Light makes mice forget scary memories University of California Davis rightOriginal StudyPosted by Andy Fell-UC Davis on October 14 2014To test a long-standing idea about how the brain retrieves memories about specific places or events scientists zapped mice with light to make them forget.�The theory is that learning involves processing in the cortex and the hippocampus reproduces this pattern of activity during retrieval allowing you to re-experience the event� says Brian Wiltgen of the University of California Davis.If the hippocampus is damaged patients can lose decades of memories.Normally mice placed in a new environment will nose around and explore. But when placed in a cage where they have previously received a shock the mice freeze will in place in a �fear response.�In this study the scientists used mice genetically modified so that when nerve cells are activated they both fluoresce green and express a protein that allows the cells to be switched off by light.They were therefore able both to follow exactly which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval and switch them off with light directed through a fiber-optic cable.Wiltgen and colleagues first showed that they could label the cells involved in learning and demonstrate that they were reactivated during memory recall.By switching off the specific nerve cells in the hippocampus they showed that the mice lost their memories of the unpleasant event.They followed fibers from the hippocampus to specific cells in the cortex and showed that turning off other cells in the hippocampus did not affect retrieval of that memory.�The cortex can t do it alone it needs input from the hippocampus� Wiltgen says.�This has been a fundamental assumption in our field for a long time and [the] data provides the first direct evidence that it is true.�They could also see how the specific cells in the cortex were connected to the amygdala a structure in the brain that is involved in emotion and in generating the freezing response.The findings are published in the journal Neuron.Grants from the Whitehall Foundation McKnight Foundation Nakajima Foundation and the National Science Foundation funded the work.Source: UC DavisYou are free to share this article under the Creative Commons Attribution-NoDerivs 3.0 Unported license.