Brain imaging reveals lower activity after chemotherapy

For years breast cancer survivors have complained about the mental cloudiness they sometimes notice before, during, and after cancer treatment. This mental fog is commonly called chemo fog or chemo brain. In a prospective, longitudinal study, women with breast cancer who had undergone chemotherapy performed less efficiently on cognitive tests.

The findings from researchers at the University Hospital Gasthuisberg of the Katholieke Universiteit Leuven in Belgium, published on May 27th, 2014 in the Journal of Clinical Oncology, show cognitive functioning disrupts after receiving chemotherapy as a treatment for breast cancer.

Lead researcher Sabine Deprez, MD, said that the effect was probably produced because of chemotherapy’s resulting in structural changes in the brain. “Cognitive complaints of people increase with chemotherapy and we are trying to find out why,” said Deprez. “Difficulty multitasking is one of the biggest complaints.”

Past research 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 and her colleagues. Previous studies used imaging to show differences in brain activity between cancer patients who had chemotherapy and healthy people not being treated for cancer.

To compare women with themselves before and after chemo, as well as with other women, the researchers 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.

“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,” researchers said.

The researchers evaluated 18 women with breast cancer before they started chemotherapy and then four to six months after the completion of treatment, and compared them with 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 an MRI machine 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. “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,” the researchers 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 researchers said.

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.

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