Mirrors have held a peculiar fascination for people ever since one of our early hominid ancestors looked at her reflection in a pool and noticed an uncanny correlation between her own muscle movements—sensed internally—and the visual feedback. Even more mysterious—and perhaps not unrelated—is our ability to “reflect” on ourselves as the first introspective primates. This ability displays itself in ways as different as the mythical Narcissus looking at his reflection in a lake to Internet pioneer Jaron Lanier's invention of virtual reality to transport you outside your own body.
Intriguingly, neuroscientists have discovered a new class of brain cells called mirror neurons that let you “adopt another's point of view,” both literally and metaphorically (“I see what you mean”). Perhaps such neurons even allow you to look at yourself from another's vantage point, so you become “self conscious” of what you are doing or wearing or even of who you are. It is as if the brain were peering into its own internal mirror.
We take all these abilities for granted, but about a decade ago Eric L. Altschuler and Steve Hillyer, both then at the University of California, San Diego, and one of us (Ramachandran) described a new neurological syndrome called mirror agnosia in which a patient with a small right hemisphere stroke cannot tell that a mirror reflection is not a physical object. Amazingly, these patients will repeatedly try to reach for, pick up or grab the reflection (which they claim is a real item) located in the mirror. Mentally, such patients are otherwise perfectly normal; they continue to have abstract knowledge of mirrors and the nature of their optics. Such patients give us a glimpse into the surreal no-man's-land between reality and illusion, and they help us realize how tenuous our hold on reality is. Mirrors are familiar yet deeply enigmatic.