Researchers at the Netherlands Institute for Neuroscience (NIN-KNAW) have discovered how the adult brain can adapt to new situations. Their study may be significant in the treatment of neurodevelopmental disorders such as epilepsy, autism and schizophrenia.
Young brains are capable of forming many new synapses, and are consequently better at learning new things. That is why we acquire vital skills – walking, talking, hearing and seeing – early on in life. The adult brain stabilizes the synapses so that we can use what we have learned in childhood for the rest of our lives.
Earlier research found that approximately one fifth of the synapses in the brain inhibit rather than excite other nerve-cell activity. Neuroscientists have now shown that many of these inhibitory synapses vanish if the adult brain is forced to learn new skills. They came to this conclusion by labeling inhibitory synapses in mouse brains with fluorescent proteins and then tracking them for several weeks using a specialized microscope. They then closed one of the mice’s eyes temporarily to accustom them to seeing through just one eye. After a few days, the area of the brain that processes information from both eyes began to respond more actively to the open eye. At the same time, many of the inhibitory synapses disappeared and were later replaced by new synapses.
Inhibitory synapses are essential for the way networks function in the brain. “Think of the excitatory synapses as a road network, with traffic being guided from A to B, and the inhibitory synapses as the matrix signs that regulate the traffic,” explains research leader Christiaan Levelt. “The inhibitory synapses ensure an efficient flow of traffic in the brain. If they don’t, the system becomes overloaded, for example as in epilepsy; if they constantly indicate a speed of 20 kilometres an hour, then everything will grind to a halt, for example when an anaesthetic is administered. If you can move the signs to different locations, you can bring about major changes in traffic flows without having to entirely reroute the road network.”
Inhibitory synapses play a immensely influential role on learning in the young brain. People who have neurodevelopmental disorders – including autism – may have trouble forming inhibitory synapses. The discovery that the adult brain is still capable of pruning or forming these synapses offers hope that pharmacological or genetic intervention can be used to manage this process. This could lead to important guideposts for treating autism, but also repairing damaged brain tissue.
Daniëlle van Versendaal, Rajeev Rajendran, M. Hadi Saiepour, Jan Klooster, Laura Smit-Rigter, Jean-Pierre Sommeijer, Chris I. De Zeeuw, Sonja B. Hofer, J. Alexander Heimel, Christiaan N. Levelt. Elimination of Inhibitory Synapses Is a Major Component of Adult Ocular Dominance Plasticity. Neuron, 2012; 74 (2): 374 DOI:10.1016/j.neuron.2012.03.015
Royal Netherlands Academy of Arts and Sciences. (2012, April 30). “Learning Mechanism Of The Adult Brain Revealed.” Medical News Today. Retrieved from http://www.medicalnewstoday.com/releases/244690.php.