I have been using a pE-4000 for optogenetic experiments using in vitro slices for just over a year now. The pE-4000 has been fantastic for my needs: the ability to simultaneously use multiple wavelengths of light has allowed me to carry out experiments using two different opsins to study how external inputs converge on hippocampal interneurons. I’m currently setting up my own research group at the University of Exeter, and all of my patch-clamp rigs will have a pE-4000 on them, as they are such versatile devices for optogenetic experiments.