rowing up, I didn’t know what was wrong with my mother. I was 25, maybe 26, when I learned she had a lobotomy. I am still trying to make sense of it.

My mother had two brain tumors. The first one, in July 1945, was operated on in Oklahoma City and she survived, her bright mind intact. The second one, in November 1953, occurred when she was pregnant with me. Shortly after I was born, my mother flew from San Diego, where we lived, to Oklahoma City. This time there was trouble during surgery, and to staunch the trouble they took both her frontal lobes.

I never knew my mother when she was well, but I do know that after the lobotomy, she was never the same. She developed grand mal epilepsy. She could not taste or smell. She drank like a fish and cursed like a sailor. Her short-term memory was shot, her vocabulary frozen in the 1950s. She had what we now call “poor impulse control,” meaning she said and did whatever sailed into her head.

This might involve any number of wild and alarming stunts. Sneaking the keys to our station wagon and going on a joy ride. Sleeping with military guys she met in the bars on Shelter Island. Running up my father’s credit cards. Frying up hamburgers for my brothers and me at 5:30 in the morning because she thought it was dinnertime. Chasing my brothers around the house with a baseball bat.

What my mother really suffered, though, was the brutal loss of her self. But it’s taken me decades to understand that, and to excavate who exactly it was that was lost.

When my mother’s cataclysmic surgery took place, she was 33, a wife and mother of four children under age 9. I don’t remember ever hearing a reason for mom’s illness; my brothers never shared with me their recollections of her in earlier years. My father was a respected doctor, with patients ranging from sportswriters to football players. But he never told me what happened to her or alluded to her brain surgeries. We just didn’t talk about my mother.

As a child I didn’t find this strange at all. As far as I was concerned, my father was a saint. He was quiet and kind. He went out on house calls and made sick people well. His patients adored him. I know because when I visited him in his office near Balboa Park, they told me.

My mother, in contrast, was a holy terror. She raged at me for nothing. She raged at my father the moment he walked in the door, poured himself a glass of gin. The last thing I wanted was to upset him, so I swallowed my anxiety and learned not to ask questions. Besides, the stigma of mental illness at the time was intense. No one I knew had a mother like mine.

Did she just wake up one day like this? I wondered. Disassembled and furious? How could I explain her to other people if I couldn’t fathom her?

For a long time the only thing I knew was what I could see. Beneath my mother’s bangs was an ugly square dent, as hard and shiny as a flattened tin can. The dent both fascinated and repelled me. No wonder she tried to cover it up with bangs. But how did it get there? Did someone punch her? Did she fall during a seizure and smash her head? Does the painful-looking impression hurt? My mother hated the dent. The times she caught me glancing at it she would snap, “What the hell are you looking at?”

I eventually learned what it was. The dent had been caused by a metal plate put inside my mother’s forehead to prevent her brain from swelling. The swelling would have killed her.

We lived in a ranch-style house in a middle-class neighborhood in San Diego. When I was a baby, my father hired a middle-aged Irish woman named Freddie to take care of us. She stayed for 16 years.

Freddie did everything my mother couldn’t do. She went grocery shopping, kept the house tidy, cooked our dinner every night. She tucked me in bed and read me Irish fairy tales and nursery rhymes. Because my mother wasn’t allowed to drive — one of many restrictions that infuriated her to no end — Freddie ferried me to my swimming lessons and Girl Scout meetings, my brothers to their baseball games. She took me to church, where I sang in the choir.

Freddie also corralled my erratic mother. When Freddie arrived, my mother often wouldn’t bathe or get dressed. She lay about in her room, the curtains closed, chain-smoking in bed, her hair a wiry brown mess. She sat on the couch in the family room for hours, watching “Dialing for Dollars” and “Queen for A Day.”

Freddie would yank her gently out of her lassitude and stubbornness, get her functioning again. She encouraged her to take her meds, took her to the beauty parlor to get her hair done.

And Freddie was there for more serious reasons as well. My mother’s seizures terrified me, erupting without warning. She would fall to the floor in a heap, her body shaking, her voice strangled. Sometimes we would have to call an ambulance, and my mother would be carted away to the hospital.

At some point when I was young, Freddie tried to explain to me that something happened to my mother’s brain. “That’s why she is the way she is, dear, she can’t help it.” But what does that mean, I remember thinking. Can she be fixed? Will she ever get better?

Mostly my mother seemed lost in her own world, oblivious to me unless I irritated her. Yet when I was 7, she demanded that I share a room with her because my father no longer wanted to sleep with her. I was shocked, inconsolable. I cried to Freddie for days. My mother didn’t even love me; why would she want this? But there was nothing Freddie could do. I prayed my father would rescue me, put a stop to my mother’s insanity. He didn’t. I felt like I had been thrown to the wolves.

I slept in a room with my mother for the next nine years. We had twin beds and matching chenille bedspreads. We shared a closet: her cocktail dresses, hats, wigs, and high heels on one side, my dresses, sweaters, and tennis shoes on the other. Initially I coped with her invasion by reading. In the closet was a bookcase, stacked with books and National Geographics. I’d sit on a stool reading for hours, looking for escape. Then my mother would burst in, ordering me to get out.

When I was 9 or 10, she started going out at night and drinking. She would call a cab, then trot out the front door down the walkway to the curb, her red lipstick perfect, smelling of Chanel No. 5. My father was mostly absent by now, off in Palm Springs playing golf, or off at Carol’s house, the woman who would become my stepmother. I found it hard to sleep. I’d lie there in the dark, waiting for her to stumble in the door, drunk. She was always drunk. There were nights when she didn’t come home at all. When I was old enough to stay over at friends’ houses, I stopped coming home, too.

Throughout, my mother was an enigma to me. No one could tell me why she was so strange. But for years, wanting to escape her, wanting to be sure I was nothing like her — bonkers, embarrassing, helpless — it’s perhaps equally true that I didn’t want to know. When I left home to go to college at Berkeley, I was ecstatic, I was finally free of her. I could begin my life, become someone new.

It wasn’t until my 20s, when I started therapy, that I began to feel compassion for my mother, and began researching her medical history. It wasn’t easy; her medical records had been destroyed in a hospital fire. My father had died, without having ever revealed to me my mother’s tumors or subsequent surgery.

But slowly I began to piece together her story, the changes she endured after she was butchered. I tracked down the neurologist who treated her when I was a child. One afternoon I called him on the phone from work. I remember holding my breath before he answered. Oh, yes, he remembered her, he said laughing. She was his worst patient. Wouldn’t do anything he said. Hated taking her medication. He’s the one who told me my mother had the lobotomy. I cried after we hung up.

I spoke with an aunt in Oklahoma, my father’s sister-in-law. She had known my parents before they got married. She gave me a packet of old family letters between members of my father’s family, some of them written by my grandfather from his ranch in Southern California, where he had retired in the 1940s. They spoke of my mother’s first brain surgery, their anxiety waiting for the call from my father, their hopes for the tumor to be safely removed. Little did they know. The lobotomy was yet to come.

Few people remained who could tell me who my mother was before the surgery: She was an only child, with few living relatives. Eventually I found an address for one of her cousins, Dorothy, who lived in Arizona. I wrote her a long letter, explaining my wish to learn more about my mother. She was delighted to hear from me, happy to share her memories, and we arranged to talk on the phone. She told me how smart and beautiful my mother had been. How sweet. All the fun they had as teenage girls, the summers they spent at their grandparents’ in Colorado, going to dances, flirting with boys. My mother had gone to college in Tennessee. She had been engaged to an Air Force pilot before she met my father. I was dumbstruck. I had never known any of this. When Dorothy saw my mother a few years after her surgery, she told me, she was shocked, heartbroken, by the changes in her.

With all that, I finally began to grieve for my mother, the young woman she had been. And for losing her.

By then she lived alone in San Diego, in an apartment complex where Freddie had an apartment too. She still did things that made me nuts. I could call her umpteen times before I visited, and she would still forget we had a lunch date. Answer the door in her housecoat. She would call me in the middle of the night, oblivious of the time. “Whatcha doin’?” she’d chirp. “Sleepin’ mom,” I’d say. She’d send me birthday cards on the wrong date, signing them with quotation marks: “Lovingly, mom.” But when I was good and patient, I was able to catch myself. It’s not her fault.

Sometimes I wonder whether the surgeons made the right choice to save my mother’s life, when she was left so debilitated after her lobotomy. I wonder if she’d had her surgery today, if she would have woken up whole, intact. This makes me feel terrible. But as medicine comes up with treatments that increasingly extend our lives, we’re all having to face wrenching decisions like this. Do we want to live if we lose who we are?

In one respect, my mother was lucky. She had the gift of not remembering her past, so she could not mourn the person she was. She lived vividly — and often, for me — infuriatingly in the present.

Learning about her past changed how I felt about her. I was finally able to stop expecting her to be the mother I never had, and to accept her to be the mother she was.