Eliminating so-called "zombie" cells in the brain has been shown to reduce cognitive decline in mice.
New research, published in the journal Nature, reveals a link between neurodegeneration and the accumulation of senescent cells.
The findings could aid developments in the diagnosis and treatment of conditions such as Alzheimer's disease, experts say.
Senescent or "zombie" cells are defective cells which can no longer reproduce or perform their normal functions, but cannot die.
US researchers, from the Mayo Clinic in Minnesota, found they gather in certain brain cells in mice before the loss of cognitive ability.
The team previously showed removing senescent cells - which are linked to a number of age-related diseases - extends the healthy life span of naturally aged mice.
In the new study, they imitated the features of Alzheimer's in the animals.
The drug was used throughout the life of the mouse, reducing the build-up of tau, a damaging chemical linked to Alzheimer's and degeneration of the brain.
"When senescent cells were removed, we found that the diseased animals retained the ability to form memories, eliminated signs of inflammation, did not develop neuro-fibrillary tangles, and had maintained normal brain mass," lead author Tyler Bussian said.
They believe the cells may provide a target for the treatment of cognitive diseases, but warn further research is needed to establish whether the findings can be replicated in humans.
Dr James Pickett, head of research at Alzheimer's Society, said: "There hasn't been a new dementia drug in 15 years so it's exciting to see the results of this promising study in mice.
"However, there are several barriers to overcome before we can say if this is a safe, effective treatment in people."
