Sunday, September 14, 2014

Mind Games

The technique of optogenetic generation of memories has already been
demonstrated for `incepting' false memories in mice by neuroscientists in the MIT lab of neuroscience. See here for details.  It has now been demonstrated that this technique can be used to erase traumatic memories, in mice again, of course!

In the optogenetic technique, neurons are labelled with a light sensitive protein, and pulses of light are used to switch the neurons on and off.The patterns of neurons activated with negative memories, e.g. when the lab mice received an electric shock (mild, the researchers take care to aver) were identified and tagged with the light sensitive protein, and so were the patterns when positive memories were formed (the mice were allowed to play with lady mice).

Later, the mice were put in an enclosure, and the natural preference of the mice for any preferred area of the enclosure was observed. Next, if the negative memories of the mice were activated when they went to the preferred area, they avoided the preferred area, and if the positive memories were excited when they went to the less preferred area, they started spending more time in the less preferred area.

When mice that had been shocked were put with females and the negative memory was activated, the pattern or em-gram of the negative memory became less strong. Conversely, electric shocks were given to mice with positive memories excited, the positive memories also became weaker. Now, if the mice were put in the enclosure again, the fear conditioned mice started spending more time in the area they had avoided earlier, and the reward conditioned mice did the opposite, indicating that both kinds of memories had been reversed.

Memory erasure via association of location, has been long used in psychiatry. Similar effects can be induced by drugs, and fear and reward conditioning of behaviour has been known since Pavlovian times. However, here the memory erasure was achieved by optic simulation of a pattern (an em-gram) stored in a specific area of the brain. As in the `inception' of memories, this also identifies  the neural circuits and the physical location of the area in the brain where specific memories are formed. An important finding in the present case was that when the negative memories were labelled and activated in the dentate gyrus, an area of the hippocampus, which forms new memories, and records
factual details of experiences,  the memories could be erased, or made less negative. On the other hand, the strength of negative memories labelled and activated  in the basolateral complex of the amygdala (which links emotion to memories)  could not be reduced.

While transferring the technique to humans is a long way off, the method also holds promise for the post-traumatic treatment of stress disorders. As in the case of the inception of false memories, similar results can be invoked by chemical means. This may constitute a more practical method of treatment. However the identification of the hard wired circuitry of the brain and the identification of the specific neuronal patterns (em-grams) associated with specific memories constitute the real strength of the optogenetic methods.

This blog post by Neelima Gupte and Sumathi Rao.

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