Recursive trace line method for detecting myelinated bundles: a comparison study with pyramidal cell arrays

Abstract

Minicolumns are thought to be the smallest cortical modules within the hierarchical organization of the isocortex. Several reports suggest alterations in minicolumnar morphometry may be involved in psychiatric disorders such as autism, dyslexia, and schizophrenia. Thus far anatomical studies of minicolumns have primarily relied on measurements of pyramidal cell arrays. This study expands on a recursive trace line segmentation method used to define morphometric measures for myelinated axon bundles. The results were compared against those of pyramidal cell arrays derived from immediately adjacent serial sections. Width estimates based on cell somas and myelinated axon bundles were highly correlated (r=0.9888). Histograms of signal intensity using the recursive trace line method produced expected features of myeloarchitectonics; that is, bundles of Meynert and intervening interradiary plexus. The close correspondence of derived values for myelinated axon bundles and pyramidal cell arrays suggests their participation and interaction within the same modular arrangement of the isocortex.

Figure 1

Serial 35 μm sections from human cortical area 22, left hemisphere, stained with silver (left) and cresyl violet (right). The scale bar measures 400 μm.

Figure 2

White matter segmentation. (A) Loyez-stained tissue from cortical area 9 of a 6.5 year old male. (B) Upper third of the image following the thresholding step. Pixels in I₂ are white and pixels in I − I₂ are black. (C) The largest connected set of pixels in I − I₂ is extracted. (D) The extracted region is filled-in to make it simply connected.

Figure 3

Convex white matter in a gyrus. Lines outside the white matter are level curves of the Euclidean distance map of the region occupied by white matter. Fiber bundle spacing CW_A is computed using profiles of the image along these level sets.

Figure 4

Columnar structure appears at essentially the same spatial frequency whether determined by cell somata or bundles of myelinated axons. The line CW_A = m CW_S + b is statistically indistinguishable from the identity function.