Nearly every day, even when she has to wear snowshoes, my friend Ann walks the beach near her home in Maine, where she shares her life with the man she loves. He has early Alzheimer’s. “My favorite place to walk is the littoral zone,” she says. “It reminds me of my life.” The littoral* zone, she tells me, is the area of the shore where the tide comes in and out. The upper part is dry and solid at low tide; at high tide, it’s all either underwater or soft and squishy from the lapping waves.