If you are in the middle of glioblastoma treatment and having trouble remembering names, following conversations, or reading, you're not alone. Cognitive changes are common during treatment but rarely discussed. Clinic visits focus on scans and tumor response, while memory problems in daily life get overlooked.
These changes are real and manageable. This guide explains what causes them and what can help you maintain your cognitive function during treatment.
What Cognitive Changes Should Glioblastoma Patients Expect?
Cognitive changes from glioblastoma treatment can include memory loss, trouble concentrating, slowed thinking, word-finding problems, and trouble multitasking. The severity depends on tumor location and treatment type. Most changes improve with early assessment, rehabilitation, and teamwork with your care team.
The National Cancer Institute recognizes that memory and concentration problems are side effects of cancer treatment affecting daily activities, work, and relationships. For glioblastoma patients, the cause is usually both the tumor and the treatments used to fight it.
Why the Tumor Itself Affects Thinking
Before treatment starts, the tumor can disrupt normal brain function. Glioblastoma grows inside and around brain tissue instead of forming a clean boundary. Depending on where it sits, it can compress or spread into areas that control memory, language, attention, and planning and decision-making.
Even tumors in areas not linked to cognition can cause widespread effects. Increased pressure in the skull, inflammation from tumor cells, and disruption of white matter (the brain's internal communication pathways) can slow thinking and impair recall. It's important to remember that cognitive problems don't always mean treatment is failing. Early in treatment, reducing the tumor can temporarily improve cognition before treatment effects emerge.
How Radiation Therapy Affects Cognitive Function
For most glioblastoma patients, radiation is a central part of treatment, typically given over six weeks with temozolomide chemotherapy. Radiation targets tumor cells effectively but also affects healthy brain tissue, which is a main cause of cognitive change during and after treatment.
A review in Frontiers in Oncology describes how radiation changes the brain's environment, triggering inflammation through immune cells called microglia and astrocytes. This inflammation can reduce the creation of new neurons in the hippocampus (the area most important for forming new memories). Some patients notice their short-term memory gets worse in the months after radiation, even when scans look stable.
Research in Neuro-Oncology followed glioblastoma patients during and after combined chemoradiation and found early declines in verbal memory and attention during active treatment. The amount of impairment varied between patients, but the pattern was consistent enough to be considered a predictable treatment effect.
Hippocampal-sparing radiation techniques (which reduce the radiation dose to the brain's memory center) are being studied and used in some centers for certain brain tumors. Whether this works for your situation depends on tumor location and anatomy. Ask your radiation oncologist if this approach is right for you.
You can read more about managing chemotherapy side effects during this phase in our guide to temozolomide for glioblastoma: how it works, side effects, and managing them.
How Temozolomide and Steroids Contribute
Temozolomide (TMZ), the chemotherapy used with radiation in the Stupp protocol, crosses the blood-brain barrier (which is why it works against GBM). That same property means it affects healthy brain tissue. Research suggests TMZ may slow brain cells in ways that could slow thinking. However, this effect is usually smaller than radiation-related cognitive changes.
Steroids, usually dexamethasone, are often given to reduce swelling around the tumor. They relieve pressure-related symptoms and can temporarily improve thinking by reducing swelling, but longer or higher-dose steroid use can hurt cognition over time. Brain and mood side effects (mood shifts, irritability, anxiety, and memory problems) happen in some patients on long-term steroids. If you're using steroids and tapering, our article on dexamethasone during glioblastoma treatment: managing steroids, side effects, and tapering safely covers important details.
Antiepileptic medications for seizures are another factor. Older antiepileptic drugs often cause sedation and cognitive slowing. Newer drugs tend to be milder. If you're taking antiepileptics and noticing significant fog, tell your neurologist. A medication review might help.
The Fatigue-Cognition Link
Cognitive and physical fatigue are closely related in GBM. When the brain is exhausted from treatment, poor sleep, anxiety, or the energy required to manage serious illness, thinking becomes much harder. This is different from depression, though they can overlap. Cancer-related fatigue is a real physiological state that impairs concentration, memory, and processing speed.
Sleep disruption is common during and after treatment. Steroids can make it hard to fall asleep. Anxiety about scans and outcomes can extend the nights. Improving sleep quality through behavioral changes or talking with your care team often helps daytime thinking.
Types of Cognitive Changes: What to Watch For
Not all cognitive changes look the same. Some patients notice a single specific problem, while others experience general fog across multiple areas. Common patterns include:
- Short-term memory gaps - forgetting conversations from minutes ago, losing track of medications, repeating questions
- Word-finding difficulty - knowing what you want to say but can't find the word (doctors call this anomia)
- Attention and concentration problems - trouble following TV shows, conversations, or reading
- Slowed processing speed - taking longer to respond and make decisions
- Executive function changes - trouble planning, managing money, or switching between tasks
- Spatial disorientation - getting confused in familiar places or misjudging distances
The National Brain Tumor Society notes that cognitive fatigue is often not discussed but should be. Naming specific changes at your clinic visits, not just saying you feel foggy, helps your team decide if formal testing is needed.
How Are Cognitive Problems Formally Assessed?
A neuropsychologist formally measures these changes using standardized tasks that cover memory, attention, processing speed, language, and executive function. The goal is to establish a baseline early so changes can be tracked over time with real measurements, not just by memory.
Not every center routinely offers neuropsychological assessment to GBM patients, and capacity varies. If a full evaluation isn't immediately available, shorter screening tools like the Montreal Cognitive Assessment (MoCA) can show whether a full assessment is needed.
Research on long-term glioblastoma survivors in the Journal of Neuro-Oncology found that cognitive problems significantly affected quality of life and function, and that real measurements guided rehabilitation planning much better than doctors' impressions alone. If you're not offered testing, ask your care team whether it's available.
What May Help With Brain Fog During GBM Treatment
Evidence supports targeted approaches to manage cognitive changes during and after brain tumor treatment. These don't fix the underlying cause, but many patients find them helpful when combined.
Cognitive rehabilitation is a structured program led by a therapist that helps patients develop ways to work around specific problems (memory cues, attention training, daily routines). A study in Neuro-Oncology found that cognitive remediation (including strategy training for attention) helped brain tumor survivors with documented problems. Ask your care team if a neuropsychologist or occupational therapist offers this.
Physical exercise is one of the most accessible tools. Aerobic activity helps the brain form new connections and adapt. Moderate exercise right for your current fitness has been linked with better attention and less cancer-related fatigue.
Organizational strategies are low-tech but work well. A notebook or app for medication reminders, appointments, and tasks reduces the burden on your memory. Written schedules, phone alarms, and visible reminders help make up for short-term memory problems without needing medical treatment.
Medication-based approaches exist but aren't proven for GBM-specific impairment. Stimulant medications have been studied for cognitive fatigue with mixed results. Talk with your neuro-oncologist about any medications for cognition, don't try them on your own.
If you're managing multiple symptoms at once - cognitive fog, fatigue, and sleep problems - talk with your care team about a comprehensive support plan for your specific treatment phase.
What Caregivers Need to Know
Cognitive changes in GBM aren't always visible to the person experiencing them. A condition called anosognosia (reduced awareness of your own cognitive problems) is recognized in brain tumor patients, especially when the frontal lobe is involved. You might notice your person repeating questions they just asked, leaving tasks unfinished without realizing, or feeling more confused than usual in busy settings.
Document these observations with specific examples and dates. This helps your treating team understand what's changing outside the clinic. At the same time, preserve the person's dignity. Create systems (lists, reminders, simplified routines) that let the person feel capable, not managed.
A 2025 analysis of cognitive decline in GBM, published in BMC Cancer, shows that caregiver observations are important for understanding how a patient's cognition is actually changing between clinic visits. Your records of day-to-day function matter.
When to Talk to Your Doctor
Contact your care team if you notice a sudden change in thinking, speech, or behavior (especially if it happens over hours or days, not weeks). This can mean new swelling, seizure activity, or tumor-related changes needing urgent evaluation. Gradual changes over weeks to months should be mentioned at your next clinic visit, with specific examples of what changed and when it started.
Ask your team if a neuropsychological assessment is available at your center, if your antiepileptic medications might be slowing your thinking, and if there's a neuro-rehabilitation program you can join.
If you want a specialist team to review your treatment plan and reports, you can upload your records and request a remote case review through the Glioblastoma Center patient journey service.
This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.