The Korea Advanced Institute of Science and Technology (KAIST) said Tuesday that its research team has discovered the basic mechanism behind how the brain encodes memories through a complex network composed of neurons and synaptic connections.

The team, led by Professor Han Jin-hee of the Department of Biological Sciences, used optogenetics to stimulate synapses that do not generate long-term potentiation under natural learning conditions in the amygdala of mice.

Researchers artificially made the synaptic connection stronger or weaker and watched whether the neurons encoding the memory changed.

Researchers found that the memory was encoded in the pre-stimulated synapse, which was induced LTP in mice before they have a terrifying experience. When they weakened the connection by stimulating the synapse again with optogenetic technology immediately after learning, memories were no longer encoded in the same synapses and neurons, however.

When they strengthened the synaptic connection through LTP stimulation in mice after fear-conditioning, memories were selectively encoded in the neurons that generated LTP compared to other nearby neurons.

Past experiences are stored in the brain as memories and recalled later. It is known that these memories are encoded and stored in a very small number of neurons, which is unclear whether these neurons are predetermined or by what principle they are chosen. Solving the matter could bring significant social and economic effects as it could provide a hint to developing a treatment for dementia, according to KAIST.

“LTP creates a new connection pattern among neurons, which create a new cell assembly in the brain-specific to experience,” Professor Han said. “The formation of these strongly interconnected neurons seems to be the basis for the encoding memories in the brain.”

The study results were published in Nature Communications, an open-access journal of Nature, on June 24.