The brain — the central "control unit" of our bodies, repository of memories and emotions. Throughout history, philosophers have believed that the brain may even house that intangible essence that makes us human: the soul. What should we know about our brains?
In a poem written around 1892, American poet Emily Dickinson described the wonder of the human brain.
Her verses express a sense of awe, considering the brain's marvellous capacities of thought and creativity.
Musing on how this fascinating organ is able to encompass so much information about the self and the world, she wrote:
"The Brain — is wider than the Sky —
For — put them side by side —
The one the other will contain
With ease — and You — beside"
The main organ of the human nervous system, the brain manages most of our bodies' activities and processes information received from both outside and inside the body and is the very seat of our emotions and cognitive abilities, including thought, long- and short-term memory, and decision-making.
The first mention of this organ was recorded in an Ancient Egyptian medical treatise known as the "Edwin Smith surgical papyrus," after the man who discovered this document in the 1800s.
Since then, our understanding of the brain has expanded immeasurably, although still we contend with many mysteries surrounding this key organ.
In this Spotlight, we look at some of the most important facts we have uncovered about the brain — and some aspects that remain to be understood.
1. How big are our brains?
Brain size varies widely, depending largely on age, sex, and overall body mass. However, studies have suggested that the adult male brain weighs, on average, about 1,336 grams, whereas the adult female brain weighs around 1,198 grams.
In terms of dimensions, the human brain isn't the largest. Of all mammals, the sperm whale — an underwater denizen weighing an impressive 35–45 tons — is known to have the biggest brain.
But, of all the animals on Earth, human brains have the largest number of neurons, which are specialized cells that store and transmit information by electrical and chemical signals.
Traditionally, it has been said that the human brain contains approximately 100 billion neurons, but recent investigations have questioned the veracity of that number.
Instead, Brazilian neuroscientist Suzana Herculano-Houzel has discovered — by using a method that required liquefying donated human brains and turning them into a clear solution — that the number is closer to 86 billion neurons.
2. What makes a brain?
The human brain makes up, alongside the spinal chord, the central nervous system. The brain itself has three main parts:
- the brainstem, which, like a plant's shoot, is elongated, and which connects the rest of the brain with the spinal chord
- the cerebellum, which is located at the back of the brain and which is deeply involved in regulating movement, motor learning, and maintaining equilibrium
- the cerebrum, which is the largest part of our brains and fills up most of the skull; it houses the cerebral cortex (that has a left and a right hemisphere separated by a long groove) and other, smaller structures, all of which are variously responsible for conscious thought, decision-making, memory and learning processes, communication, and perception of external and internal stimuli
Brains are made of soft tissue, which includes gray and white matter, containing the nerve cells, non-neuronal cells (which help to maintain neurons and brain health), and small blood vessels.
They have a high water content as well as a large amount (nearly 60 percent) of fat.
The brain of the modern-day human — Homo sapiens sapiens — is globular, unlike the brains of other early hominids, which were slightly elongated at the back. This shape, research suggests, may have developed in Homo sapiens about 40,000–50,000 years ago.
3. How 'hungry' are our brains?
Despite the fact that the human brain is not a very large organ, its functioning requires a whole lot of energy.
"Although the [human] brain weighs only 2 percent of the body [mass], it alone uses 25 percent of all the energy that your body requires to run per day," Herculano-Houzel explained in a presentation.
And why does the brain need so much "fuel?" Based on studies of rat models, some scientists have hypothesized that, while most of this energy is expended on maintaining ongoing thought and bodily processes, some of it is probably invested in the upkeep of brain cells' health.
But, according to some researchers, at first sight, the brain, seemingly inexplicably, uses up a lot of energy during what is known as the "resting state," when it is not involved in any specific, targeted activities.
According to James Kozloski, "Inactivity correlated networks appear even under anesthesia, and these areas have very high metabolic rates, tipping the brain's energy budget toward a large investment in the organism's doing nothing," he writes.
But Kozloski's hypothesis is that no large amount of energy is spent for no reason — so why does the brain seem to do it? In fact, he says, it doesn't.
Energy spent "doing nothing," he says, is actually put toward assembling a "map" of accumulating information and experiences that we can fall back on when making decisions in our day-to-day lives.
4. How much of our brains do we use?
One long-circulating myth has it that humans typically use only 10 percent of their brain capacity, suggesting that, if only we knew how to "hack into" the other 90 percent, we might be able to unlock amazing abilities.
While it remains unclear exactly where this myth originated and how it spread so speedily, the idea that we could somehow tap into as yet unclaimed brain power is certainly a very attractive one.
Still, nothing could be farther from the truth than this piece of urban lore. Just consider what we discussed above: even in a resting state, the brain is still active and requires energy.
Brain scans have shown that we use pretty much all of our brains all of the time, even when we're asleep — though patterns of activity, and the intensity of that activity, might differ depending on what we're doing and what state of wakefulness or sleep we're in.
"Even when you're engaged in a task and some neurons are engaged in that task, the rest of your brain is occupied doing other things, which is why, for example, the solution to a problem can emerge after you haven't been thinking about it for a while, or after a night's sleep, and that's because your brain's constantly active," said neurologist Krish Sathian, who works at Emory University in Atlanta, GA.
"If it were true that we only use 10 percent of the brain, then we could presumably sustain damage to 90 percent of our brain, with a stroke [...] or something like that, and not [experience] any effects, and that's clearly not true."
5. Right- or left-brained?
Are you right-brained or left-brained? Any number of Internet quizzes will claim to be able to assess whether you predominantly use the right or left hemisphere of your brain.
And this has implications about your personality: allegedly, left-brained people are supposed to be more mathematically inclined and analytical, while right-brained people are more creative.
But how true is this? Once more the answer, I'm afraid, leans toward "not at all." While it is true that each of our hemispheres has slightly different roles, individuals do not actually have a "dominant" brain side that governs their personality and abilities.
Instead, research has revealed that people use both of the brain hemispheres pretty much in equal measure.
However, what is true is that the left hemisphere of the brain is more concerned with the use of language, while the right hemisphere is applied more to the intricacies of nonverbal communication.
6. How do brains change with age?
As we age, parts of our brain begin to shrink naturally and we begin to gradually lose neurons. The frontal lobe and the hippocampus — two key brain regions in regulating cognitive processes, including memory formation and recall — start shrinking when we hit 60 or 70.
This means that we could naturally begin to find learning new things, or performing several tasks at the same time, more challenging than before.
There is some good news, as well, however. Till not too long ago, scientists used to believe that once we started to lose neurons, that would be it — we would be unable to create new brain cells and had to resign ourselves to that.
However, it turns out that this isn't true. Researcher Sandrine Thuret, from King's College London in the United Kingdom, has explained that the hippocampus is a crucial part in the adult brain in terms of generating new cells.
(And this makes sense if you consider that it plays an important role in processes of learning and memory.)
The process in which new nerve cells are created in the adult brain is called neurogenesis, and, according to Thuret, estimates suggest that an average adult human will produce "700 new neurons per day in the hippocampus."
This, she suggests, means that when we reach middle age, we will have replaced all the neurons that we had in this brain region in the beginning of our lives with ones that we produced during adulthood.
7. Is perception 'a controlled hallucination?'
A great mystery of the human brain is linked with consciousness and our perception of reality. The workings of consciousness have fascinated scientists and philosophers alike, and though we are slowly inching closer to an understanding of this phenomenon, much more still remains to be learned.
Anil Seth, a professor of cognitive and computational neuroscience from the University of Sussex in the U.K., who specializes in the study of consciousness, has suggested that this intriguing process is based on a sort of "controlled hallucination," which our brains generate to make sense of the world.
"Perception — figuring out what's there — has to be a process of informed guesswork in which the brain combines these sensory signals with its prior expectations of beliefs about the way the world is to form the best guess of what caused those signals."
Prof. Anil Seth
According to him, in delivering perceptions of things to our consciousness, our brains often make what you might call "informed guesses," based on how it "expects" things to be.
This explains the uncanny effect of many optical illusions, including the now-notorious "blue and black, or white and gold dress," when, depending on how we think the light in the picture is, we may see a different color combination.
Below, you can watch Prof. Seth's 2017 TED talk. He explains how our brains make sense of the world around us — and within us.
Despite the many advances in research and clinical technology, a lot of questions about the brain remain unanswered. For example, we still don't quite understand how complex information is processed in the brain.
Every day, we take who we are, what we perceive, and what we are able to do for granted, without sparing so much as a thought for the marvellous organ that helps to make it all possible.
So, the next time you pick a flower and smell it or rummage for the ripest apple at the market, take a moment to acknowledge how truly wonderful each and every one of your smallest actions is.