As treatments for cancer improve, survival rates increase, as do the number of cancer survivors.
This growing population of people who have come through cancer and lived to tell the tale often report cognitive deficits.
It affects memory, concentration, and an individual's ability to multitask, among other reductions in function.
Some women with chemo brain report that their ability to follow conversations is impaired and that they are more easily fatigued and confused.
A review that looked at the prevalence of chemo brain estimated that it affects 17-50 percent of female breast cancer survivors.
Although research has established chemo brain as a genuine consequence of chemotherapy, there are still many questions that need to be answered. One such question asks how long chemo brain is likely to last.
Measuring the length of chemo brain
A study, conducted at the University of Illinois and published in the journal Behavioural Brain Research, set out to investigate the effects of chemo brain over a longer period of time. For this purpose, the team designed a mouse model that will help researchers of the future investigate this problem and, potentially, rectify it.
The study's lead author, Catarina Rendeiro, worked with a group of researchers across the university, including Justin Rhodes, a psychology professor, and William Helferich, a professor of nutrition.
"Quality of life after chemotherapy is critically important, and chemo brain is significant in these survivors."
Prof. William Helferich
Earlier research has shown that the intense physical toll of chemotherapy accounts for the short-term deficits in cognitive ability seen in chemo brain. As Prof. Rhodes says: "The question is, after they completely recover from the acute assault of chemotherapy, many months or years later, do they still have cognitive impairments?"
The researchers used a female mouse model designed to mimic post-menopausal women as closely as possible. To measure the potential long-term effects of chemo brain, they measured how chemotherapy impacted learning and memory. Additionally, they charted the formation of new neurons in the hippocampus - a part of the brain important in memory, among other roles.
The mice were put through their paces using a Morris Water Maze. This type of trial has been widely used in behavioral neuroscience to study memory and spatial learning since the early 1980s. It involves placing a mouse in a circular pool and timing it while they search for a submerged platform.
Mice subjected to chemotherapy were found to take substantially longer to learn the task.
When the brains of the chemotherapy-treated mice were examined, they were found to have 26 percent fewer surviving hippocampal neurons created during the course of treatment, and generated 14 percent fewer hippocampal neurons in the 3 months directly after chemotherapy.
Three months for a mouse corresponds to around 10 years in human terms. If these results can be extrapolated to humans, they demonstrate that the effects of chemotherapy do indeed lead to long-term deficits.
Future treatments for chemo brain
Although it may be possible to design drugs to reduce the cognitive effects of chemotherapy, that would bring with it the worry that additional chemicals might interact with the chemotherapy itself, causing other unwanted effects or preventing it from working as it needs to.
Instead, the team hopes that natural interventions might be uncovered that can ward off the damage that results from chemo brain.
To that end, the researchers investigated whether a diet with additional omega-3-fatty acids might help reduce the cognitive impacts of chemotherapy on the mice. Unfortunately, this intervention did not yield significant results.
The current study is the first to produce an animal model demonstrating the long-term effects of chemotherapy on the brain. In the future, the team hopes that the model will be used to investigate other potential nutritional components and chart their effects on chemo brain.
Long-lasting impairments in adult neurogenesis, spatial learning and memory from a standard chemotherapy regimen used to treat breast cancer, Catarina Rendeiro et al., Behavioural Brain Research, doi: http://dx.doi.org/10.1016/j.bbr.2016.07.043, published online 18 August 2016, abstract.
University of Illinois news release, accessed 19 August 2016.
Additional source: Cancer Research UK, Chemo brain, accessed 19 August 2016.