COMPARING RESTING BRAIN GLUCOSE METABOLISM IN MONKEYS, APES AND HUMANS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cognitive neuroscientists have recently turned their attention to the resting state in humans, arguing for the existence of a default neural network that is tonically active at rest. Among the brain areas implicated in this resting state network, the dorsomedial prefrontal cortex is hypothesized to relate to reflecting on the mental states of self and others. Given the complexity of their social lives, as well as their potential capacity for self-awareness, it is possible that great apes also default to a resting state mode that involves thinking about mental states. If so, they should exhibit a similar pattern of resting brain metabolism as seen in human subjects. Here, we use 18F-FDG Positron Emission Tomography (PET) imaging to compare regional cerebral glucose metabolism at rest in monkeys, apes and humans. We collected scans from eight human, five chimpanzee and four macaque subjects. Macaques were scanned with a high resolution, small animal dedicated Concorde microPET scanner (~2 mm FWHM), chimpanzees were scanned with a Siemens HRRT (High Resolution Research Tomograph, ~2mm FWHM)), and humans were scanned with an ECAT EXACT 921 scanner (~5 mm FWHM). The 5% and 1% most metabolically active voxels were identified and compared across species. These analyses revealed common regions of activation across species, as well as species differences in activation that are plausibly related to differences in resting cognition. All three species showed dorsolateral prefrontal cortex (BA 46) activation, only humans and chimpanzees showed activation in medial prefrontal regions related to social cognition, and only humans showed activation in Wernicke's and Broca's areas that might reflect an inner mental monologue at rest.