Historical Overview and General Methods of Membrane Potential Imaging
Voltage imaging was first conceived in the late 1960s and efforts to find better organic voltage-sensitive dyes began in the 1970s and continue until today. At the beginning it was difficult to measure an action potential signal from a squid giant axon in a single trial. Now it is possible to measure the action potential in an individual spine. Other chapters will discuss advances in voltage imaging technology and applications in a variety of biological preparations. The development of genetically encoded voltage sensors has started. A genetically encoded sensor could provide cell type specific expression and voltage recording.
Optimizing the signal-to-noise ratio of a voltage-sensitive dye recording requires attention to several aspects of the recording apparatus. These include the light source, the optics, and the recording device. All three have improved substantially in recent years. Arc lamp and laser sources are now stable, more powerful, and less expensive. Cameras for recording activity have frame rates above 1 kHz and quantum efficiencies near 1.0 although they remain expensive. The sources of noise in optical recordings are well understood. Both the apparatus and the noise sources are discussed in this chapter.
KeywordsShot Noise CMOS Camera Intrinsic Signal Squid Giant Axon Dark Noise
The author is indebted to his collaborators Vicencio Davila, Amiram Grinvald, Kohtaro Kamino, Ying-wan Lam, Leslie Loew, Bill Ross, Brian Salzberg, Alan Waggoner, Matt Wachowiak, Jian-young Wu, and Michal Zochowski for numerous discussions about optical methods. The experiments carried out in my laboratory were supported by NIH grants.
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