Optical recording of membrane potential allows simultaneous measurements to be taken from many different locations in the nervous system. This is important in studies of the nervous system in which simultaneous activity can occur at the regional, cellular, and subcellular levels. New "blue" dyes, developed by Amiram Grinvald's group, are a great advance for in vivo voltage-sensitive dye imaging of mammalian cortex. The blue dyes are excited by red light (630 nm) that does not overlap with light absorption of hemoglobin (510-590 nm). This virtually eliminates the heart pulsation artifact.
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