Common cancer drugs may be more harmful to the brain than the tumour cells they are meant to destroy, a study suggests.
Laboratory tests showed that brain cells are highly vulnerable to the drugs.
Dose levels typically used when treating patients killed 70% to 100% of neural cells but just 40% to 80% of cancer cells.
Several types of healthy brain cell continued to die for at least six weeks after exposure.
The findings, published in the Journal of Biology, may help explain the little understood cancer therapy side effect of "chemo brain".
Patients can suffer symptoms ranging from memory loss to seizures, loss of vision and even dementia.
Until recently, these problems were often dismissed as having nothing to do with cancer treatment, and blamed on a patient's mental state.
However a growing body of evidence is now leading doctors to accept the reality of chemo brain.
A study earlier this year suggested that more than 82% of cancer patients may suffer from some form of mental impairment.
While scientists have suspected that chemotherapy could have an impact on the central nervous system, it was not clear how this might occur.
Dr Mark Noble, from the University of Rochester Medical Center in New York, who led the new research, said: "This is the first study that puts chemo brain on a sound scientific footing, in terms of neurobiology and cellular biology."
