Neural Modeling: Synaptic Connectivity

Mind Hacks posted a link to an interesting paper (Gray and White Matter in the Brain) that aims to answer the question "What's the reason for brain segregation into white and gray matter?". According to the authors of the paper:

... the optimal design [of the brain] depends on the number of neurons, interneuronal connectivity, and axon diameter. In particular, the requirement to connect neurons with many fast axons drives the segregation of the brain into white and gray matter.

One of the authors, Dmitri Chklovskii, co-authored several other papers on the same subject (Network Motifs: Simple Building Blocks of Complex Networks and Geometry and Structural Plasticity of Synaptic Connectivity). The second paper has a brief summary of three categories of synaptic plasticity and different timeframes associated with those categories (the paper itself focuses on the third category and its implications for the structure of the brain):

  • Changes in pre-existing synapses without alterations of interneuronal connectivity that can be realized within a minute
  • Formation of new spines that takes tens of minutes, and
  • Major remodeling of dendritic and axonal branches, usually occuring on the time scale of days.

Dmitri Chklovskii's page also has information on how optimization theory can be applied to brain design with wiring economy principle being one example of a successful optimization hypothesis.

There is also a paper that presents the map of the whole cortical circuit; the connectivity model from this paper was used in the simulation of a model with the number of neurons there is in a human brain.

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