Biological brains are the most complex and powerful learning machines that scientists know of, and figuring out how they work is one of the great tasks of modern science. Among the many mysteries of brain science is the question of how memory works; how we remember things. But another often overlooked but key function of how our brains work is the question of how we forget.
Forgetfulness is essential to the function of a complex learning machine, because this is how insignificant information can be discarded to make room for more important information. Now for the first time, scientists have discovered another material in nature that seems capable of forgetting just like the brain does: a quantum crystal called perovskite.
"The brain has limited capacity, and it can only function efficiently because it is able to forget," said nanoscientist Subramanian Sankaranarayanan, one of the researchers on the breakthrough study, in a press release. "It's hard to create a non-living material that shows a pattern resembling a kind of forgetfulness, but the specific material we were working with can actually mimic that kind of behavior."
Sankara works at the U.S. Department of Energy's Argonne National Laboratory, which partners with different universities and institutions to solve big ideas like this one.
How perovskite works
Perovskite is an atomic crystal that appears to "adapt" or "habituate" when scientists fiddle with its protons.
"When scientists add or remove a proton from the perovskite lattice, the material's atomic structure expands or contracts dramatically to accommodate it in a process called 'lattice breathing'," explained Badri Narayanan, another member of the research team.
As this process is repeated, however, the perovskite changes its properties to accommodate for its unusual environment, until eventually seeming to "forget" that things were ever any different.
"Eventually, it becomes harder to make the perovskite 'care' if we are adding or removing a proton," explained Hua Zhou, who also worked on the project. "It’s like when you get very scared on a water slide the first time you go down, but each time after that you have less and less of a reaction."
It's a fascinating effect on the quantum level that represents the first known mechanism outside of a biological brain that can so closely mimic neurological forgetfulness. The process could eventually be used to create more advanced artificial intelligence — to give machines the kind of flexibility and complexity that we see in our brains but which is so difficult to duplicate in other natural materials. The research can also help scientists better understand how these mechanisms might work within biological brains.
"These simulations, which quite closely match the experimental results, are inspiring whole new algorithms to train neural networks to learn," said Mathew Cherukara, an Argonne postdoctoral scholar.