![]() In particular, fMRI studies have found evidence of 3D-structure-from-motion processing in human but not macaque intraparietal sulcus ( Vanduffel et al., 2002) and sensitivity to the observation of tool use in human but not macaque anterior inferior parietal cortex ( Peeters et al., 2009). Studies in macaques reveal a similar network, but with relatively greater frontal activation and less parietal activation during grasping observation ( Nelissen et al., 2005) and relatively greater prefrontal activation when viewing objects ( Denys et al., 2004). Human neuroimaging studies have identified a distributed frontoparieto–occipitotemporal network involved in the observation of object-directed grasping actions ( Iacoboni et al., 1999 Buccino et al., 2001 Caspers et al., 2010 Jastorff et al., 2010 Molenberghs et al., 2012). This faculty for object-mediated action creates a new medium for the elaboration of human culture and cognition and may provide a foundation for key aspects of human uniqueness ( Schiffer, 1999 Clark, 2008 Iriki and Sakura, 2008). ![]() We manipulate and alter objects individually and cooperatively create and use tools and understand, learn from, and copy each other's object-related actions in ways that other species do not. Humans' manual interactions with objects are part of what sets us apart from the rest of the animal kingdom. This indicates a more “bottom-up” representation of observed action in the human brain and suggests that the evolution of tool use, social learning, and cumulative culture may have involved modifications of frontoparietal interactions. Chimpanzee activation showed a prefrontal bias, including significantly more activity in ventrolateral prefrontal cortex, whereas human activation was more evenly distributed across more posterior regions, including significantly more activation in ventral premotor cortex, inferior parietal cortex, and inferotemporal cortex. However, in a direct chimpanzee/human comparison, we also identified unique aspects of human neural responses to observed grasping. ![]() ![]() Like humans and unlike macaques, these regions were also activated by observing movements without results. Performance and observation of the same action activated a distributed frontoparietal network similar to that reported in macaques and humans. We compare activations during performance of an object-directed manual grasping action, observation of the same action, and observation of a mimed version of the action that consisted of only movements without results. To study the evolution of this system, we performed functional neuroimaging in humans' closest living relatives, chimpanzees. In humans and macaques, observing object-directed grasping actions activates a network of frontal, parietal, and occipitotemporal brain regions, but differences in human and macaque activation suggest that this system has been a focus of selection in the primate lineage. The human faculty for object-mediated action, including tool use and imitation, exceeds that of even our closest primate relatives and is a key foundation of human cognitive and cultural uniqueness.
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