the application of two-photon optogenetics to understand the brain code underlying behavioural perception (Panzeri et al. Neuron 2017).
The scientific results obtained within the NEURO-PATTERNS project in this first reporting period have produced novel technologies to manipulate neurons in the intact mouse brain while simultaneously monitoring neural activity (Aim 1a and Aim 1b). This greatly expands previous experimental capabilities by, for example, allowing simultaneous imaging and optogenetic manipulation with minimal crosstalk between imaging and stimulation in the intact mouse brain, by allowing bidirectional cellular resolution manipulation across cell types and layers, and by allowing detection of neural GCaMP6-mediated signals with unprecedented temporal resolution. Moreover, we have contributed to the development of the theoretical framework for the application of two-photon optogenetics to the investigation of the brain code underlying sensory perception, a necessary step towards the experimental application of holographic stimulation to the investigation of the neural code.
We now plan to use these novel technologies to perturb population activity with spatiotemporal patterns of arbitrary complexity in animals and measure: 1) how the fine temporal structure in population activity patterns can be conveyed from one network to another, downstream network (Aim 2a); 2) the behavioral consequences of the changes induced by two-photon stimulation (Aim 2b). Understanding how information is represented in the brain – in other words, understanding the neural code – requires knowledge of how that information is actually decoded and used for behavior. We will use this novel method to take the first steps forward toward understanding the nature of the neural code.