Turn memory on, off with a switch, literally!

Washington: Scientists have developed a way to turn memories on and off, literally with the flip of a switch, but in rodents for now.

Using an electronic system that duplicates the neural signals associated with memory, a team at the University of Southern California managed to replicate the brain function in rats associated with long-term learned behaviour, 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 lead scientist Theodore Berger. In the experiment, the scientists had rats learn a task, pressing one lever rather than another to receive a reward. Using embedded electrical probes they 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, their prior work has shown. "No hippocampus, no long-term memory, but still short-term memory," Berger said.

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 behaviour.

"The rats still showed that they knew 'when you press left first, then press right next time, and vice versa'. 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," he said.

Using a model, the team then developed an artificial hippocampal system that could duplicate the pattern of interaction between CA3-CA1 interactions. Long-term memory capability returned to the pharmacologically blocked rats when the team activated the electronic device programmed to duplicate the memory encoding function, say the scientists.

"These integrated experimental modelling 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," said Berger.

The findings are to be published in the 'Journal of Neural Engineering'.