Regions of the cerebal cortex characterized by a particularly well-developed inner granular layer (layer 4); this type of cerebral cortex is represented by the primary sensory Brodmann area 17 of the visual cortex, Brodmann areas 1-3 of the somatic sensory cortex, and Brodmann area 41 of the auditory cortex. [ http://www.medilexicon.com/medicaldictionary.php?t=47303 ]