What makes human brains different from animals

This similarity in brain structure exists because of the evolutionary history that all these brains share. In fact, if we put brains of different mammals next to each other, the similarities are easy to spot. Even though the brains vary a lot in their size and in their folds, they all have the same parts.

All these brains have a cerebral cortex , a cerebellum , and a brain stem see Figure 1B. Also, the same kinds of cells make up all brains: they are made of neurons, glial cells, and the cells that make the capillaries small blood vessels that bring blood into the brain Figure 1A.

Neurons transmit information to other neurons through their branches, across connections called synapses. Glial cells are of three kinds. Microglia are the immune system in the brain. Oligodendrocytes wrap the branches of the neurons and make information move faster from one neuron to the next. Astrocytes do a lot of things, keeping everything in order—from helping neurons make synapses to providing them with nutrients. 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 a capybara is the largest rodent alive, it looks like a giant guinea pig. Both brains weigh about 80 g.

You would probably say the brains have the same number of neurons—and so would many scientists. Until about 10 years ago, most researchers expected brains of the same size to have the same number of neurons. That also meant that the bigger the brain, the more neurons it would have.

We now know that neither of these things is true. In , one of us Suzana developed a new method that lets us count how many neurons make up a brain [ 1 ]. This method dissolves the brain into soup Box 1 , starting with a recently dead brain that has been treated with a chemical called paraformaldehyde PFA to make the cells more resistant if the brain is not treated with PFA, you could damage it just by touching it.

If you do not use the soup method and instead take a piece of a brain and count how many cells are there, you might count cells from a place in the brain that is full of neurons and then you would think that the whole brain has a lot of neurons. But the number of cells is not the same in all parts of the brain—some brain parts have more neurons, some have fewer. Here is the idea: we want to take a brain and destroy everything to make soup—except the nuclei of the cells that make up the brain.

Because each brain cell has only one nuclei, if we find the number of nuclei, we find the number of cells that make up the brain. Step 1: Put the brain in paraformaldehyde PFA for a few days. This process is called fixation. Step 2: Separate the part of the brain that you want to know about. Then slice it into small pieces. Step 4: Add a detergent to help break up the tissue. Step 5: Move the inside glass up and down and rotate it, to break up the brain tissue.

This is called fractionating. By rubbing these two pieces of the glass against each other, the friction breaks the brain pieces into smaller and smaller pieces, eventually leaving only the nuclei of the cells which is what we count on the microscope. This is sort of like making juice: you press the brain against the glass, just like a fruit is pressed against the rotating juicer reamer to extract its juice. Let us take imaginary brains in our hands again, this time two primate brains, one twice the size of the other.

How many neurons would the larger one have? Well, in this case, about twice the number of neurons of the smaller brain. Now, if brains were all built in the same way, with the same uniform recipes, we would see the same thing in rodents. So, if we took now two rodent brains, one brain twice as big as the other, we would expect the larger one to have twice as many neurons as the smaller one.

How can this be possible? Each brain cell in the group responds with a unique signalling pattern to a particular magnetic field intensity, which the pigeon is able to interpret. Therefore, if scientists started a human v pigeon race home from far away, the pigeon would undoubtedly cross the finish line first while the human wandered around trying to find a GPS signal.

A substantial number of human children have a photographic memory, also known as eidetic imagery. This enables them to memorise large amounts of information when exposed to it for just a short period of time, but unfortunately this miraculous talent fades as the individual ages. When this remarkable working memory was examined , challenging humans against chimpanzees, young chimpanzees were found to have a superior ability to retain a sequence of numbers than human adults.

It was even found that the time the chimpanzees were exposed to the numbers did not affect their memory of them, suggesting the memory capture was almost instant. However, to really crown the champion of this battle, young chimpanzees should face human children and adult chimpanzees should take on adult humans, to account for the decline of eidetic memory with age. Traumatic brain injury is the biggest risk to people under 40 in England and Wales, indicating humans lack efficient mechanisms to avoid this fate.

One adaptation is a thick skull layered with closely woven strips of bone forming a mesh-like structure that absorbs the shock of the impact. Woodpeckers possess another shock absorber — a band of bone the hyoid bone surrounding their skull like a seatbelt. With all these inventive adaptations, woodpeckers would defeat any rock star in a head-banging showdown.

The enlarged foreheads and skull capacity of humans has enabled our brains to grow in size dramatically from that of our ancestors. However, it is still not the biggest brain in existence. Thrashing the measly 1. Many dispute the relevance of this, arguing that a brain-to-body mass ratio is more informative of intellect. Taking this into account, we would still lose; in this instance to the treeshrew because this humble creature has the greatest brain-to-body mass ratio of any species.

There are two major cell types in the brain: neurones, the more widely recognised brain cell, and glia, the lesser-known brain cell. This fluid circulates around the brain and spinal cord, cushioning it from injury, and is eventually absorbed into the bloodstream. In addition to cushioning the central nervous system, CSF clears waste from the brain.

In what's called the glymphatic system, waste products from the interstitial fluid surrounding brain cells move into the CSF and away from the brain, according to the Society for Neuroscience. Studies suggest this waste clearance process mostly happens during sleep.

Clearing potentially neurotoxic waste from the brain or "taking out the trash" through the glymphatic system could be one reason that sleep is so important, the authors suggested in their paper.

Overall brain size doesn't correlate with level of intelligence for non-human animals. For instance, the brain of a sperm whale is more than five times heavier than the human brain, but humans are considered to be of higher intelligence than sperm whales.

A more accurate measure of an animal's likely intelligence is the ratio between the size of the brain and body size, although not even that measure puts humans in first place: The tree shrew has the highest brain-to-body ratio of any mammal, according to BrainFacts.

Among humans, brain size doesn't indicate a person's level of intelligence. Some geniuses in their field have smaller-than-average brains, while others have brains that are larger than average, according to Christof Koch , a neuroscientist and president of the Allen Institute for Brain Science in Seattle. For example, compare the brains of two highly acclaimed writers. The Russian novelist Ivan Turgenev's brain was found to weigh 71 ounces 2, grams , while the brain of French writer Anatole France weighed only 36 ounces 1, g.

The reason behind humans' intelligence, in part, is neurons and folds. Humans have more neurons per unit volume than other animals, and the only way they can all fit within the brain's layered structure is to make folds in the outer layer, or cortex, said Dr. Other intelligent animals, such as monkeys and dolphins, also have these folds in their cortex, whereas mice have smooth brains, he said. How the brain is integrated also seems to matter when it comes to intelligence.

A genius among geniuses, Albert Einstein had an average size brain; researchers suspect his mind-boggling cognitive abilities may have stemmed from its high connectivity, with several pathways connecting distant regions of his brain, Live Science previously reported.

Humans also have the largest frontal lobes of any animal, Holland said. The frontal lobes are associated with higher-level functions such as self-control, planning, logic and abstract thought — basically, "the things that make us particularly human," he said. The human brain is divided into two hemispheres, the left and right, connected by a bundle of nerve fibers called the corpus callosum.

The hemispheres are strongly, though not entirely, symmetrical. Generally, the left brain controls the muscles on the right side of the body, and the right brain controls the left side.

One hemisphere may be slightly dominant, as with left- or right-handedness. Related: What's the difference between the right brain and the left brain?