Researcher found where pleasant memories are stored

Posted on October 4, 2013

Did you have a good time? We know where you’ll store the memory of it!

Where do you go for a tasty bite and where the food is not so good? Where are you likely to meet an attractive partner and where you risk damage to your health? For every person – but also for animals – the information about pleasant and unpleasant experiences is of key importance. Researchers from the Nencki Institute in Warsaw discovered how and where nice memories are stored.

As shown by researchers from the Nencki Institute of Experimental Biology in Warsaw, Poland, nice memories are stored in an area of the brain known as the central nucleus of the amygdala. The results obtained by the group of Prof. Leszek Kaczmarek and Dr. Ewelina Knapska, which were published in the well-known Journal of Neuroscience show that just one protein plays the key role in the process of memorizing pleasant experiences. In the future these results may help design more effective treatment of addictions, depression and schizophrenia.

Neurobiologists differentiate between many types of memory, the most basic types of which are characterized by clear duality. For example we have short and long term memories, declarative (referring to events/data) and procedural (memory of actions). Researchers from the Nencki Institute focused on another dichotomy of great importance to every animal. They focused on appetitive memory related to memories of pleasant experiences and aversive memory related to unpleasant experiences.

wenty five years ago Nencki researchers have observed changes in the activity of a gene known as c-fos in the nervous cell nuclei during learning. One of the proteins, the production of which is regulated by a protein encoded by the c-fos gene, is the MMP-9 enzyme active outside of the cell. Researchers decided to investigate the role of MMP-9 in memorizing pleasant and unpleasant experiences. In order to do this a series of experiments was conducted on control mice and on mice either lacking this protein entirely or with its selective blocking only within the central amygdala.

The amygdala is a small structure within the cerebral hemisphere and it is located at the base of the brain, close to the hippocampus. It consists of two groups of nuclei responsible for innate and acquired emotional reactions, such as laughter or fear.

Researchers were surprised by the experiments. When placed in the IntelliCages, the control mice after three days of learning almost always chose the corner with sweet water. Mice lacking MMP-9 behaved distinctly different: they showed no preference for any of the corners. At the same time all mice equally well remembered the corner where they received the unpleasant puff on their noses. Furthermore, selective blocking of MMP-9 just in the central amygdala produced the same effect – the memory for the sweet water location could not be formed.

“The results are clear. Pleasant experiences are memorised due to changes in plasticity within the neurons of the central nucleus of the amygdala. At the same time we have shown that just one protein, the MMP-9, is responsible for learning about pleasant experiences themselves and memorizing them. At the same time this protein has no impact on the memory of unpleasant experiences. These are important discoveries and to tell the truth making them was… very pleasant”, says Prof. Kaczmarek.


Source material from Nencki Institute

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