16 October 2016

The Secrets of the Learning Brain

Something must change in our brain to store the information, and how it does so, remains a mystery. Researchers investigated what happens, at the smallest scales, in a single one of the quadrillion (a million times a billion) connections in our brain. By modeling the biophysical processes that take place there, they discovered that the shape of the connections plays a crucial role in regulating their strength. The brain contains billions of interconnected nerve cells. On each of the ‘tentacles’ of these cells, tiny ‘microspines’ reach out to the tentacles of other nerve cells. The point at which they are closest together is called the synapse. At the synapse, the sending nerve cell converts electrical signals into chemical signals, which are picked up at the receiving nerve cell and converted back into an electrical signal so that it may continue its journey. Precisely how this signal transmission is regulated at the synapse is key to our ability to learn and remember. Using models and computer simulations, researchers examined the physical processes that happen on, and in, the microspine.

 
As it turns out, that this particular shape is important – and remarkably effective – in regulating the strength of the connection. For this strength, the number of receptors that are around to relay the signal is crucial. These receptors must, of course, come from somewhere. They are transported in small membrane containers that have to pass through the neck of the mushroom. If it is too narrow, the supply comes to a halt, weakening the strength of the brain connection. So it would appear that the neck of the mushroom is hindering strong connections. Kusters discovered, however, that there is a different side to this story. The receptors are small proteins that are able to move around, exploring the surface of the mushroom. This means that they may spontaneously escape. Narrow necks, it turns out, make it much more difficult for the receptors to drift away. The narrow neck also serves to keep receptors already on the mushroom around for longer. So, the shape of the mushroom controls the balance between supply and loss of receptors, and thereby the strength of the neuronal connection.

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