Sholl analysis

"In order to study the way in which the number of branches varies with the distance from the perikaryon, it is convenient to use a series of concentric spherical shells as co-ordinates of reference.

[1] Sholl appreciated that his method is good for comparing neurons, for instance in figure 8[1] the differences in the number of dendritic intersections correlated with distance from the cell body is compared between neurons from the motor and visual cortex.

Sholl also realized his method is useful to determine where and how big is the region where synapses are possible, something he called the neuron's 'connective zone'.

[2][3] Curves produced from the 'number of intersections vs. distance from the cell body data' are usually of somewhat irregular shape, and much work has been done to determine appropriate means of analyzing the results.

[1] Sholl's Regression Coefficient is the measure of the change in density of dendrites as a function of distance from the cell body.

Using the Sholl analysis, a mathematical algorithm named the branching index (BI) has been described to analyze neuronal morphology.

[8] The BI compares the difference in the number of intersections made in pairs of consecutive circles of the Sholl analysis relative to the distance from the neuronal soma.

Several software packages perform Sholl analysis, namely those dedicated to neuronal tracing.

An open-source implementation for the image processing package Fiji can be used to perform the analysis directly from microscope imagery of neurons or their traced reconstructions.