“MIT researchers turn on a memory”

Researchers chose to test a simple kind of memory — a fear memory. In one experiment, mice were put in a chamber, allowed to explore, and given a foot shock. The next time the mice were put in the same dangerous chamber, they remembered the unpleasant electric shock and froze, taking on a defensive stance. Researchers had, however, inserted a gene that codes for a light-sensitive protein into the cells involved in making a memory. They then tested what happened when they turned on a light to activate those cells, without putting the mice in the same chamber. They saw the freezing behavior, as if the mice were reliving the memory.

“This is the most dramatic way to show that high cognitive phenomenon, like memory recall, can be generated, can be artificially generated by poking cells in the brain,” Tonegawa said in an interview.

He said there were about 20,000 neurons, or brain cells, involved in this particular kind of memory.  [via]

I’ve seen a couple of these optogenetic experiments. It’s pretty fascinating to be able to manipulate the neural response in vivo.