Fig. 6.

Detection and assessment of faces in neurite skeletons for use in the branch-count correction. (A) A cultured neuron demonstrating three types of simple neurite contacts: t, tip-to-neurite; d, tip-to-tip; x, neurite crossover. (B) Neurite skeleton depicting all faces resulting from neurite contacts. The unbounded face is beige and bounded faces are other colors. The tip-to-neurite contact at t causes the light green face; the tip-to-tip contact at d causes the lavender face; and the crossover at x causes the red face. (C) Enlargement of a self-fasciculating region of a cultured neuron. Note that the distance between adjacent neurites varies, resulting in periodic contacts in the neurite skeleton. (D) View of the whole neuron. (E–F) Corresponding neurite skeletons with each face a different color. Faces are labeled based on their classification by size and shape: s, small; m, medium; e, elongated medium; L, large. (E) Enlarged view of faces along a region of self-fasciculation. The series of adjacent small faces results from self-fasciculation rather than from tip touching. They are categorized as F₁ faces and are excluded from the branch-count correction as desired. The two elongated faces are categorized as F₂ faces and are excluded from the branch-count correction. This is the desired outcome for the purple elongated face, but not for the rose face which results from a tip-to-neurite contact. (F) View of all faces in the neuron. Note that the large faces, non-elongated medium faces, and isolated small faces often result from tip touching. Using categorized faces to correct for obscured neurite tips improves the branch count estimate: 13 of the 15 faces in panel (B) and 4 of the 12 faces in panel (F) are added to the respective endpoint counts.