Intelligence and the Brain

The brain is a remarkable part of the body. It is an extensively complex network of nerve cells which each connect with dozens of other nearby cells to form signal pathways and structures and circuits, etc. A brain can simulate logic and emotion, and is the only organ in the body that, when removed, causes instantaneous death. Almost all animals cannot survive without a brain. And despite the vitality of it, we do not understand nearly as much about the brain as we would like to. One of the biggest fields of study is related to intelligence in various organisms, which I will talk about in this post.

The first question crossing the mind of a scientist tackling this topic is likely "How do you define intelligence?". For humans this can be very generally assessed by the IQ test. There are some longer and broader tests that can be somewhat accurate (a particularly good one can be found here), but they often fail to take into account creativity and unorthodox answers. But for other animals, which are far less intelligent, the IQ test is too advanced and we need to make something simpler. At the primate center in Duke University the lemurs are being tested by a computer that displays two images with different numbers of dots of varying size and shape. They are trained to select the image with fewer dots for a reward (found here).

Another study devised a puzzle box which required pressing a button with one limb and opening the lid with another to get food, and intelligence was measured by the percent of organisms that were able to open the box and get the food (found here).

In these studies it is explained that the ability to open the box or distinguish quantities can be linked to intelligence, but that isn't all there is to it. Some of the lemurs in the first experiment were able to complete the test faster than some college undergraduates at the prestigious Duke University, but that doesn't mean they are actually more intelligent. Also, in the box experiment, bears were far more successful at opening the box than meerkats, but meerkats often have much more complex social groups than bears do. Plus, we are still missing one crucial aspect of intelligence, curiosity.

None of the animals in these experiments were curious about the box on their own, they all had to be tempted by food to try to solve it. Like other traits on this topic, it is hard to measure curiosity scientifically. One way is to introduce something foreign into the species environment and see whether they notice it at all and if so how long it captures their attention, but beyond that it is difficult. Humans, most apes, and some other mammals like dolphins are curious, but the vast majority of animals are not. Being curious is often not an evolutionary advantage, because it involves getting within a dangerous proximity to unknown things or animals and can lead to higher mortality rate.

Despite all of these tests for problem solving and curiosity and quantity differentiation, there is no way to test total intelligence simply by tests. Every species on earth requires its own set of skills to survive, and anything else is unnecessary and not selected for. Asking a bull frog to open a puzzle box to get food out is like asking a chess computer to predict the weather. The frog would breeze through the complex task of raising tadpoles, but cannot perform a much simpler task because it is not important for survival.

So, now that we know assessing the true intelligence of an animal is all but impossible, lets assume that we can test intelligence. What kind of patterns might emerge between intelligence and the physical brain? The first thing to look at would likely be brain size. After all, having a bigger brain means more neurons, more connections, and more complex neural networks. But we run into an issue doing this. (paper found here)

As this graph demonstrates, the mass of an organism's brain is inversely related to its neural density. Basically, as brain size gets larger, fewer neurons can fit in a certain volume so we end up with a brain that is larger but also less complex for a given volume. Also, larger animals simply have larger bodies with more nerve endings on the skin and more, larger muscles to move.

For example, lions and mice have nerves on every hair that can each relay a different signal to the brain to detect movement. The lion has far more surface area on its body so it has many more signals that need to be processed individually in the brain. Plus, the lion has to have more nerves taking the signal to larger muscles requiring stronger signals. Then there is the fact that any signal traveling from one part of the brain to another will take much longer in larger animals because the brain is bigger and nerve signaling pathways are likely indirect. These effects combine to cause brain size to be primarily dependent on the organism's size. 

There are two ways to get around this. One is to exclude from measurement the parts of the brain used for the senses, motor controls, memory, and other size-dependent areas. This is impractical though because the brain's neural networks span many different areas of the brain and it would be impossible to isolate and extract only neurons used for logical thinking. The second option is to measure the brain size to body size ratio and compare that between species. Sadly we meet another issue. A mouse brain takes up about 10% of its body's mass, while a human brain takes up 2% and a blue whale brain takes up .01% (still 5 times larger than a human brain though). We can't base intelligence purely off of that ratio. But there seems to be a pattern in that ratio between body and brain mass. Scientists have graphed the ratio for a large collection of animals, resulting in the graph below.

And sure enough, all of the animals included follow a nice straight distribution. Now we are able to measure the amount of brain mass dedicated to logical processing by saying the line of best fit is the average amount of brain mass dedicated to logical thinking, and say that animals further above the line are considered more intelligent. At a glance it seems to work fairly well. Primates are considered very curious and clever compared to other animals, and they are mostly above the line. Plus, humans are the furthest above the line of any species measured in this study, which is significant on a logarithmic graph. Also notice that the line of best fit does not have a slope of 1, it has a slope less than one, which accounts for the difference in ratio between mice, humans, and whales discussed earlier. 

However, even though we may be able to make a general assessment based off of this graph, There has been little experimentation relating this ratio to actual intelligence. Many scientists steer clear from this topic of discussion because of the extreme difficulty of obtaining large enough samples of quantitative data from multitudes of species. So to finish off this post I want to talk specifically about human intelligence.

Scientists have been looking for ways to predict intelligence accurately for a long time. There are, of course, IQ tests, but there are also brain activity monitors (often used to compare savants to average people), a test involving only a raisin and a cup (here), and plenty more just a google search away. A very intuitive answer is just to say that larger brains mean more intelligence. We aren't dealing with any evolutionary differences or other factors like before, so it may work. However, that doesn't seem to correlate at all with intelligence.

One study that analyzed a large group's brain size and intelligence through a series of tests found that the intelligence of an individual was basically random chance when using brain size. Also, men have very slightly larger brains on average but women get slightly higher grades in high school and college on average. Even Einstein, considered one of the most intelligent and creative humans to have existed, had a brain weighing about 1230 grams, much less than the average mass of 1400 grams. Brain size is definitely not a good measurement.

While we are on the topic of Einstein's brain, is there anything different between his brain and most people's? According to various studies, his brain is not larger as a whole, but it's main communication pathways between brain areas were much stronger than those found in most brains. Also, he had a larger number of glial cells, which nourish neurons providing ATP and ions and allowing the neuron to be activated easily and recover quickly. This reinforces the ideas about intelligence emphasized so far, that intelligence is not based off of the size of part or all of the brain, or about how developed one part of it is. Instead intelligence can be thought of as the ability to use more of your brain and use it more effectively.

One big reason brains are so complex and hard to understand is that every single one is different. Neurons in the brain increase in strength and density, along with their bonds at synapses, in areas they are used consistently. So when Einstein was thinking about physics as a child he was building and strengthening complex structures inside his brain that specialize in physics. As a result, he had one of the most mathematically brilliant minds in history. Anyone can have the brain of a genius in any field. You just have to put the work in and build your own brain to do what you want it to do. Genetics, size, neuron density, and every other genetically determined factor, do very little when compared to the ability for a brain to build it's own structures to serve it's functions. You can take control of your own intelligence. All you have to do is think.