There were three objectives to the work undertaken
for this paper: (1) to provide a comprehensive characterization
of the statistical properties of arrays of β-cell somata;
(2) to develop a model that simulates cellular arrays with
the same properties; and (3) to use this model to examine
whether the array of β-cells should be viewed as one
array or as two arrays, one each for its OFF- and ON-center
cells. β-cells are morphological correlates of the
electrophysiological X-cells and those β-cells whose
dendrites stratify within the outer and inner sublamina
of the retina's inner plexiform layer correspond,
respectively, to OFF- and ON-center X-cells. Arrays of
peripheral β-cell somata from two retinas were studied.
A Delaunay triangulation and a Voronoi tessellation were
generated for each array and measures derived from these
constructs used to analyze the arrays' spatial organization.
As others have shown previously with a less complete statistical
characterization, we found that the arrays of OFF- and
ON-center β-cells have similar spatial properties and
are more regular than the array of all β-cells. We
developed a model to simulate cellular arrays with spatial
properties like those of arrays of β-cells. A good
fit between model and real arrays was found when the model
assumed an explicit spatial dependence between the placement
of OFF- and ON-center cells. We propose therefore that
a single array of β-cells formed of both OFF- and ON-center
cells is consistent with the data currently available for
β-cell somatic arrays.