"...In the 1950s prizewinning biologist and doctor Jonas Salk was working on a cure for polio in a dark basement laboratory in Pittsburgh. Progress was slow, so to clear his head, Salk traveled to Assisi, Italy, where he spent time in a 13th-century monastery, ambling amid its columns and cloistered courtyards. Suddenly, Salk found himself awash in new insights, including the one that would lead to his successful polio vaccine. Salk was convinced he had drawn his inspiration from the contemplative setting. He came to believe so strongly in architecture’s ability to influence the mind that he teamed up with renowned architect Louis Kahn to build the Salk Institute in La Jolla, Calif., as a scientific facility that would stimulate breakthroughs and encourage creativity." (FTB: Treehouses can do the same for your spirit.)

You can read the remainder of the article here (fee). But what it says, if I may summarize, is that:

1) A room with a view of nature promotes focus, and rests the mind. Furthermore, the more green the view, the greater the effect. “We evolved in an environment that predisposes us to function most effectively in green spaces,” says researcher Stephen Kaplan. (A well-designed treehouse will often have a limb or two growing and spouting leaves inside the structure.)
2) Another finding: "students with unrestricted views of at least 50 feet outside the window, including gardens, mountains and other natural elements, had higher scores on tests of vocabulary, language arts and math than did students without such expansive vistas or with primarily urban views." (A treehouse can usually be positioned to catch the best possible view.)
3) Re: The need for natural lighting.. (A treehouse is apt to provide soft natural lighting to the occupant, enhancing the body circadian systems, with a fun interplay of sunshine and leaf shadows).
4) It's equally appropo, if the contours of the interior reflect green, organic shapes as well, and parcularly shuns sharp angular interior corners. (Hey that's a treehouse.)

SO, new science research confirms the long-standing Fine Treehouse Building premises that 1) nature abhors a rectangle and so do we:-); - 2) the tree is the ultimate architect of any treehouse project, to the good of all; 3) "don't get even, get odd"; and 4) we are happier, feel better, think clearer. and create more easily in a tree than in a house or dorm or hotel or most any other structure, period. AND, most importantly, and this is one conclusion science hasn't drawn yet, but I'm betting will soon, which is: The common architectual over-reliance on the use of the rectangular shape, and the 90% right angle, is really square, man, and we're not kidding. Standard home building practices will make you stupid and probably sterile. Seriously, I've noticed many times how much better I felt, i.e. calmer, more peaceful, wiser even, when I was living (sleeping, working, and playing) in my "orginal treehouse" in the Berkeley HIlls, than when I lived totally inside. I still sleep outside (on a screened in porch, our dogs now claiming the treehouse) every night, it is so restful, though not as connected to the Big Wow as being in close contact with a tree, but still very nice. It's no coincidence that Buddha reached enlightment sitting under, and on the roots of, a giant tree. Try it sometime, you'll see!