The study of consciousness is a long-standing central challenge in the relationship between the brain and the mind. One key step towards understanding consciousness is to empirically narrow down neural processes associated with the subjective experience of a particular content (neural reductionism). The fundamental methodological problem in consciousness research is the subjectivity of the target phenomenon― the fact that conscious experience is always tied to an individual, first-person perspective. The core empirical question is whether and how physical states of the human nervous system can be mapped onto the content of conscious experience. The search for the neural correlates of consciousness (NCC) has become a highly active field of investigation in recent years. In functional imaging studies, several regions have been proposed to constitute possible candidates for NCC. Extended reticular-thalamic activation system, 40-hertz rhythmic activity in thalamocortical systems, and neurons in the visual cortex projecting to prefrontal areas are possible candidates for NCC. Recent advances in neuroimaging methods are now allowing scientists to obtain new information about NCC. The brain can be understood as a complex system or network, in which consciousness emerges from the interaction between multiple physical and functional levels. This emergent property of consciousness is the challenge that must be addressed in modern science. This review briefly introduced various academic perspectives on the problem of human consciousness, which have been studied by many philosophers and brain scientists up to now and reviewed the results of recent studies on consciousness from a neuroscientific perspective.