A, B: Median nearest neighbor distance between feedback cells in the
supragranular (A) and infragranular (B) layers of areas 18, 19, 21, and Ssy as a
function of age. Median NND increases monotonically at the same rate in all
areas. Regression lines are plotted for each visual area. Error bars represent
±SEM C: Conformity ratio (mean NND/Standard deviation of NND) in supra-
and infragranular layers of each area as a function of age. This measure of
regularity of spacing between feedback cells remains unchanged with age, and
provides no strong evidence for a nonrandom distribution of cells.