Extreme Sports, Sensation Seeking and the Brain; Men: The Scientific Truth; Scientific American Presents; by Zorpette; 4 Page(s)

Deep underwater off Grand Cayman Island, I hovered over an ethereal, sandy tableau that sloped steeply away into an inky void. I had dipped into the upper edge of a twilight world seen by relatively few scuba divers, where the abundant hard corals of shallower water begin giving way to a sparser assortment in which large soft corals predominate. Off to my left, a big eagle ray flapped slowly and serenely, its white-spotted black body undulating against the dark-blue background of the abyss.

I glanced at my depth gauge, saw that it read 200 feet (61 meters) and grinned. Breathing a mixture of helium, oxygen and nitrogen from two of the four large tanks strapped to my body, I was beyond the depths that could be visited safely with ordinary scuba equipment and techniques. I was oddly, ineffably elated.