Why the brain folds where it does

Jack Scannell J.W.Scannell at ncl.ac.uk
Tue Apr 8 23:21:20 EST 1997

Folds are the most obvious and striking anatomical feature of the
cerebral cortex of many mammals.  Folds follow from the need to fit a
large cortical sheet into a small head, but this explains neither their
pattern, nor why they provide useful landmarks to the location of
cortical areas.  If fold placement serves to reduce white matter volume
and conduction delays, the space on convex folds (gyri) should be
occupied by densely inter-connected areas, leaving the concave folds
(sulci) between sparsely connected areas.  Analyses of connection data
from the cat and macaque show that connections between nearby areas
within gyri are indeed significantly denser than connections between
nearby areas separated by sulci.  Thus the development of the cortex
coordinates folding with connectivity in a way that produces smaller,
faster and cheaper brains. 

see http://www.psychology.ncl.ac.uk/jack/gyri.html for full details.

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