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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - MultisensoryIntegration (Multisensory Integration in Time and Space)

Teaser

Summary

In natural environments, the brain is bombarded with multisensory signals and must continually assess whether such signals are produced independently, or by the same physical object. For example, when a rabbit hears footsteps and sees a blur, is the blur responsible for the footsteps, or are there two sources of danger? The rabbit uses two types of information to make this decision: spatial correlations (are the footsteps and blur localized together) and temporal correlations (does the blur get bigger as the footsteps get louder). My research question is: How and where these multimodal object representations are formed in the brain?

Physiological studies of sensory perception have historically focused on isolated sensory modalities. However, humans constantly combine multimodal sensory cues to better understand their environment, such as matching lip movements and auditory cues during a conversation. Mounting evidence suggests that brains are optimized to process naturalistic sensory cues, yet despite its ethological significance, little is known about the neural mechanisms underlying audiovisual integration. Thus, establishing how and where multisensory cues are integrated has wide-ranging importance for understanding the principles of sensory processing.

Several competing models have attempted to explain how sensory information, correlated in space or time, is combined within or across sensory modalities. For example, whether sensory information is exchanged between primary sensory cortices remains a controversial topic. Without recordings of cortical activity during multisensory integration, these controversies will remain unresolved. My proposed research will provide critical experimental data to constrain existing models of sensory processing and inform future research.

Furthermore, deficits in combining multisensory cues have been linked to a number of psychological disorders, including autism and schizophrenia. Although it has been established that autistic individuals show decrements in recognizing audiovisual temporal correlations, until we understand how and where the brain integrates this information, clinical progress will be limited. By establishing a rodent model of temporal multisensory integration, my work will create a new tool to probe the mechanistic underpinnings of these disorders.
Thus, my proposed research is both important to progress our basic understanding of sensory processing and bears direct clinical relevance to existing disorders.

I proposed to characterize the role of cortex in both the spatial and temporal aspects of multisensory integration by exploiting the advanced behavioural repertoire and recording techniques in the mouse model system. This project relies on the completion of three key objectives
1) Train mice to perform multisensory spatial and temporal integration tasks.
2) Characterize cortical regions which respond to audiovisual correlations in space and time.
3) Determine which cortical regions are required for multisensory behaviours.

Work performed

Since beginning this project, I have designed and built state-of-the-art behavioural chambers for developing multisensory behaviours in the mouse. These chambers are both sound-attenuating and temperature controlled to allow for the simultaneous presentation of visual stimuli on monitors (which had previously been untenable due to heating problems) and auditory stimuli from a speaker array.

Using these chambers, I have trained mice to perform simple tasks that demonstrate a basic level of audiovisual integration. Thus, although I only utilized nine of the originally scheduled twenty-four-month grant, I have made substantial progress toward the completion of my first objective: to train mice to perform multisensory spatial and temporal integration tasks.

In addition, I have used two-photon microscopy to record from thousands on neurons in the visual cortex of multiple mice. This data is still preliminary, but will reveal to what extent this classically unisensory region is involved in processing multisensory stimuli. This is a key step toward the completion of my second objective: to characterize cortical regions which respond to audiovisual correlations in space and time.

Final results

This project is not yet complete. Moving forward, I intend to develop more complex behavioural tasks in my multisensory chambers. I will both record and perturb neural activity in mice whilst they perform these tasks. These experiments promise to elucidate which regions of cortex are responsible for spatial and temporal multisensory processing. As deficits in combining multisensory cues have been linked to a number of psychological disorders, understanding the mechanisms of rodent multisensory processing may provide insights into new avenues of diagnosis and treatment in humans.