Primate cognition requires interaction processing. Interactions can reveal otherwise hidden properties of intentional agents, such as thoughts and feelings, and of inanimate objects, such as mass and material. Where and how interaction analyses are implemented in the brain is unknown. Using whole-brain functional magnetic resonance imaging in macaque monkeys, we discovered a network centered in the medial and ventrolateral prefrontal cortex that is exclusively engaged in social interaction analysis. Exclusivity of specialization was found for no other function anywhere in the brain. Two additional networks, a parieto-premotor and a temporal one, exhibited both social and physical interaction preference, which, in the temporal lobe, mapped onto a fine-grain pattern of object, body, and face selectivity. Extent and location of a dedicated system for social interaction analysis suggest that this function is an evolutionary forerunner of human mind-reading capabilities.

Recognition of a particular individual occurs when we reactivate links between current perceptual inputs and the previously formed representation of that person. This recognition can be achieved by identifying, separately or simultaneously, distinct elements such as the face, silhouette, or voice as belonging to one individual. In humans, those different cues are linked into one complex conceptual representation of individual identity. Here we tested whether rhesus macaques (Macaca mulatta) also have a cognitive representation of identity by evaluating whether they exhibit cross-modal individual recognition. Further, we assessed individual recognition of familiar conspecifics and familiar humans. In a free preferential looking time paradigm, we found that, for both species, monkeys spontaneously matched the faces of known individuals to their voices. This finding demonstrates that rhesus macaques possess a cross-modal cognitive representation of individuals that extends from conspecifics to humans, revealing the adaptive potential of identity recognition for individuals of socioecological relevance.cross-species | vocal communication | nonhuman primates | picture recognition I n humans, both faces and voices convey information about identity, providing some of the many cues we use to recognize individuals we know (1). The multifaceted nature of identity code suggests that a complex cognitive representation binds semantic information with information of different sensory modalities. In rhesus monkeys, however, it has typically been assessed only via single-modality information. For instance, rhesus monkeys can discriminate between calls of two conspecifics in a playback experiment using a spontaneous habituation-discrimination paradigm (2). They are also able to discriminate faces of two conspecifics in a match-to-sample task (3) and monkey faces or human faces in visual paired comparison tasks (4-6). These observations demonstrate that monkeys can discriminate idiosyncratic characteristics ("individual A is different from B") for their own or other species. However, they do not provide evidence of individual recognition ("this is individual A, this is B"). In comparison with discrimination, individual recognition requires an additional associative level that allows retrieval of information belonging to a specific individual. In rhesus monkeys, coarse recognition processes such as of their own species, kin, gender, reproductive status, or hierarchy are well documented (2, 7-12). However, these rudimentary recognition abilities fail to account for some sophisticated behaviors that are observed in rhesus macaques' societies. In particular, rhesus macaques live in large groups and maintain elaborate social relations involving, e.g., nonkin alliances during aggressive interactions, fight interference, reciprocal support, friendly grooming, and reconciliation (13-15). Such an organization would benefit well from the finest-grain individual recognition based on a cognitive multimodal representation of identity.Individu...

We compare several major white-matter tracts in human and macaque occipital lobe using diffusion magnetic resonance imaging. The comparison suggests similarities but also significant differences in the tracts. There are several apparently homologous tracts in the 2 species, including the vertical occipital fasciculus (VOF), optic radiation, forceps major, and inferior longitudinal fasciculus (ILF). There is one large human tract, the inferior fronto-occipital fasciculus, with no corresponding fasciculus in macaque. We could identify the macaque VOF (mVOF), which has been little studied. Its position is consistent with classical invasive anatomical studies by Wernicke. VOF homology is supported by similarity of the endpoints in V3A and ventral V4 across species. The mVOF fibers intertwine with the dorsal segment of the ILF, but the human VOF appears to be lateral to the ILF. These similarities and differences between the occipital lobe tracts will be useful in establishing which circuitry in the macaque can serve as an accurate model for human visual cortex.