Herman, A.M. et al. eLife 3, e01481 (2014).

Optogenetics tools allow researchers to use light to activate specific neurons expressing a light-sensitive protein, enabling studies of synaptic connectivity and how it relates to animal behavior. The transmembrane channel protein channelrhodopsin-2 (ChR2) in particular has been widely used for this purpose. When ChR2 is hit with blue light, its retinal chromophore absorbs photons, causing the channel to open and allow cations to pass across the cell membrane. Herman et al. now deliver a public service message to users of ChR2 technology. They found that shining light onto neurons expressing ChR2 for long durations can actually cause the cells to become silenced, rather than activated, and that interneurons are especially prone to this so-called depolarization block. They recommend that ChR2-technology users carefully empirically evaluate their choice of light-pulse time intervals in order to avoid this effect.