Why Dreams Are Hard to Remember

PASADENA, Calif. -- Researchers at the California Institute of Technology are making progress in sleep science and understanding why it's difficult to remember dreams.

According to the findings published last month in the journal Neuron, memories are formed in the brain's hippocampus but stored elsewhere -- most likely in the neocortex, the outer layer of the brain.

During the transfer of memories, a neuron symphony of precisely timed bursts occurs. But during rapid-eye-movement (REM) sleep, the phase during which dreaming occurs, the neuron pairs seemed to talk right past each other, firing at the same rates as before but no longer in concert.

"It was surprising to find that the timing relationship almost completely went away during REM sleep," said Casimir Wierzynski, a Caltech graduate student in computation and neural systems.

Scientists speculate that the absence of memory-consolidating chatter may eventually help to explain why dreams can be so difficult to remember.

The findings only raise possibilities, providing avenues for further research in the field, said team leader Athanassios Siapas.

"Now that we've shown this link, we have a framework we can use to study these questions further. This is just a step toward our goal of some day fully understanding the relationship between memory and sleep," Siapas said.

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