Scientists, for the first time, have completely reversed memory loss resulting from traumatic brain injuries (TBI) in mice, a team of researchers announced Monday.

An experimental new drug, ISRIB, restored the ability to learn and remember in brain-damaged mice. More strikingly, the drug appeared to work even when the injuries were a month old.

"This is extraordinarily exciting," said Peter Walter, who discovered ISRIB and is co-senior author of the UCSF study, in a statement. "We think that ISRIB may uncover an untapped reservoir in the brain that allows damaged memory circuits to be repaired."

Researchers found ISRIB was effective in reversing the effects of two different types of brain injuries: localized brain injuries, in which only certain regions of the brain are damaged, and concussive brain injuries, when the trauma effects the entire brain.

"In general, animals with these injuries never learn well again," Susannah Rosi, the other co-senior author, said in a statement. "So it's remarkable that ISRIB could restore the ability to form new memories even when we delayed giving the drug for four weeks after the injury. This has not been considered possible."