Following radiation to the head, rats transplanted with human embryonic stem cells had greater improvements in learning and memory, showed a research team based at the University of California.

The scientists, publishing their results in the Proceedings of the National Academy of Sciences, hope that one day human embryonic stem cells could be used to help restore learning and memory in patients who have had radiotherapy for brain tumours. Radiotherapy remains a frontline treatment of brain cancer, however, patients undergoing such treatment are affected by varying degrees of decline in their ability to learn and remember which can affect their quality of life and limit the course of their radiation treatment.

'It's a progressive, debilitating side effect of cranial irradiation,' said Professor Charles Limoli, senior author of the study. 'Any treatments showing promise at reversing this are worthy of pursuit'.

It is thought that the debilitating side effects of radiation arise from the depletion of stem cell pools in a central region of the brain called the 'hippocampus'.

In the study, the scientists transplanted human embryonic stem cells directly into the hippocampus of the rat two days after radiation treatment. Four months post-treatment, these rats demonstrated superior performance in tasks testing learning and memory compared to irradiated rats, which did not receive the stem cell treatment. Furthermore, the scientists showed that the transplanted cells had survived, migrated to other parts of the brain and assumed the appearance of other neurons in the brain.

'Our findings provide the first evidence that such cells can be used to ameliorate radiation-induced damage of healthy tissue in the brain,' said Professor Limoli.

The next step is to uncover the mechanism by which this treatment is working: for example, are the cells replacing damaged brain tissue, or are they helping repair and support existing tissue?