SPECIALTY OF HUMAN BRAIN

What is so special about human brain ,why is that we study other animals instead of them studying us ,what does the human brain have or do that no other brain does when I became interested in these questions ,I began to research about it . Scientists thought they new what different brains are made of although it was based on very little evidence , many scientists thought that all mammalian brains including the human brain were made in the same way with the number of neurons that was always propositional to the size of brain, this means that two brains of the same size lets say brain of a champ and a cow should have similar number of neurons .now if the neurons are the functional information processing units of brain then  these two owners of brain with same size should have similar cognitive abilities ,now may be the cows have a really rich internal mental life and are so smart and they chose to not let us realize it but we eat them . I think most people will agree that champs are capable of much more complex elaborating flexible behaviors than cows are .so this is the first indication that all brains are made of same way scenario  is not quit right but lets play along if all brains were made the same way and you were to compare animals with brains of different sizes  ,larger brains should always have more neurons than smaller brains and larger the brain ,the more cognitive it's owner should be .so the largest brain around should also be the most cognitively able but here comes the bad news our brain , not the largest one around .it seems quit vexing our brain weighs between 1.2-1.5 kg but elephant brain weighs between 4-5 kg and wale brain can weigh up to 9 kg which Is why scientists used to resort to saying that our brain must be special  , to explain our cognitive abilities ,it must be really extraordinary and exception to the rule , there's may be bigger but ours is better and it could be better for example it seems larger than it should be with a larger cerebral cortex then we should have for the size of our body so that gives us extra cortex do more Interesting things than just operating our body , that is because the size of the brain usually fallows the size of body so the main reason for saying that our brain is larger than it should be actually comes from comparing ourselves with great apes .Gorillas can be 2-3 times larger than we are so there brain should also be larger than ours but instead it is out of way around our brain is 3 times larger than a gorilla brain . The human brain also seems special  in the amount of energy that  it uses .although it weighs only 2% of the body but it alone uses 25% of all the energy that your body requires to run per day , that is 500 cal out of total of 2000 cal /day just to keep your brain working so the human brain is larger than it should be it uses much more energy then it should so it is special and this is where the story started to bother me in biology we look for rules that apply to all animals and the life in general so why should the rules of evolution apply to everybody else but not to us (humans). May be the problem was with the basic assumption that all brains are made in the same way may be two brains of similar size can actually be made of different number of neurons, may be a very large brain does not necessarily have more neurons than a more modest size brain may be the human brain actually has the most neurons of any brain regardless of its size especially in the cerebral  cortex . So this to me became an important question to answer how many neurons does the human brain have ? And how does that compare to other animals . Now you may have heard or rad somewhere that we have a 100 billion neurons so 1 year ago I asked my colleges did they new where this number came from but nobody did, I have been digging through the literature for the original reference for that number and I could never find it it seems that nobody had actually counted the number of neurons in the human brain or any other brain for that matter . So I came up with suzano Herculano houzels  method , and it essentially consists of dissolving that brain into soap . It works like this , you take a brain or a part of that brain and you dissolve it in the detergent which destroys the cell membranes but keeps cell nuclei intact so you went up with a suspension of free nuclei that looks like a clear sop which contains free nuclei . Now the beauty of this sop is that because it is sope you can agitate it and make those nuclei be distributed homogeneously in the liquid so that by now looking under the microscope at just 4 or 5 samples of the homogeneous solution you can count nuclei and therefore tell how many cells the brain had .it is simple it is straightforward and it is really fast .so we have used that method to count neurons in dozens  of different species so far and it turns out that all brains are not made the same way .Take rodents and primates for instance in larger rodent brain the average size of the neuron increases so the brain inflates very rapidly and gain size much faster than it gains neurons but primate brains gain neurons without the average neurons becoming larger which is the very economical way to add neurons to your brain .the result is that the primate brain will always have more neurons than a rodent brain of the same size and larger the brain the larger this difference will be . Well what about our brain then . We found that we have an average 86 billion neurons 16 billion of which are in the  cerebral cortex and if you consider that the cerebral cortex is the seat of functions like awareness

,logical and abstract resigning and that 16 billion is the most neurons that any cortex has . I think this is the simplest explanation for our remarkable cognitive abilities but just as important is what the 86 billion neurons mean , because we found that the relationship between the size of the brain and it's number of neurons could be described mathematically we could calculate what a human brain would look like if it was made like a rodent brain , so a rodent brain with 86 billion neurons would weigh 36 kg which is not possible , a brain that huge will be crushed by its own weight so this brings us to a very important conclusion already which is we are not rodents , the human brain is not a large rat brain compare to rate we might seem special...yes ,but that is not the fare comparison to make given that we know we are not rodents but we are primates so the correct comparison is to other primes and there if you do the math you will find that a generic primate with 86 billion neurons would have a brain of 1.24 kg which seems just right in a body of some 66 kg  which in my case is exactly right which brings to a very unsurprising but still in indescribably important conclusion I am a primate and all of you are primates and so was Darwin . So the human brain may be remarkable ..yes but it is not spacial in its number of neurons it is just a large primate brain . I think that is a very humbling and sobering thought that should remind us of our place in nature .why does it cost so much of energy then ? Well other people have figured out how much of energy  human brain cost , since now we new how many neurons each brain was made of , we could do the math and it turns out that both human and other brains cost about the same an average of 6 cal per billion neurons per day . So the total energetic cost of brain is a simple linear function of its number of neurons and it turns out that the human brain costs just as much energy as you would expect . So the Reason why the human brain cost so much energy is simply because it has a huge number of neurons and because we are primates with many more neurons for a given body size than any other animal the relative cost of brain is large but just because we are primates not we are spacial . Let's question then how did we come by this remarkable no. Of neurons and in particular if grate apes are larger than we are why don't they have a larger brain than we do with more neurons. When we realize how expensive it is to have a lot of neurons in the brain I figured may be there is a simple Reason they just can't effort the energy for both the large body and the large no of neurons so we did the math we calculated on the one hand how much energy a primate gets per day from eating Raw foods and on the other hand hand how much a body of certain size costs and how much energy a brain of a certain number of neurons costs and we looked for a combination of body size ad no. Of brain neurons that a primate could effort if it eats certain no of hours per day and what we found is because neurons are so expensive  , there is a trade-off  between body size and number of neurons . So a primate that eats 8 hours per day can effort at most 53 billion neurons but then it's body can not be bigger than 25 kg , to weigh anymore than that it has to give up neurons . So it is either a large body or a large number of neurons when you eat like a primate you can't effort both . One way out of this metabolic limitation would be to spend even more hours per day eating but that gets dangerous and to pass a certain point is just not possible . Gorillas and Orangutans for instance effort about 30 billion neurons by spending 8 and half hours per day eating and that seems to be about as much as they can do .9 hours per day seems to be a practical limit for a primate , what about us ? With our 86 billion neurons  and 60-70 kg body mass we should have to spend over 9 hours every single day feeding which is just not feasible . If we eat like a primate we should not be here , how did we get here then well if our brain costs just as much energy as it should and if we can't spend every waking hour of the day feeding , then the only alternative really is to somehow get more energy out of the same foods and remarkably that matches exactly what our  ancestors are believed to invented one and a half million years ago when they invented cooking . To cook is to use fire to predigest foods outside of your body .cooked foods are softer so they are easier to chew and to turn completely into mush in your mouth which allows it to be completely digested and absorbed in your gut which in turn allows you to extract much more energy in much less time . So cooking frees time for us to do much more interesting things with our day and with our neurons then just thinking about food looking for food and gobbling down food all day long . So because of cooking what once was a major liability this large dangerously expensive brain with a lot of neurons could now become a major asset . Now we could both effort the energy for a lot of neurons and the time to do Interesting things with them . So I think this explains why the human brain grew to become so large so fast in evolution all the while remaining just a primate brain .with this large brain now affordable by cooking we went rapidly from raw foods to culture , agriculture, civilization , grocery stores , electricity , refrigerators all these things now a days allow to get all the energy we need for whole day .So what is the human advantage what is what we have that no other animal has . My answer is we have the largest no of neurons in the cerebral cortex and I think that is the simplest explanation for our remarkable cognitive abilities and what it is that we do that no other animal does , which I believe was fundamental to allow us to reach that largest number of neurons in the cerebral cortex in two words "we cook ". No other animal cooks it's food only humans do and I think that is how we got to become human . Studying the human brain change the way I think about food and I thank my ancestors to come up with the invention that made us human.