The article presents a review of modern studies of the hippocampus’s functions in the implementation of cognitive phenomena, a review which covers a wide range of experimental areas, including high-precision brain morphometry, functional neuroimaging, electroencephalography, deep navigational electrode implantation, and dosed radiation effects on the brain. Literary sources demonstrate the involvement of the hippocampus in almost all spheres and aspects of human mental activity, from memory to eye movements, from circadian rhythms to spatial navigation. The literature review allows us to generalize the results of many works and to speak about the basic characteristic of the hippocampus’s functional activity in information processing: that the hippocampus is a comparator which continuously marks impressions of the current experience according to the degree of novelty. The authors see such a functional analysis as much more productive than attempts to correspond brain structures with mental processes (perception, memory, attention) and, accordingly, than the customary discussion in the scientific literature of the hippocampus functioning mainly as a brain substrate of memory