Optical Recording of Action Potentials and Other Discrete Physiological Events: A Perspective from Signal Detection Theory

摘要

Many physiologists rely on optical techniques for measuring spatially and temporally resolved physiological signals in living cells. The signals typically originate from synthetic or biosynthetic sensor molecules that report changes in physiological variables as changes in fluorescence intensity. Such sensors now exist for numerous parameters and events, such as the concentrations of Ca2+ and various other second messengers, membrane potential, pH, and vesicle release (12, 27, 28, 50). Although wide-field microscopy remains the most commonly employed method for detecting fluorescence in living cells, its performance is often poor in thick tissue, where background fluorescence from focal planes above and below the region of interest can severely degrade the signal-to-noise ratio. To overcome this problem, different forms of laser scanning microscopy have been developed that possess the capacity to excite fluorescence in (or collect fluorescence from) only a single focal plane, thereby eliminating out-of-focus light. However, scanning microscopy in itself carries a price of massively reduced photon counts, which decreases the signal-to-noise ratio and defeats some of the advantages of optical sectioning.