Melanin-concentrating hormone (MCH) neurons are unlike most neurons: they are most active during sleep. Scientists have studied their role in regulating sleep and feeding behavior for some time, but the Yamanaka lab at Nagoya University in Japan has found that they may also have a role in preventing the consolidation of memories during sleep.  

Prof. Yamanaka (a co-developer of Teleopto) found that MCH neurons can suppress neurons in the hippocampus responsible for memory consolidation. His lab confirmed this role by using 

Teleopto Wireless Optogenetics: blue light and channelrhodopsin 2 were used to activate MCH neurons; green light/archaerhodopsin were used to inhibit them. This was done bilaterally during both memory consolidation (REM sleep) and awake periods. Teleopto was used so that the animals were able to move freely and interact naturally with objects during Novel Object Recognition (NOR) tests.

When mice had MCH neurons activated during sleep, their ability to remember events decreased: they forgot which objects they had encountered before sleeping and treated them the same way they treated novel objects. Conversely, when their MCH neurons were inhibited they were able to remember which objects they had already interacted with. They ignored the familiar objects and explored the novel objects instead.

When Teleopto was used to illuminate MCH neurons during awake periods, there was no effect on hippocampal-dependent memory.

 When interviewed by The New York Times, Prof. Yamanaka explained

“These results suggest that hypothalamic M.C.H. neurons help the brain actively forget new information that is not important.” And because the neurons are most active during R.E.M. sleep, they may explain why humans usually do not remember their dreams when they wake up. “The neurons may be clearing up memory resources for the next day,” Dr. Yamanaka said.

The article, “REM sleep–active MCH neurons are involved in forgetting hippocampus-dependent memories.” is available at:

https://science.sciencemag.org/content/365/6459/1308