Do you have a lemon in your kitchen? Put this magazine down for a moment, go cut the fruit in half, and squeeze some juice into your mouth. Notice how you react.Don’t have a lemon? Try this little thought experiment: Imagine that you have one. Picture yourself slicing through the bright yellow rind, exposing the translucent fruit inside. See yourself holding it up, squeezing it, and letting a stream of tart juice splash onto your tongue. Can you feel yourself puckering and salivating—not in your mind’s eye, but in “real life”?Western thinkers have tended to draw a line between reality—that which we “actually” experience—and imagination, seen as a frivolous, dreamlike diversion. For millennia, though, spiritual contemplatives and artists have taken flights of fancy much more seriously and challenged the firmness of that line. And surprising recent advances in neuroscience, particularly in the field of brain scanning, have added support to their conviction that our imagination and sense of reality are closely intertwined.In some ways this is obvious. Back in 1928, the sociologists W. I. Thomas and D. S. T …