Approaching this blog, I am reminded of the song in Les Miserables (musical) with the same name as our title. The protagonist, Jean Valjean debates revealing his identity, thereby saving an innocent man, but condemning himself to prison. Questions of slef-identity, like conscience and moral decision, are part of the nebulous properties of "the mind"and are more appropriately in the realm of psychology than neuroscience.
Yet we know that developing human children go through phases of discovering self vs. external world, without the cliche of the teenage who leaves home to "discover himself." A toddler does not *like* the game of peek-a-boo at first, because they have not yet learned that objects don't disappear when the eyes are closed. Later they treat it as a game, discovering that yes, they can close eyes or hide, and the external world remains the same. Newborns are *all* self, and children do not truly learn that there are others that are "not self" until well after they discover language skills. At least one theory of child development attributes this to the learning of symbols - newborn brains process only raw data, and it is not until they learn to group data into symbolic representation that children are capable of learning language, music, art, and to share their crayons.
This skill is associated with brain development in two areas - prefrontal cortex of the Frotnal lobe, and the hippocampus and surrounding parahippocampal areas of the Temporal Lobe. The role of the former is perhaps obvious: Frontal lobe is necessary for executive function, for decision-making, and for abstract thought. Orbitofrontal cortex is involved in prediction and correction (by means of assessing the accuracy of prediction) of behavior, so it likewise is important to development of a symbology of self and nonself. From this you could surmise that hippocampus and amygdala, with their roles in memory processing and assessment of expected vs. actual outcome, would interact with prefrontal areas to develop a "history" of what objects and actions represent consequences of one's own actions, and which outcomes are the result of external factors - and you'd be partially correct.
To gain the other part, we need to examine a lab rat. Well, actually, a LabRat. Up there to the right is Ratface, one of my (fictional) intelligent LabRats that assist me in teaching and writing. Well, the intelligence part is debatable, as you can see, he's always getting in trouble, stuck, trapped, mistaken for a paperweight or even a computer mouse. Ratface has been a laboratory subject for many years, participating in a lot of pharmacological studies of cognitive enhancers, hallucinogens, psychedelics, euphorics and stimulants and is sort of an example for the new public service announcement: "This is your rat on drugs." Yet Ratface's hippocampus does something amazing - it creates and maintains a map of the environment. OK, maybe not unique - since all mammals do so, as well as some birds, reptiles and even a few insects - still the hippocampal map is amazing.
Neurons in hippocampus are content to fire slowly (if at all) most of the time, but some greatly increase their firing when the Ratface is in a very specific place in his surroundings. Neighboring neurons do not necessarily fire in adjacent positions, and the firing can be highly dependent on the context, but the result is a complete map of the surrounding space in what we call a "sparse, distributed network" (meaning it uses a few, widely scattered neurons, and it requires a specific set of connections - a "wiring diagram" if you will - to read it). Neuroscientists have found that the hippocampal mapping system is actually two maps, and it requires lots of sensory input to make it work: vision, hearing, smell, touch, proprioception, and memory of prior movements. The two maps are what are important to today's blog about self: One map is centered on "self" and moves with Ratface through his environment - we call this the "egocentric" map. The other map is structured on the relationship of external objects to each other, and remains fixed no matter where Ratface moves within that environment - this is the "allocentric" map. In the laboratory we can also see that the egocentric map is active no matter what environment Ratface enters (or leaves) and the allocentric map is inactive when Ratface leaves the room, but instantly reactivated. when he returns.
Again this is probably tied to the ability of the brain to handle symbols instead of raw sensory input - the map and all of hippocampal function relies on associations or relationships between places, events and time. Still, the division of the hippocampal map into self-centered and non-self-centered coordinates is an important means by which Ratface can assert that he most definitely is not a mouse - even if he does sometimes get his tail caught in the mousetraps.
So, "self" can be defined in abstract (prefrontal) and physical (hippocampal) terms, and contribute to the sense of identity. As for those folks out wandering the globe trying to "find themselves" - perhaps they just need a map.