Do animals think? What are the mechanisms supporting their behavior? Can we compare these mechanisms with human mind? These questions animate scientific, philosophical and theological debates for millennia. The idea of a fundamental discontinuity between human mind and animal-machine workings, advocated by Descartes, is opposed to Darwin's assumption of continuity that supposes a difference of degree and not of kind between humans' and animals' minds. In this thesis, based on recent theoretical and methodological advances in animal behavior and neuroscience, we go in search of the Rosetta Stone that can inform this debate: a functional neurocognitive homology. Is there a neural mechanism, shared by several species (including humans), supporting the same cognitive function? We focus our research on one of the key functions of human mind, which also seems widespread in the animal world: categorization ability. The making of concepts - to mentally regroup objects, or events we face in categories - simplifies, makes sense and allows responding appropriately to the continuous perceptual streams. Testing humans and macaques in exactly the same protocol of rapid visual categorization, in particular by controlling the influence of contextual information from the visual scene on object categorization performances, we show here that the two primates seem to rely on similar concepts or visual representations to solve this task. More, with a new multivariate pattern analysis for cortical field potentials, we can read, trial by trial, the emergence of neural representations associated with such categorization task. By applying these methods in monkeys, surface EEG in humans and in patients with epilepsy, implanted for medical reasons, we highlight the similar role of the ventral visual pathway to build quick categorical representations, in both species of primates. To summarize, the ability of rapid visual categorization seems to be a neuro-cognitive trait shared by humans and macaques, probably inherited from a common ancestor. The existence of such homology is an argument for the continuity hypothesis and can therefore justify an evolution of cognition. Finally, if we consider the categorization as a key element of human thought, then these results suggest the existence of a thought in macaques, which at least partially works like ours.
