Alternative MethodsConventional Methods


March 29

The Purpose of Sleep? To Forget, Scientists Say

Hector Arnold
Core Spirit member since Dec 24, 2020
Reading time 4 min.

Over the years, scientists have come up with a lot of ideas about why we sleep.

Some have argued that it’s a way to save energy. Others have suggested that slumber provides an opportunity to clear away the brain’s cellular waste. Still others have proposed that sleep simply forces animals to lie still, letting them hide from predators.

A pair of papers published on Thursday in the journal Science offer evidence for another notion: We sleep to forget some of the things we learn each day.

In order to learn, we have to grow connections, or synapses, between the neurons in our brains. These connections enable neurons to send signals to one another quickly and efficiently. We store new memories in these networks.

In 2003, Giulio Tononi and Chiara Cirelli, biologists at the University of Wisconsin-Madison, proposed that synapses grew so exuberantly during the day that our brain circuits got “noisy.” When we sleep, the scientists argued, our brains pare back the connections to lift the signal over the noise.

In the years since, Dr. Tononi and Dr. Cirelli, along with other researchers, have found a great deal of indirect evidence to support the so-called synaptic homeostasis hypothesis.

It turns out, for example, that neurons can prune their synapses — at least in a dish. In laboratory experiments on clumps of neurons, scientists can give them a drug that spurs them to grow extra synapses. Afterward, the neurons pare back some of the growth.

Other evidence comes from the electric waves released by the brain. During deep sleep, the waves slow down. Dr. Tononi and Dr. Cirelli have argued that shrinking synapses produce this change.

Four years ago, Dr. Tononi and Dr. Cirelli got a chance to test their theory by looking at the synapses themselves. They acquired a kind of deli slicer for brain tissue, which they used to shave ultrathin sheets from a mouse’s brain.

Luisa de Vivo, an assistant scientist working in their lab, led a painstaking survey of tissue taken from mice, some awake and others asleep. She and her colleagues determined the size and shape of 6,920 synapses in total.

The synapses in the brains of sleeping mice, they found, were 18 percent smaller than in awake ones. “That there’s such a big change over all is surprising,” Dr. Tononi said.

The second study was led by Graham H. Diering, a postdoctoral researcher at Johns Hopkins University. Dr. Diering and his colleagues set out to explore the synaptic homeostasis hypothesis by studying the proteins in mouse brains. “I’m really coming at it from this nuts-and-bolts place,” Dr. Diering said.

In one experiment, Dr. Diering and his colleagues created a tiny window through which they could peer into mouse brains. Then he and his colleagues added a chemical that lit up a surface protein on brain synapses.

Looking through the window, they found that the number of surface proteins dropped during sleep. That decline is what you would expect if the synapses were shrinking.

Dr. Diering and his colleagues then searched for the molecular trigger for this change. They found that hundreds of proteins increase or decrease inside of synapses during the night. But one protein in particular, called Homer1A, stood out.

In earlier experiments on neurons in a dish, Homer1A proved to be important for paring back synapses. Dr. Diering wondered if it was important in sleep, too.

To find out, he and his colleagues studied mice genetically engineered so that they couldn’t make Homer1A proteins. These mice slept like ordinary mice, but their synapses didn’t change their proteins like the ones in ordinary mice.

Dr. Diering’s research suggests that sleepiness triggers neurons to make Homer1A and ship it into their synapses. When sleep arrives, Homer1A turns on the pruning machinery.

To see how this pruning machinery affects learning, the scientists gave regular mice a memory test. They put the animals in a room where they got a mild electric shock if they walked over one section of the floor.

That night, the scientists injected a chemical into the brains of some of the mice. The chemical had been shown to block neurons in dishes from pruning their synapses.

The next day, the scientists put all the mice back in the chamber they had been in before. Both groups of mice spent much of the time frozen, fearfully recalling the shock.

But when the researchers put the mice in a different chamber, they saw a big difference. The ordinary mice sniffed around curiously. The mice that had been prevented from pruning their brain synapses during sleep, on the other hand, froze once again.

Dr. Diering thinks that the injected mice couldn’t narrow their memories down to the particular chamber where they had gotten the shock. Without nighttime pruning, their memories ended up fuzzy.

In their own experiment, Dr. Tononi and his colleagues found that the pruning didn’t strike every neuron. A fifth of the synapses were unchanged. It’s possible that these synapses encode well-established memories that shouldn’t be tampered with.

“You can forget in a smart way,” Dr. Tononi said.

Other researchers cautioned that the new findings weren’t definitive proof of the synaptic homeostasis hypothesis.

Marcos G. Frank, a sleep researcher at Washington State University in Spokane, said that it could be hard to tell whether changes to the brain at night were caused by sleep or by the biological clock. “It’s a general problem in the field,” he said.

Markus H. Schmidt, of the Ohio Sleep Medicine Institute, said that while the brain might prune synapses during sleep, he questioned whether this was the main explanation for why sleep exists.

“The work is great,” he said of the new studies, “but the question is, is this a function of sleep or is it the function?”

Many organs, not just the brain, seem to function differently during sleep, Dr. Schmidt pointed out. The gut appears to make many new cells, for example.

Dr. Tononi said that the new findings should prompt a look at what current sleeping drugs do in the brain. While they may be good at making people sleepy, it’s also possible that they may interfere with the pruning required for forming memories.

“You may actually work against yourself,” Dr. Tononi said.

In the future, sleep medicines might precisely target the molecules involved in sleep, ensuring that synapses get properly pruned.

“Once you know a little bit of what happens at the ground-truth level, you can get a better idea of what to do for therapy,” Dr. Tononi said.

Comments

Leave your questions here

To write a comment you must
or
Services
Category filter
Concern filter
Type filter
Sort
 

All categories

Wellness Coaching
$10 USD
Ask a Question?

Supportive reflection of a current question that you would like clarity around. Using the SMART method to seek quidance in stepping onto your path of potential…

Beverly Lynn
Reiki
$150 USD
Reiki Services (distant healing session)

In this hour long distant healing session I will use long distance Reiki, crystals and essential oils to balance your Chakras. Balancing your Chakras allows en…

Erin Kirby
Tarot Reading
$10 USD
Intuitive Tarot Reading

Affordable Tarot reading to offer guidance on any given concern.

Elphie Shoppe
Telepsychology
$10 USD
Talk Therapy Sessions

Hello there: These times are dread. Do you need to talk with a safe professional about a troubling personal challenge? I am a professional listener and will li…

Eulalee Thompson
Tarot Reading
$10 USD
Tarot Reading

I offer tarot readings with a 100% accuracy rate. The tarot is meant to give you advice, to point you in the right direction or to provide you with clarity. Bu…

Zara Kalil
Angel Healing
$10 USD
Mental Health Advice & Tips

I can help you with past issues and give advice and tips on how to better your life. I can see through my third eye and receive messageson what you need to do …

Beings Of Light
Life Coaching
$10 USD
Discovery call

Are you interested in supporting your health with safe and effective holistic medicine? Not sure if you should switch diets, work with a health coach or explor…

Suzana Da Costa
Wellness Coaching
$50 USD
Mental Health and Holistic Lifestyle Coaching

Hi there! I’m Doug and I offer 1 on 1 Holistic Lifestyle and Mental Health Coaching sessions. Navtigating life with mental health issues of any sevarity is a h…

Doug Peterson
Wellness Coaching
$10 USD
Mental Health and Holistic Lifestyle Coaching Consultation

Hi there! I’m Doug and I offer 1 on 1 Holistic Lifestyle and Mental Health Coaching sessions. Navtigating life with mental health issues of any sevarity is a h…

Doug Peterson
Career Coaching
$195 USD
Holistic Lifestyle & Nutrition Coaching

ARE YOU TIRED? STRESSED OUT? STRUGGLING WITH YOUR WEIGHT? UNDER SLEPT? LOST YOUR ZEST FOR LIFE?

If this sounds like you, then you don’t need a new diet… you n…

David Giddings
Bach flower therapy
$120 USD
Bach Flower Essence Consultation

Exploration of where you’re feeling stuck or limited in life and recommendations of Bach Flower Essences to help loosen and dissolve old patterns.

Suzana Da Costa
Cognitive-behavioral therapy
$100 USD
Subliminal therapy

In this service we will use Subliminal therapy and Sound healing as alternative to tradition cognitive behavioral therapy.

We are born with our thoughts. Do n…

Ahmed Amin Youssef
Psychic Reading
$10 USD
I will do oracle and tarot card readings

I will do oracle & tarot card reading in any area of your life. You will get answer from the Angelic, Elemental, Faerie or Galactic realms. I will share wi…

Wisdom Realms
Spiritual Healing
$10 USD
Intro 2 Alignment Healing Chant

Namaste.

That is my greeting to the spirit within you. Join me for a welcome introduction session to celebrate my arrival at Core Spirit!

For 15 minutes I wi…

Ti3rc3 Fire
Mediumism
$55 USD
Psychic Medium Readings

READINGS Currently, all readings will be offered virtually. Appointments are available on Tuesday and Thursday mornings between 9am-1pm (UK Time Zone). When we…

Jan Morgan
Oracle Cards Reading
$25 USD
Psychic Reading 15 Minutes

Well-versed in the main 5 clairs, I will Intuitively answer your questions for 15 minutes.

Jyll Hoyrup
Emotional Stress Release
$150 USD
Creatrix® Breakthrough

This is a revolutionary process, SPECIALLY designed for women. You will be able to clear your most depeest BLOCKS and limiting beliefs. 

This is the only too…

Tamar Viva
Distance Healing
$10 USD
Energy Healing (Distant)

Distant Energy healing promotes relaxation, reduces tension and stress and will support an overal sense of well being after a treatment. It is an effective ad…

Beverly Lynn
Emotional Freedom Technique
$10 USD
Transform Your Relationship With Your Money

In this session, you will learn the basics of Emotional Freedom Technique, or EFT. Together we will use that technique, sometimes called simply tapping, to sor…

Nancy Allen
Personal Development Coaching
$10 USD
Anxiety and Depression - Coaching Consultation and Assessment Call

Are you looking to begin making a change in your life and become the best version of yourself by breaking free from the emotional barriers that has been blocki…

Amritha Kailas
Mind Control
$72 USD
Women's Emotional Wellness and Transformation Coaching

Are you dealing with confusion, low esteem, anxiety, depression, overthinking , relationship issues and trying to find focus, confidence, purpose, peace and b…

Amritha Kailas
Past Life Regression
$10 USD
Soul Readings

Your Soul is an accumulated repository of existential experience.

Access your creativity, things you learned from past lives.

Healing, you learned how to mak…

Core of Your Spirit
Emotional Freedom Technique
$105 USD
EFT tapping - Heal your past and uncover your authentic self

EFT (Emotional Freedom Techniques) is also know as EFT tapping. It is a mind-body approach which helps us to improve our physical, emotional and mental well-be…

Sina Weber
Tarot Reading
$10 USD
Single Card Pull

I will pull one single card for you to answer any question or concern. Typically, these types of quick readings are good for yes or no questions or simple answ…

Megan Zavar