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The brain is deeply connected.
The brain gets its resilience from being a deeply connected network in which
information has many ways of navigating from one point to another. Consider the analogy to the
Internet, which
has become increasingly stable as the number of its constituent nodes has increased. Nodes, even entire hubs of
the Internet, can become inoperative without ever bringing down the entire network. Similarly, we continually
lose neurons without affecting the integrity of the entire brain.
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The brain does have an architecture of regions.
Although the details of connections within a region are initially
random within constraints and self-organizing, there is an architecture of several hundred regions that perform
specific functions, with specific patterns of connections between regions.
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The design of a brain region is simpler than the design of a neuron.
Models often
get simpler at a higher level,
not more complex. Consider an analogy with a computer. We do need to understand the detailed physics of
semiconductors to model a transistor, and the equations underlying a single real transistor are complex.
However, a digital circuit that multiplies two numbers, although involving hundreds of transistors, can be
modeled far more simply, with only a few formulas. An entire computer with billions of transistors can be
modeled through its instruction
set and register description, which can be described on a handful of written pages
of text and mathematical transformations.
The software programs for an operating system, language compilers, and assemblers are reasonably complex, but
modeling a particular program—for example, a speech-recognition program based on Markov modeling—may be
described in only a few pages of equations. Nowhere in such a description would be found the details of
semiconductor physics. A similar observation also holds true for the brain. A particular neural arrangement that detects
a particular invariant visual feature (such as a face) or that performs a band-pass filtering (restricting
input to a specific
frequency range) operation on auditory information or that evaluates the temporal proximity of two events can be
described with far greater simplicity than the actual physics and chemical relations controlling the neurotransmitters
and other synaptic and dendritic variables involved in the respective processes. Although all of this neural complexity
will have to be carefully considered before advancing to the next higher level (modeling the brain), much of it can be
simplified once the operating principles of the brain are understood.