Mapping the Neural Networks Behind “Chemo Brain” in Breast Cancer Patients
If you're a breast cancer survivor who feels like your brain is different after treatment, you're not alone—and you're not imagining things.
Many breast cancer patients report lingering cognitive problems such as difficulty with attention, memory, processing speed, fatigue and concentration that can persist for years after treatment.
This constellation of challenges is often referred to as cancer-related cognitive impairment (CRCI) or “chemo brain.”
A recent review by Alberto Benelli, PhD, and Emiliano Santarnecchi, PhD, from the Precision Neuroscience & Neuromodulation Program in the Department of Psychiatry at Mass General Brigham, analyzed brain imaging research to better understand what is happening inside the brains of breast cancer survivors.
They also wanted to learn which neural networks may be involved in the symptoms of chemo brain.
The research team, which included Michael Parsons, PhD, from the Pappas Center for Neuro-Oncology, and Jorge Dietrich, MD, PhD, from the Department of Neurology, reviewed previously published studies that used brain imaging to examine CRCI.
They looked at brain imaging studies that compared breast cancer patients who were treated with chemotherapy to those treated without chemotherapy (i.e. with surgery or radiation) and to healthy individuals.
Their findings offer important evidence that chemo brain has measurable biological underpinnings and may one day be better diagnosed and treated through network-based approaches to brain health.
What is chemo brain or cancer-related cognitive impairment (CRCI)?
Symptoms of chemo brain or CRCI can include challenges with memory, processing and concentration as well as difficulty multitasking and trouble finding words.
These symptoms can persist for months or even years after treatment and may significantly affect breast cancer survivors’ quality of life.
Studies suggest that 40% to 70% of breast cancer survivors experience some degree of cognitive impairment after chemotherapy.
Is there a biological basis to chemo brain?
The short answer is yes, there are changes in brain functioning that can be identified as a result of chemotherapy treatment.
Although this has been recognized for decades, scientists still do not fully understand its biological basis and why some patients are more affected than others.
Previous brain imaging studies have reported changes in brain structure and function among breast cancer survivors, but these findings have often been scattered across different brain regions and imaging methods.
In this study, the researchers wanted to clarify the picture by identifying whether specific large-scale brain networks are consistently affected in breast cancer survivors experiencing cognitive difficulties.
What approach did the researchers use?
The team conducted a systematic review of neuroimaging studies involving breast cancer patients that used three different imaging techniques:
- Diffusion tensor imaging, or DTI, which looks at the integrity of communication pathways in the brain’s white matter
- Voxel-based morphometry, or VBM, which looks for differences in the density of brain tissue
- Functional MRI, or fMRI, which measures patterns of brain activity by detecting changes in blood flow and blood oxygen levels
They then mapped the reported brain changes onto a widely used framework of seven major functional brain networks.
What did they find?
The analysis revealed significant associations between CRCI and changes in four major brain networks:
- Default Mode Network (DMN)
- Frontoparietal Network (FPN)
- Dorsal Attention Network (DAN)
- Ventral Attention Network (VAN)
These findings suggest that CRCI is not linked to damage in a single brain region.
It appears to involve disruptions across multiple interconnected networks that support attention, memory and higher-level thinking.
What is the Default Mode Network, and why is it important?
The Default Mode Network (DMN) is active during activities such as reflecting on personal experiences, recalling memories and daydreaming.
It plays a major role in memory consolidation and self-referential thinking.
The disruption of this network could contribute to memory problems and other cognitive symptoms experienced after breast cancer treatment.
Interestingly, the DMN is also known to be affected during aging and in neurological disorders such as Alzheimer's disease, making it a promising target for future CRCI research.
What role do the Frontoparietal Network and the Dorasal and Ventral Attention Networks play?
The Frontoparietal Network is responsible for many executive functions, including working memory, planning, decision-making, and cognitive control.
The Dorsal and Ventral Attention Networks are important for sustaining, focusing, and shifting attention between competing tasks.
Alterations in regions belonging to these networks could contribute to difficulties that breast cancer survivors report with concentrating, organizing information, solving problems and managing complex daily tasks.
Which imaging method was most informative?
Although all three imaging approaches provided beneficial information, fMRI appeared to be the most consistent method for detecting CRCI-related network alterations.
The researchers suggest that fMRI may be particularly effective because it captures changes in how brain regions communicate and function (using blood flow and oxygen levels as a measure of cell activity), even when structural damage is not obvious.
What are the potential clinical implications?
Brain imaging is not currently ready to be used as a routine screening tool for chemo brain or CRCI.
However, these findings provide important clues about the biological basis of chemo brain, help with understanding the mechanisms of these problems and may identify biological markers that predict the severity of symptoms and guide the development of new treatments.
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