Children with certain types of brain tumors who undergo radiation therapy are less likely to recall the specifics of events occurring after radiation than to remember pre-treatment happenings, according to a Baylor University study. 

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 with 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.

For the study, published in The Journal of Neuroscience, researchers focused on “autobiographical memory,” which is linked to unique personal events. Autobiographical memory involves the recollection of emotional and perceptual details that allow a person to re-experience the event mentally, said Sekeres, assistant professor of psychology and neuroscience in Baylor University’s College of Arts & Sciences.

Radiotherapy and chemotherapy are used to treat the most common malignant brain tumor in children — a medulloblastoma. The reduced volume of the hippocampus is likely due, in part, to radiation’s impact on the development of new cells in the nervous system, including the growth of new neurons in the hippocampus, or neurogenesis.

Comparing radiotherapy and chemotherapy treatment

“We know that these new cells play crucial roles in regulating memory and spatial learning, which is required to navigate. These treatments limit the brain’s ability to produce these new cells, which, in turn, limits the ability to form new memories,” Sekeres said.

Research participants were 13 child survivors of brain tumors who had previously received radiotherapy and chemotherapy treatment at least one year before the study.

Twenty-eight healthy youths of similar ages (ranging from 7 to 18) also were recruited for the study, conducted with The Hospital for Sick Children in Toronto, Ontario, Canada. All the youths completed the Children’s Autobiographical Interview a standardized memory test and underwent magnetic resonance imaging (MRI) of the brain.

In individual interviews, children in both groups also were asked to recall memories from personal events that occurred at a specific time and place. Children were asked to recall a very old memory from an event before their radiation treatment (or an equally old memory for the healthy children), and a recent memory from within the past month.

They were offered a list of events such as a birthday party, family trip, graduation and getting a pet but were told that they could choose another happening. The interview allowed children to freely recall without prompting before being asked general and specific questions about the event.