There is a biological reason why events that occur in tandem with emotions such as fear, anger and joy are far more memorable, a U.S. study found.

Researchers at The John Hopkins University in Baltimore, Cold Spring Harbor Laboratory in New York and New York University have identified a hormone that is released during emotional arousal; they believe the hormone "primes" nerve cells to remember events.

The Johns Hopkins study leader Richard Huganir described the brain as a big circuit board in which each new experience creates a new circuit. The research team found that during emotional peaks, the hormone norepinephrine dramatically sensitizes synapses -- the site where nerve cells make an electro-chemical connection -- to enhance the sculpting of a memory into the big board.

Norepinephrine, also known as a "fight or flight" hormone, energizes the process by adding phosphate molecules to a nerve cell receptor called GluR1.

The phosphates help guide the receptors to insert themselves adjacent to a synapse and when the brain needs to form a memory, the nerves have plenty of available receptors to quickly adjust the strength of the connection and lock that memory into place, Huganir explains.

The findings are published in the journal Cell.