Architectonic characteristics of visual areas 17 and 18. Coronal sections from occipital cortex were processed for (A) Nissl substance, (B) synaptic zinc, (C) parvalbumin (PV), (D) neurofilaments with the SMI-32 antibody, or (E) the vesicle glutamate transporter 2 (VGluT2). The boundaries of proposed cortical areas are shown on a dorsal view of a squirrel brain in panel F. The vertical line through areas 17 and 18 indicates the locations where sections were taken for panels A–E. The blue line marks the regions shown in these sections. Occipital areas 17, 18 and 19 are adopted from Brodmann (1909). 17u refers to the monocular region, while 17b refers to the binocular region of area 17. Arrowheads mark architectonic boundaries. Short lines under 17/18 arrow heads separate cortical layers 1–6. See table 1 for abbreviations for other areas. The scale bar for brain sections (panel E) = 2mm. The scale bar on the brain (panel F) = 5mm. Sections were from squirrel 06-18.