Researchers at the Institut Pasteur and the CNRS have identified the role played by neo-neurons formed in the adult brain of mice.

By using selective stimulation, the researchers were able to show that these neo-neurons increase the ability to learn and memorize difficult cognitive tasks, which c0uld open up new avenues in the treatment of some neurodegenerative diseases.

The discovery that new neurons could be formed in the adult brain created a stir in 2003 by debunking the age-old belief that a person is born with a set number of neurons and that any loss of neurons is irreversible. But the function of these new neurons remained undetermined until now.

Using mice models, the team, working under Pierre-Marie Lledo, head of the Laboratory for Perception and Memory (Institut Pasteur/CNRS), revealed the role of these neo-neurons formed in the adult brain with respect to learning and memory.

Smarter mice

With the help of an experimental approach using optogenetics*, developed by this very same team and published in December 2010, the researchers were able to show that when stimulated by a brief flash of light, these neo-neurons facilitate both learning and the memorization of complex tasks.

This resulted in smarter mice models that were able to memorize information given during the learning activity more quickly and remember exercises even 50 days after experimentation had ended. The study also shows that neo-neurons generated just after birth hold no added advantages for either learning or memory; it is only the neurons produced by the adult brain that have any considerable significance.

“This study shows that the activity of just a few neurons produced in the adult brain can still have considerable effects on cognitive processes and behavior,” explains Lledo. “Moreover, this work helps to illustrate how the brain assimilates new stimulations seeing as normally electrical activity (which we mimic using flashes of light) is produced within the brain’s attention centers.”

Role of mood

The study has also reaffirmed the clear link between “mood” (defined here by a specific pattern of stimulation) and cerebral activity. It has been shown that curiosity, attentiveness, and pleasure all promote the formation of neo-neurons and consequently the acquisition of new cognitive abilities.

Conversely, a state of depression is detrimental to the production of new neurons and triggers a vicious cycle which prolongs this state of despondency. These results, and the optogenetics technologies that enabled this study, may prove very useful for devising therapeutic protocols which aim to counter the development of neurologic or psychiatric diseases, the researchers suggest.

*Professor Pierre-Marie Lledo’s work in optogenetics.

Ref.: Mariana Alonso et al., Activation of adult-born neurons facilitates learning and memory, Nature Neuroscience, 2012, DOI: 10.1038/nn.3108