Memories in the Night: How Your Brain Comes Alive While You Sleep

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A Common Denominator

So is there a link between both new findings? Memory consolidation and the removal of waste proteins seem to be two different processes, but their commonality (sleep) seem a little coincidental.

“It makes sense that these processes both happen during a time when animals are not actively interacting with the world,” Majewska says. “Processes like homeostasis and others that need energy to physically remodel networks aren’t happening when the brain’s energy should be focused on sensory stimuli, computation, and action.”

And once we’ve finally unlocked the secrets of the sleeping brain and disentangled the myriad functions it fulfills, who knows what applications might emerge? If, for example, we can see a memory being synthesized by the hippocampus, then reactivated while the organism is asleep and replayed somewhere else to further entrench itself in experience, can’t we access that “memory” (“engram,” “qualia,” call it what you will …) and do things to the contents by enforcing different patterns of cells firing?

As Ólafsdóttir points out, we can already slow a memory down from taking hold by interrupting the reactivation process. Research published by the Society for Neuroscience even showed a memory could be “transferred” from one rat’s brain to another using RNA (the messaging molecule for DNA). Whether it’s done chemically or electrically, maybe we can rewire firing neurons to delete or even edit the contents of memories in transit.

She calls it a “dangerous” area of research and there would indeed be reams of ethical constraints in humans, but she says we basically have the technology to induce post-traumatic stress disorder (PTSD) in rats, re-engineer the memory, and look for a reduction in symptoms and behavior.

The Challenges of Today

But looking away from a sci-fi future and a little more at the here and now, there’s also the possibility of treating disorders like Alzheimer’s or Parkinson’s disease. Majewska says they could be caused or contributed to by the neurological breakdown of the cleaning process she’s studied one that inevitably slows with age.

So if we could synthesize a drug compound that promotes microglia activity artificially or somehow fools the brain into thinking it’s asleep so they spend longer doing their work, wouldn’t that be a good thing?

As always, no process or substance in the brain (or the entire body, for that matter) is an island, and Majewska warns that it’s a tough question. “It’s probably important to have the appropriate activity of microglia at the appropriate time. Promoting repair and synaptic interactions might be a benefit for diseases that disrupt the process, but enhancing it might have unintended consequences. It might interfere with other functions or processes that need microglia to stay out of the way. It’ll be powerful to be able to manipulate microglial function, but we need to be very careful.”

Ólafsdóttir’s research is particularly applicable to memory-eroding diseases like Alzheimer’s, in which the worst neural degeneration is found in the hippocampus. One of the strange and heartbreaking properties of Alzheimer’s is the seemingly unshakable nature of much older memories alongside the loss of newer ones.

But when viewed in relation to her work in the brain filing memories away, older memories being intact long after having left the hippocampus to become more cemented and permanent in the cortex makes perfect sense. Neuroscience also accepts that memory retention has a strongly emotional dimension, and as Ólafsdóttir says, previous work has shown selective coupling between the hippocampus and the amygdala, the region considered in overarching terms as the seat of emotion in the brain.

Maybe, she suggests, the very strong and easily-triggered memories associated with a disorder like PTSD are “over-consolidated reactors,” given more emotional juice thanks to input from the amygdala. Majewska adds that quality sleep is an effective treatment in neurodevelopmental and neurodegenerative disorders like PTSD and Alzheimer’s. “Recovery that includes procedures and education to promote sleep is helpful,” she thinks. “Understanding the molecular mechanisms that impact cell types during sleep could also let us to put microglia ‘to sleep’ so the rest of the brain can function normally.”

For now, sleep’s true purpose is still something of a mystery, but important neuroscience is shining a light on the microscopic particles and activities that wake up when we drift off. The true answer to the question “what is sleep for” will likely be a multi-faceted web of chemical and bioelectrical behaviors, and with better technology and expanded understanding, we’re getting closer one step at a time …

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