Optogenetic simulation of region of hippocampus thought to active fear memory recall

Yesterday I went to a seminar held by Steve Ramirez from Boston University who is studying a way to artificially activate positive and negative memories in healthy and maladaptive states. He explained optogenetic reactivation of hippocampal dentate gyrus neurons activated during fear conditioning were sufficient to induce freezing behaviour.  That is, activating these neurons without actually presenting the mouse with the fear stimulus was sufficient for the mouse to show signs of fear. In a similar proportion of cells, the freezing was not detected upon light-stimulation on ChR2 in non-fear conditioned mice. The freezing, act of fear, was also not detected upon fear-conditioned mice with cells labeled by a different protein instead of ChR2.