How does the brain work?

Thursday, 26 December 2013 - 7:00pm IST Updated: Thursday, 26 December 2013 - 11:56am IST | Agency: DNA
The human brain is far more versatile than we can imagine.
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Thinking about thinking is a lot of fun and, in fact, very informative. We all have brains that we use for thinking, and we all believe we think with our brains. Yet, our brain does far more than we can imagine. It is continuously at work, forever checking on things and mending them where needed.

Brains were originally designed not to sit in air conditioned offices, manipulating numbers and machines that manipulate numbers, but for survival in the wild, as a central organ to assimilate all the information of our surroundings for three purposes: to eat, to not be eaten, and to reproduce.

You need to be able to identify food, danger and a suitable partner with minimum fuss and without experimenting much with options. You can’t get eaten by a tiger before you mark it as dangerous. You should be able to decide at first glance that a tiger is best avoided.

To achieve this, we have five senses: sight, hearing, smell, taste and touch. The brain uses information from these five senses and combines it with its existing experience to create a three-dimensional image of the world, to which it continues to add new experience to maximise our chances of survival. Of these senses, sight is by far the most important and versatile, followed by hearing and smell. Touch and taste are a bit more limited in their reach.

Taking survival seriously, the brain has evolved a whole host of strategies to deal with the information it receives in order to undertake the tasks it is supposed to do with maximum efficiency. Even so, it consumes around 30% of the body’s energy budget, and is so protective of itself that it will not even allow blood to deliver nutrients to it directly. It has special protective barriers that only let a limited number of molecules to pass through.

So what is this 1350 cc mass of nerves sitting inside a hard skull do, and how does it achieve its objectives?

As when we were hunter-gatherers, the human brain’s first priority is to find food. In order to eat, it is important to develop an instinctive realisation for what is edible and what isn’t. That means looking for things that can most efficiently deliver nutrients to the body, with specific digestive capabilities. It also requires development of skills that help acquire the food. This requires short term instincts to hunt (or steal), and long term intelligence to plant seeds that will provide fruits months later.

As regards desiring food, the control of the brain on this process is remarkable. For example, no tongue in its right mind (!) would be willing to accept chillies and all right-thinking stomachs react badly to them. Yet, chillies have excellent nutritional value and provide more vitamin C, for example, than any other natural source. So the brain can force the tongue and stomach to reduce their sensitivity to chillies and accept them as food. Two senses, touch and taste, primarily help to eat, though limbs also help in avoiding being eaten.

As regards the issue of not being eaten, the brain is spectacularly successful. Primarily using visual signals, it judges the level of threat, and when the eyes cannot provide complete data, in dense jungle or open grassland for instance, the brain is adept at taking audio or nasal inputs to assess the threat level and guide the body. In case early warning fails and danger becomes imminent and unavoidable, the brain can instantaneously activate a whole host of activities. Its response is fight or flight: to either fight off the threat or move out of harm’s way as quickly as possible.

To achieve this, the brain takes several steps. By increasing the flow of adrenaline in the blood it primes limbs for action and makes more energy available to them. It will ensure a larger blood supply to the limbs by increasing the heart beat and making the body breathe faster to purify the blood quicker. It will quickly assimilate the visual path to decide which the best way to run is, and the best rhythm of muscle movement to employ if it decides to fight. In doing so, the brain actually significantly increases its speed of decision making. To achieve this without overheating, it shuts down all non-essential activities. For example, even if a person is offered chocolate cake while running away from a tiger, s/he is most likely to reject it since the brain is just not paying attention.

If the danger is very close, the best thing to do is to play dead in the hope that no self-respecting hunting animal will eat already dead meat. The body goes limp and we faint. But this is a risky proposition and a desperate measure. Fainting is an important defence mechanism when faced with unusual danger that the brain cannot assimilate easily. Emotional response is also a defence when one needs to respond urgently. A well thought through response needs the time to be thought.

But the brain is more complex than a linear thinking machine, processing one thought after another. For example, if suddenly asked the colour of your toothbrush or even the number of rooms in your house, you will be at a loss for words since such routine information is not processed by the primary brain. The brain develops separate pathways and small separate processors to do this work without involving the main brain.

This ability to process a whole host of information simultaneously is crucial for our survival even in the cities. Imagine you’re driving a car. You don’t just monitor the speed of the car, you also continuously pay attention to the cars in front and behind you. You also monitor your field of vision for the colour red. If you do see something red, you instinctively check if it is a traffic signal. If it is, you check if it is meant for you. If it is, you begin to gauge how best to slow down to halt at the correct time and location. You also judge the rate at which the car in front of you is slowing down, because if you don’t synchronise, your car will collide with it. You then use prior knowledge about how much pressure to put on the brake pedal to stop the car in a synchronised manner. During this process, if a pedestrian suddenly steps in front of the car, you will overrule all attempts at synchronisation and slam the brakes.

All this time, you’re also checking to see if the signal turns green so you can start accelerating again. And you can, in principle, do all this while talking to your friend. A phenomenal amount of computing power goes into this.

For other interactions we have what is called the theory of mind, an ability to perceive the possible intentions and thoughts of another mind and brain, and take anticipatory action. This has very important consequences in a whole host of human interactions and environments, and provides the basis of making us a social animal, where we decide ‘us’ and ‘them’ and collective intelligence.

The last major task of the brain is to reproduce. Ensuring reproduction is the most difficult and also the most important task, dominating the life cycle of all animals. It is so crucial that in his book The Selfish Gene, Richard Dawkins argues that genes are singularly focused on reproducing themselves and decide on various fitness based adaptors that best ensure their reproduction. A hen is an egg’s way of making another egg!

In order to reproduce effectively we must identify the most appropriate mate, and then proceed to convince the mate to mate. But how do you decide which genes are the fittest?

The first check is for appearance, for which the brain uses symmetry as a basic criterion. If the genes carried by the person cannot make a symmetrical body, they are obviously of poor quality. This idea of symmetry can be quantified and generally refers to left-right symmetry, the placing of the eyebrows, eyes, nose, mouth and ears on the face, followed by aspects like shoulders, and so on. The instinct to recognise symmetry is built into our brains; even a six-month-old child can distinguish between a symmetrical and an asymmetrical face.

Once this is checked, other aspects such as physical and mental fitness are considered. In tortoises, for example, the female can make the male run several tens of metres (which can take several days for a tortoise) to check his physical strength before accepting him as a mate.

In higher animals, other interactions occur. Since they tend to live in groups, it is important would-be mothers are pre-trained. Similarly, males would like to minimise the challenge they face from other males. This plays out in a fascinating way in reality. The human body, for example, is capable of reproducing from the age of about 17. Yet, a female will declare her coming of age by 15 or 16 years, while a male will not do so until he is 18 or 19 years old. This is because once a female declares her physical fitness, other older females will come forward to help her, while in the case of a male, other/older males will try to destroy his self-confidence and ambition so that he is not a threat to them. The younger male will have to wait until he is fit enough to fight for what he wants. So if you look at adolescent humans, females are fast learners at a younger age and more cooperative, while males are more aggressive and far less cooperative. It is in their genes.

Living in a group has several advantages in terms of survival, access to tools, a specialised workforce, etc., and so is a good strategy. But brains in a group also develop extra capabilities. For example, the map memory of a taxi driver’s brain is far more advanced than in other people.

The most interesting property of the brain is to sleep. In the wild, it is the most dangerous thing to do, yet, most animals sleep. This is because our brain acquires so many experiences and so much information while it is awake, that it assimilates all this information while it is asleep.

So, do we modern-day humans have the most efficient brains? Well, human beings do have the highest brain to body ratio, indicating a lot of surplus power that we call intelligence. But if you measure the size of the brain by the size of the skull cavity, it turns out that our ancestors 20,000 years ago had more brains (1500 cc compared to our 1350 cc) than us. We are dumber than our ancestors.

A more charitable explanation is that we have learnt to optimise the wiring within the brain, and so work with smaller, leaner circuitry than our ancestors. But this also means that the brain is now at its optimum size. If you make it bigger it will become too hot and sluggish, and if you make the circuits finer, the noise will kill the signal – we will go mad more often than we do now. It seems the brain has reached a limit of how intelligent it can be. What a scary thought!

 

Dr Mayank Vahia is a scientist working at the Tata Institute of Fundamental Research since 1979. His main fields of interest are high-energy astrophysics, mainly Cosmic Rays, X-rays and Gamma Rays. He is currently looking at the area of archeo-astronomy and learning about the way our ancestors saw the stars, and thereby developed intellectually. He has, in particular, been working on the Indus Valley Civilisation and taking a deeper look at their script.


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