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Lateral Inhibition: Our Senses Making Use of an Unbalanced Network

Our bodies are fine-tuned to detect edges tactilely. The millions of sensory neurons in our fingertips seem to work together to give us the ability to tell exactly where the edge of the table is, differentiate the thickness of a dime from that of a quarter, and even read braille. As it turns out, though, the sensory cells in our fingertips don’t work together. In fact, the only reason that we can sense edges and dots so well is the fact that our sensory cells work against each other. This phenomenon is known as lateral inhibition. When one sensory cell is activated by touching something, it chemically inhibits all of its neighboring neurons, allowing our brains to easily comprehend where edges are based on which neurons are firing more than usual and which have ceased firing altogether (there is always a baseline level of firing when nothing is being touched to allow for this).

Lateral inhibition is an example of an unbalanced network actually being put to good use. If one were to draw a graph of the neurons in relation to each other, with the nodes being sensory neurons and the edges being synaptic connections, it’s easy to see that this network is unbalanced. Assuming that each cell only shares edges with its neighbors, every triangular section of the network consists of three negative (enemy) edges. In fact, every edge in this network is negative. The basis, in general, for this setup being considered unstable is that two nodes will eventually team up on the third and form a positive relationship with each other. This does not occur with these cells, of course, because they cannot make the conscious decision to do so. It’s a good thing that the network remains unbalanced, too, or else our image of the world would be much blurrier.

http://library.iyte.edu.tr/tezler/master/malzemebilimivemuh/T000533.pdf

http://courses.washington.edu/psych333/handouts/coursepack/ch11-Somatosensory_system_and_topographic_organization.pdf (page 73)

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