April 24, 2015

Cross-level cascades

I recently read Hallucinations by Oliver Sacks. It's a fascinating book; one of my main takeaways is that the structure of our brains makes a lot of different types of malfunctions possible (in this case, hallucinations).

Brains can be seen as communication networks. Neurons have synapses and axons which allow them to communicate their local environment to other neurons. In ways that aren't fully understood, this network-level communication leads to perception, consciousness, thought, and memory.

Some hallucinations, such as those that accompany migraines, appear to come from networks of neurons that are firing without the right input. This made me think of Information cascades. In networks, like the brain, the output of a node is related to the inputs it receives, and those inputs often come from other nodes. This structure means that changes in one part of the network can quickly spread and magnify to other parts of the network. In the brain, this can look like a migraine or a hallucination. Different networks have different properties, but most real-world networks are what we call Small-world networks. These networks have certain properties - they allow for complex, deep interactions between neighboring nodes, high-level interactions between groups of nodes, and are robust to interference. However, they are also susceptible to certain problems, and runaway cascades is one of those problems.

Brains (and the people that own them) are part of social networks and organizations, which are in turn part of communities and organizational networks. Both of these are parts of nations, which are part of inter-national networks (other networks could also be identified, such as the cell network, the protein network, the genome network, etc.) At each level, the actions of one "node" or actor can be an input into the actions of others, and can cascade through the network. In social networks, an information cascade could be a chain email, a viral Facebook post, or a new fashion. In general, cascades are kept in check by negative feedback loops, but when the conditions are right, they can spread quickly and distantly.

I've been thinking about ways that cascades can move from one network to another. In the book, Sacks talks about Joan of Arc, and how her visions may have been hallucinations. I thought about how neural cascades in the brain could have led to Joan of Arc changing her behavior, which led to an informational/behavioral cascade in her social network, which led to a cascade in her community, which led to a cascade in her nation, etc.

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