Everyday events are easy to forget, but unpleasant ones can remain engraved in the brain. A new study published in the Proceedings of the National Academy of Sciences identifies a neural mechanism through which unpleasant experiences are translated into signals that trigger fear memories by changing neural connections in a part of the brain called the amygdala. The findings show that a long-standing theory on how the brain forms memories, called Hebbian plasticity, is partially correct, but not as simple as was originally proposed.
The effort led by Joshua Johansen from the RIKEN Brain Science Institute in Japan and New York University scientists Lorenzo Diaz-Mataix and Joseph LeDoux, tested an influential theory proposed in 1949 by the Canadian psychologist Donald Hebb that neurons that are connected and fire electrical impulses at the same time increase the strength of their connections to form a memory. Previous work in reduced brain preparations had demonstrated that this process, called Hebbian plasticity, can increase the connection strength between neurons, but it remained untested during memory formation in behaving animals. To directly test this question, the team examined whether coincident electrical excitation of neurons which are known to store fear memories is necessary and sufficient to trigger changes in neural connections and memory formation.
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