That would be the precuneus. The precuneus is located on the inside of the brain between the two cerebral hemispheres in the rear region between the somatosensory cortex and forward of the visual cortex, which contains the cuneus. One of the reasons so few people are aware of the precuneus is that it has been difficult to study because it is difficult to access. Moreover, it is rarely subject to isolated injury due to strokes or trauma, such as gunshot wounds.
The precuneus appears to be a recently expanded part of the brain. It is poorly developed in the less developed primates such as New World monkeys. The human precuneus comprises a larger portion of the brain than in non-human primates or other animals. It has the most complex columnar organization and is among the last regions to myelinate.
Mental imagery regarding the self has been located in the forward part of the precuneus with the poster areas being involved in episodic memory. Episodic memory refers to events in our own personal lives. Another area of the precuneus has been linked to visuospatial imagery. Visuospatial imagery is central to many mnemonic techniques.
Functional imaging has linked the precuneus to processes involved in self-consciousness. This includes the important function of reflective self-awareness. For example, it would be involved in comparing ones own personality traits to those of other people.
Not surprisingly the precuneus is involved in many memory tasks, for example when people look at images and try to respond based on what they have remembered in regard to verbal questions about spatial details. It is also involved in source memories such as when you try to remember where you read a particular article or where you saw a particular person. It is believed that the precuneus is involved in a variety of processes in addition to episodic memory retrieval such as attention, working memory, and conscious attention.
One idea is that the precuneus, together with the posterior cingulate is pivotal for conscious information processing. The evidence for this idea comes from the effects of its disruption in epilepsy, brain lesions, and vegetative state. It is also thought that the ventral precuneus is involved with the default mode network, and that this involvement might underlie its role in self-consciousness.
As this research is fairly new some of these ideas should be regarded with caution. But even at this early state of research it is clear that the precuneus is important and and deserves to be more widely known.