Why Shirley MacLaine Doesn't Think About Who She Wants to Be in Her Next Life (Exclusive)

Shirley MacLaine was having a major moment in 1983, the year she starred in Terms of Endearment, the movie for which she would finally win the best actress Oscar on her fifth nomination.

That was also the year she released Out on a Limb, a groundbreaking, esoteric nonfiction book that delved into aspects of her spiritual journey, most famously her belief in reincarnation. For a moment, MacLaine became as famous for what she wrote about her past lives as she was for her accomplishments in this one, and she was at once praised and ridiculed for her openness.

MacLaine's latest book, The Wall of Life: Pictures and Stories from This Marvelous Lifetime stays true to its title and doesn't venture outside of her current life, except for when she writes about her parents and grandparents.

But MacLaine, 90, tells PEOPLE, that although she does "wonder about how long" she has left, she hasn't put too much thought into what will happen in her next life.

"Oh, honey, I don't know," she says when asked who she would like to be the next time around. "I can't do that. I've got to spend some time in heaven first."

In The Wall of Life, MacLaine writes about laying out her spiritual leanings to the public in her 1983 book and in the 1987 TV miniseries based on it: "I was never nervous about being open about any of that; people came up to me regularly and said the book changed their life, knowing that someone else thought the same way or believed the same truth."

MacLaine devotes just one page of the 243-page book to Out on Limb. The rest of it covers her life, career, friendships and loves through never before-seen-photos and revealing anecdotes and musings.

The project was inspired by a wall of in her home that's covered with decades worth of meaningful personal photos.

"One day I was looking at my wall of pictures and just taking everything into consideration specifically," she says, "and I thought I should write about this — and that's what happened."

"Because I've had an enchanted life," she adds. "By looking at my wall that day, I realized the enchantment. I really have, and I really mean it. I felt that way. So it's something that comes out of appreciation."

The Wall of Life came out on Oct. 22 from Crown Publishing and is available now, wherever books are sold.