For some women with breast cancer, changes in brain activity while multitasking could explain “chemo brain” – reduced mental functioning that many experience after chemotherapy, Belgian researchers say.
“Cognitive complaints of people increase with chemotherapy and we are trying to find out why,” said Sabine Deprez, who led the new study. “Difficulty multitasking is one of the biggest complaints.”
Past research has documented changes in mental performance following chemotherapy – and in some cases, in cancer patients before chemotherapy, suggesting disease-related processes may also play a role, according to Deprez’s team.
Other studies have used imaging to show differences in brain activity between cancer patients who had chemotherapy and healthy people not being treated for cancer, the researchers write in the Journal of Clinical Oncology.
To compare women with themselves before and after chemo, as well as with other women, Deprez and her colleagues at the University Hospital Gasthuisberg of the Katholieke Universiteit Leuven, used functional Magnetic Resonance Imaging (fMRI).
The imaging technique indirectly assesses brain activity by signaling changes in blood and oxygen delivered to various regions of the brain.
Eighteen women with breast cancer scheduled to receive chemotherapy performed a multitasking exercise in an MRI machine before starting treatment and four to six months after treatment ended.
Two comparison groups - one of women with breast cancer not scheduled to receive chemotherapy and another of healthy women - also performed the tasks.
“The special thing about how we did the design was that before we did it we adjusted the difficulty for each patient, and the performance of everyone was between 70 and 80 percent,” Deprez said.
That meant patients’ performance on the test, which included indicating if two sounds were the same frequency and if two moving circles with lines through them were at the same orientation or not, while remembering two symbols presented earlier, did not change over time. This allowed the researchers to measure changes in brain activity levels during the task, not in the women’s ability to complete the task, Deprez said.
Neither of the two comparison groups seemed to change in terms of the parts of the brain activated by the tasks or their level of activation, while in the chemotherapy group brain activation significantly decreased, the authors report.
Meanwhile, patients in the chemotherapy group also complained of “foggy thinking” more than those in the other groups. Before the chemotherapy started, all the participants had about the same amount of cognitive complaints.
“The important thing that we found was a relation with subjective cognitive complaint,” Deprez said.
The decreased brain activation seen with fMRI may help explain why many chemotherapy patients complain of chemo brain.
“It feels like they have to do more effort to get the same result after chemo,” Deprez said.
That could be because chemotherapy causes structural changes in the brain, but experts still don’t know, she said.
Functional MRI is very useful for research, but for the cognitive effects of cancer treatment it can only be used to draw conclusions about people in general, not individual patients, Brenna C. McDonald said in an email.
McDonald, of the Radiology and Imaging Sciences department at Indiana University School of Medicine in Indianapolis, has investigated this topic but was not part of the new study.
“There is a more limited literature suggesting that other cancer treatments, like antiestrogen therapies, may be related to some cognitive symptoms, but this effect, if present, appears to be smaller than the effects noted after chemotherapy,” McDonald said. “Generally, however, the most significant effects have been shown with regard to chemotherapy.”
Patients who are older at diagnosis seem to be at greater risk for foggy thinking problems from chemotherapy, she added.
“As we advance our understanding of which patients are at greatest risk, hopefully we will be able to personalize medical treatment to minimize cognitive risks while still effectively treating the cancer,” McDonald said.
“Being aware of the possibility of cognitive effects of treatment is important in the same way it is important to know about other possible treatment-related side effects,” she said.