The brain evolved in animals because there is a strategic advantage in being able to detect and capture food (as in say a mollusc) and later to search and find food and sexual partners. The brain is thus a mechanism for locomotion and for avoiding hazards.
The brain’s chief job therefore is to store and operate the controls that command many inherited (or instinctive) body functions. This section discusses a little of what happens during this process, so that the difference between what the brain does and what is involved when thinking can be made clearer.
Instinctive behaviours are transmitted from one generation to the next through gene codings, as has been demonstrated many times. For instance, fruit flies normally wake up with daylight, nap in the afternoon, then fall asleep at dusk. This behaviour is controlled by a gene, the so-called “period gene.” If this gene is removed from male and female flies which then mate, their descendants sleep at random times. If the gene is then returned to these time-less progeny, they and their offspring will resume regular sleep patterns.
The first, tiny part of this instinctive behaviour started as the result of a mutation eons ago that caused one fly to sleep during the dark, with the concomitant reduced danger of being eaten compared to flies that were sleeping during the day. Surviving and passing this mutation to its descendants, this fly became the progenitor of successive generations that also fell asleep at dusk, so surviving in greater numbers than those lacking this Jonathan Weiner provides an example that nicely illustrates the value of instinctive behaviour in animals larger than fruit flies. He describes an experiment that uses a blackened piece of cardboard or wood cut into a bird-like shape. When this shape is moved in one direction across a light sky or ceiling it appears to be the silhouette of a goose flying; if it is moved in the other direction it resembles a hawk. When newly hatched goslings, raised in an incubator and having had no contact whatsoever with any adult goose, are shown the cut-out moving in the goose-resembling direction, they pay no attention. When the same cut-out is moved in the opposite direction, they scatter and attempt to hide.
Instinctive behaviours, like all others, depend upon the brain recognizing the significance of signals received from body sensors, or from the presence or absence of chemicals in body fluids. The question slowly being answered is, “how does the brain know what to do when it receives such signals?” Neurons in the brain (Hercule Poirot’s “little grey cells”) hold the answer.
Most human neural cells (neurons) resemble minute, spiky blobs with tails. The blob, or body, is called the soma. The tail, a long, thin, branching, tube-like extension, is called the axon. The hundreds of short, spiky structures fringing the soma are called dendrites. When activated, electrical signals in the form of electrically charged chemical ions travel from the dendrites, through the soma, along the axon and its branches (the fanout), to a number of bubble-like terminating vesicles. Ions arriving at the vesicles cause the discharge of neurotransmitter chemicals into the minute gaps that separate one neuron from another. These chemicals are detected by so-called synaptic knobs on dendrites belonging to neighbouring neurons, where they may start new ion flows within receptive neurons.
Neural networks store information for later use. This is done in a two-step process. First, flows of chemical ions circulating in tiny closed networks of neurons hold data temporarily. Much information from eyes, ears and other sense organs is temporarily stored in such neural loops while being screened for significance. Since the majority of incoming information is of little interest, most of it is discarded. (Cutting off the energizing nutrients prevents the loops from becoming significant.) Second, information having a relationship to other pre-stored or incoming data that is deemed significant can be kept active by constantly re-energizing the loops. This induces the growth of synaptic knobs on dendrites. Additional synaptic knobs facilitate the transmission of neurochemicals across the dendritic gaps and thus build pathways of lowered electro-chemical resistance connecting one neuron to another. These pathways form neural networks that can retain the bytes of information that induced their formation for many years. Millions and millions of neural networks, each storing tiny bits of information, are to be found within everyone’s brain (most laid down during our first few years of life).
The brain analyzes and interprets information coming from the senses by routing it through earlier-formed neural networks. These respond (think “resonate”) to the presence of specific, tiny, chunks of information that match the chunks that earlier caused the network to form. This can be illustrated by electronically tracing what happens to information received by the eye, a well-explored example that helps us to understand what the brain does with data from other body sense organs. Light, reflected from the object we are looking at, enters the eye and falls upon the light-sensitive rods and cones in the eye’s retina. This creates millions of tiny signals, and these travel along the optic nerve to the brain. Key aspects of the component signal, such as information bytes denoting vertical edges, excite existing neural patterns (i.e., tiny memories) of the kinds of objects that have vertical edges. The same “analysis” is done for horizontal edges, relative sizes, colours, shapes (for instance, the vertices of any triangular aspects the object may possess), and so on. This process continues until the brain excites a pattern that matches stored patterns of objects similar to the one being viewed and the object is “recognized.” “Recognition” is complete when additional characteristics, retrieved from other neural networks storing “memories,” can be added.
Memories of objects and events are built up by a reverse process. Early in life, a toddler, staring at a fir tree, for example, would have stored information in his or her brain about its general shape, colour, branch pattern, leaf shape and other characteristics. Each aspect would have been broken into smaller bytes, temporarily then permanently stored and linked by neural pathways to other related bytes (including, but added much later, bytes representing the name of the tree). If more fir trees were noted, neurotransmitting chemicals would continue to induce the formation of synaptic knobs linking and reinforcing stored memories of tree parts and whole trees. Eventually, neural networks storing relatively detailed memories of fir trees would be built. Information received upon seeing a maple tree, having many similar features, would connect into many of the same neural patterns used by the fir tree memory, but would, of course, connect into other quite different ones. (At least, it would for those who had learned the difference between a fir and a maple. Those who had not discovered the similarities and differences would have to make do with a generic tree-memory.)
Whether or not any of this knowledge affects survival would be a matter of circumstance, but it is clear that memories built up through experience do greatly affect what we know, as well as what we come to believe and how we behave. Much more about this later.
Information that depicts frequently seen objects travels along, and reinforces, the same neural pathways, making them evident by the thousands of synaptic knobs (as many as 10,000 or more) that form on the dendrites of neurons along these routes. Such large numbers of synaptic links vastly increase the brain’s sensitivity to similar stimuli, thereby decreasing response time—an important survival feature in potentially dangerous environments. Conversely, seldom-seen objects take more mental effort and may be only slowly recognized. Because our brains can carry out many unconscious functions simultaneously, we experience signal analysis and recognition as though it happens instantaneously. However, information flow along neural axons and across synaptic gaps is slow compared to information flow in computers.
Of course, recognizing the significance of incoming stimuli involves a lot more than described above. To better appreciate how information from our senses is used within our brains, consider what must be happening if, for example, we suddenly notice that we are about to walk into the branch of a tree. Before the brain can induce any action, it must, at the very least, understand the following. First, it must understand the nature of the tree’s relationship to us (e.g., that the tree will do nothing to us if we do not bump into it). Second, the brain—as well as the mind—must have access to, and be able to use, memories of what actions have succeeded in the past (e.g., that we can avoid trouble by simply ducking our head or by stepping sideways). Third, the brain needs to be constantly aware of the body’s abilities and limitations (e.g., it must know that we can’t jump out of the way if, for example, we walk with a cane). All these things, and many more, must be known to the brain just so that it can cause the body to act in a suitable manner.
It is important to note that most of what has been described above is not thinking, for even simple life forms perform many of the same functions. They react to stimuli, and show evidence of possessing memories by using the information stored in these memories when reacting. Amoebae move away from acidic areas. Earthworms sense the void of large holes in the ground and move around them. Spiders feel their web trembling and emerge to envelop prey, and so on. All living entities respond to changes in their environment by sensing stimuli of one kind or another, then acting upon what these stimuli represent to them. These sensing, analyzing and danger-avoiding activities are continually being carried out, even by primitive animals. Advanced animals have inherited these same abilities, most of which occur within the brain. But almost all of these are programmed activities which take place without any thought. They form what may be considered to be a lower level of neural functioning. Although collecting, storing and recognizing signals are important and necessary functions significant to thinking (just as buying and storing tools and materials are important functions in a factory’s operation), they are not “thinking” per se. They are simply operations that trigger the release of action-inducing chemicals. In as much, these functions are similar to many others that support and maintain the body’s welfare. First- And Second-Level Thinking clarifies this distinction.
- Breaks in the DNA strands of a sperm, ovum or zygote (caused by such factors as carcinogens, naturally occurring free-radical oxidation within cells, energetic electromagnetic radiation such as ultra-violet and X-rays, radon gas, and so on) are, to a large extent, repaired. The few that may not be repaired (or are incorrectly rebuilt) are called mutations; these become reproduced, as are all DNA molecules, in all of the cells formed from the zygote—including those of future generations. Since DNA controls cell formation and growth by affecting protein synthesis and the sequence in which sets of genes are turned on, these mutations can have various wide-ranging effects, from insignificant to fatal.
- A later different mutation in the same gene caused a fly to nap in the heat of the afternoon, which must also have contributed to that fly’s survival, and to the survival of many descendants, for this behaviour has also become inherited by the majority of fruit flies.
- Read Jonathan Weiner, Time, Love, Memory (New York: Vintage Books, 1999) for an eloquent description of some of the experiments with fruit flies and mice that proved that instinctive behaviour can be genetically inherited.
- The use of computers and a variety of instruments has greatly expanded our knowledge of the brain in the past few decades. Magnetic Resonance Imaging (MRI) provides detailed, thin, cross-sectional images. (This technology, which uses high frequency radio waves and strong magnetic fields, can also detect chemical changes that occur in the brain during various behaviours.) Functional Magnetic Resonance Imaging (fMRI) maps changes in oxygen concentration and shows localized neural activity. (For instance, an analysis of fMRI patterns can tell researchers, to an 85% accuracy, which particular picture, from a selection of several different pictures, subjects were viewing while being scanned.) Positron Emission Tomography (PET), using radioactive tracer chemicals, shows the formation of neurotransmitters as signals disseminate from neuron to neuron. Electroencephalography (EEG) and minute wire probes detect chemical and electrical changes occurring within single neurons. Voltage sensitive dyes show groups of neurons lighting up in sequence following sensory stimulation. Advanced Magnetoencephalography (MEG) scanners show that visual recognition and decision making processes within the brain move from the visual cortex, through memory and speech (i.e., sub-vocalization) regions, to the right parietal cortex, where decisions are consciously made. New ways of investigating the brain’s functioning are continually being introduced, and undoubtedly our understanding of what is occurring will grow rapidly over the next few years. (MEG scanners, which use an array of super-conducting quantum interference devices bathed in liquid helium, are one such recent introduction.)
- Axon fanouts can have between one and ten thousand branches.
- Synapses have been photographed growing in rats following stimulation of the optic nerve. New knobs take about an hour to grow.
- The development of the brain from its simplest beginnings to its current complexity in human beings is ably discussed by John Morgan Allman in Evolving Brains (New York: Scientific American Library, 1999). See also John H. Holland, Emergence: from Chaos to Order (Reading, Massachusetts: Helix Books, Addison-Wesley Publishing Company, Inc., 1998). Larry R. Squire and Eric R. Kandel, Memory: From Mind to Molecules (New York: Scientific American Library, 1999) provide a different perspective.
- Neurons transmit data from body sensors to the brain, and from the brain to body muscles, as well as within the brain itself.
- Studies have shown that stimuli from the retina move successively through the lateral gemiculate nuclei (which respond to changes of brightness or colour), to the primary visual cortex (which can detect motion and its direction), then on to well over twenty other cortical regions (which detect shapes), and eventually on to more specialized regions such as the inferior temporal cortex (which can recognize objects and identify their form). The sequential detection of optical stimulation shows how vision has evolved over time to become what it is today. Many hundreds of millions of years ago one or more genetic mutations occurred, producing a slight cellular sensitivity to light. Helping the entity to survive, the altered genes were passed on to descendants. Subsequent mutations, perhaps forming several light-sensitive patches, and probably occurring many generations later, gave additional survival benefits, and these were also passed on. Gradually, after many thousands of genetic modifications (the majority of which would not have helped survival, and whose possessors would not have had a greater chance of surviving to reproduce), primitive eyes and the associated decoding memory networks in the brain, would exist. All organisms’ body tissues and systems have been constructed in this manner, with non-lethal modifications being passed to descendants as additions to those already present.
- One of these memories would likely be its name, for animals having language abilities. See section three of this chapter for more details.
- Magnetic Resonance Imaging (MRI) is able to show brain activity when mental tasks are performed. When a subject is shown pictures of places visited, memories of those places cause particular brain areas to activate. Pictures of places not visited do not elicit such a response. The techniques which detect this mental behaviour can be used to examine people suspected of taking part in criminal activities. This creates an interesting moral problem: should such a technology be developed? See Brad Evenson, “The guilty mind,” National Post, February 8, 2003, A1 and A6.
- Brains of rats raised in stimulating environments possess many more synaptic knobs, are heavier, and have a better blood supply than the brains of rats raised in uninteresting conditions. See Susan Greenfield, The Private Life of the Brain: Emotions, Consciousness, and the Secret of the Self (New York: John Wiley & Sons, Inc., 2000). Rats (and mice) raised in enriched environments also learn better. See page 42 of “New nerve cells for the adult brain,” in The Hidden Mind, a special edition of the Scientific American, May 2002, 38-44.
- Plants also do this; for instance, gravity orients stem growth upwards, roots develop toward nutrients, and branches shape so that their leaves gather maximum sunlight.
- William H. Calvin, in The Ascent of Mind: Ice Age Climates and the Evolution of Intelligence (Bantam Books, 1990) discusses this topic in a straight-forward manner. He explains reflex actions as due to “sensory schemas” being firmly linked to “movement programs” (see page 39 of his book). Computers can be programmed to carry out similar functions, i.e., to oversee and care for the well-being of machines, vehicles and factories. Although many expect computers to eventually be able to think, these care-giving electronic chips certainly do not. The parallels between the human brain and a computer have been interestingly developed in Chapter Seven, “The Evolution of Consciousness,” of Daniel C. Dennett’s book, Consciousness Explained (Boston: Little, Brown and Company, 1991).