Brain imaging technologies are increasingly used to find networks and brain regions that are specific to the functional realization of particular aspects of the self. The assumptions underlying this view are challenged in this chapter by first showing how a Cartesian framework underlies the interpretation and usage of brain imaging technologies as functional evidence. To illustrate how material-technological inventions and developments can have a significant and lasting impact on views of the self, it is demonstrated how this framework was influenced by another technology: the camera obscura. Subsequently, it is argued that brain imaging technologies challenge the idea that privileged access to the self can be obtained merely through introspection, indicating a strong discontinuity between the Cartesian and the current neuroscientific framework. Building on these insights, the self is reframed in terms of self-formation. Instead of offering representational knowledge of an “inner self,” the potential use of brain imaging technologies within this framework lies in their capacity to offer what can be called “extrospective knowledge” that pragmatically can contribute to self-formation. Brain imaging technologies contribute to this process because they foreground our neurophysiology, which helps to critically integrate biological aspects into self-formation.