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How much oxygen does a brain consume?

How much oxygen does a brain consume?


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I am not a biologist - my background is in quantitative sciences, and I am trying to answer a rather quantitative question:
How much oxygen does a brain consume?

This however raises many sub-questions of purely biological nature:

  • How is the brain supplied by oxygen? (My naive understanding is that lungs tie oxygen to hamoglobin, which is then carried by blood to cells, which then ingest the oxygen, converting it to ATF. Is this correct? Does this apply to neurons as well?)
  • How much energy a neuron or the whole brain consumes per unit time? (e.g., per hour, in energy units or oxygen content)

I will appreciate explanations in laymen terms or references to accessible literature.


As has been commented, the answers to some of the questions here can be found in the literature. The nutrients and oxygen reach all tissues by the circulatory system - i.e. in the blood. And the link supplied by @trondhansen suggests a litre of oxygen a day. (I wouldn't know - I never studied physiology.) However, as regards energy, I supply the following from the biochemistry text, Berg et al.

Brain. Glucose is virtually the sole fuel for the human brain, except during prolonged starvation. The brain lacks fuel stores and hence requires a continuous supply of glucose. It consumes about 120 g daily, which corresponds to an energy input of about 420 kcal (1760 kJ), accounting for some 60% of the utilization of glucose by the whole body in the resting state.

Note the correct form of expression:

the brain / consumes fuel / to generate energy / to perform 'work'

Glucose is the fuel, ATP is the chemical energy currency, and the work performed (as the text makes clear) is for the main (60%-70%) to:

maintain the sodium/potassium ion membrane potential required for the transmission of the nerve impulses.

(I am afraid that's about as layman's terms as I do. It does say on the label that this site is for students of biology.)


Coronavirus does not infect the brain but still inflicts damage, study finds

SARS-CoV-2, the virus that causes COVID-19, likely does not directly infect the brain but can still inflict significant neurological damage, according to a new study from neuropathologists, neurologists, and neuroradiologists at Columbia University Vagelos College of Physicians and Surgeons.

"There's been considerable debate about whether this virus infects the brain, but we were unable to find any signs of virus inside brain cells of more than 40 COVID-19 patients," says James E. Goldman, MD, PhD, professor of pathology & cell biology (in psychiatry), who led the study with Peter D. Canoll, MD, PhD, professor of pathology & cell biology, and Kiran T. Thakur, MD, the Winifred Mercer Pitkin Assistant Professor of Neurology.

"At the same time, we observed many pathological changes in these brains, which could explain why severely ill patients experience confusion and delirium and other serious neurological effects -- and why those with mild cases may experience 'brain fog' for weeks and months."

The study, published in the journal Brain, is the largest and most detailed COVID-19 brain autopsy report published to date, suggests that the neurological changes often seen in these patients may result from inflammation triggered by the virus in other parts of the body or in the brain's blood vessels.

No Virus in Brain Cells

The study examined the brains of 41 patients with COVID-19 who succumbed to the disease during their hospitalization. The patients ranged in age from 38 to 97 about half had been intubated and all had lung damage caused by the virus. Many of the patients were of Hispanic ethnicity. There was a wide range of hospital length with some patients dying soon after arrival to the emergency room while others remained in the hospital for months. All of the patients had extensive clinical and laboratory investigations, and some had brain MRI and CT scans.

To detect any virus in the neurons and glia cells of the brain, the researchers used multiple methods including RNA in situ hybridization, which can detect viral RNA within intact cells antibodies that can detect viral proteins within cells and RT-PCR, a sensitive technique for detecting viral RNA.

Despite their intensive search, the researchers found no evidence of the virus in the patients' brain cells. Though they did detect very low levels of viral RNA by RT-PCR, this was likely due to virus in blood vessels or leptomeninges covering the brain.

"We've looked at more brains than other studies, and we've used more techniques to search for the virus. The bottom line is that we find no evidence of viral RNA or protein in brain cells," Goldman says. "Though there are some papers that claim to have found virus in neurons or glia, we think that those result from contamination, and any virus in the brain is contained within the brain's blood vessels." "If there's any virus present in the brain tissue, it has to be in very small amounts and does not correlate with the distribution or abundance of neuropathological findings," Canoll says.

The tests were conducted on more than two dozen brain regions, including the olfactory bulb, which was searched because some reports have speculated that the coronavirus can travel from the nasal cavity into the brain via the olfactory nerve. "Even there, we didn't find any viral protein or RNA," Goldman says, "though we found viral RNA and protein in the patients' nasal mucosa and in the olfactory mucosa high in the nasal cavity." (The latter finding appears in an unpublished study, currently on BioRxiv, led by Jonathan Overdevest, MD, PhD, assistant professor of otolaryngology, and Stavros Lomvardas, PhD, professor of biochemistry & molecular biophysics and neuroscience.)

Hypoxic Damage and Signs of Neuronal Death

Despite the absence of virus in the brain, in every patient the researchers found significant brain pathology, which mostly fell into two categories.

"The first thing we noticed was a lot of areas with damage from a lack of oxygen," Goldman says. "They all had severe lung disease, so it's not surprising that there's hypoxic damage in the brain."

Some of these were large areas caused by strokes, but most were very small and only detectable with a microscope. Based on other features, the researchers believe these small areas of hypoxic damage were caused by blood clots, common in patients with severe COVID-19, that temporarily stopped the supply of oxygen to that area.

A more surprising finding, Goldman says, was the large number of activated microglia they found in the brains of most patients. Microglia are immune cells that reside in the brain and can be activated by pathogens.

"We found clusters of microglia attacking neurons, a process called 'neuronophagia,'" says Canoll. Since no virus was found in the brain, it's possible the microglia may have been activated by inflammatory cytokines, such as Interleukin-6, associated with SARS-CoV-2 infection.

"At the same time, hypoxia can induce the expression of 'eat me' signals on the surface of neurons, making hypoxic neurons more vulnerable to activated microglia," Canoll says, "so even without directly infecting brain cells, COVID-19 can cause damage to the brain."

The group found this pattern of pathology in one of their first autopsies, described by Osama Al-Dalahmah, MD, PhD, instructor in pathology & cell biology, in a case report published last March in Acta Neuropathologica Communications. Over the next few months, as the neuropathologists did many more COVID brain autopsies, they saw similar findings over and over again and realized that this is a prominent and common neuropathological finding in patients who die of COVID.

The activated microglia were found predominantly in the lower brain stem, which regulates heart and breathing rhythms, as well as levels of consciousness, and in the hippocampus, which is involved in memory and mood.

"We know the microglia activity will lead to loss of neurons, and that loss is permanent," Goldman says. "Is there enough loss of neurons in the hippocampus to cause memory problems? Or in other parts of the brain that help direct our attention? It's possible, but we really don't know at this point."

Persistent Neurological Problems in Survivors

Goldman says that more research is needed to understand the reasons why some post-COVID-19 patients continue to experience symptoms.

The researchers are now examining autopsies on patients who died several months after recovering from COVID-19 to learn more.

They are also examining the brains from patients who were critically ill with acute respiratory distress syndrome (ARDS) before the COVID-19 pandemic to see how much of COVID-19 brain pathology is a result of the severe lung disease.

The study, titled "COVID-19 Neuropathology at Columbia University Irving Medical Center/New York Presbyterian Hospital," was published April 15, 2021, in Brain.

Other contributors (all at Columbia unless otherwise noted): Emily Happy Miller, Michael D. Glendinning, Osama Al-Dalahmah, Matei A. Banu, Amelia K. Boehme, Alexandra L. Boubour, Samuel L. Bruce, Alexander M. Chong, Jan Claassen, Phyllis L. Faust, Gunnar Hargus, Richard Hickman, Sachin Jambawalikar, Alexander G. Khandji, Carla Y. Kim, Robyn S. Klein (Washington University School of Medicine), Angela Lignelli-Dipple, Chun-Chieh Lin (Dartmouth-Hitchcock Medical Center), Yang Liu, Michael L. Miller, Gul Moonis, Anna S. Nordvig, Serge Przedborski, Morgan L. Prust, William H. Roth, Allison Soung (Washington University School of Medicine), Kurenai Tanji, Andrew F. Teich, Dritan Agalliu, and Anne-Catrin Uhlemann.


How Brain Death Works

First, one must clarify that everyone dies of "brain death." Whether an old person suffers cardiac arrest resulting in the lack of oxygen and nutrients to the brain, or a younger person suffers a gunshot wound to the head resulting in brain death, it's the same diagnosis.

The brain controls all our bodily functions, but there are three things it cannot do:

  • It cannot feel pain. The brain can feel pain from all over the body, but not within itself.
  • The brain cannot store oxygen. A person can feel a lack of oxygen after only a few seconds. When someone stands up too quickly and becomes dizzy, this is an example of the loss of blood flow to the brain that can be sensed.
  • The brain cannot store glucose (blood sugar). Diabetics who give themselves too much insulin can drop their blood sugar level and faint, and without immediate glucose infusion the brain can die.

The brain can survive for up to about six minutes after the heart stops. The reason to learn cardiopulmonary resuscitation (CPR) is that if CPR is started within six minutes of cardiac arrest, the brain may survive the lack of oxygen. After about six minutes without CPR, however, the brain begins to die. (See How CPR Works to learn more about the procedure.) Prompt resuscitation allows the physician time to assess and treat the damaged brain. Medication and mechanical ventilation permit tissue oxygenation, but severe brain damage or a prolonged period without oxygen or glucose causes the death of the brain.

By definition, "brain death" is "when the entire brain, including the brain stem, has irreversibly lost all function." The legal time of death is "that time when a physician(s) has determined that the brain and the brain stem have irreversibly lost all neurological function."


Anger and the Brain: What happens in your head when you get angry

I think understanding information on the brain is essential in laying a foundation for anger management. Your brain is the center of your logic and emotions. By understanding how your body works, you can make better sense over why you think and feel what you do when angry.

Scientists have identified a specific region of the brain called the amygdala, as the part of the brain that processes fear, triggers anger, and motivates us to act. It alerts us to danger and activates the fight or flight response. Researchers have also found that the prefrontal cortex is the area of the brain that controls reasoning, judgment and helps us think logically before we act.

Stereotypically, women are thought of as emotional and men as logical, but biology reveals this as false. Curiously, the inverse in true. Scientists have discovered that men have a larger part of their brain devoted to emotional responses and a smaller region for logical thinking than women. This makes sense if you consider the energy needed to be vigilant for self-protection. Men are hard wired for hunting, competition and dominance. Their powerful emotional outbursts of anger, when seen through the hunter gatherer lens, are helpful to come out on top during a confrontation.

Men in the hunter-gatherer world needed a large amygdala to quickly respond when scanning the terrain for potential danger: Is this bad? Could it hurt me? If the information registered as dangerous, the amygdala broadcasts a distress signal to the entire brain, which in turn, triggers a cascade of physiological responsesfrom a rapid heart rate to jacked-up blood pressure to tense muscles to the release of adrenaline. Within milliseconds, men explode with rage or freeze in fear, well before their prefrontal cortex can even grasp what is happening.

For example, say youre in a crowded restaurant and the noise of chatter from dozens of conversations fills the air. Suddenly a waiter drops a tray with several glasses, which crashes and shatters as they hit the floor. Automatically, the restaurant comes to a dramatic halt as everyone simultaneously falls to a hush. There is an instinctual reflex to stop and freeze when there is a sudden loud noise.

This raises the important point that the brain doesnt immediately know if an experience is real or imagined. How can this be? While the amygdala and prefrontal cortex are working towards the same goal, to help you survive, they come at the problem from different directions.

Say youre watching a movie. If it is a scary movie and you hear a noise outside, your amygdala will say, Get up and lock the door. Your prefrontal cortex knows there is no ax murderer outside but you will likely get up and lock the door anyways. Or say youre watching a sad movie. You know it is a movie and no one died, but you may begin to cry anyways. All of these circumstance sets off false alarms, which unleashes the same level of feeling as if the real event were happening. This means that if the brain cant tell what is dangerous and what isnt, everything seems like a threatened.

The amygdala&rsquos emotional response provides a mechanism to work around the limitation of the prefrontal cortex&rsquos reasoning. For example, the prefrontal cortex will remember what your ex-partner looks like, that petite brunette who dumped you for a new lover. It is the amygdala that is responsible for the surge of fury that floods your body when you see someone who looks even vaguely like your former mate.

And &ldquovaguely&rdquo is the operative word here. For when the amygdala tries to judge whether a current situation is hazardous, it compares that situation with your collection of past emotionally charged memories. If any key elements are even vaguely similarthe sound of a voice, the expression on a faceyour amygdala instantaneously lets loose its warning sirens and an accompanying emotional explosion.

This means even vague similarities can triggers fear signals in the brain, alerting you of a threat. This false alarm happens because the goal is to survive, there is an advantage to react first and think later.


Sounding the alarm

The stress response begins in the brain (see illustration). When someone confronts an oncoming car or other danger, the eyes or ears (or both) send the information to the amygdala, an area of the brain that contributes to emotional processing. The amygdala interprets the images and sounds. When it perceives danger, it instantly sends a distress signal to the hypothalamus.

Command center

When someone experiences a stressful event, the amygdala, an area of the brain that contributes to emotional processing, sends a distress signal to the hypothalamus. This area of the brain functions like a command center, communicating with the rest of the body through the nervous system so that the person has the energy to fight or flee.

The hypothalamus is a bit like a command center. This area of the brain communicates with the rest of the body through the autonomic nervous system, which controls such involuntary body functions as breathing, blood pressure, heartbeat, and the dilation or constriction of key blood vessels and small airways in the lungs called bronchioles. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system functions like a gas pedal in a car. It triggers the fight-or-flight response, providing the body with a burst of energy so that it can respond to perceived dangers. The parasympathetic nervous system acts like a brake. It promotes the "rest and digest" response that calms the body down after the danger has passed.

After the amygdala sends a distress signal, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. These glands respond by pumping the hormone epinephrine (also known as adrenaline) into the bloodstream. As epinephrine circulates through the body, it brings on a number of physiological changes. The heart beats faster than normal, pushing blood to the muscles, heart, and other vital organs. Pulse rate and blood pressure go up. The person undergoing these changes also starts to breathe more rapidly. Small airways in the lungs open wide. This way, the lungs can take in as much oxygen as possible with each breath. Extra oxygen is sent to the brain, increasing alertness. Sight, hearing, and other senses become sharper. Meanwhile, epinephrine triggers the release of blood sugar (glucose) and fats from temporary storage sites in the body. These nutrients flood into the bloodstream, supplying energy to all parts of the body.

All of these changes happen so quickly that people aren't aware of them. In fact, the wiring is so efficient that the amygdala and hypothalamus start this cascade even before the brain's visual centers have had a chance to fully process what is happening. That's why people are able to jump out of the path of an oncoming car even before they think about what they are doing.

As the initial surge of epinephrine subsides, the hypothalamus activates the second component of the stress response system — known as the HPA axis. This network consists of the hypothalamus, the pituitary gland, and the adrenal glands.

The HPA axis relies on a series of hormonal signals to keep the sympathetic nervous system — the "gas pedal" — pressed down. If the brain continues to perceive something as dangerous, the hypothalamus releases corticotropin-releasing hormone (CRH), which travels to the pituitary gland, triggering the release of adrenocorticotropic hormone (ACTH). This hormone travels to the adrenal glands, prompting them to release cortisol. The body thus stays revved up and on high alert. When the threat passes, cortisol levels fall. The parasympathetic nervous system — the "brake" — then dampens the stress response.


What percentage of our brain do we use?

The brain is the most complex organ in the human body. Many believe that a person only ever uses 10 percent of their brain. Is there any truth to this?

A person’s brain determines how they experience the world around them. The brain weighs about 3 pounds and contains around 100 billion neurons — cells that carry information.

In this article, we explore how much of the brain a person uses. We also bust some widely held myths and reveal some interesting facts about the brain.

Share on Pinterest Studies have debunked the myth that humans use only 10 percent of their brain.

According to a survey from 2013, around 65 percent of Americans believe that we only use 10 percent of our brain.

But this is just a myth, according to an interview with neurologist Barry Gordon in Scientific American. He explained that the majority of the brain is almost always active.

The 10 percent myth was also debunked in a study published in Frontiers in Human Neuroscience.

One common brain imaging technique, called functional magnetic resonance imaging (fMRI), can measure activity in the brain while a person is performing different tasks.

Using this and similar methods, researchers show that most of our brain is in use most of the time, even when a person is performing a very simple action.

A lot of the brain is even active when a person is resting or sleeping.

The percentage of the brain in use at any given time varies from person to person. It also depends on what a person is doing or thinking about.

It’s not clear how this myth began, but there are several possible sources.

In an article published in a 1907 edition of the journal Science, psychologist and author William James argued that humans only use part of their mental resources. However, he did not specify a percentage.

The figure was referenced in Dale Carnegie’s 1936 book How to Win Friends and Influence People. The myth was described as something the author’s college professor used to say.

There is also a belief among scientists that neurons make up around 10 percent of the brain’s cells. This may have contributed to the 10 percent myth.

The myth has been repeated in articles, TV programs, and films, which helps to explain why it is so widely believed.

Like any other organ, the brain is affected by a person’s lifestyle, diet, and the amount that they exercise.

To improve the health and function of the brain, a person can do the following things.

Eat a balanced diet

Eating well improves overall health and well-being. It also reduces the risk of developing health issues that may lead to dementia, including:

The following foods promote brain health:

  • Fruits and vegetables with dark skins. Some are rich in vitamin E, such as spinach, broccoli, and blueberries . Others are rich in beta carotene, including red peppers and sweet potatoes. Vitamin E and beta carotene promote brain health.
  • Oily fish. These types of fish, such as salmon, mackerel, and tuna, are rich in omega-3 fatty acids, which may support cognitive function.
  • Walnuts and pecans. They are rich in antioxidants, which promote brain health.

There is a selection of walnuts and pecans available for purchase online.

Exercise regularly

Regular exercise also reduces the risk of health problems that may lead to dementia.

Cardiovascular activities, such as walking briskly for 30 minutes a day, can be enough to reduce the risk of brain function declining.

Other accessible and inexpensive options include:

Keep the brain active

The more a person uses their brain, the better their mental functions become. For this reason, brain training exercises are a good way to maintain overall brain health.

A recent study conducted over 10 years found that people who used brain training exercises reduced the risk of dementia by 29 percent.

The most effective training focused on increasing the brain’s speed and ability to process complex information quickly.

There are a number of other popular myths about the brain. These are discussed and dispelled below.

Left-brained vs. right-brained

Many believe that a person is either left-brained or right-brained, with right-brained people being more creative, and left-brained people more logical.

However, research suggests that this is a myth — people are not dominated by one brain hemisphere or the other. A healthy person is constantly using both hemispheres.

It is true that the hemispheres have different tasks. For instance, a study in PLOS Biology discussed the extent to which the left hemisphere is involved in processing language, and the right in processing emotions.

Alcohol and the brain

Long-term alcoholism can lead to a number of health problems, including brain damage.

It is not, however, as simple as saying that drinking alcohol kills brain cells — this is a myth. The reasons for this are complicated.

If a woman drinks too much alcohol while pregnant, it can affect the brain development of the fetus, and even cause fetal alcohol syndrome.

The brains of babies with this condition may be smaller and often contain fewer brain cells. This may lead to difficulties with learning and behavior.

Subliminal messages

Research suggests that subliminal messages can provoke an emotional response in people unaware that they had received emotional stimulus. But can subliminal messages help a person to learn new things?

A study published in Nature Communications found that hearing recordings of vocabulary when sleeping could improve a person’s ability to remember the words. This was only the case in people who had already studied the vocabulary.

Researchers noted that hearing information while asleep cannot help a person to learn new things. It may only improve recall of information learned earlier, while awake.

Brain wrinkles

The human brain is covered in folds, commonly known as wrinkles. The dip in each fold is called the sulcus, and the raised part is called the gyrus.

Some people believe that a new wrinkle is formed every time a person learns something. This is not the case.

The brain starts to develop wrinkles before a person is born, and this process continues throughout childhood.

The brain is constantly making new connections and breaking old ones, even in adulthood.


Brain Attack = Stroke

You may know someone, a parent or grandparent, who has had a "stroke," also called a "brain attack." What exactly is a stroke? A stroke occurs when the blood supply to the brain is stopped. If this happens for enough time, neurons will start to die because they will not get enough oxygen. Paralysis or aphasia (loss of speech) are possible consequences of a stroke.

There are two major causes of a stroke:

1. Blockage of a blood vessel (in the brain or neck) caused by:

  • a blood clot in the brain or neck (this is called a thrombosis)
  • a blood clot from somewhere else that has moved and now blocks a blood vessel in the brain or neck (this is called an embolism)
  • constriction or narrowing of an artery in the head or neck (this is called a stenosis)

2. Bleeding of a blood vessel (this is called hemorrhagic stroke)

There are several warning signs that occur with a brain attack. (Reprinted with permission from The National Institute of Neurological Disorders and Stroke

  • Sudden weakness or numbness of the face, arm, or leg on one side of the body.
  • Sudden dimness or loss of vision, particularly in one eye.
  • Sudden difficulty speaking or trouble understanding speech.
  • Sudden severe headache with no known cause.
  • Unexplained dizziness, unsteadiness, or sudden falls, especially with any of the other signs.

There are several conditions linked to stroke. Reprinted with permission from The National Institute of Neurological Disorders and Stroke


Ketosis

During the initial phases of starvation or water fasting, the body converts glycogen stored in the liver and muscles into glucose. After about 24 hours of using stored glycogen as an energy source, the body switches to fat burning. Some muscle and connective tissue also is used to provide the building blocks for important biological catalysts. As fats cannot cross the blood-brain barrier, the brain cannot use fats as a source of energy. However, fat metabolism in the liver produces ketone bodies as a byproduct. The brain can use these substances as an energy source. A state in which ketone bodies have become the main source of energy for the brain is called "ketosis."


Conditions Affecting Oxygen Saturation

Blood disorders, problems with circulation, and lung issues may prevent your body from absorbing or transporting enough oxygen. In turn, that can lower your blood's oxygen saturation level.

Examples of conditions that can affect your O2 sat include:

  • Chronic obstructive pulmonary disease (COPD): a group of chronic lung diseases that make it difficult to breathe : a chronic lung disease that causes airways to narrow : a partial or total collapse of the lung : a lack of healthy red blood cells : a group of conditions that affect the heart's function : when a blood clot causes blockage in an artery of the lung : a structural heart condition that is present at birth

The teenage brain

The brain releases dopamine when something makes us feel good &mdash like pulling off an exciting trick. The strength of this &ldquofeel good&rdquo response in teens helps explain why they sometimes chance real risks.

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October 17, 2012 at 1:20 pm

It’s not easy being a teenager.

The teen years can play out like a choose-your-own-adventure novel, where everyday temptations lead to tough decisions. What if I took that big jump on my bike? What’s the worst thing that could happen if I snuck out after curfew? Should I try smoking?

Teenagers must act on an endless parade of choices. Some choices, including smoking, come with serious consequences. As a result, adolescents often find themselves trapped between their impulsive tendencies (Just try it!) and their newfound ability to make well-informed and logical choices (Wait, maybe that’s not such a good idea!).

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So what makes the teenager’s brain so complex? What drives adolescents — more than any other age group — to sometimes make rash or questionable decisions? By peering into the brains of teenagers, scientists who study brain development have begun finding answers.

The evolved teenager

If you have ever thought that the choices teenagers make are all about exploring and pushing limits, you are on to something. Experts believe that this tendency marks a necessary phase in teen development. The process helps prepare teenagers to confront the world on their own. It is something all humans have evolved to experience — yes, teens everywhere go through this exploratory period. Nor is it unique to people: Even laboratory mice experience a similar phase during their development.

For example, laboratory experiments show that young mice stay close by their mothers for safety. As mice grow, their behavior does too. “When they reach puberty, they’re like, ‘I’m gonna start checking out how this environment looks without my mom,’” explains Beatriz Luna, of the University of Pittsburgh.

As a developmental cognitive neuroscientist, Luna studies those changes that occur in the brain as children develop into adults. She and other researchers are showing how the teen experience can lead to powerful advantages later in life. Take mice again: Young mice that explore most tend to live longest — that is, unless a cat eats them, Luna adds.

Jackpot!

What really goes on in a teenager’s brain? Of course, neuroscientists can’t actually peer inside the brains of living teenagers. So they do the next best thing Researchers scan teen brains while their owners are thinking, learning and making critical decisions.

Eveline Crone is a psychologist at Leiden University in the Netherlands who studies how the brain develops. To do so, Crone uses a huge, high-tech instrument called a magnetic resonance imaging (MRI) scanner. The scanner relies on a powerful magnet and radio waves to create detailed images of the brains of Crone’s young volunteers. It is painless and safe. All that Crone’s adolescent subjects have to do is lie back — and play a few games.

A young boy prepares to enter a magnetic resonance imaging (MRI) scanner. Earplugs will protect him against the loud noises produced by the rapid pulses of electricity that create the MRI’s powerful magnetic fields. Beatriz Luna

As Crone’s volunteers look up, they see a mirror that reflects a computer screen on which they can play casino-like computer games. Press a button and a slot machine appears, allowing teens to gamble — and win. Three bananas in a row? You win a dollar! “Kids love it. They always want to come back,” laughs Crone.

Teens also can play games that require them to make choices, such as whether to pull a trigger, smile at an attractive face or accept a tempting offer. Some choices earn them rewards, such as coins or food.

While her subjects play away, Crone and her coworkers are hard at work observing and measuring which parts of the teens’ brains are most active. The researchers can pinpoint activity by observing how much oxygen various brain regions are using. Very active parts of the brain use a lot of oxygen.

During the risk-taking and rewards-based tests, one region deep inside the brain shows more activity in adolescents than it does in children or adults, Crone says. This region, known as the ventral striatum, is often referred to as the “reward center” of the brain. The region can drive us to repeat behaviors that provide a reward, such as money and treats.

Concludes Crone: This physical difference in adolescent brain activity “shows that adolescence is a unique phase in development.”

Tug-of-war

Adolescents are particularly sensitive and responsive to influence by friends, desires and emotions, researchers say. It’s one of the hallmarks of this stage in life.

A major reason why teenagers often respond to those influences with irrational decisions is the presence of a brain chemical known as dopamine. The brain releases dopamine when something makes us feel good, whether it’s receiving a teacher’s compliment or finding a $20 bill. Dopamine levels in general peak during adolescence. In teenagers, the strength of this “feel good” response helps explain why they often give in to impulsive desires.

B.J. Casey of Cornell University tries to understand these biological patterns in teenagers. In laboratory experiments, this brain scientist and her coworkers have seen increased activity in the ventral striatum whenever someone at any age is confronted by a risky decision or the offer of a reward. However, this brain region seems “to be shouting louder” between the ages of 13 and 17 than at any other time during human development.

Crucially, the ventral striatum also communicates with another brain region, this one located just behind the forehead. Called the prefrontal cortex, it’s the brain’s master planner.

These brain scans highlight the prefrontal cortex, just behind the forehead, and the ventral striatum, deeper inside the brain. Beatriz Luna

Another way to think of the prefrontal cortex is as the conductor of an orchestra. It gives instructions and enables chatter among other brain regions. It guides how we think and learn step-by-step procedures, such as tying our shoelaces. Even preschoolers rely on the prefrontal cortex to make decisions. Overall, the prefrontal cortex’s ability to boss the brain increases with age.

Casey’s research shows how the adolescent brain is locked in a tug-of-war between the logical pull of the prefrontal cortex and the impulsive pull of the ventral striatum. Although teens can make good decisions, “in the heat of the moment — even when they know better,” the reward system can outmuscle the master planner. That can lead to poor decisions, Casey says.

In fact, teenagers almost cannot help but respond to the promise of a reward, Casey says. “It’s like they’re pulled toward it.” It even happens if the choice appears illogical.

While this would appear to push teenagers toward years of serious risk-taking, it is no mistake of evolution. Casey and other researchers believe the adolescent brain specifically evolved to respond to rewards so teens would leave behind the protection provided by their parents and start exploring their environment — a necessary step toward the independence they will need in adulthood.

Improved chatter

While all of this is going on during adolescence, the prefrontal cortex seems to lag in developing. It turns out this delay serves an important evolutionary function, says Michael Frank of Brown University. Frank studies the brain processes that occur during learning and decision making.

The prefrontal cortex is important because it teaches the rest of the brain the rules about how the world works. So it’s important that the master planner not be too rigid or restrictive during adolescence. Instead, it stays open to learning. Only later on in development can the brain disregard less useful information, Frank says.

Prior to adolescence, the master planner isn’t quite advanced enough to guide all the other brain regions. That’s because it still doesn’t know the rules of the game. “So that’s why you have parents to act as your prefrontal cortex,” Frank jokes. Then, all too often, he says, “you reach adolescence and you don’t listen to your parents anymore.”

Pruned, not shriveled

During adolescence, two key processes appear to play an important role in the maturing of our brains. One of the processes involves axons, or fibers that connect nerve cells. From infancy, these fibers allow one nerve cell to talk to another. Throughout the teen years, fatty tissue starts to insulate the axons from interfering signals — it is a bit like the plastic that coats electrical cables.

Psychologist Eveline Crone studies the teenage brain by observing which parts of it are most active when adolescent volunteers in an MRI scanner play casino-like computer games. University of Leiden

In axons, the insulating tissue allows information to zip back and forth between brain cells much more quickly. It also helps build networks that link the prefrontal cortex with other brain regions, allowing them to work together more efficiently. Eventually, the master planner can send messages throughout the brain with speed and precision.

The second key process involves synapses. A synapse is like a dock between nerve cells. Nerve cells communicate by transmitting chemical and electrical signals. Those signals move through the synapses.

In their first three years of life, children develop seemingly endless connections in their brain circuitry. Then, beginning in adolescence, the brain starts discarding many of these connections. Luna, the developmental cognitive neuroscientist, compares it to an artist who begins with a block of granite and carves away any unneeded stone to create a sculpture. In this case, the brain acts as the sculptor and chops away excess synapses. Scientists refer to this process as synaptic pruning.

By this stage, the brain has learned which synapses are most useful, Luna explains. So the brain strengthens the synapses it really needs and eliminates those that either slow things down or aren’t useful. For example, as people grow older, they become more proficient in their native tongue but find it harder to learn a language they have never spoken before. They may lack some of their earlier language-learning synapses.

Synaptic pruning and other changes that occur in the adolescent brain give teenagers the tools to start making decisions on their own — even if they’re bad decisions, says Luna.

“Now you have a brain that says, ‘I can make my own decisions. I can skateboard down those steps,’” says Luna. “When you’re a kid, you’d check with Mom. But now you have the prefrontal system that gives you the ability to make decisions.”

Combined, all of these processes help explain the sometimes logical — but often impulsive or unpredictable — decisions that the teenage brain can make. So next time you are torn over whether a reward is worth a certain risk, remember the tug-of-war that’s taking place in your brain — and that somewhere in there, you have the tools to make the best decision.

Power Words

(for more about Power Words, click here)

adolescence A transitional stage of physical and psychological development that begins at the onset of puberty, typically between the ages of 11 and 13, and ends with adulthood.

axon The long, tail-like extension of a neuron that conducts electrical signals away from the cell.

evolve To change gradually over generations.

magnetic resonance imaging (MRI) An imaging technique used to visualize internal structures of the body.

neuron An electrically excitable cell that receives, conducts and transmits messages throughout the nervous system.

prefrontal cortex The front portion of the brain, just behind the forehead, which controls executive functions in the brain.

synapse The junction between neurons that transmits chemical and electrical signals.

synaptic pruning The reduction in the number of neurons and synapses that begins in infancy and is mostly complete by early adulthood.

ventral striatum A region deep inside the brain known as the brain&rsquos reward center.

Citations

(in Dutch with English subtitles).

S. Gaidos. “Contemplating thought.” Science News for Kids. Feb. 20, 2009.

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How does food affect our brain?

Almost everything you choose to consume will directly or indirectly affect your brain. Obviously, some things we consume affect us more than others. I'm going to assume that spices, plants, animal parts, drugs of any kind, coffee, tea, nicotine and chocolate are all just food and define food as anything we take into our bodies whether it's nutritious or not. In order to better understand how foods affect the brain it will be helpful to divide them into three categories.

First, those foods we consume in high doses with acute dosing: for example, coffee, sugar, heroin, alcohol, nicotine, marijuana, some spices and a few psychoactive plants and mushrooms. Their effects are almost immediate and depend upon how much reaches the brain. In this class, the most important consideration is getting enough of the chemical from within the food to its site of action in our brain to actually produce some kind of effect that we can notice and associate with consuming that particular food. Most of the time, this simply does not happen. For example, consider nutmeg: low doses will be on pies next month and most of us will not notice that it contains two chemicals that our bodies convert into the popular street drug Ecstasy. Yet, if we consumed the entire canister of the spice our guts will notice (with a terrible diarrhea) and there is a good chance that we will hallucinate for about 48 hours! According to my students, the experience is quite unpleasant.

Secondly are those foods that affect our brain slowly over a period of a few days to weeks. This is usually called "precursor-loading" and would include many different amino acids (tryptophan and lysine are good examples), carbohydrates that have a high glycemic index such as potatoes, bagels and rice, fava beans, some minerals (iron and magnesium in particular), lecithin-containing products such as donuts, eggs and cakes, chocolate and the water-soluble vitamins. Their purpose is to bias the function of a specific transmitter system usually to enhance its function in the brain. For example, scientists once thought that drinking a glass of warm milk before bed or eating a large meal of protein made us drowsy because of tryptophan loading - the current evidence does not support this but the claim makes my major point: we must get enough of any particular nutrient/chemical to the right place and at the right dose in our brain in order for us to notice any effects. Unfortunately, tryptophan has difficulty getting across the blood-brain barrier into our brain.

So, what's the scientific evidence for considering the cognitive effects of these foods? Mostly, it's related to what happens when we do not get enough of them. For example, studies have shown that consuming too little tryptophan makes us depressed and angry and has been blamed for multiple wars and acts of cannibalism. Too little sugar or water-soluble vitamins (the B's and C) will induce changes in brain function that we will notice after a few days of deprivation. Many authors jump to the conclusion that giving high doses of such nutrients will rapidly improve our mood or thinking: sadly, this is rarely the case. Ordinarily the foods in this category require far more time to affect our brains than do those foods in the first category.

The third category includes the slow acting, life-time dosing nutrients that have been popular topics in the press recently. This category includes the anti-oxidant rich foods such as colorful fruits and vegetables, fish and olive oils, fruit juices, anti-inflammatory plants and drugs such as aspirin, some steroids, cinnamon and some other spices, nicotine, caffeine and chocolate, the fat-soluble vitamins, nuts, legumes, beer and red wine. People who eat these foods do not report acute changes in their thoughts or moods (depending upon how much they consume!) but certainly benefit from consuming them regularly over their life span. In general, the benefit comes from the fact that all of these foods provide our brains with some form of protection against the most deadly thing we expose ourselves to every day - Oxygen. Because we consume food, we must consume oxygen. Because we consume oxygen, we age. Thus, people who live the longest tend to each food rich in anti-oxidants or simply eat a lot less food. Recent studies suggest that nicotine and caffeine may prevent the toxic actions of oxygen in our brain which is why I've included them here.

You can see that depending upon how you frame the question about foods and the brain you get a different list of foods and a different reason for consuming them. If you wish to alter your current brain function or slow your brain's aging you need to consume foods that target specific chemical processes. In truth, no one ever considers these distinctions when eating - we just eat what tastes good. Sadly, our brains powerfully reward us when we eat sugar, fat and salt thus there is an oncoming epidemic of obesity-related illnesses. Food has both negative and positive effects and it all depends upon what you consume, how much you consume and for how long.


Watch the video: How Much Oxygen Our Brain Needs? (January 2023).