SeminarsBACK

Optogenetic Monitoring Neural Circuit Dynamics with Voltage-Sensitive Fluorescent

Time:16:00-17:30, May 30, 2014

Venue: McGovern Hall (Cheng Yu Tung Medical Sciences Building, Second Floor)

Reporter:Thomas Knöpfel Ph.D. Professor, Imperial College London, Division of Brain Sciences

Abstract

A key objective of neuroscience is to understand the emergence of behavior from the coordinated electrical activities of large number of neurons across multiple brain regions. In the cerebral cortex, primary sensory inputs and motor outputs are processed in local neuronal circuits in specific brain areas while cortex-dependent behavior usually requires a coordinated interaction between local circuits across cortical space. Linking the neuronal activities of local neuronal circuits with behavior requires, therefore, understanding how the processing of information at the level of local circuits is integrated at the larger scale of cortical space. Conventional electrophysiological approaches towards understanding of this large-scale integration provide rasters of neuronal activities that can cover large portions of the cortical space (millimeters to centimeters) but provide a low spatial resolution (electroencephalogram,local field potentials, etc) or that focus on local circuits with single cell resolution (single cell microelectrode techniques) but miss the “bigger picture”. Classical voltage sensitive dye imaging techniques overcome these spatial resolution and coverage limitations, but like the widely used electrophysiological approaches they are mostly blind to cellular diversity in terms of functionally distinct cell classes. Protein-based fluorescent indicators of membrane potential are at the core of emerging approaches that overcome these classical technical limitations.

Work in our and other laboratories during the last 15 years resulted in several families of voltage-sensitive fluorescent proteins (VSFPs) based on an isolated voltage-sensing domain (VSD) that is functionally linked to fluorescent proteins.Our most recent VSFP family, VSFP-Butterflies, enable the optical recording of action potentials from individual neurons in single sweeps and voltage imaging of population activity, including synchronized activities in the gamma frequency band, from defined cell populations in acute brain slices. In living mice, VSFPs afford sufficient SNR for probing sensory-evoked responses and enables univocal detection of spontaneous cortical population activity (brain waves) during light anesthesia or quiet alertness.

Along with the ability to target specific genetically-defined cell populations, VSFPs open a new experimental window for the study of the interaction dynamics of neuronal assemblies, facilitate the investigation of information processing mechanisms of the brain, such as the circuit operations involved in sensing our environment and generation of body movements, but will also be applicable to directly visualize cognitive functions.