Sunday, May 13, 2012
Saturday, May 12, 2012
Why don't we normally hallucinate?
In the brain, the firing of a neuron can either encourage or prevent the firing of its connected neighbors, which means that neurons can act as both activators and inhibitors, making Turing patterns possible. In fact, the researchers suggest that if the visual cortex had a slightly different structure, the Turing mechanism would produce spontaneous neural patterns in it all the time, leading to permanent hallucinations. While this might be fun, it would barely let us see our surroundings. "There would be strong selection pressure against people who think they are seeing weird spiral patterns when in fact what is in front of their face is a hungry tiger!" explains Goldenfeld. Instead, the researchers posit that the topology of the visual cortex does not allow the "inhibitor" signals to travel long distances, which is a requirement for the Turing mechanism. This prevents the Turing mechanism from working properly, giving neurons uniform diffusion patterns rather than geometric Turing patterns. Without the Turing mechanism to create interfering neural excitation patterns, the dominant patterns will be based on external stimuli: namely, normal visual signals from the eyes.