Cytochrome oxidase 'blobs' and other characteristics of primary visual cortex in a lemuroid primate, Cheirogaleus medius.

We recently obtained the brain of a rare lemuroid primate, Cheirogaleus medius. The brain was not perfused before death, but rather fixed by immersion shortly thereafter. In both flat-mounted and transversely sectioned tissue, we were able to clearly demonstrate periodic zones of high cytochrome oxidase (CO) activity in the primary visual cortex, resembling the so-called 'blobs' described in many other primate species. Our results contrast with a previous report indicating that blobs are absent in Cheirogaleus medius and provide support for the view that blobs are an evolutionary specialization of primate visual cortex that evolved only once, early in primate history. In other aspects of architectonic organization, area V1 of this Cheirogaleus individual closely resembles that of other strepsirhine primates, such as Galago. We were able to identify additional divisions of cortex in this individual, including the middle temporal visual area (MT), auditory cortex, and the primary somatosensory area (S1 or area 3b). These observations indicate that valuable neuroanatomical information can, in favorable cases, be obtained from rare mammalian species that die of natural causes in captivity or which must be euthanized, even though the animals have not been perfused.