Brain Activity Non-stop
Our brains use about 20 W—much energy for an organ weighing about 2-3% of our body weight (Considine 2008, p. 986). The whole body has been estimated to consume only 116 W (Berg 2012, p. 549). To support its energy consumption, 20% of the brain consists of blood vessels (Oshea 2005, p. 3). Much energy is used for signaling: transmission, amplification, and manufacturing of signaling chemicals. The chemicals are called neurotransmitters and are usually simple molecules, swiftly produced from common diets. The brain uses glucose (a simple sugar) as a preferred energy source but can switch to ketones (acids) if our carbohydrate intake is low. This happens if we starve or switch to a carbohydrate-restrictive diet.
In one second, a neuron can fire 400 times and a neural impulse can travel 100 m—slow compared with near-light-speed copper wire signals (299,792,458
meters per second). But the brain is thought to make up for its slow signaling through parallel processing.
Researchers are increasingly exploring the contribution of glial cells to mental life. The Spanish neurologist Santiago Ramon y Cajal (1852-1934), a 1906 recipient of the Nobel Prize for his work on the neuron theory of the brain (Shepherd 1991), was aware of the remarkable landscape of brain cells apart from neurons and speculated about the role of glia in modulating neural signaling. But few others paid much attention to them. It has only recently become clear how important glia are for cognitive function.
Neurons are outnumbered by glia, and the number of cells involved in our mental lives could, by a rough estimate, be in the half-trillion range. All brain cells are always active in evolving patterns. Nothing lies dormant. For instance, visual cortex cells in the blind can be hijacked by the auditory cortex, seemingly for improved hearing. This may explain why a blind person with a cane gets around so well—the person’s auditory perception might be neurally beyond normal capacity.
In some cases, neurons self-destruct. This can be the case with neurons that have survived a stroke but lost connections to other neurons—they go through genetically programmed cell death if the brain fails to reintegrate or repurpose them. It can also happen with damaged cells.
Whatever you encounter—a crowd of people rushing by you on your way to work, a conversation you are overhearing, or the cacophony of a chaotic traffic intersection—your brain produces a unified, coherent, conscious experience. Our brains deliver a comprehensible world through relentless, largely nonconscious processes. Consider Jastrow’s duck-rabbit. You can see it as a duck or a rabbit, switching back and forth.
Your brain seems unable to decide which way of seeing is best. If the duck-rabbit does not switch for you, perhaps the Necker cube will. The cube can be perceived from two angles, and the angle of perception alternates. Brains have no status quo—no stillness. Sometimes the perception of what is still becomes that of movement, as in the following illustration, where lines jump around.
Gaze at this dot in a Zen-style meditative fashion, and you will see that it is never perceptually still.
Our visual apparatus is looking for change so much that it sees it where there is none.
Let us take a step back and look at the big picture of perception. Physicist Richard Feynman (1918-1988) asks us to consider perception from the perspective of an insect sitting in the corner of a pool (Feynman and Sykes 1994, p. 130). In this thought experiment, could it be that such an insect is aware of what is going on in the pool—that someone dives in, that this and that is on the surface, and so on, just by changes in water movements? This seems inconceivable. But we must accept that something like that would be the case for ourselves if we were laying poolside. We can perceive what is going on around us through changes in light and sound waves—a remarkable feat, illustrating for Feynman the “inconceivable nature of nature.” Feynman’s thought experiment reminds us of the essential problem of perception. The brain starts out with basic environmental physical energies to construct conscious experiences of the world around us. It has evolved to be perceptually hungry to sustain consciousness for survival rather than for truthful representation. If we accept that survival is the priority, it becomes easier to understand how conscious perception works as a pragmatic process with possible misrepresentations and peculiarities. It doesn’t matter if we occasionally perceive movement when there is none, as long as we detect movement when it matters, such as with falling rocks above us, breaking ice under our feet, and approaching predators.
The brain has evolved to be dynamic and plastic, helping us to maintain and further develop mental, motor, and other capacities. If we could see the active microscopic brain at work, we would observe how (1) cells move about; (2) new cells are born and others die; (3) cells change shape; (4) cells rebalance the strength of their connections; (5) new connections are sprouted and others pruned; (6) axonal connections are insulated with myelin; (7) synapses move around, and other structural changes occur. The brain is plastic enough to make both neural reallocations and connective modifications in the case of brain damage (stroke-related, from tumors, etc.). As mentioned earlier in this section, some blind people recycle visual cortex cells for other purposes. The common view is that such neural hijacking is a general phenomenon, which applies to other sense modalities as well. The brain nonetheless does not require trauma to change on a grand scale. This becomes evident when we examine how brains control movement. We can make large-scale changes to our brains through practice. A professional piano player has more motor cortex dedicated to hand movements than normal, as well as thicker white matter tracts connecting various parts of the brain.
New cells are also generated throughout our lives to a greater extent than was previously thought. Research suggests that generation occurs after trauma such as a stroke. Patient recovery, in such cases, is likely attributable to a combination of cell reallocation and regeneration. Research on neurogenesis (forming of new brain cells) is at an early stage, and it remains unclear to what extent and where it happens.