Fig. 1

a A block of cerebral cortex tissue isolated from Brodmann area 47. The arrows point to one of the pencil fibers that prominently extend into the cortical grey matter. The inset labeled ‘D’ is shown at higher power in panel (d). b Same image shown in panel (a) in which the outline of the pencil fibers is delineated with a black line. c A section of tissue obtained from the block stained for Nissl substance. Arrows in panel c point to the location of the pencil fiber that is also indicated with arrows in panel a. The inset labeled ‘D’ is shown at higher power in panel (d). d Higher power magnification of the inset shown in panels (a) and (c). This image shows the histology within the pencil fibers. Glial nuclei are observable in the Nissl, but not neurons. Scale bars: a–c 600 μm; d 150 μm