Plane of section effects on data transfer from histological section of experimental brain (En, black) to reference Atlas Levels (R1-R3, red and light red). Morphological features (b, c, g, m, y) of the brain are assumed to be the same in the experimental and atlas brains, and for simplicity the problem is reduced from three dimensions to one. A. If experimental data (En, black) is warped or transferred (thin black arrows) to a single Atlas Level (R2, red), misidentifications occur (structure b as m, and y as c), and their magnitude increases with greater angle between the two sections, with greater distance from the point of intersection in structure g, and with smaller and/or more convoluted morphological features. B. Transfer error is reduced significantly if data from the experimental section is mapped onto segments (A-C, red) of three adjacent Atlas Levels (R1-R3) instead of one (R2, Fig. 3A), although distortions remain (indicated by the horizontal black arrows, especially obvious in the blue rectangle. Adapted with permission of the Publisher (Elsevier) from Swanson (2004).