I sat in a chair across from the hospital bed, watching each shallow breath shrug its way out, into, and out of my grandfather’s chest. The amount of time between the conclusion of one breath and the start of the next one was just long enough that my eyes constantly flicked up to the monitor to make sure his heart was still beating. A stroke had paralyzed his right side from the shoulder down and severely impaired his ability to speak, and at 96 years old, he was already in less than peak condition.

He looked so fragile; his limbs thin and gangly, his liver-spotted bald head seeming shrunken against the pale blue pillow, mouth gaping open while he slept. There was no telling what he would be like when he woke up; sometimes he didn’t seem to understand questions like “Are you in pain?” or “What year were you born?” Now and then he just said “No” repeatedly to everything. But sometimes when he fixed his pale blue eyes on me and gave a somewhat weaker version of his signature, mischievous smile, I knew he was the Grandpa I had known my whole life, even though he couldn’t tell me with words. “He’s in there,” I thought during my vigil at the foot of his bed. “It’s still Grandpa inside that debilitated body.”

I replayed scenes in my head from years ago: Grandpa chasing me around the house trying to give me a playful spanking for some innocuous thing I’d done; the way he would widen his eyes and look at the floor when trying to hide that he was fibbing; the games we played at the dinner table. The man who had done all those things looked very different from the man across from me at the hospital, but I knew they were the same person. I looked up at the nurses, physical therapists, and doctors who were constantly drifting in and out of the room. To them, my grandpa was just the patient in room 101 who had suffered a middle cerebral artery stroke, couldn’t sit upright on his own, and needed a feeding tube directly into his stomach. They asked questions about his medical history, but those answers didn’t tell them anything about who he was as a person. The grandpa I’d known my whole life, at that moment, only existed in my memories.

* * *

Memory is a notoriously fickle beast. We remember that time our friend stole our popsicle when we were eight years old, but we forget what we had for dinner last Friday. Catchy songs get stuck on “repeat” in our brains for hours or days, yet we struggle to remember the words to poems we used to know by heart. I find myself telling the same stories to friends who have heard them dozens of times, and forgetting the names of their siblings. No wonder Death Cab for Cutie called memory “a faulty camera in our minds” in their song “What Sarah Said.” Sometimes our mental film is corrupted, and we recall being at a party even if we’ve only heard about it. Sometimes the camera’s shutter doesn’t open, and we have no record that entire parts of our lives ever happened.

But memory doesn’t exactly work like a camera. Rather than taking a picture of a scene and storing it away into a filing cabinet, our brains tear our memories into little pieces, storing them in different folders. When we recall a memory, we reconstruct it like a puzzle, gathering the different elements and fitting them together: emotional responses from the amygdala, facts from the medial temporal lobe, associations from the cerebellum. We also create different types of memories for different things that need remembering. My friend’s phone number that I need to remember long enough to type into my phone is processed as a short-term memory, while the best meal I ever had is encoded into long-term memory.

Damage to the brain can disrupt the entire process of creating new memories, or affect a specific form of memory while leaving others intact. Henry Molaison, possibly the most famous memory disorder patient in history, suffered damage to his medial temporal lobe and afterward couldn’t learn new facts but could develop new skills, despite not remembering learning them.

The prefrontal cortex, the foremost part of the brain, is associated with “higher” functions like abstract thinking and interpreting information about the world that we take in with our senses. When this area of the brain is damaged, it not only impairs the recall of memories of people and events from our pasts, but also results in significant personality changes. Memory and identity, it seems, are inherently linked.

But if our memories are changeable and unreliable, does that mean our personalities are also mutable? If my memory tells me that my Grandpa has a dry sense of humor but the hospital staff haven’t heard him crack a joke once since they’ve known him, is it more accurate to say he’s funny or serious? Do my memories of him make my perception of his personality more accurate?

Famed psychologist Erik Erikson defined identity as “a subjective sense as well as an observable quality of personal sameness and continuity,” arguing that is both innate and ascribed by others. Having a solid sense of your own identity is crucial to developing into a functional adult. The ancient Greek maxim “Know thyself” reflects the deeply human need to define ourselves and our place in the world on our own terms. People without a strong sense of self are prone to “identity crises,” in which victims are overwhelmed by the struggle to figure out who they are and may turn to substance abuse or other destructive behaviors.

My grandpa had his own self-identity, independent of who anyone else thought he was, before his stroke. But now his inability to move or speak fully meant there was no way to know how much he could remember about his life, and he couldn’t correct us if our version of his identity didn’t match the one in his head. Essentially, he was limited to the Grandpa that existed in the memories of his family members, which was clearly not the complete picture of who he was. Without the innate part of our identities to serve as the blueprint, only the projected part, which is subject to others’ perceptions and memories, remains.

Sometimes our self-identity and the identity others ascribe to us can vary wildly. On the personal level, it can be the difference between an Alzheimer’s patient’s memory of themselves and their family’s memories of them. An Alzheimer’s sufferer might think they were never married, causing great pain to their spouse and children when they realize they have been written out of their loved one’s life. Different ideas about identity can also have larger, even global impacts. Jesus, for example, has many identities: Christians consider him the Son of God, Jews see him as an idolater leading the faithful astray, and Muslims believe he was a prophet who paved the way for Muhammad. But we have no way of knowing how Jesus viewed himself, so we have to rely on the collective memories of those who wrote about him in ancient times, and all of the alterations, omissions, additions and other changes those texts have endured through the ages. The disagreements between those written accounts have fueled bloody conflict for centuries, as followers of all three traditions argue over whose version of Jesus is the “real” one. But without access to his own memories, we will never truly know.

* * *

I’ve kept journals since middle school and now have about six of them, filled with everything from how bored I was in my ninth-grade Government class to enraptured attempts to describe the color of the sky during a spring thunderstorm in North Carolina. I started keeping them as a way to record things that I wanted to remember but didn’t trust my faulty mental camera to keep error-free as it accumulated newer memories. I also thought that in the future I might want to pick up a journal every now and then for an hour or two of nostalgia, and that if I became a writer I might find inspiration in the annals of my past.

My journal entries have become fewer and far between as the demands of daily life have increased. I’m often frustrated that I can’t remember funny inside jokes I’ve made with friends or concerts I’ve gone to in the weeks or months that have passed. Sometimes I’m tempted to just stop altogether and trust myself to remember the things that are really important. Not once have I re-read one of my journals. I’ve started asking myself why I still do it.

I realize now that I’m not just recording events for history or my possible grandchildren’s interest. Journaling is my attempt to preserve my self-identity. Whatever I become in life, I was once a little girl with pigtails crouching in the dirt at recess gently replanting bluebells into paper Dixie cups; I have climbed glacier-covered Alpine peaks with ice axes and crampons; Beethoven’s Pathetique sonata gives me chills. All those things and more, things that others might not know about or think are important, are crucial elements that make up my being. I want them all recorded on paper so that if ever I have a stroke or fall victim to a memory-eating disease, those around me can have authoritative evidence of who I am, beyond the identity that anyone else creates for me, that won’t be subject to the whims of fluid, faulty memory. And maybe one of my descendants will flip open one of my journals a century later and be amused to learn that my brother and I “climbed to the top of one of the little islands around Il Galli on the Amalfi Coast of Italy, speaking in British accents the whole time, and proclaimed it Mount Whimple before jumping back into the warm, blue Adriatic sea.”