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Invariant area-interconnectedness

Principles of connectivity and parcellation in neocortex, and Why there are as many cortical areas as there are. Mark Changizi Sloan-Swartz Center for Theoretical Neuroscience Caltech http://www.changizi.com changizi@caltech.edu. a. Invariant area-interconnectedness. b.

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Invariant area-interconnectedness

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  1. Principles of connectivity and parcellation in neocortex,and Why there are as many cortical areas as there are.Mark ChangiziSloan-Swartz Center for Theoretical NeuroscienceCaltechhttp://www.changizi.comchangizi@caltech.edu

  2. a Invariant area-interconnectedness b Invariant area-infiltration Well-connectedness hypothesis

  3. ~A~N1/2 ~N1/2 Economical well-connectedness implies

  4. Area-area connectivity

  5. Predict that… total number of area-area edges ~ #areas2.

  6. Predict that… area-degree ~ N1/2

  7. Therefore… Area-networks are, up to a constant factor, fully-connected, independent of the number of areas.

  8. Parcellation

  9. Percent sizes of all areas versus network size a b Average percent size versus network size Predict that… # areas ~ N1/2

  10. Therefore… One main driver of neocortical parcellation is the size of the brain alone, independent of the “complexity” of the brain, or the number of specialized functions it computes. But…

  11. Changizi, 2003 Parcellation also increases with behavioral complexity Aside… Encephalization “measures” behavioral complexity

  12. Distinctive scaling of V1 and V2

  13. Conclusions • Area-networks are, up to a constant factor, fully connected. • For reasons of economical well-connectedness, independent of functional reasons, the number of areas increases as the square root of neocortex network size. • But more areas also in “smarter” mammals. (Each explains approximately half the variance.) • V1 and V2 fill invariant fraction of neocortex, whereas the typical area fills a smaller and smaller fraction of larger neocortices. • These features may not be unique to neocortex…

  14. a Neocortex b Electronic circuits c Web sites How connectivity scales in other networks as well Diameter  2 Diameter  1.6 Diameter  6

  15. How area-area connectivity scales in other networks a b Area-area connectivity versus # areas Area-degree versus network size Neocortex Neocortex Computer software Computer software

  16. How parcellation scales in other networks Neocortex a b Computer software c Universities

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