Scientists at two California universities have isolated single neurons responsible for holding the memory of an image, in what they called an unprecedented finding that could be used as a building block in the study of how memory works.

Professor Christof Koch of the California Institute of Technology, one of the scientists involved in the study, said pictures of celebrities like Halle Berry in her skin-tight leather suit from the movie “Catwoman” and former “Friends” television star Jennifer Aniston were used in their experiment because they are so widely recognizable.

“We only have very little time” to probe inside people’s heads, he said, “and we have to have something we are reasonably sure our subjects will respond to.”

Scientists, including researchers at the University of California, Los Angeles, tested eight patients with epilepsy by implanting electrodes in the brain. They then determined which neurons were stimulated when shown pictures of celebrities, buildings and other familiar images, including Bill Clinton and the Beatles.

The single brain cells could also apparently differentiate similar images. When a new person was substituted in the catsuit, there was no response from the cell that had earlier responded to Berry.

The study has serious implications for learning about the way memories are retained, scientists said.

For years, researchers have known that images initially excite many neurons in the brain, but they did not know that collective memories can be stored in a single, isolated cell.

Koch said practical implications are few for now, but he likened the knowledge discovery to a starting point from which to understand how the brain’s memory functions.

Dr. Eric Braverman, director of PATH Medical in New York and author of “Edge Effect,” a specialist in memory study not involved with the experiment, said the finding might have a significant impact on research into illnesses like Alzheimer’s disease and dementia.

He said, for example, that if a single cell is responsible for a memory and that image is impaired, then perhaps that single cell can be treated or maybe even replaced.