Researchers edge closer to details surrounding chemo brain
Three University researchers may shed new light on the medical condition known as chemo brain, the fog-like state of mind experienced by many cancer patients undergoing chemotherapy.
Disruptions in attention, working memory, and slowed processing of information characterize the condition, medically known as chemotherapy-induced cognitive impairment, said Miriam Nokia, a University post-doctorate fellow who is now a researcher at University of Jyvaskyla in Finland.
“While the patients have no problem performing daily routines, they have trouble doing more cognitively demanding things, like multitasking,” said Tracey Shors, a behavioral neuroscientist who worked with Nokia.
Chemo brain affects a vast majority of cancer patients, Nokia said.
Under chemotherapy, cancer patients encounter problems with their working memory, she said, which is the part of short-term memory required to consciously process language and perception.
Chemotherapy works by stopping cell division, which is useful for some types of tumors, but it also hits other cells as well, said Shors, a professor in the Department of Psychology.
She said one of the treatment’s side effects is it stops neurogenesis, or the production of new neurons. The new cells are sensitive to the drug.
Shors worked at her laboratory with Nokia and graduate student Megan Anderson on the relationship between chemo brain and the disruption of neurogenesis in the hippocampus, the brain’s center of memory and learning, said Anderson, who has worked on adult neurogenesis for the last six years.
To model chemotherapy, the team gave laboratory rats doses of temozolomide, or TMZ, a drug used to treat brain tumors and skin cancer, Nokia said. The team tested different types of learning to determine if TMZ decreased neurogenesis and disrupted brain rhythms called theta rhythms.
These rhythms are particularly important for learning new associations, Shors said. Their disruption hinders the ability to acquire new information.
She said the team found the rats undergoing mock chemotherapy treatment had less frequency of these rhythms in their brain, and they did not learn new information very well, if at all.
While the team tested different kinds of learning, only those where stimuli were separated by long periods of time were affected by the treatment, Anderson said.
In humans, the struggles of the rats would translate to difficulty in tasks like remembering long strings of numbers or following instructions, she said.
“The rats were treated with similar doses as humans were, so we concluded that maybe some of the cognitive deficits people have after chemotherapy were due to these disruptions in rhythms and loss in new cells,” Shors said.
After the rats stopped receiving doses of TMZ, the cognitive deficits they experienced while on the drug had a rebound effect, Anderson said.
Chemotherapy does not disrupt any knowledge gained prior to treatment, so after treatment ends, Shors said it makes sense for the patient’s brain resumes normal behavior.
This result is consistent with what patients have described their experience with chemotherapy to be like, Anderson said.
“It puts their risk in perspective,” Anderson said. “It gives them a reason behind their symptoms.”
Still, Nokia said it is still too early to definitely say what the long-term effects of TMZ are on human patients. They often show symptoms of chemo brain even after years of chemotherapy.
Given their results, however, Shors said she is hopeful.
“There’s no reason to be think these effects are permanent,” she said.
No matter what the long-term effects of the treatment are, Shors said their work gives cancer patients some comfort.
“A lot of people think [the side effects are] just in their mind,” Shors said. “Research gives it some data. It’s real.”