Several times when Subject 23 was asked to imagine playing tennis, Monti said, the region of the brain most closely associated with complex motor planning became highly active, and stayed active for 30 seconds after researchers prompted such imagery by saying "tennis."

Similarly, when researchers asked the patient to imagine walking through the house where he grew up and then said the word "navigate," Subject No. 23 responded with bursts of activity in the region of the brain involved in constructing and navigating a mental map.

The young, French-speaking man was the only subject who was then trained to answer simple yes or no questions -- whether his father's name was Paul (yes) or Alexander (no), whether he had siblings and how many -- using the imagery technique he had already learned.

Checking the patient's responses for accuracy and comparing them to the yes-no brain responses of a group of healthy volunteers, researchers discerned that Subject No. 23 was not only still "in there," but capable of purposeful thought and communication.

Gopnik argues that, in many respects, babies are more conscious than adults. She compares the experience of being a baby with that of watching a riveting movie, or being a tourist in a foreign city, where even the most mundane activities seem new and exciting. "For a baby, every day is like going to Paris for the first time," Gopnik says. "Just go for a walk with a 2-year-old. You'll quickly realize that they're seeing things you don't even notice."