Evidence That Chemo Decreases Brain Activity During Multitasking
The “brain fog” many patients experience after chemotherapy might be related to chemotherapy-induced damage to the brain or reduced connectivity between brain regions, according to new research.
In a prospective longitudinal study, women with breast cancer who received chemotherapy were found to have significantly less brain activity than women with breast cancer who did not receive chemotherapy and than healthy women.
This longitudinal study — the first to provide evidence of a relation between brain activity changes and cognitive complaints after chemotherapy — was published online May 27 in the Journal of Clinical Oncology.
“We believe that this is an important step in our understanding of the neurobiologic basis of the cognitive adverse effects of chemotherapy experienced by patients,” write Sabine Deprez, MD, and colleagues from Katholieke Universiteit Leuven in Belgium.
In their study, the researchers used functional MRI to examine whether cognitive complaints after treatment for breast cancer are linked to detectable changes in brain activity during multitasking.
“Cognitive dysfunction is a well-known adverse effect of cancer and its treatment, and although the degree of complaints may differ among patients, such cognitive deficits often have a negative impact on their quality of life,” they write.
Patients have been told that their symptoms are psychological; however, recent research has demonstrated that objective and subjective cognitive symptoms can be linked to cancer treatment, they note.
Advanced neuroimaging techniques could be more sensitive than neuropsychological examination for uncovering actual brain changes associated with cognitive complaints, the researchers reasoned. They note that the small number of imaging studies that have been done have reported both structural and functional brain changes after cancer treatment.
The researchers evaluated 18 women with breast cancer before they started chemotherapy and then 4 to 6 months after the completion of treatment, 16 breast cancer patients who did not receive chemotherapy, and 17 matched healthy women.
To assess the relation between the performance of tasks and brain activation, all the women were scanned with a 3 Tesla MRI scanner while they performed a visual task, an auditory task, a combination of the visual and auditory tasks, and the combination plus an independent short-term visual memory task (the multitask condition).
The researchers adjusted the difficulty of the tasks for individual participants so that 70% to 80% of responses would be correct.
At baseline, there were no differences in brain activation during the multitasking performance between the 3 groups.
However, in the chemotherapy group, activation in task-related brain circuitry decreased after treatment, compared with the pretreatment level (P < .05), specifically in the left anterior cingulate gyrus and intraparietal sulcus. No such changes were seen in the other 2 groups.
The women treated with chemotherapy also had significantly more cognitive complaints than the other women (P < .05). This increase was correlated with decreased brain activation in multitasking circuitry, specifically in the left anterior cingulate and inferior frontal sulcus, in the chemotherapy-treated women only.
Such changes in brain activity might underlie the cognitive impairments patients report after chemotherapy, the researchers suggest.
In an accompanying podcast, Brenna McDonald, MD, from the Indiana University School of Medicine in Indianapolis, notes that the findings “demonstrate treatment effects on a putative neurocircuit underlying cognitive complaints after cancer chemotherapy with activation changes particularly evident in brain regions thought to be important for attention and working or short-term memory.”
Dr. McDonald agrees that the study results “offer additional validation of the concerns often reported by patients.”
Longer-term follow-up studies will be needed to monitor the course of these symptoms and functional brain changes over time, she adds.
“It will also be helpful for future work to further examine the relationship between task difficulty, performance accuracy, objective and subjective cognitive functioning, and brain structure and function,” she explains. “In addition, larger cohorts, perhaps via multicenter studies, will be needed to determine which patients are most vulnerable to such difficulties, and why, through study of demographic, genetic, and treatment variables.”
J Clin Oncol. Published online May 27, 2014.