Our Bodies’ Amazing Electric Current – Part 4

The human brain.

Continuing our essay series on our bodies’ electric current, primarily through Frances Ashcroft’s The Spark of Life: Electricity in the Human Body, and Sally Adee’s We Are Electric: Inside the 200-Year Hunt for Our Bodies’ Electric Code, and What the Future Holds, this essay explores the human brain.

As Ashcroft writes:

Your brain is one of the most sophisticated machines on the planet. It has over 100 billion nerve cells and each of them communicates with many thousands of others. There are trillions of connections, as many as in the whole of the world’s telephone system and far too many to fully comprehend. But the brain is not simply a great mass of interconnected nerve cells. It is a highly organized structure, with different parts being specialized for different purposes. The most important bit of the brain – that responsible for our thoughts and actions – is the forebrain or cerebrum. It makes up about 80 per cent of the weight of the human brain and is divided into two mirror- image cerebral hemispheres, each of which primarily interacts with one side of the body. For unknown reasons, the wiring is crossed, with nerves from the left side of the body going to the right side of the brain and vice versa. The outer layer of the forebrain, known as the cerebral cortex, is made up of a thin sheet of nerve cells that is thrown into numerous folds to increase its surface area and enable more to be packed into the skull. Its highly convoluted structure makes it look rather like a walnut kernel. It is this four-millimetre thick layer of cells that mediates thinking, conscious actions, sensation, learning and memory, and different parts of it are specialized for different functions. Below the outer shell of nerve cells the forebrain is packed with nerve fibres that run to and fro wiring the nerve cells of the cortex together. Below the forebrain lie regions of the brain that are involved in controlling the emotions, in regulating appetite and sleep, and that act as relay centres for processing information coming in from the sense organs and handing it on to the cerebral cortex. Even further down, at the base of the brain, sits the brainstem, which connects the upper parts of the brain to the spinal cord. It controls all your unconscious actions: here is where breathing, blood pressure, heart rate, digestion and so on are regulated. These regions may continue to survive and function even when higher brain functions have ceased, a condition known as a persistent vegetative state, in which the patient is often referred to as a vegetable. This bit of the brain is similar in structure to that found in many other creatures, and serves the same role: indeed, it is sometimes known as the reptilian brain.

Ashcroft then describes various milestones in brain scanning technology:

There is only one animal on the planet for which the complete wiring diagram of the nervous system is known and that is a microscopic nematode worm called Caenorhabditis elegans that lives in the soil. It is a scientific supermodel and has received even more attention than the catwalk variety. Because it is so small and has such a simple nervous system, every single nerve cell and every connection is known. It has 302 neurones, about 5,000 chemical synapses, 600 electrical synapses and 2,000 nerve–muscle connections. The enormous complexity of the human brain and the difficulty of identifying individual connections make construction of a similar circuit diagram for our own brains an almost insurmountable problem … Brain-scanning technology is transforming our understanding of how the brain works and what we think about ourselves. But it is worth remembering that the smallest brain region that can be distinguished in such scans still contains many hundreds or thousands of neurones, and what is detected (indirectly) is their summed activity. Thus there remains a huge gap between our highly detailed knowledge of what happens at the level of a single nerve cell, and how individual nerve cells are wired together to produce the electrical activity of our brains. Recently, a team of scientists of Cambridge and Liege universities have shown that it is possible to communicate with people’s brains directly, simply by asking them to answer ‘yes’ or ‘no’ to a question and then looking at their brain scans. Not that it is possible to determine if someone is simply thinking ‘yes’ or ‘no’, but if you are asked to envisage playing a game of tennis if your answer is affirmative, it is possible to detect a response in your motor cortex, and if you are asked to think of navigating around your house if your answer is negative, then a different region of your brain lights up. The patterns of brain activity are so distinctive that even an untrained observer can identify the subject’s response with almost 100 per cent accuracy. While it seems somewhat uncanny to be able to talk to someone this way, even more scary is the fact that four out of twenty-three patients who were believed to be in a persistent vegetative state were also able to give correct answers to questions, suggesting they may be at least minimally conscious and able to hear, but are totally cut off from the world because they cannot move at all, not even flicker an eyelid.

Ashcroft then describes the intricate ways in which the brain sends and receives communications, including happiness and memory:

Some nerve cells seem to be specialized for detecting movement, others fire only when a human face is detected and some, known as mirror neurones, fire both when an animal acts and when it observes the same action performed by another. Once the image is recognized, signals are sent to the amygdala, the emotional core of the brain, where its significance is evaluated. Is this a lover about to embrace you, or are you in fact about to be mugged? Is this the bus you have been waiting for? Or are you just looking at a beautiful landscape? You must then decide if what you see requires action. This involves signals being sent to the prefrontal cortex, the executive region of the brain, where you decide, for example, whether it is worth sticking out your hand to signal the bus to stop. If so, then more signals pass to the motor cortex, which instructs the necessary muscles to move your arm. Those signals that came in from the eyes via the optic nerve thus result in a multitude of complex messages that whizz back and forth around the brain. Bear in mind that we have not yet even considered how such visual information is integrated with that coming from other senses to build up a complete sensory picture of the world, or how that picture may be laid down as memory … The brain constantly filters the information it receives. Consider. Only the centre of our visual field is actually in focus, yet we see the whole of it in sharp definition. This happens because our eyes are constantly moving, focusing on different parts of the visual field, and the brain pieces the bits together into a coherent picture. We are blissfully unaware of what is happening because the brain ignores any visual inputs during the time our eyes are moving. This explains why if you stare in a mirror you will not see that your own eyes are constantly flicking from side to side – but another person will do so. Likewise, we ‘tune out’ background conversations and hear only the person we are talking to – unless we hear our name spoken, at which point our attention suddenly shifts. Our ability to attend to the most important information and disregard the irrelevant is very valuable, but it can also fool us. I vividly recall one evening when I and a bunch of other scientists were asked to watch a film of a ball game between two teams, one dressed in blue and one in red. This film is now familiar to many people, but at the time it was new to me. We were instructed to count the number of times each team touched the ball. I was mortified when at the end of the film the lecturer said the number was of no consequence, what he really wanted to know was how many of us had seen the gorilla. Gorilla?! I had seen nothing, but to my surprise four people claimed to have done so, and when the film was replayed it was obvious – a man dressed in a gorilla suit walked into the centre of the screen, thumped his chest several times, and then strode off. How could I have missed it? It was an impressive demonstration that by focusing my attention elsewhere, my brain had ignored other information it had received … Happiness and despair are the two faces of the neurotransmitter serotonin. Serotonin is produced by neurones of the raphe nucleus, whose processes ramify throughout the brain. Their targets include the nucleus accumbens and the ventral tegmental area, part of the brain’s reward system. Because serotonin is released in many brain regions and interacts with at least fourteen different kinds of receptor, it affects many types of behaviour, but one of its most important roles is mood control. Elevated levels of serotonin are associated with feelings of optimism, contentment and serenity. Too little brings despair, depression, anxiety, apathy, and feelings of inadequacy. One way of increasing your serotonin levels is by vigorous exercise, which is why a brisk walk or a game of squash (if you can drag yourself off the sofa) helps relieve the blues … Quintilian [a Roman educator] recommends that when learning a long text you should break it up into shorter pieces. Then you should visualize a familiar place – your home, for example – and put different bits of the text in different rooms. To recall the text again, you just walk through the imaginary house, room by room, recollecting the text as you go. The place method, and continual repetition, are still the best ways to remember something and are often used by memory savants today.

Ashcroft then concludes her discussion of the brain with these thoughts:

So where does it come from, this precarious feeling of ‘I’, this person sitting here inside my head, looking out of my eyes … There must be many reasons why humans have evolved consciousness, but perhaps one is that self-awareness is linked with our ability to appreciate the thoughts and feelings of others. This is crucial for teamwork and social cohesion, attributes that have been critical for the success of our species. The only other creatures to evidence self-awareness in the mirror test are also social animals – they include chimpanzees, elephants and dolphins.

In the next essay in this series, we’ll explore Sally Adee’s discussion of the role electricity plays in differentiating our cells.