Human Brain is wonderful and the more we get deeper into the understanding of its functionality, the more exciting and amazing facts we come through.
Human brain has perhaps the most remarkable cognitive abilities, and it would take huge processing and computational resources to perform the same recognition tasks by a machine or a robot, which are otherwise done by human brain in a very simple fashion, such as object recognition in images/videos/scenes. For example, the Google Brain project took three days to train itself with 10 million YouTube videos, in order to recognize pictures of cats (using unsupervised features) and came out with a 74.8 percent accuracy of recognizing cats. The experiment involved a usage of 1000 machines with a total 16,000 cores, running over three days, and using parallel mode processing .
On the other hand, the human performs similar task without much supervision and an almost perfect accuracy.
What is so special about human brain? What gives the cognition abilities to human brain? How many neurons are there in the human brain? Is the human brain larger in size than an Elephant brain? If these and similar questions have ever bothered you, this article is definitely for you.
The human beings study animals, rather than animal perform study on human beings. Until recently, scientists believed that all mammals have brains built in the same way, with the number of neurons proportional to the size of the brain. This apparently implies that if two brains are having the same size, it means they have the same number of neurons, and thus the two brains should have same cognitive capabilities, (given the assumption that neuron is the functional processing unit of the brain). Now, the brain of a cow is typically of 400 grams, matching the size of the chimpanzee’s brain, yet, the two species widely differ in terms of complex analytical abilities. Thus, Neuroscientist Suzana Herculano  suggests that this hypothesis cannot be true and the size is not the factor which defines the cognition abilities of the brain. For example, if a larger size brain has more cognitive abilities than a smaller because the former has more number of neurons, then, the largest brain on earth must be the one with the highest index of cognition. But, the human brain is just 1.5 kg on average, but an elephant has brain of about 4.5 kg, and the whale has even larger brain with a weight of 9 kg.
But still the human brain has more cognition abilities.
The size of the brain usually follows the size of the body, but comparing a guerilla brain to human brain does not follow this general notion. A guerilla is almost three times bigger in size than a human body i.e. up to 210 kg of body weight, but its brain is just 0.5 kg, almost one-third of human brain.
Energy Facts The human brain is much smaller in comparison to the body mass, contributing to only two percent of the total body mass, yet it consumes 25 percent of the body energy i.e. 500 kilo Calories per day. So, the human brain is larger than it should be and it consumes huge energy, making it more special. The human brain is having larger cerebral cortex than it should be. Then, some of the possible explanations may be;
Two different brains of same size may actually have different number of neurons.
A larger brain may not necessarily have larger number of neurons.
The human brain may have the largest number of neurons, especially in the cerebral cortex. Then, a very important question arises;
“What is the total number of neurons in human brain?”
Till now, it has been a strong belief that human brain consists of 100 billion (or more) neurons. However, Dr. Suzana Herculano actually proved it wrong. First, where did this belief of 100 billion come from? And no satisfactory answer could be provided for this. Is there any reference in the literature which may prove this number? Again, the answer was NO.
So, the neuroscientist came up with her own approach to count the number of neurons in the human brain and this approach is the Brain Soup in which the brain or part of the brain was turned into soup, by dissolving it in a detergent and thus achieving a suspension of free nuclei, just like a soup.
The experimentation on various species showed that all brains are not made the same way. It turned out that human brain has 86 billion neurons on average (14 billion less than the previous assumption of 100 billion neurons). Out of the total 86 billion neurons, 16 billion neurons are in the cerebral cortex. If the cerebral cortex is the CPU inside the human CPU, i.e. the functional processing and logical reasoning part of the brain, then, 16 billion is the largest number of neurons that any cortex actually has, which gives a very good explanation of the remarkable cognitive abilities of the human brain.
Neurons number vs Brain Size 86 billion neurons in rodents would correspond to a brain size of 36 kg, which is impossible, as 36 kg of brain would roughly require 89 Tons of body, so that the brain may be placed in.
Usually, one billion neurons of brain may require 6 kcal energy per day, so the total number of calories required for 86 billion neurons can be calculated by simple mathematics.
Energy required by 1 billion neurons (per day) = 6 kcal.
Energy required by 86 billion neurons (per day) = 516 kcal.
This calculation justifies the size of the human brain vs its daily energy requirements.
Science is helping us in understanding human brain and the more we dig deeper into it, the denser the facts are revealed.
Disclaimer: The research outputs presented in this article are NOT owned by the writer and original contributors should be acknowledged wherever required, as presented in the references. Note: The writer is an Assistant Professor at COMSATS Institute of Information Technology. He can be reached at hazrat dot ali at live dot com
 TED Talk by Suzana Herculano http://www.ted.com/speakers/suzana_herculano_houzel.html
 Brain Images from http://shukran.cocolog-nifty.com/photos/uncategorized/2010/01/18/jpgblb.jpg