Scientists have developed a way to turn memories on and off – literally with the flip of a switch.
Using an electronic system that duplicates the neural signals associated with memory, they managed to replicate the brain function in rats associated with long-term learned behavior, even when the rats had been drugged to forget.
“Flip the switch on, and the rats remember. Flip it off, and the rats forget,” said Theodore Berger of the USC Viterbi School of Engineering, who holds the David Packard Chair in Engineering and is director of the USC Center for Neural Engineering.
Berger is the lead author of “A Cortical Neural Prosthesis for Restoring and Enhancing Memory,” which was published in the Journal of Neural Engineering. His team worked with scientists from Wake Forest University in the study, building on recent advances in our understanding of the brain area known as the hippocampus and its role in learning.
In the experiment, the researchers had rats learn a task, pressing one lever rather than another to receive a reward. Using embedded electrical probes, the experimental research team, led by Sam A. Deadwyler of the Wake Forest Department of Physiology and Pharmacology, recorded changes in the rat’s brain activity between the two major internal divisions of the hippocampus, known as subregions CA3 and CA1.
During the learning process, the hippocampus converts short-term memory into long-term memory, the researchers’ prior work has shown.
“No hippocampus,” Berger said, “no long-term memory, but still short-term memory.” CA3 and CA1 interact to create long-term memory, prior research has shown.
In a dramatic demonstration, the experimenters blocked the normal neural interactions between the two areas using pharmacological agents. The previously trained rats then no longer displayed the long-term learned behavior.
“The rats still showed that they knew ‘when you press left first, then press right next time, and vice versa,’ ” Berger said. “And they still knew in general to press levers for water, but they could only remember whether they had pressed left or right for five to 10 seconds.”
Using a model created by the prosthetics research team led by Berger, the teams then went further and developed an artificial hippocampal system that could duplicate the pattern of interaction between CA3 and CA1.
Long-term memory capability returned to the pharmacologically blocked rats when the team activated the electronic device programmed to duplicate the memory-encoding function.
In addition, the researchers went on to show that if a prosthetic device and its associated electrodes were implanted in animals with a normal, functioning hippocampus, the device actually could strengthen the memory being generated internally in the brain and enhance the memory capability of normal rats.
“These integrated experimental modeling studies show for the first time that with sufficient information about the neural coding of memories, a neural prosthesis capable of real-time identification and manipulation of the encoding process can restore and even enhance cognitive mnemonic processes,” the study reported.
The next steps, according to Berger and Deadwyler, will be attempts to duplicate the rat results in monkeys, with the aim of eventually creating prostheses that might help the human victims of Alzheimer’s disease, stroke or injury recover function.
In addition to Deadwyler and Berger, other authors included USC Viterbi’s Vasilis Z. Marmarelis, a biomedical engineering research professor, and research assistant Dong Song, as well as Wake Forest’s associate professor Robert E. Hampson and postdoctoral fellow Anushka Goonawardena.