On a summer night you can see the lantern lights gliding like fireflies along the streets of Salem, Mass. They look disembodied in the late evening gloom, but when you walk closer you can discern that each lantern is held aloft by a woman in long skirts, doing her best to look like a 17th-century crone. Pulling along a tail of sheepish, smirking tourists in their T-shirts and shorts; making the rounds of the town’s “ghost sites.”

I recently spent most of a week in Salem — or “the Witch City,” as it styles itself today. Each day, I would take my mother to her appointments with one doctor or another, then come back to my hotel and stroll in the stultifying night air, observing all the spectral doings around the downtown pedestrian mall.

Salem, you see, long ago gave up trying to overcome the stigma of brutally executing 20 men and women for the crime of witchcraft. Silhouettes of witches riding broomsticks adorn the local newspaper and the shoulder patches of town police officers; and the high school team’s nickname is the Witches. The downtown mall is lined with shops carrying all your Goth and New Age needs, along with witch chatchkes of every conceivable variety. Some of these approach a sort of Zen perfection in their witlessness, such as my personal favorite, a bumper sticker that reads LIFE’S A WITCH AND THEN YOU FLY. There is even a prominent statue of Elizabeth Montgomery, star of the 1960’s sitcom “Bewitched.”

Actually, Salem is quite a beautiful town in that way that only neat, prosperous New England towns can be. It has streets full of fine old federal homes, a first-class art museum, and a broad, tree-lined common. But hey, witches sell. I know how it is. I grew up not far from Salem, in another gorgeous little town along the North Shore of Massachusetts called Rockport, which decades ago saw its granite-cutting business collapse and reinvented itself as a tourist haven. Our civic fathers weren’t prescient enough to have executed any innocent old women, so we had to fall back on shops selling fudge, bad paintings and statues of sea captains sculpted from lobster shells. You do what you must to survive in postindustrial America, and this is a very gracious corner of the world, no matter how it’s financed.

I get back here much more often than I used to, to see to my mother, who suffers from late-onset Huntington’s disease and lives in an assisted-living facility in the area. Huntington’s is a merciless affliction, one that steadily shrinks the brain and erodes the sufferer’s physical and mental capabilities as it progresses. In my mother’s case, it has stripped away her personality one layer at a time. A shy, dignified, genial woman her entire life, she was suddenly prone to fits of irrational anger; a near teetotaler, she developed an overwhelming desire to drink, no doubt to try to cope with the organic changes going on inside her head.

With the help of medication, these symptoms have been contained, but nothing can halt the course of the disease. It fills me with sorrow whenever I see my mother, noting silently what new deterioration there is, the basic things she no longer knows how to do, the favorite family anecdotes she no longer can recall. Once a voracious reader, she has trouble concentrating on the copies of Science News she still buys. Poised and attractive enough to have worked as a model in New York when she was a young woman, she now walks with an awkward gait, throwing her arms out to the side to keep her balance. She is no longer the woman I knew.

And yet the time I spend with her feels so worthwhile. My sisters and I visit her regularly, and talk on the phone with her every day, but I know that she still feels confused and abandoned. At age 76, this is the first time she has had to live among strangers without some sort of family around her. She always seems delighted to see me, to get out. She keeps referring to our endless rounds of doctor visits as a “vacation,” and she is ebullient as we go from one appointment to the next. I have to keep her from talking to people on the street, or reaching out to touch them — a heedless gregariousness that has also come late in life.

She has insisted on removing all her makeup and nail polish for the doctor appointments, despite the dozen or so times I have told her it isn’t necessary, and now she frets repeatedly over when she can put them back on. Huntington’s is all about forgetting and obsession, at the same time. She worries over how she has done on a cognitive test, but submits patiently to more exams intended to measure her hand-eye coordination, her balance, the size of her brain. A doctor brings me into a viewing room where I can see her having an M.R.I., but I can glimpse only her shoes, sticking out from a blanket that covers the lower half of her body in a darkened room. The doctor tells me to wave, that she can see me in a mirror. I do, but there is no response, and the M.R.I. technician wonders if she is sleeping. Later, she tells me that she thought she had seen me, but she wasn’t sure if the image was real.

Each day, I take her to lunch and she always orders the same thing — a lobster roll — and seems delighted with it. We talk as best we can together, and everything seems almost like it used to be. But I am thrown into a momentary panic when, in a cab stuck in Boston traffic in this awful heat, she suddenly becomes short of breath. Walking out on a Charlestown street just after her M.R.I., I look away for just a moment and she steps on a ridged manhole cover and goes down as if she’s been shot, bruising an arm, a leg and her forehead. She looks dazed, but insists cheerfully that she’s fine. When I’m finally convinced that nothing’s broken and she’s able to walk, we proceed very carefully to the restaurant down the street, with her holding tightly on my arm. Once inside, she seems fully recovered, nibbling happily at her lobster roll, holding a napkin full of ice on the bump over her eyes. I sit across from her and watch her closely as I always do when she eats now, knowing that Huntington’s patients have atrophied throat muscles and are especially vulnerable to choking.

I doubt that my experiences are too different from what countless sons and daughters go through now, in this age of longevity. But this is a disease that no one even suspected was in our family until it manifested itself in her, and it has come as something of a shock. Looking at my mother, it’s hard not to imagine her future, or my sisters’ and mine. All of us have an even chance of inheriting this, and not necessarily in old age. But this sort of thinking is not useful; better to get what enjoyment I still can out of the company of someone who has meant so much to me.

At night, I take my mother back to her assisted-living facility and return to my hotel in Salem. The night air is truly smothering, as hot as it has been back in New York, as hot as I can ever remember it in New England. Still, I take a long walk around the lovely common and the pedestrian mall, and think about the past, and how it changes on us. Watching the lantern lights glide along like fireflies, until they are gone in the darkness.