GCaMP is a genetically encoded calcium indicator, or GECI initially developed by Junichi Nakai. GCaMP is created from a fusion of green fluorescent protein (GFP), calmodulin, and M13, a peptide sequence from myosin light chain kinase. The advantage of GECI's are that they can be genetically specified for studies in living organisms. The first transgenic mouse expressing a GCaMP was reported in 2004 and GCaMP was subsequently improved to GCaMP2, which was stable at mammalian body temperatures and enabled the first in vivo mammalian recordings using a GECI. GCaMPs have been subsequently modified to progressively improve the range of the fluorescence signal, resulting in GCaMP3 through GCaMP8. Additionally, red fluorescence GECIs have been developed that expand the spectral options for multi