Cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase staining in human supratemporal and insular cortex: evidence for multiple auditory areas.

The pattern of cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase activity was studied in the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula of normal human brains. Five dark cytochrome oxidase regions were found: (i) on Heschl's gyrus (area TC of von Economo and Koskinas); (ii) on the planum polare (area TC/TG); (iii) posterior to Heschl's gyrus (within area TA); (iv) on the posterior convexity of the superior temporal gyrus (within area TA); and (v) on the posterosuperior insula (area IB). More lightly stained cortex separated these regions (areas IA, TD, and part of TB). The laminar distribution of cytochrome oxidase activity varied in different areas. Acetylcholinesterase-positive fibers predominated in area TC and pyramidal neurons in areas TA and IA and in parts of TB; a mixture of fiber and neuronal staining was found in TC/TG, TD, and IB. NADPH-diaphorase positive profiles included large darkly stained nonpyramidal neurons, mostly in infragranular layers and in subcortical white matter, small faintly stained cells, and a dense array of fibers. The NADPH-diaphorase staining pattern did not vary between areas. The present results suggest that the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula contain at least eight putative cortical areas. Comparison with activation studies by others suggest that, apart from the primary auditory area, six other putative areas may be auditory whereas one putative area, on posterior insula, may be vestibular.