What makes up our sense of self has been an important focus of discussion for centuries. It has vexed philosophers and thinkers who have debated what the self is—and is not—with passion. A few years ago, neuroscientists also entered the fray. Some, such as the neuroscientist and philosopher Georg Nothoff, even attempted to locate the self within the brain. Early efforts were motivated by an intuitive question: if we can localize vision, language, and motor control, why not the self?

With the rise of functional brain imaging in the 1990s, neuroscientists began designing experiments that contrasted self-referential mental states with non-self states. In the scanner, people might be asked to judge whether adjectives applied well to themselves or others—questions such as, “Am I honest?” These studies repeatedly identified activity along the cortical midline from front to back. Because these regions were more active when people thought about themselves than when they performed externally focused tasks, some researchers proposed that they formed a neural core of the self.

This idea gained further traction with the discovery of the so-called “default mode network” of brain regions—a set of interconnected brain areas that become active when the mind is at rest, engaged in introspection, retrieving memories from one’s past, or imagining one’s future. Because these mental activities feel intimately tied to selfhood, this collection of brain areas was sometimes described loosely as the brain’s “self network.” However, problems with this interpretation soon became apparent.

First, the same regions are active during many cognitive tasks that are not necessarily about the self. Second, different kinds of “self” tasks activated overlapping but not identical patterns of brain regions within the network. These findings led many researchers to conclude that what was being localized was not the self, but processes related to self-reference: self-evaluation, autobiographical recall, perspective-taking, and narrative construction. The consensus is that the self has not been localized by these sorts of brain scanning studies.

This comes as no surprise to many people. Daniel Dennett, the philosopher, famously argued that searching for the self in the brain was........

© Time