Thursday, June 28, 2012

Brain Networks

The human brain contains 100 billion (10^11) neurons, which combine to form almost 1 quadrillion (10^15) electro-chemical connections. Neurons are also affected by chemical signals that come via the blood, interstitial tissues, and glial cells. If we had to understand all the activity in the brain in order to understand the brain itself, we would be lost.

Fortunately, the brain organises itself in specific ways which simplify the task of discovering how the brain works.
2007 M. Raichle PNAS
The image above reveals particular nodes which participate in important brain networks. It is important that these nodes are able to communicate with other nodes participating in specific networks. Loss of nodes -- or the communication links between them -- can have devastating effects on normal brain function.

2011 van den Heuvel and Sporns Jnl Neurosci
The image above reveals the complexity of an average "connectome" which intervenes between the brain nodes participating in the 12 most important brain networks -- as measured by numbers of connections and activity levels. These networks begin to develop sometime between the 20th and 36th weeks of pregnancy.
Teasing out these connections, and following their activity in real time, is quite difficult work. But it is nothing when compared to the effort involved if one tried to follow the activity of 100 billion neurons simultaneously.

It is not only the ability of the brain nodes to function that counts, it is also vital that the nodes be able to communicate with each other. Depending upon which nodes or interconnections are disrupted, different types of alteration in normal brain function will take place.

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