Young people who received radiation therapy for the most common pediatric brain tumor struggle to create new memories about specific events, according to a study of children and adolescents published in The Journal of Neuroscience. Their ability to recall events prior to treatment, however, remains intact.

Although it greatly improves survival from a brain tumor, radiotherapy has disruptive effects on the developing brain. In their study of seven- to 18-year-olds who underwent radiotherapy as children and a healthy control group, Melanie Sekeres, Paul Frankland, and colleagues asked participants to recall two different memories – an event from the previous month and another from as long ago as they could remember. The researchers found that the brain tumor patients reported fewer episodic details, such as time and place, about the recent memory and comparable episodic details about the old memory compared to the healthy children.

The finding is significant because children after treatment had less volume in the hippocampus – a part of the brain that plays an important role in memory. But while such a decrease usually is associated Alzheimer's disease, dementia, brain injury, epileptic amnesia, encephalitis and aging, with those conditions both remote and recent memories are impaired, said lead author Melanie Sekeres, Ph.D., director of Sekeres Memory Laboratory at Baylor University.

"They have a hard time forming new, detailed memories," Sekeres said. For example, when talking about a recent birthday party for a friend, they might tell how they met the friend and what that individual likes to do, but few specifics such as what they wore, the type of cake, what friends were there and what activities they did at the party, she said.

"Such specific details might seem trivial, but these are precisely the kinds of details that allow us to vividly replay important events in our lives," Sekeres said. "For most events, though, even healthy people forget a lot of specific details over time because we typically don't need to retain all that incidental information. Some forgetting is normal and adaptive, and what we remember is the gist of an older event." The patients were just as capable as healthy children of recalling these older memories, she said.

But for children with brain tumors who have undergone radiation, the study suggested "deficits in their ability to either encode and/or retrieve highly detailed memories for personal events," Sekeres said. "And those are the kind of memories that allow us to understand who we are and give us rich personal lives."

"The surprise, and the up side, is that episodic memories from before the children's treatment were spared," Sekeres said.

The study identifies an area of cognition that is inadvertently impacted by standard treatment methods, which has real consequences for the quality of life of the survivors. The physicians' ultimate goal is to allow their patients to survive and to live as well as possible," Sekeres said. "Although these treatments are often crucial in the effective management of the cancer, if the physicians and the family know there are these unintended side effects, that may be an additional factor to consider when exploring the treatment options."

The preservation of old memories and difficulty forming new ones may be related to reduced neurogenesis in the hippocampus observed in these patients. Overall, the study suggests a previously unknown effect of radiotherapy on the ability to create personal memories that could impact a survivor's quality of life.

The study was conducted with the Brain Tumor Program and the Program in Neurosciences and Mental Health at The Hospital for Sick Children in Toronto, Ontario, Canada. Funding was provided through the Canadian Institutes of Health Research.