It Is Better to Forget
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Today, I’m grateful that my brain is so good at forgetting! If you’re confused, listen to this story. In nineteen-twenty-nine, a timid man known in psychology as Subject S, complained he couldn’t forget a thing. When they tested him, he could recite page after page of words or numbers. Retested fifteen years later, his recall was perfect.

Who wouldn’t want that, right? Not really. You see, he couldn’t understand abstract concepts and his thoughts were weighted down with excessive detail.

He eventually turned to alcohol to dampen the noise of his mind. So, if forgetting is an important part of memory, how does our brain know what to remember and what to forget? A team of neuroscientists may have found one piece of the answer.

They discovered a new brain pathway involving a cell type they call “melanin-concentrating hormone”, or M.C.H. These are neurons in the brain involved in memory regulation. In mouse studies, they presented toys to two groups of mice. Next, each groups’ MCH neurons were stimulated or inhibited, and the mice were shown the toys again. The stimulated mice acted like the toys were brand new, but the inhibited mice seemed to remember the toys.

The team believes that M.C.H. neurons are activated during sleep to help us “forget” excess details of the prior day, which might also explain why we often forget our dreams. What this study affirms is the value of good sleep. If forgetting is key to memory, we can maximize brain performance by giving it time to store and remove information so we’re ready for a new day.

For more information…

REM sleep–active MCH neurons are involved in forgetting hippocampus-dependent memories
Sleep affects memories via several mechanisms. Izawa et al. identified a possible new pathway in the brain: REM sleep–active hypothalamic melanin-concentrating hormone (MCH)–producing neurons, which, among others, project to the hippocampus. Surprisingly, genetic ablation of MCH neurons increased memory performance in mice. Conversely, pharmacogenetic activation of MCH neurons impaired memory. In vitro physiological experiments showed that activation of MCH fibers in hippocampal slices suppressed spiking activity of pyramidal cells. These findings indicate that the MCH pathway may become a target for memory modulation...

Scientists Identify Neurons That Help the Brain Forget
In mice, cells in the hypothalamus clear out old memories while the animals sleep. Akihiro Yamanaka, a neuroscientist at Nagoya University in Japan, found brain cells in mice that actively disrupt neurons that help consolidate memories...

Dopamine Is Required for Learning and Forgetting in Drosophila
Psychological studies in humans and behavioral studies of model organisms suggest that forgetting is a common and biologically regulated process, but the molecular, cellular, and circuit mechanisms underlying forgetting are poorly understood...