The Human Brain - Fact or Fiction?

Written by Gala Konteva; a 3rd-year student of Biological Sciences at the University of Leeds and Neural Networks' science writer

Neuroscience is an incredibly complex field, which is constantly evolving. Although we have studied the human brain for centuries, we are still learning more of its secrets each day. The search of facts can sometimes lead to fiction that fills the gaps of knowledge and understanding of the human brain, and fiction can become a myth. While many such myths have been busted, we are still not immune to errors - what we think we know to be a fact now, supported by scientific evidence, can turn out to be wrong. And these are not just falsifications and distortions circulated on social media and unsupported by scientific evidence, but erroneous scientific knowledge made by scientists themselves. So, how much do we know about the human brain? And most importantly - how much of that is actually true, or just a myth we believe in? Let's explore several interesting theories about the human brain and try to tell fact from fiction.

Contents

(All these are hyperlinked! Feel free to go directly to the one you're interested in!)

1) You only use 10% of your brain

2) Your brain consists of 86 billion neurons

3) You are either left-brained (more logical) or right-brained (more creative)

4) You can grow new brain cells as an adult

5) Babies grow up smarter if they have been exposed to classical music

6) Playing a musical instrument in childhood improves brain cognition

7) Alcohol kills brain cells

8) The brain is the fattiest organ in the human body

9) The larger your brain, the smarter you are

10) 50% of your intelligence is set by your genes

1) You only use 10% of your brain

The truth is that you constantly use all of your brain, even while sleeping. Your brain is crucial for your body survival needs, such as breathing and digestion, and it is absolutely not true that you only use 10% of it. Even people, suffering from degenerative disorders, still use more than 10% of their brain. You may not use all of your brain parts simultaneously, but the same goes for your muscles - do you use only 10% of your muscle strength?

Moreover, if only 10% were used, then why does your brain require such amount of energy? The adult human brain, accounting for 2% body mass, consumes around 20% of daily glucose burned. In children, this number is even 50%. Could all of this energy be used up by only 10% of your brain? No, as even simple actions, such as slight movement of your hand, require way more than tenth of your brain. Furthermore, if such a big part of the brain was not used, then why brain injury of those 90% inactive parts can be so fatal to human health?

Brain scan studies, such as functional Magnetic Resonance Imaging (fMRI), have shown that all areas of the human brain are active, proving this theory as wrong. Every part of the human brain has a critical function in your body; therefore, it is not possible that the other 90% of your brain just sits there inactive as spare capacity.

Where did that myth come from?

This myth is believed to be one of the most common misconceptions among the public. It is thought to have started from an article ''The Energies of Men'' published in the journal Science (1907), in which the psychologist William James claims that only a part of the human mental resources can be used, but this argument does not include any percentage. Where did the 10% come from then? We can't know for sure, but it is possible it came from the belief that 10% of your brain's cells are neurons, which is not true as well. However, this cannot be linked to the idea that we only use 10% of our brain, because the other brain cells are non-neuronal and they cannot give us extra brain power under any circumstances. Nevertheless, the media spread this myth amongst our society and there are still many people believing in it. For instance, the movie Lucy (2014) is based on the question what would happen if a person used all 100% of its brainpower.

2) Your brain consists of 86 billion neurons

Many people believe that there are 100 billion neurons in the human brain and we can still see this number in textbooks and journals. However, although an excepted fact, there is no supporting evidence and actually, this number is a few billions smaller.

In a ground-breaking study conducted in 2016, the Brazilian neuroscientist Herculano-Houzel tested how many neurons were in the human brain by dissolving the brain into a solution, known as isotropic fractionation, instead of testing brain slices (von Bartheld et al., 2016). This method of ''brain soup'' is believed to give a more accurate count of cellular composition and the results showed we have around 86 billion neurons and 85 billion of non-neuronal cells (which are both glia and endothelial cells).

Subsequent research provided support to these numbers, which breaks not only the believed myth that we have 100 billion neurons, but also that glial cells outnumber neurons. In the past, it was widely thought that neurons contributed to only 10% of the brain cellular composition, when in fact the ratio of glia to neurons is about 1:1. This shows us how neuroscience evolves each day, as new research makes us question what we already knew to be scientific fact.

3) You are either left-brained (more logical) or right-brained (more creative)

Some people tend to be more creative or more logical, but this is not determined by the sides of their brain. However, it is widely believed that one of your brain hemispheres dominates, playing a role in your personal abilities and qualities. Right-brain thinkers are thought to be more thoughtful and artistic, whereas left-brain thinkers analytical with stronger math and logic skills. However, there is no scientific evidence supporting this theory.

You do not have a dominant brain half, but it is true that the two hemispheres of your brain differ. Research has shown that the left hemisphere plays a role in processing language, whereas the right in processing emotions. In addition, your brain's left side controls the motion of your left arm and leg and vice versa. Nevertheless, you use both of your brain hemispheres and neither of them dominates over the other. In fact, even though performing different tasks, the two sides of your brain work together, as they are connected by the corpus callosum.

Where did that myth come from?

A study performed in the mid-1800s by two neurologists, Dr. Pierre Paul Broca and Dr. Karl Wernicke, gave rise to this misconception. The researchers found that patients struggling from language processing had damage in their left temporal lobes. This led to the conclusion that the left side of the brain is involved in language processing, which is true, however, language is not entirely controlled by it, as the right side helps you understand context (Nielsen et al., 2013). In addition, in 30% of left-handed people, the language-processing centres are actually located in the right side of the brain.

This study then inspired the author Robert Louis Stevenson, who introduced the idea of the logical left hemisphere versus the emotional/creative right hemisphere in his novella "The Strange Case of Dr. Jekyll and Mr. Hyde". As a result, this enduring myth became widely spread as a scientific fact, leading to numerous online left-brain/right-brain quizzes, which unfortunately many people take and believe in.

4) You can grow new brain cells as an adult

For a long time, neuroscientists thought that the number of brain cells we are born with is fixed. Nevertheless, many other animals are able to grow neurons through much of their brains, so why it is widely believed that we, humans, cannot?

Neurogenesis, the process of new neurons formation, is crucial for embryo development and it is true that once you become an adult, the creation of new brain cells stops at most regions of your brain. However, research from the past two decades has shown that neurogenesis does occur at some parts of the developed brain.

How and what part of your brain creates new brain cells?

The hippocampus, the region of the brain responsible for learning and spatial memory, contains stem cells that can differentiate into neurons throughout your life (Ming and Song, 2011). Interestingly, scientists have discovered another region of the adult brain able to create neurons - the amygdala (Roeder et al., 2022). This part of the brain is important for emotional memories and processing fear and stem cells in the amygdala have shown to play a role in fear learning. These findings may be associated and used for treatment of depression and anxiety disorders such as PTSD, which are linked to disrupted connection in the amygdala. For example, studies have shown that neuron numbers increase in the human amygdala throughout a person's lifespan, but not in people suffering with autism (Avino et al.).

This topic holds some controversy amongst neuroscientists, as some of them think the theory of adult neurogenesis is not fully proven. There are some conflicting studies and many questions are still unanswered. For instance, it is still believed that neurogenesis in the hippocampus steadily decrease with age, which could play a role in neurodegeneration. In addition, research has shown that impaired adult neurogenesis has impact on Alzheimer's disease (Winner and Winkler, 2015). Therefore, further research in this field can not only help us understand our brain better, but also contribute to treating neurodegenerative diseases.

5) Babies grow up smarter if they have been exposed to classical music

According to the theory of the ''Mozart effect'', listening to Mozart's music (or classical music in general) makes you more intelligent. In addition to this, it has been widely believed that exposing babies to classical music has an impact on their brain development and intelligence. It is true that playing any music to babies has many benefits, such as supporting speech and language development. However, there is no evidence that classical music makes babies smarter and has long-term effects on their brain.

Where did that myth come from?

The story behind this myth started from a study conducted by Rauscher et al. in 1993, in which 36 college students temporarily achieved higher scores on spatial reasoning tests after listening to the Mozart's Sonata (Rauscher et al., 1993). The students sat in silence for 10 minutes or listened to Mozart's Sonata, after which they completed a series of mental tasks, such as being able to remember where an object was located in an array of objects. The results showed that the students who listened to Mozart did a little better on the tests, indicating that listening to Mozart had an impact on better performance.

It is important to note that this study only tested 36 graduate students, not children, and it showed effects on spatial reasoning, not on overall intelligence. However, the media misinterpreted these findings and people believed that playing classical music to babies has a lasting impact on their intelligence. The belief became so popular, that they started producing classical music CDs and DVDs for babies. Furthermore, in 1998, the governor of Georgia added 105,000$ of the state budget to send every new-born baby a tape of classical music, although at this time there were no further studies testing the effects of music on children.

More experiments have been conducted after that, showing small positive effects of listening to classical music on spatial performance, but these effects were also observed in people who listened to other type of music. Thus, there is nothing unique about Mozart, but rather a short-time impact of music on spatial-task performance, which can even be linked to the music's effect on a person's mood.

6) Playing a musical instrument in childhood improves brain cognition

Although listening to music may not have such impact on intelligence, playing a musical instrument does have an effect by engaging practically every area of the brain at once, evidence of which are MRI scans. Playing an instrument improves cognitive function by increasing the volume and activity of the brain's corpus callosum, the bridge between the two hemispheres. This results in enhanced neuronal communication between the left and right hemispheres of the brain, leading to improved problem-solving, learning, memory and motor skills (Stoklosa and Fisher,2016). Thus, research has shown that playing a musical instrument in childhood is associated with improved thinking skills in older age.

Are those benefits unique to music?

Currently, the answer is yes, as previous research has shown that the effects of learning to play a musical instrument are different from any other activity studied, such as spots and painting.

7) Alcohol kills brain cells

It is true that alcohol has serious effects on brain function, but it does not directly kill your brain cells.

Then what does alcohol do to your brain?

Alcohol causes brain damage in different ways, for instance, by damaging dendrites, which disrupts neuronal signalling. When you drink, alcohol reaches your brain within five minutes and firstly, it triggers the release of endorphins. This is why you start to feel more relaxed and happier after a few glasses. However, if you continue to drink more and more, alcohol starts to interfere with your brain's communication pathways, causing changes in your behaviour, slurred speech and poor coordination, and this can lead to alcohol poisoning.

If we look at the long-term effects of alcohol, associated with heavy/binge drinking, booze can lead to decreased cognitive function, memory issues and brain atrophy. Furthermore, alcohol has a negative impact on neurogenesis, thus even though it does not kill neurons, it interferes with your brain making new ones. Moreover, long-term alcohol abuse is associated with dementia, for instance the Wernicke-Korsakoff syndrome. In this syndrome, the loss of neurons is not caused directly by alcohol, but by deficiency in a vitamin called thiamine. Thus, alcohol can in fact kill brain cells, but not directly. Drinking can have long-lasting effects on developing brains as well, as they are more vulnerable, which can lead to permeant brain damage. This is the reason why you are not allowed to drink alcohol until your early twenties.

Therefore, although alcohol doesn’t directly lead to neuronal death, it still causes damage (usually reversible) to your brain, especially if you drink too much.

8) The brain is the fattiest organ in the human body

Although you've might been told to treat and exercise your brain like a muscle, the human brain is actually 60% fat.

How can the organ, the command centre making trillions of electrical connections, be considered fat?

What makes our brains fat is the lipid layer, covering the axons of our neurons, through which electrical impulses travel. Myelin sheath serves as an insulating layer of fat, protecting the axon and allowing electrical impulses to transmit much more quickly (up to 50 times faster!). Interestingly, this is why you have white and grey matter - the white matter of your brain contains those myelinated axons, whereas the grey matter consists of the neuronal somas. Therefore, your brain may be your fattiest organ, but it is unique in that it uses this fat as an insulator of electricity, compared to the adipose tissue, in which fat has energetic function.

Moreover, your brain needs additional fat, supplemented by diet, because fatty acids are crucial molecules for proper brain function (Chang et al., 2009). For instance, omega-3 fatty acids are not synthesized in your body, therefore it is essential you get them through food, such as fish or walnuts. Thus, although fat is considered something bad, the right kind of fat is crucial for proper brain function.

9) The larger your brain, the smarter you are

People believe that if you have a bigger brain, you're smarter, but there is no scientific evidence supporting this idea. Therefore, brain size is not an accurate way to judge intelligence, what's important is how complex your brain is.

If looking at brain size not relative to the body, other animals such as whales and elephants have much bigger brains than us. Does that make them smarter though? No, because most of these animals' brain get dedicated to their massive bodies, which require lots of processing power and energy. It is true that relative to the body size, the human brain is bigger than the brains of other primates and as a result of evolution, it has gotten even bigger. In this context it would make sense that brain size affects intelligence. But then why was Albert Einstein's brain of an average size?

The answer behind what has made us as organisms so intelligent actually lies on brain development and different brain components. Our brains have much more developed frontal cortex compared to other primates. Furthermore, brain connectivity, how your neurons communicate and form connections, is way more important than your brain size. When you learn new skills, your brain doesn’t physically grow, but new neuronal connections form, highlighting that efficiency is more important than quantity.

Why does then brain size vary from person to person?

Every person has a different size of their brain and it's proven that men have bigger brains than women. The reason behind this is simple - brain size is controlled by your genetics. Researchers suggest that there are specific genes, such as HMGA2, which get switched on in some people, making their brains bigger.

10) 50% of your intelligence is set by your genes

Intelligence is a complex trait, which is influenced by both genetic and environmental factors. In fact, there is a lot of conducted research on how our genes influence IQ and the results show that genetics do play an important role. For instance, genetic analysis of Scottish families has shown that ''more intelligent'' people have fewer mutations in their genes, responsible for intelligence (Hill et al.). In addition, research on twins suggests that intelligence heritability ranges from 50% to around 80%., as identical twins achieve higher IQ scores than fraternal twins. Thus, genetic variation actually plays a key role in individual differences in human intelligence.

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