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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