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How Many Brains Does A Human Have

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The Human Brain Contains Approximately One Hundred Billion Neurons

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This is about the same as the number of stars in the Milky Way galaxy. These neurons are connected by trillions of connections, or synapses. Experts call this a neuron forest. Information runs between these neurons in your brain for everything we see, think, or do. These neurons move information at different speeds. The fastest speed for information to pass between neurons is about 250 mph. That being said, neurons only make up 10% of the brain.

Intraspecific Variability In Size Numbers And Abilities

One final caveat to keep in mind when studying scaling of numbers of brain neurons, particularly in regard to cognition, is that relationships observed across species need not apply to comparisons across individuals of the same species. Not only the extent of intraspecific variation is much smaller than interspecific variation , but also the mechanisms underlying interspecific and intraspecific variation are also likely to differ. Our own preliminary data suggest that, indeed, variations in brain size across rats of the same age are not correlated with variations in numbers of neurons . There is no justification, therefore, to extend the linear correlation between brain size and number of neurons across primates to a putative correlation across persons of different brain sizes . In fact, although men have been reported to have more neurons in the cerebral cortex than women , there is no significant correlation between brain size and general cognitive ability within families . Across these individuals, other factors such as variations in number and identity of synaptic connections within and across structures, building on a statistically normal, albeit variable, number of neurons, and depending on genetics and life experiences such as learning, are more likely to be determinant of the individual cognitive abilities .

How Does The Brain Work

The brain sends and receives chemical and electrical signals throughout the body. Different signals control different processes, and your brain interprets each. Some make you feel tired, for example, while others make you feel pain.

Some messages are kept within the brain, while others are relayed through the spine and across the bodys vast network of nerves to distant extremities. To do this, the central nervous system relies on billions of neurons .

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Brain Activity Can Power A Small Light Bulb

When you are awake, your brain generates about 12-25 watts of electricity which is enough to power a small light bulb. The brain also works fast. The information going from your arms/legs to your brain travels at a speed of 150-260 miles per hour. The brain consumes glucose from the body to produce this amount of the energy.

The Human Brain Gets Smaller As We Get Older

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Human brain keeps developing until you are in your late 40s. It is the only organ in the human body to undergo development for such a long time. It also sees more changes than any other organ. Around mid-life, the brain will begin to shrink. However, size doesnt matter in the brain. There is no evidence that a larger brain is smarter than a smaller one.

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Other Cool Facts About The Brain

  • The brain can’t multitask, according to the Dent Neurologic Institute. Instead, it switches between tasks, which increases errors and makes things take longer.
  • The human brain triples in size during the first year of life and reaches full maturity at about age 25.
  • Humans use all of the brain all of the time, not just 10% of it.
  • The brain is 60% fat, according to Northwestern Medicine.
  • The human brain can generate 23 watts of electrical power enough to fuel a small lightbulb.

Reading Out Loud Uses Different Brain Circuits Than Reading Silently

Reading aloud promotes brain development. Children first learn to read by speaking words out loud. Once that knowledge is established, then they learn to read to themselves. Its indeed one of the strange facts about the brain because we usually teach our children to read and talk politely. But to promote brain development in your child, you should read and talk aloud in front of them.

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Does Brain Size Matter

Obviously, not all people have the same size brain. Some are larger, and some are smaller. You might find yourself wondering if brain size might be linked to characteristics such as disability or intelligence.

Researchers have found that in some cases brain size can be linked to certain diseases or developmental conditions.

For example, autistic children tend to have bigger brains than non-autistic children. The hippocampus tends to be smaller in elderly adults suffering from Alzheimer’s disease. This area of the brain is strongly associated with memory.

What about intelligence? The answer to that question depends largely upon who you ask. According to one analysis of many studies that looked at this issue by Michael McDaniel of Virginia Commonwealth University, bigger brains were correlated with higher intelligence.

Not all researchers necessarily agree with McDaniel’s conclusions. Such studies also raise important questions about how we define and measure intelligence, whether we should account for relative body size when making such correlations, and what parts of the brain we should be looking at when making such determinations.

It is also important to note that when looking at individual differences among people, brain size variations are relatively small. Other factors that may influence or play a pivotal role include the density of neurons in the brain, social and cultural factors, and other structural differences inside the brain.

A Brain Freeze Is Really A Warning Signal

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Officially called a sphenopalatine ganglioneuralgia, a brain freeze happens when you eat or drink something thats too cold. It chills the blood vessels and arteries in the very back of the throat, including the ones that take blood to your brain. These constrict when theyre cold and open back up when theyre warm again, causing the pain in your forehead. This is your brain telling you to stop what you are doing to prevent unwanted changes due to temperature.

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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.

Blood Supply To The Brain

Two sets of blood vessels supply blood and oxygen to the brain: the vertebral arteries and the carotid arteries.

The external carotid arteries extend up the sides of your neck, and are where you can feel your pulse when you touch the area with your fingertips. The internal carotid arteries branch into the skull and circulate blood to the front part of the brain.

The vertebral arteries follow the spinal column into the skull, where they join together at the brainstem and form the basilar artery, which supplies blood to the rear portions of the brain.

The circle of Willis, a loop of blood vessels near the bottom of the brain that connects major arteries, circulates blood from the front of the brain to the back and helps the arterial systems communicate with one another.

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Animals Share An Evolutionary History

Not only humans have brains, of course. Almost all animals have a nervous system of some kind . The brains of different animals are different in some ways but similar in many other ways. This is because all life on the planet shares a history: all animals evolved from common ancestors, so they inherited some of the characteristics from these ancestors. This is like a brother and a sister who are alike because they have the same parents, first cousins who have the same grandparents, second cousins who share great-grandparents, and so on. All life shares a great-great-great-grandparent in the distant past.

We can use these similarities and differences between animals to put the animals together into groups. Two birdssay, an eagle and a parrothave more in common than an eagle and a monkey. And they are closer relatives. In a family, this would be like saying that a brother is more like his sister than he is like his cousin. A brother and a sister have the same parents, but with their cousin they only share the same grandparents, further back. Still, all mammals have fur and produce milk to feed their young. Every bird has feathers and lays eggs. And these similarities between close relatives appear in their brains, too.

Is There Only One Rule To Build Brains

Human Brain stock illustration. Illustration of neurology ...

Even though the parts are the same, this does not mean that brains of the same size are built of the same amounts of each kind of cell. It is also not true that a bigger brain is always made of more cells than a smaller brain.

We can think about this with an example. Imagine that you receive two brains of the same weight but belonging to different species. This is what we see in Figure 2: a rhesus monkey brain and a capybara brain . Both brains weigh about 80 g. You would probably say the brains have the same number of neuronsand so would many scientists. Until about 10 years ago, most researchers expected brains of the same size to have the same number of neurons. They thought that there was only one recipe in nature for building brains, and that all brains were made the same way. That also meant that the bigger the brain, the more neurons it would have.

  • Figure 2 – Nature has different ways of adding neurons to primate and rodent brains as they change in size from one species to another.
  • This means that when a rodent brain gets larger, it does not gain many neurons. In contrast, when a primate brain gets bigger, its number of neurons grows more or less in proportion to how much larger the brain is.

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Conflict Of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Herculano-Houzel, S., and Lent, R. 2005. Isotropic fractionator: a simple, rapid method for the quantification of total cell and neuron numbers in the brain. J. Neurosci. 25:251821. doi:10.1523/JNEUROSCI.4526-04.2005

Azevedo, F. A., Carvalho, L. R., Grinberg, L. T., Farfel, J. M., Ferretti, R. E., Leite, R. E., et al. 2009. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J. Comp. Neurol. 513:53241. doi:10.1002/cne.21974

Herculano-Houzel, S., Manger, P. R., and Kaas, J. H. 2014. Brain scaling in mammalian evolution as a consequence of concerted and mosaic changes in numbers of neurons and average neuronal cell size. Front. Neuroanat. 8:77. doi:10.3389/fnana.2014.00077

Herculano-Houzel, S., Avelino-de-Souza, K., Neves, K., Porfírio, J., Messeder, D., Mattos Feijó, L., et al. 2014. The elephant brain in numbers. Front. Neuroanat. 8:46. doi:10.3389/fnana.2014.00046

The Human Brain In Numbers

How many neurons does the human brain have, and how does that compare to other species? Many original articles, reviews and textbooks affirm that we have 100 billion neurons and 10 times more glial cells , usually with no references cited. This leaves the reader with the impression that the cellular composition of the human brain has long been determined. Indeed, an informal survey with senior neuroscientists that we ran in 2007 showed that most believed that the number of cells in the human brain was indeed already known: that we have about 100 billion neurons, outnumbered by about 10 times more glial cells but none of the consulted scientists could cite an original reference for these numbers . Curiously, the widespread concept that neurons represent about 10% of all cells in the human brain might be one of the arguments behind the popular, but mistaken, notion that we only use 10% of our brain .

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Debunking The 10% Myth

  • Ph.D., Materials Science and Engineering, Northwestern University
  • B.A., Chemistry, Johns Hopkins University
  • B.A., Cognitive Science, Johns Hopkins University

You may have heard that humans only use 10 percent of their brain power, and that if you could unlock the rest of your brainpower, you could do so much more. You could become a super genius, or acquire psychic powers like mind reading and telekinesis. However, there is a powerful body of evidence debunking the 10 percent myth. Scientists have consistently shown that humans use their entire brain throughout each day.

Despite the evidence, the 10 percent myth has inspired many references in the cultural imagination. Films like “Limitless” and “Lucy” depict protagonists who develop godlike powers thanks to drugs that unleash the previously inaccessible 90 percent of the brain. A 2013 study showed that about 65 percent of Americans believe the trope, and a 1998 study showed that a full third of psychology majors, who focus on the workings of the brain, fell for it.

Testing And Changing Rules

How Many Neurons Are in the Brain?

If you know the rule relating brain size to the number of neurons, you can predict how many neurons a brain of a certain size would have, according to that rule. The rules will also show what limits exist for building brains.

To pick a familiar example, a generic primate brain of 1.5 kg, just like our brain, should have 93 billion neurons, according to the primate rule. Our best estimate for how many neurons we have is 86 billion neurons, on average . That is pretty close. What this tells us is that, well, we have a primate brain: we are that generic primate. In other words, as far as numbers of neurons go, our brains are not special compared to those of our closest relatives, the apes and monkeys. We have just as many neurons as a primate with our brain size should have. But because we are the primate with the biggest brain, we have the most neurons of any primate.

  • Figure 3 – If there were a rodent with as many neurons as a human has86 billionits brain would weigh over 30 kg.
  • This means that this hypothetical rodent would need a body of 80 t to carry the super heavy brain. To get an idea of what this super rodent would have to look like, imagine putting it on a scale: it would weigh the same as 20 elephants!

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Early Brain Development In Children

Neuroscience research has shown us that early childhood is a time of tremendous brain development. The young brain literally changes shape and size in response to everything encountered in this early period of development. New environment, life experiences, caretakers and relationships can all affect the way complex brain circuits are wired.

Find out how to help your childs brain develop optimally.

Is It True That You Get New Brain Wrinkles When You Learn Something

Not all brains are wrinkled. In fact, most animals have fairly smooth brains. Some exceptions are primates, dolphins, elephants, and pigs, which also happen to be some of the more intelligent animals.

The human brain is exceptionally wrinkled. Thats probably why people conclude that we gain more wrinkles as we learn new things. But thats not how we acquire brain wrinkles.

Your brain starts developing wrinkles before youre even born. The wrinkling continues as your brain grows, until youre about 18 months old.

Think of the wrinkles as folds. The crevices are called sulci and the raised areas are called gyri. The folds allow room for more gray matter inside your skull. It also decreases wiring length and improves overall cognitive functioning.

Human brains vary quite a bit, but theres still a typical pattern to brain folds. Research shows that not having the major folds in the right places could cause some dysfunction.

  • motivate you to do things you probably wanted to do anyway

Learning entirely new things is far more complicated.

Say youve been studying a foreign language. Theres only a small chance that listening to vocabulary words in your sleep can help you remember them a bit better. A 2015 study found that this is true only under the best of circumstances. The researchers noted that you cant learn new things during your sleep.

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Structure Of The Brain

The cerebrum has a right half and a left half, known as the right and left hemispheres. The two hemispheres are connected via a thick bundle of nerve fibers called the corpus callosum. Each hemisphere is made up of six areas that have different functions. The cerebrum controls movement and processes sensory information. Conscious and unconscious actions and feelings are produced here. It is also responsible for speech, hearing, intelligence and memory.

The functions of the two hemispheres are to a great extent different: whereas the left hemisphere is responsible for speech and abstract thinking in most people, the right hemisphere is usually responsible for spatial thinking or imagery. The right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body. This means that damage to the left hemisphere due to a stroke, for example, can lead to paralysis on the right side of the body.

The left cerebral cortex is responsible for speech and language. The right cerebral cortex supplies spatial information, such as where your foot is at the moment. The thalamus provides the cerebrum with sensory information from the skin, eyes and ears, as well as other information. The hypothalamus regulates things like hunger, thirst and sleep. Together with the pituitary gland, it also regulates the hormones in your body.

The cerebellum coordinates movements and is responsible for balance.

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