Go with the FLOW: Visualizing spatiotemporal dynamics in optical widefield calcium imaging

TL;DR

This paper introduces FLOW portraits, a visualization framework using fluid dynamics techniques to analyze and interpret spatiotemporal brain activity in widefield calcium imaging data, revealing coherent neural structures.

Contribution

The paper presents a novel visualization method applying fluid dynamics analysis to calcium imaging data, capturing dynamic neural structures not visible with traditional methods.

Findings

FLOW portraits effectively visualize cortical wave dynamics.

The method captures coherent structures in neural activity.

Application to datasets demonstrates clear visualization of activity spread.

Abstract

Widefield calcium imaging has recently emerged as a powerful experimental technique to record coordinated large-scale brain activity. These measurements present a unique opportunity to characterize spatiotemporal coherent structures that underlie neural activity across many regions of the brain. In this work, we leverage analytic techniques from fluid dynamics to develop a visualization framework that highlights features of flow across the cortex, mapping wave fronts that may be correlated with behavioral events. First, we transform the time series of widefield calcium images into time-varying vector fields using optic flow. Next, we extract concise diagrams summarizing the dynamics, which we refer to as FLOW (flow lines in optical widefield imaging) portraits. These FLOW portraits provide an intuitive map of dynamic calcium activity, including regions of initiation and termination, as well as the direction and extent of activity spread. To extract these structures, we use the finite-time Lyapunov exponent (FTLE) technique developed to analyze time-varying manifolds in unsteady fluids. Importantly, our approach captures coherent structures that are poorly represented by traditional modal decomposition techniques. We demonstrate the application of FLOW portraits on three simple synthetic datasets and two widefield calcium imaging datasets, including cortical waves in the developing mouse and spontaneous cortical activity in an adult mouse.