Researchers turn long-term memories on and off with the flip of a switch

Using electrical probes embedded into the brains of rats, scientists have managed to replicate the brain function associated with long-term behaviour and found a way to literally turn memories on and off with the flip of a switch.

The scientists hope their research will eventually lead to a neural prosthesis to help people suffering Alzheimer's disease, the effects of stroke or other brain injury to recover long-term memory capability.

For their experiments, the research team from the University of Southern California (USC) Viterbi School of Engineering's Department of Biomedical Engineering, working with scientists from Wake Forest University, had rats learn which of one of two levers to press to receive a reward.

Building on their previous work showing that the hippocampus is responsible for converting short-term memory into long-term memory, the researchers used embedded electrical probes to record the rat's brain activity between two major internal divisions of the hippocampus as they were learning.

These divisions, which are known as subregions CA3 and CA1, had previously been shown to interact to create long-term memory.

"No hippocampus," says USC's Theodore Berger, "no long-term memory, but still short-term memory."

The researchers then drugged the rats to block the normal neural interactions between CA3 and CA1. The rats that had previously been trained to choose the correct lever no longer displayed the long-term learned behaviour.

"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 5-10 seconds."

The next step of the experiment involved creating an artificial hippocampial system that could duplicate the pattern of interaction between CA3-CA1 interactions. When the team activated the electronic device programmed to duplicate the memory-encoding function, long-term memory capability returned to the pharmacologically blocked rats.

Additionally, when the team applied the same technique to rats with a normal, functioning hippocampus, the device actually strengthened the memory being generated internally in the brain to enhance their memory capability.

The researchers are now looking to duplicate the results in monkeys, with the aim of creating prostheses that can return long-term memory function to human victims of Alzeimer's disease, stroke or other types of brain injury.

The research team's paper entitled "A Cortical Neural Prosthesis for Restoring and Enhancing Memory," appears in the Journal of Neural Engineering.