Single-Neuron and Population Methods to Study the Circuit-Level Cortical Mechanisms of Multisensory Processing

In the past decade, the study of the circuit-level mechanisms of cortical multisensory processing has made great progress, thanks to the development of methods to record and manipulate the activity of neuronal ensembles in head-fixed rodent models, in which the controlled delivery of sensory stimuli can be associated to behavioral tasks. However, compared to unisensory processing, the field is still in its infancy, and our understanding of how multiple sensory modalities are integrated and compared in the neocortex keeps being disrupted by novel findings. In this context, the emergence of tools to record and analyze the activity of large populations of neurons localized across multiple brain regions has emerged as a key strategy to link multivariate patterns of spiking activity to sensory stimuli and the associated behavioral responses. This chapter aims to provide a manual for researchers aiming to apply these techniques. Specifically, we provide an overview of the main experimental steps required to study multisensory processing in head-fixed mice with laminar electrophysiology. Furthermore, we discuss in depth the main preprocessing steps and the most relevant techniques used to analyze how single neurons and neuronal populations process sensory information.