sulabh swatchh bharat

Tuesday, 22-August-2017


Going by absolute brain volume and number of neurons, one elephant brain could have produced several Einsteins, but that does not happen. Here’s why:

With an increasing advancements in science and technology, scientists are now better able to study the human brain in comparison to other animals’ to see what makes the human brain unique when it comes to cognitive abilities. The common narrative dictates that the human brain is the apex of biological evolution when it comes to cognition. Merely looking around and realising that the human brain has developed to the point of contemplating the reason for its own existence and function is enough to make us realise that there is something about the human brain that no other brain on the planet has.
Common sense would dictate that if the brain is the source of our cognition, having more of it would mean more cognition. But then why don’t we see elephants becoming scientists? They clearly have larger brains than we do. To be able to compare cognition in terms of brain size alone would presuppose that all brains are built the same and that the biggest brain should be the highest cognizant. Since this is not the case, neuroscientists looked elsewhere to establish a reason as to why humans are more cognizant than other animals. 
Suzana Herculano-Housel, associate professor and the head of the Laboratory of Comparative Anatomy, Institute of Biomedical Sciences, Federal University of Rio de Janeiro, argued that if the number of neurons dictated cognition, then the brains with the most number of neurons would be the most cognizant. She believed that contrary to past speculations by neuroscientists, the differences in cognition observed in humans and animals are a quantitative difference rather than a qualitative one. 
Housel argued that considering biological restrictions, animals like chimpanzees and elephants are in fact able to perform cognitive activities similar to humans but, single observations like these are not sufficient for cross-species comparisons of cognition. She explained that perhaps another way to understand the differences in cognitive capacities of different animals would be by testing self-control in animals. Since self-control involves the prefrontal part of the cortex in the brain, a measure of varying pre-frontal structures would provide an explanation for differences in cognitive capacities. She cited an example of a 2014 study that measured self-control exhibited by animals in a laboratory setting. It was observed that absolute brain volume turned out to be the best correlation in regards to the ability to exert self-control. The one and only outlier of this study were the Asian elephants who, despite having the largest absolute brain volume, failed at the self-control test.
She said “The most interesting possibility to me, however, is that the African elephant might not have all the prefrontal neurons in the cerebral cortex that it takes to solve self-control decision tasks like the ones in the study. Once we had recognized that primate and rodent brains are made differently, with different numbers of neurons for their size, we had predicted that the African elephant brain might have as few as 3 billion neurons in the cerebral cortex and 21 billion neurons in the cerebellum, compared to our 16 billion and 69 billion, despite its much larger size—if it was built like a rodent brain.”
She further added “On the other hand, if it was built like a primate brain, then the African elephant brain might have a whopping 62 billion neurons in the cerebral cortex and 159 billion neurons in the cerebellum. But elephants are neither rodents nor primates, of course; they belong to the superorder Afrotheria, as do a number of small animals like the elephant shrew and the golden mole we had already studied—and determined that their brains did, in fact, scale very much like rodent brains.”
Her hypothesis that cognitive abilities are directly related to the number of neurons present would be disproven if elephants possess more neurons than humans. This is why she wanted to measure the number of neurons present in an elephant brain. She said “The logic behind my expectation was the cognitive literature that had long hailed the cerebral cortex (or, more precisely, the prefrontal part of the cerebral cortex) as the sole seat of higher cognition—abstract reasoning, complex decision making, and planning for the future. However, nearly all of the cerebral cortex is connected to the cerebellum through loops that tie cortical and cerebellar information processing to each other, and more and more studies have been implicating the cerebellum in the cognitive functions of the cerebral cortex, with the two structures working in tandem. And, because these two structures together accounted for the vast majority of all neurons in the brain, cognitive capabilities should correlate equally well with the number of neurons in the whole brain, in the cerebral cortex, and in the cerebellum.”

Suzana Herculano-Houzel and her students cross-sectioned an elephant brain to determine the number of neurons it has and compare that with what’s found in the human brain.
She said “Next, we had to separate the internal structures—striatum, thalamus, hippocampus—from the cortex, then cut the cortex into smaller pieces for processing, then separate each of these pieces into gray and white matter. In all, we had 381 pieces of tissue, most of which were still several times larger than the 5 grams we could process at one time. It was by far the most tissue we had processed. One person working alone and processing one piece of tissue per day would need well over one year—nonstop—to finish the job.”  With the help and support of her team, she was able to finish the counting in over six months.


It was discovered that the African elephant brain had three times the number of neurons present than those in human brains. However, another discovery was made that the majority (up to 98 percent) of neurons were present in the back of the cerebellum. This unusual distribution of neurons gave way to the understanding that there was a clear difference in the number of neurons present in the prefrontal cortex. Elephants, with a mere 5.6 billion neurons in the prefrontal cortex paled in comparison to a whopping 16 billion neurons present in humans. This gave her the answer that even though human brains do not have more neurons in total when compared with that of elephants, it was evident that the concentration of neurons in prefrontal regions of the brain was the deciding factor when it came to cognitive abilities.
She explained “As it turns out, there is a simple explanation for how the human brain, and it alone, can be at the same time similar to others in its evolutionary constraints, and yet so different to the point of endowing us with the ability to ponder our own material and metaphysical origins. First, we are primates, and this bestows upon humans the advantage of a large number of neurons packed into a small cerebral cortex. And second, thanks to a technological innovation introduced by our ancestors, we escaped the energetic constraint that limits all other animals to the smaller number of cortical neurons that can be afforded by a raw diet in the wild” “So what do we have that no other animal has? 
A remarkable number of neurons in the cerebral cortex, the largest around, attainable by no other species, I say. And what do we do that absolutely no other animal does, and which I believe allowed us to amass that remarkable number of neurons in the first place? We cook our food. The rest—all the technological innovations made possible by that outstanding number of neurons in our cerebral cortex, and the ensuing cultural transmission of those innovations that have kept the spiral that turns capacities into abilities moving upward—is history.” She added.