Chemo Brain: It's Not All in Your Head

About six weeks into my chemotherapy, I sat down to write an email that I had written a hundred times before. A routine “Five Bullet Friday” update to the FCA board. Nothing complicated. I knew exactly what I wanted to cover.

And I could not find the words.

Not in a poetic, searching-for-the-right-phrase kind of way. In a genuinely frightening, the-cabinet-is-open-and-the-shelf-is-empty kind of way. I sat in front of that screen for ten minutes. I got up. I came back. I tried again. What eventually came out was stilted and strange — not wrong, exactly, but not mine. Not the way I think or write or lead.

I was the CEO of a $28 million organization. I had a Ph.D. I had completed dozens of triathlons on the discipline of mental toughness alone. And in the moment, I struggled to write a quick and easy update.

I didn’t see it coming. Nobody had mentioned it in any of the pre-treatment conversations. The oncology team was meticulous about preparing me for the physical side effects — the fatigue, the nausea, the immune suppression. Not one person said: by the way, as we are getting the tumor out of your ass, we’re going to fuck with your brain.

There’s a joke about proximity there, but I forget the punch line.

It Has a Name. Most Survivors Don’t Know That.

It’s called cognitive impairment associated with cancer treatment. Patients and clinicians have called it “chemo brain” for decades. Researchers prefer terms like cancer-related cognitive impairment, or CRCI, well because researchers are like that, but also because the cognitive effects aren’t limited to chemotherapy, and because calling it “brain fog” minimizes what’s actually happening.

Studies suggest that somewhere between 20 and 75 percent of cancer patients experience meaningful cognitive changes during or after treatment — a range that wide reflecting how differently researchers have defined and measured the phenomenon. What most of them agree on is this: it is real, it is neurologically explicable, and it is not all in your head.

Actually it is.

Functional MRI studies of patients undergoing chemotherapy have shown measurable reductions in gray matter density, decreased activity in the prefrontal cortex and hippocampus, and disrupted connectivity in the networks responsible for attention, processing speed, and working memory. These are not subtle changes. These are the structures and systems responsible for the cognitive functions most of us take for granted — the ability to hold multiple pieces of information in our minds simultaneously, to filter distraction, to retrieve words and names and sequences, to plan and sequence complex tasks.

In other words: the things you need to do your job. To have a conversation. To be yourself.

What’s Actually Happening in There

The mechanisms are still being mapped, but the current research points to several overlapping processes.

Chemotherapy drugs, designed to destroy rapidly dividing cells, don’t discriminate cleanly between cancer cells and healthy ones. Some agents cross the blood-brain barrier — the brain’s primary defense against circulating toxins — and directly affect neural tissue, including the progenitor cells responsible for generating new neurons in the hippocampus, the brain’s primary memory and learning structure.

Beyond the direct chemical effects, treatment triggers a sustained inflammatory response throughout the body, including the brain. Neuroinflammation disrupts synaptic function — the electrochemical signaling between neurons that underlies everything we think of as cognition. It also suppresses neurogenesis, the process by which the brain grows new cells, which the hippocampus does continuously in healthy adults.

Add to this the secondary effects: the sleep disruption that is nearly universal during treatment, the chronic stress and anxiety that alter cortisol levels and directly impair prefrontal function, the hormonal changes that accompany many cancer treatments, the simple physiological depletion of a body fighting simultaneously on multiple fronts. The brain doesn’t operate in isolation from the rest of the body. When the body is under sustained assault, the brain pays a toll.

Radiation therapy to the brain or skull carries its own documented cognitive risks. Hormonal therapies — common in breast and prostate cancers — affect cognitive function through different pathways. Even immunotherapy, increasingly standard in many treatment protocols, can produce neurological effects in some patients.

The straight-up truth is this: cancer treatment is cognitively expensive, through multiple mechanisms, in ways that vary by treatment type, patient age, baseline cognitive reserve, and factors we don’t yet fully understand.

The Part Nobody Prepares You For

The cognitive effects of treatment are one thing. What I was not prepared for - and what is rarely discussed in survivorship literature - is the identity disruption that follows.

Cognition is not just a functional capacity. It is deeply bound up with who we understand ourselves to be. When the way you think changes or when you reach for a word and it isn’t there, when you lose the thread of a conversation you were leading, when you read the same paragraph three times and it won’t stick - it’s more than a pesky side effect.

I had spent my entire adult life in a role that demanded intellectual agility; the complex decisions, rapid synthesis of competing information, the kind of sustained analytical thinking that running a large human services organization requires. My mind was not separate from my professional identity. It was the instrument of it.

And for a period during and after treatment, that instrument was unreliable in ways I could not predict or control.

I want to name that directly because I think the survivorship narrative, riddled with words like “brave”, “resilient”, “fighting”, doesn’t leave much room for the specific grief of cognitive loss. We talk about hair loss and weight changes and fatigue as legitimate physical consequences of treatment. The sense that your thinking has been altered, that your memory has gaps, that you are not quite as sharp as you were — that tends to get whispered, if it gets said at all. People are afraid it sounds like a trivial complaint. Or weakness. Or a reason someone might question whether they’re still capable.

It is none of those things. It is a documented neurological consequence of a treatment that saved your life. It deserves to be discussed.

How It Comes Back

Here is what I want to tell every person who is sitting where I sat, frustrated, freaked-out and quietly wondering if this is permanent:

For most Prevagen-popping patients, it is not.

The brain is not a fixed structure. It is a living system with a remarkable capacity to adapt, reorganize, and recover — a property neuroscientists call neuroplasticity. The same mechanisms that allow stroke patients to relearn speech and motor function after brain injury allow cancer survivors to recover cognitive function after treatment. The timeline varies. The degree of recovery varies, especially if age factors into the equation. But the trajectory, for most people, is toward recovery — and there are specific, evidence-based practices that accelerate it.

I exercised during chemo and good thing since physical exercise is the most robustly supported intervention in the cognitive recovery literature. Aerobic exercise increases production of brain-derived neurotrophic factor — BDNF — which promotes the growth and maintenance of neurons and supports synaptic plasticity. It increases blood flow to the prefrontal cortex and hippocampus. It reduces neuroinflammation. In multiple studies, regular aerobic exercise has been associated with measurable improvements in memory, attention, and processing speed in cancer survivors — and with structural brain changes visible on imaging.

I kept training through treatment, on the days my body would allow it. Not heroically — some days “training” meant walking to the end of the block and back. But I kept moving, because I knew at some level, before I could have cited the research, that movement was protecting me.

Sleep is the brain’s primary recovery mechanism, and its importance in cognitive rehabilitation cannot be overstated. During deep sleep, the glymphatic system — the brain’s waste-clearance pathway — flushes the metabolic byproducts that accumulate during waking hours, including inflammatory proteins implicated in neurodegeneration. Chronic sleep disruption during and after treatment is both a consequence of cognitive impairment and a cause of its persistence. Treating sleep as a medical priority — not a luxury — is one of the most important things a recovering patient can do.

Though I do Wordle everyday and cognitive engagement matters, though the research here is more nuanced than the popular “brain training” narrative suggests. The evidence for app-based cognitive training programs is mixed at best. What the research does support is sustained engagement with meaningful, moderately challenging cognitive activity — learning something new, reading substantively, engaging in complex problem-solving. The key word is meaningful. The brain responds to engagement that has stakes and context. Novelty alone is not the mechanism.

Stress reduction is not a wellness platitude in this context — it is a neurological intervention. Chronic elevated cortisol directly suppresses hippocampal neurogenesis and impairs prefrontal function. Practices that reliably lower cortisol — things like mindfulness meditation, structured breathing, time in nature, social connection — are not just complementary to cognitive recovery. They are part of it.

Patience is not my strong suit, but time is also, genuinely, part of the answer. Most studies that follow cancer survivors over multiple years show continued cognitive improvement long after treatment ends. The brain’s recovery is not always linear, and it is not always fast. But for the majority of survivors, the trajectory is upward.

What I Know Now

I’m probably not the same thinker I was before cancer. There are ways in which the treatment left marks that haven’t fully resolved — a forgotten name, a slightly longer reach for certain words, an occasional fatigue in sustained concentration that wasn’t there before.

But I am also not the person who sat staring at that blank email, a little freaked out because I’m never at a loss for words. The recovery was real. Neuroplasticity is real. The practices that support it are real and available and not especially complicated.

What I wish someone had told me at the beginning of treatment is this: what is happening to your brain is not a character flaw, not a crumbling of your abilities, and not permanent. It is a neurological consequence of a chemical intervention that is keeping you alive. It’s part of the trade-off.

Give your brain what it needs: movement, sleep, engagement, reduced stress, and time. And be patient with yourself as you find just the right word.