Self is a reference by an individual to the same individual person. This reference is necessarily subjective and it follows that self is a reference by a subject to the same subject. The sense of having a self - or self-hood - should, however, not be confused with subjectivity itself. Ostensibly, there is a directedness outward from the subject that refers inward - back to its "self" (or itself). Examples of psychiatric conditions where such 'sameness' is broken include depersonalization, which sometimes occur in schizophrenia: the self appears different to the subject.
The first-person perspective distinguishes self-hood from personal identity. Whereas "identity" is sameness, self-hood implies a first-person perspective. Conversely, we use "person" as a third-person reference. Personal identity can be impaired in late stage Alzheimer's disease and other neurodegenerative diseases. Finally, the self is distinguishable from "others". Including the distinction between sameness and otherness, the self versus other is a research topic in contemporary philosophy) and contemporary phenomenology (see also psychological phenomenology), psychology, psychiatry, neurology, and neuroscience.
The nationally funded research Center for Subjectivity in Copenhagen, Denmark, is just one example of the importance of research on/into the self. More recently, the relationship between the self and technology has generated a research field called Technoself Studies. Although subjective experience is central to self-hood, the privacy of this experience is only one of many problems in the philosophical and scientific study of consciousness.
The insula is an area in the brain, which is located below the neocortical surface of the brain, in the allocortex. It appears to be involved in self-reference. In addition, mirror neurons are neurons that fire both during the self performing a task and when watching someone else (other) executing the same task.