The true differences between the right and the left brain, the link between the brain size and intelligence, and what percentage of the brain do we really use? Six common mistakes regarding the organ hiding in our skulls

Humans possess remarkable cognitive faculties, characterized by abstract thinking, a particularly advanced capability for self expression and a talent for solving complex problems, surpassing those of other species. These abilities, along with many others, form the foundation of human civilization. The primary source of humans' unique thinking skills is, first and foremost, the human brain.

The brain serves as the central hub for processing sensory input - it receives messages and signals from sensory organs, transmits signals, and controls all the body's systems. Its importance is evidenced by the fact that, although it comprises only about two percent of our body mass, the brain consumes roughly one-fifth of the body’s energy output. Therefore, it is no wonder that the human brain garners significant attention, frequently  becoming the focal point in discussions concerning consciousness, memory, and morality. Extensive research in the field of neuroscience has deepened our understanding of how the brain functions and its connection to our cognitive and expressive capabilities. Often, these insights prompt us to reassess and challenge many previously unquestioned assumptions about the brain. 


First Claim:
We Utilize Only Ten Percent of Our Brain

The myth that humans use only ten percent of their brain cells lacks a definitive origin, yet its appeal is understandable. Imagine the immense potential of skills and capabilities that might be hidden in the ninety percent that are supposedly left untapped. This idea gives us hope that this may be a barrier that we can overcome in the future through "brain unlocking" techniques or as part of our evolutionary progress. Who knows then to which new and exciting realms we might be able to extend human cognitive abilities? Such a notion inspires hope of transcending current cognitive limits.

It is possible that the source of this claim is the common conception that nerve cells account for only ten percent of cells in our brain, though it is growing clear that this ratio is also incorrect. Another theory suggests that the myth may stem from the observation that at any given moment, certain areas of the brain are more active than others. Additionally, an 1890 theory proposed by psychologists from Harvard University who studied a child with extremely high intelligence,might also have influenced this belief. They speculated that humans have very high untapped mental potential and that we use only a fraction of it. It is easy to imagine how this theory likely morphed over time from a discussion about potential to one about actual brain usage. 

Regardless of its origin, modern functional Magnetic Resonance Imaging (fMRI) studies clearly demonstrate that both during rest and while performing active, focused tasks, humans use more than ten percent of their brain simultaneously. Every part of the brain is active to a certain degree, which varies according to its function. For example, areas critical for facial recognition become highly active when we see people, or photos of people, while under different conditions their activity will be reduced.

Many tasks that occupy us on a daily basis require synchronized and simultaneous activity across multiple brain areas.This means that when the activity in one area is increased, other areas that are linked to it in the same neural network will also increase their activity, which will later decrease in a synchronized manner. This dynamic activity pattern enables the transfer of information between different areas in the brain. There are also events when many parts of the brain are activated at high intensity all at once, with no synchronization. This is an example for the occurrence during epilepsy-induced seizures, when many nerve cells are activated in an uncontrolled manner, resulting in convulsions and loss of muscle control


What percentage of the brain do we utilize? All of it, even when certain areas exhibit increased activity. An X-ray image of a human brain | Shutterstock, Jalisko

Second Claim:

Creative People Are 'Right-Brained' and Logical Thinkers Are 'Left-Brained'


Our brain is composed of two halves, known as hemispheres, and it's common to associate analytical thinking with the left hemisphere and artistic or creative thinking with the right. This distinction is not completely detached from reality, as indeed there are differences between the two hemispheres, but it is highly imprecise. 

The human brain has areas that specialize in certain roles or enable specific abilities. For example, in the 19th century French physician, Paul Pierre Broca found that an area in the left side of the brain, currently named after him, plays a vital role in language formation. It was discovered that people with injuries to Broca's area suffer from aphasia: severe impairment in the ability to speak, which manifests as difficulty conjuring words and composing sentences with proper grammar. Damage to a nearby area in the left side of the brain, called Wernicke's area, causes a different type of aphasia This condition gained publicity recently when it was revealed that actor Bruce Willis suffers from it.  

Nevertheless, understanding and forming language are highly complex activities that are not limited to Wernicke's and Broca's areas. Many parts of the brain participate in linguistic processing processes, and damage to any of them could result in impairments in speech, writing, or comprehending language. While a significant part of linguistic processing does occur in the left hemisphere, both hemispheres play a part in this processing to some extent.

The right hemisphere also specializes in certain functions. For example, the prefrontal cortex is essential for deciphering emotions in facial expressions. The right  dorsal anterior cingulate cortex has been linked with the cerebral processing of music. However, these functions do not solely rely on the right hemisphere; both hemispheres are necessary to invoke a proper human response.

These distinctions led to the belief that artistically inclined individuals predominantly use their right brain, while analytical thinkers rely more on their left brain. In a 2013 study, researchers attempted to directly examine the claim that some people have one side of their brain stronger than the other. For this purpose they used fMRI to scan the brains of over one thousand subjects, aged 7-29, and examined their activity during rest. The findings did not present any evidence for the existence of a tendency for right or left brain dominance. While certain brain functions may be more related to a certain hemisphere, it is not sufficient to conclude that people have a dominant side to their brain.

In most people, areas important for language development are located in the left side of the brain. However, language processing, like many other complex functions, combines the activity of both hemispheres. Illustration of the part of the brain where Broca's area is located, which is important for language formation | Kateryna Kon. Science Photo Library


Third Claim:

A Larger Brain Is Indicative of Higher Intelligence


It might seem intuitive to assume a correlation between brain size and intellectual complexity. After all, a larger brain contains more nerve cells, forming a denser network of connections between them, which could potentially lead to increased intelligence. 

However, numerous examples in nature challenge the existence of a simple link between brain size and intelligence. For instance, elephants and whales possess brains significantly larger than humans, yet humans display mental capabilities that far surpass them.  

Other factors may play a more crucial role than mere brain size. Studies suggest  a partial correlation between intelligence and the number and density of nerve cells in the brain, as well as the level of connectivity between them. This connectivity refers to how well nerve cells are linked and the volume of information that can be transmitted between them. Therefore, while brain size may offer some indication of intelligence,  it is not a definitive measure.

It appears that intelligence is influenced by a multitude of factors, some of which remain elusive to our understanding.  This complexity is exemplified by the brains of individuals deemed exceptionally intelligent, which often do not deviate significantly in size from the average. For example, physicist Albert Einstein's brain was relatively small, weighing only 1,230 grams compared to the average male brain mass of 1,376 grams. Generally speaking, there is no conclusive evidence to support a direct correlation between physical brain size and intelligence among individuals.

Despite their significantly larger brains, whales do not surpass humans in cognitive abilities. Illustration of a humpback whale's brain | Shutterstock, BlueRingMedia


Fourth Claim:
Drinking Alcohol Kills Brain Cells

While it is widely accepted that excessive alcohol consumption is detrimental to brain functions, it appears that the primary and immediate damage is not to the integrity of brain cells themselves but rather to their functionality and the network of connections between them, known as synapses. These synapses are crucial for communication between brain cells and the brain's complex processing abilities. Exposure to high quantities of alcohol enhances the effect of the neurotransmitter GABA, for example, which slows the transmission of messages between nerve cells. Over time, cells adapt by reducing their sensitivity to GABA, resulting in symptoms of stress and irritation.

However, prolonged and excessive alcohol consumption can indeed lead to irreversible brain damage and a reduction in the volume of certain brain areas, thus indirectly contributing to the death of nerve cells. This cell death occurs as a secondary effect due to prolonged exposure to alcohol, which increases the production of free radicals and triggers an inflammatory response. Alcohol's impact is particularly severe on brains that have not yet fully developed, highlighting its dangers for children.

Moreover, excessive alcohol consumption might result in Wernicke–Korsakoff syndrome, which impairs memory and the ability to learn new information. The syndrome is indeed caused by direct cell damage, though not in the brain but in the intestines.  It impairs the intestines' ability to absorb vitamin B1 (Thiamine), essential for brain function. Its deficiency can result in irreversible disruptions to many critical processes.

 Excessive alcohol consumption impairs brain functions, but at least initially does not directly harm brain cells. Illustration of a brain submerged in a glass of beer | Shutterstock, Chizhevskaya Ekaterina

Fifth Claim:

Serotonin is the “Happiness Hormone” and Its Deficiency Causes Depression


Humans are naturally inclined to catalog complex phenomena and provide easily understandable explanations. Imprecise and overreaching interpretation of limited research findings might encourage people to attribute one substance with the full responsibility for complex patterns of human behavior. For instance, oxytocin, which is active in the brain, was dubbed the “love hormone”. Similarly, the neurotransmitter serotonin, which influences a wide range of functions in the central nervous system, was once known as the “happiness hormone.”

The association between serotonin and happiness arose from the chance discovery of its effectiveness in popular antidepressants like Prozac, which elevate serotonin levels in the brain's nervous junctions. This led to the belief that since increasing serotonin can alleviate depression, it must also enhance overall mood.

However, current understanding acknowledges that our state of mind is influenced by numerous factors and dynamic processes. Thus, even if serotonin does play a role, it is just one component in a complex system. While we continue to uncover serotonin's functions in the brain, it is clear that solely increasing serotonin levels does not guarantee an improved state of mind, as demonstrated by numerous studies.

Serotonin is implicated in our state of mind, but it does not singularly dictate our feelings. Illustration of the brain areas where serotonin is active | PIKOVIT, Science Photo Library


Sixth Claim:

After Puberty the Brain Stops Developing


In the first years of a child’s life, the brain experiences rapid growth and development. During this period, there is a notable increase in brain volume and the complexity of connections between nerve cells. However, contrary to what some may believe, the brain's development does not halt after this early surge. Throughout our lives, redundant neural connections degenerate while new ones form in response to our activities and environmental interactions.Although the rate of growth and development diminishes over the years, the brain never ceases to change.

Throughout our lives, our brains continue to consolidate existing connections and form new ones in response to the body's activity and environmental input. Learning new skills and experiences contribute to the formation of new synapses, enabling ongoing development as thinking and learning organisms. Even in older age constant processes of transformation continue to occur in the brain. Contrary to popular belief, the generation of new nerve cells is still possible later in life, particularly in regions associated with the formation of new memories.

In the first years of a child’s life the brain grows and develops rapidly - but continues to reshape throughout life. A drawing of a cross section of a child at ages nine months (left), two years and four years | JACOPIN, Science Photo Library


The Brain And Us

Since the dawn of history, our brains have provided humans with a significant advantage, enabling us to become the dominant species on Earth, harness nature to our needs, and settle in nearly every corner of the globe. These accomplishments require immense complexity and it will take many more years of research to fully understand the mysteries of the organ that defines us more than any other.

It is also important to recognize that the brain does not function in isolation, but instead it is an inseparable part of the complex network of our body's systems.As such, we will undoubtedly continue to encounter numerous unusual claims about the human brain. Over time, many of these claims will be disproved, though a few might be confirmed. In the meantime, science will continue to perform its indispensable role: uncovering the truth.