A computer technique for the estimation of the absolute three‐dimensional array of basal dendritic fields using data from projected histological sections

SUMMARY The standard projection methods of dendritic field analysis have revealed that dendritic density decays exponentially with increasing distance from the centre of the perikaryon and present ideas about dendritic connectivity are largely based on this theory. However, inherent in the projection method are a series of errors which have not hitherto been defined and which indicate that much of the data obtained by the projection technique may be an artefact of the method itself. However, it is possible, given the projection data from a sample of neurons, to extrapolate the three‐dimensional array of dendritic fields by employing a computer technique. In this technique the perikaryon is enclosed in concentric spheres set 20 mμ apart and dendritic endings ( E ) and branching nodes ( B ) are positioned within the volume of the total sphere according to known distributions. The number of dendritic intersections ( I ) at the surface of the n th concentric sphere can be calculated given the number of primary dendrites from the relationship; I ( n − 1) + B n — E n . These numbers may then be corrected for the distortion due to projection and sectioning. Comparison of these corrected data with those obtained from conventional histological methods suggests that the distribution of dendritic parameters may be quite different from the conventionally held view and that the decay of dendritic density is not exponential.