by Zeev Nitsan
Part A: Aspects of Brain Function
Chapter 1: Selected Aspects of Brain Function
Facts About the Brain
The brain—the universe of our being—is also a fluttery chunk of protoplasm that weighs about one thousand and three hundreds grams. It is confined to its bony cage, grooved like a walnut and its texture resembling a ripe avocado. But, as one should not judge a book by its cover, we should not draw conclusions about the essence of the brain merely by focusing on its structure. A fragment of a memory, a line of thought, and a mental image—we cannot assess their weight, although many of them are part of the flesh-and-blood tissue of the brain.
The forefront of contemporary knowledge still leaves behind a broad explanatory gap about the structural and functional aspects of brain function and is still lacking with respect to the formation of thought and spirit. In this sense, the brain is like the philosophers’ stone that, according to the alchemists, had the power to turn cheap metal into gold. The brain, which in a way is still unknown to us, knows how to translate biochemical and bioelectrical responses into thoughts and emotions.
Speedy Journey in Brain Kingdom—the Structural Outline
The brain scenery is characterized by a repetitive motif of crevices and ridges that grant it a unique fingerprint, or ‘brain-print’. This configuration derives from evolution’s attempt to maximize the surface area of the cortex within the skull.
As we age, the crevices encircling the ridges become deeper and wider as a result of the wearing of the ridges, which results from the decrease in the number of neurons that create the ridges.
The external neurons layer, located in the brain mantle, is called the cortex. The thickness of this layer that covers the brain like a handkerchief is between one and a half to four millimeters in different areas of the brain, and its average thickness is three millimeters—as thick as a pack of nine playing cards. The cortex is made of layers of neurons that are organized horizontally and layered one on top of the other, but they also connected to one another in the vertical dimension. Different cortex layers have different features due to the differences in the nature of the cells that form them, their density, and the nature of connections between them.
The number of the layers varies in different areas of the brain. In areas that are “recently acquired” in the sense of evolution (such as the frontal lobes), one can detect six separate layers of neurons, and in more ancient areas of the brain (such as the hippocampus) one can detect three separate layers of neurons.
The cortex area is between 2,000 and 2,400 square centimeters—as small as a tablecloth. Due to the grooved structure, two-thirds of this area are located in the depths of the cortex channels.
The Columns of Neurons—the Pillars of the Thinking Hall
A common communication pattern between the neurons in the brain is in the form of a vertical column called the “neurons column.” The six layers characterizing the neocortex are represented in each of the columns. The column penetrates through them and is formed out of their contribution. The number of neurons in a cerebral column varies significantly, from clusters of fifty neurons to clusters of ten thousand neurons. On average, most columns consist of several hundreds of neurons, which rise to the height of the brain cortex—three millimeters on average.
The neurons that form a column are operated in a sequential manner as a response to the same initial stimulus. Lateral connections exist between the vertical columns—hence the crisscross pattern of neurons connections. The neurons column is the basic information processing unit of the brain. According to common estimations, there are about a hundred million columns in the human brain.
The Negative Demography of the Brain Kingdom
Our brain loses neurons in different periods of our life, and in an adult’s brain very few neurons are created.
A common assumption among brain researchers is that our brain loses 0.25 percent of its volume every year. In other words, our brain loses 2.5 percent of its volume every decade from the third decade of life. Most of the loss is ascribed to the frontal lobes.
Along with the process of neurons loss, a process of cellular differentiation of stem cells into neurons takes place in a few parts of the brain. The inspiration for the discovery of the formation of new neurons in the human brain partially came from the study of the ornithologist Fernando Nottebohm, who investigated, in 1980, the courting habits of songbirds and discovered that the winged troubadours recompose their songs every season. While studying their brains, Nottebohm discovered that new brain cells grow every season in the specific area of the brain that is in charge of birds singing.
With respect to the brain of an adult person, as far as we know today, we can make a generalization and claim that the demography of neurons in the brain is negative, with the exception of three “districts” as far as we know today. In these districts, new neurons are formed even in the brain of adults. This takes place in the area of the dentate gyrus, which is a substructure of the hippocampus located at the internal part of the temporal lobes, as well as in the subventricular zone of the lateral ventricles and in the olfactory bulb, which is the thickened part of the olfactory nerve located at the bottom of the frontal lobe close to the nasal bridge. Moreover, there are certain reports (yet to be validated) about the creation of new brain cells in the central core of the brain in an area called the caudate nucleus and in other locations in the brain, though these assumptions are still controversial.
The Maps of the Brain
As with the map of Earth, the brain-surface map can be analyzed topographically and mapped according to various functions.
The sensorial representation map of the body, the somatosensory cortex, is located in the cortex at the front of the parietal lobes in the hemisphere opposite to the relevant side of the body. The motor representation map, the motor cortex, is located in the cortex at the rear of the frontal lobes, in the hemisphere opposite to the relevant side of the body. These two representation maps are formed in a somatotopic pattern (which creates correlation between body areas and a unique representation area in the brain). The area that maps the entire body is called “homunculus” (“little man” in Latin). In this area, the representation of the areas in the body is in correlation with the level of its innervations or movement. So, for example, in the sensorial representation map, the hands have a greater area compared to the legs—whose surface area is much bigger—since the sensorial sensitivity of the hand fingers, and in particular of fingertips, is the highest in the body. The representational maps of the brain can be changed with respect to representational relations of the various areas of the body that reflect them.
When a certain organ of the body is damaged, its representational area in the cortex changes accordingly, based on the general brain flexibility rules: the inactive elements will lose their vitality and will vanish gradually. On the other hand, active brain maps will strike their roots deeper into the bed of neurons.
Similar to the popular belief in the spell power of voodoo dolls, stimulation of the homunculus area will create, in a corresponding pattern, stimulation in the specific area of the body represented by it.
The Structure of the Brain
The Algebra of Neurons
There are about one hundred billion neurons in the brain, each of which “chats” regularly with the other ten thousand neurons on average. We have the ability to listen to this chat by means of various technological devices, created by human wisdom, whose purpose is studying this very same wisdom.
The teamwork of neurons is at the basis of the brain activity. It is possible due to mediation of the “runners” who pass on information directly between the various parts of the brain. These runners are actually chemical information molecules, which can be divided into several types: hormones, peptides (small proteins), and neurotransmitters.
Except for the neurons, the other cells that compose the brain are divided into several types and are generically called “glia cells.”
These cells were traditionally considered to be the cells responsible for the logistics in the brain—some sort of support cells that assist the neurons in performing their role.
The glia cells are divided into three types:
The oligodendrocytes—These cells constitute about three-quarters of the glia cells population. This type of cell constitutes the workshop that creates the coating of the axons, which are the main traffic avenue of passing information between neurons. This coating is called myelin, and its main components are oily.
The astrocytes—These cells constitute one-fifth of the glia cells. New studies emphasize their role, and it seems, in addition to “plain support” and providing a “convenient working environment” for the neurons, they contribute an active component for the thinking functions.
The microglia—These cells constitute between 5 to 10 percent of the glia cells. They serve as the brain’s immune protective shield.
There is controversy surrounding the overall number of glia cells in the brain. According to a common estimation, there are nine times more glia cells than neurons. Thus, the total number of cells in our brain is about one trillion (a thousand billion), and the neurons constitute one-tenth of the cells. Another estimation states a similar figure—one hundred billion neurons and glia cells in the brain.
The total length of axons, which connect the neurons in our brain, is estimated at 170,000 kilometers—an overall length that allows them to circle Earth about four and one-quarter times.
Fundamental aspects of our intelligence skills are formed in the cortex. Anatomy researchers estimate that a typical cortex contains about thirty billion neurons. These thirty billion cells are a core infrastructure of our identity as human beings. Some claim they host most of our memories, knowledge, skills, and life experiences. It seems the main fabric of our worldview is woven in the loom of this thin layer of neurons.
The branched connectivity pattern between the neurons in the brain creates a huge potential of neural circuits, which is estimated at the figure 10 followed by a million zeros (for sake of comparison, the estimated number of particles in the known universe is the figure 10 followed by seventy-nine zeros). According to a common assumption, in practice, the number of links between brain cells is about one hundred trillion, similar to the estimated number of leaves in the rain forests of the Amazonas.
This is the inspiration for the common saying that the human brain is the most complex system known to man. This infrastructure is the source of the great gap between the culture developed by human beings and the spiritual heritage of the most intelligent animals on our planet. In other words, this is the course on which the preeminence of human was built. We should not, however, ignore the fact that the basic building blocks of the human brain are also found in animals’ brains.
Neural Darwinism
In different periods of life, neural Darwinism exists due to two forces: genetic dictation and development that depends upon environmental stimulus.
A volume unit in the skull is a real-estate asset of great value. In the spirit of the Middle Ages theological question regarding the number of angels that can crowd together on one pinhead, one can claim that if we draw a tiny square whose side is one millimeter long it is enough to mark the location of a hundred thousand neurons. Due to space and energy-saving considerations, neural connections that carry unnecessary or less-necessary information are unraveled. According to the “usage-dependent existence” rule, brain areas that are frequently used are probably essential to survival from an evolutionary point of view. On the other hand, areas that are not used frequently are doomed to destruction.
Survival of the Fittest—Natural Selection—the Inner-Skull Version
A process of neural Darwinism takes place in our brain. The evolutionary selectivity instrument within the skull box is, in many senses, the replica of the natural selection process that takes place in the kingdom of nature.
The human brain, as might be said of our whole body, is probably the creation of a blind watchmaker who created it after a great many trial-and-error attempts in the figure of mutations and selections that brought the product to its final status.
Science philosopher Richard Dawkins described in his book The Selfish Gene an idea according to which the entity that fights a survival battle in the killing fields of natural selection is the genes rather than the animal or plant that carries them. In fact, the latter serves as a tool and a springboard toward the future.[4] In this case, Dawkins stepped up in the resolution hierarchy from the whole-animal level to the level of the genes it carries. If we consider the opposite direction—stepping down in the resolution hierarchy—it seems that the entity that fights the survival battle in the inner part of the skull is a group of neurons or a column of neurons rather than a sole neuron.
The neural columns constitute the material dimension of thoughts, and they are actually the main operational units in the brain. Neural Darwinism takes place primarily at their level; thus, in the neural Darwinism process, the basic unit that undergoes the selection process is not the sole neuron, but a group of neurons that represents a piece of information, a certain perceptual recording, etc.
The Serengeti Plains Between Our Ears
As in the savannas of the Serengeti reserve in Tanzania, there are the Serengeti plains of the developing brain—unused neuron columns deleted as cannon fodder of the brain’s evolution, exactly like a wildebeest that cannot run fast enough.
There are two types of evolutionary selectivity. The first is developmental and the second is acquired (fruit-of-life experience). Developmental selectivity takes place prior to birth; thanks to it, all creatures, including identical twins, are born with a different brain. The genes and their products dictate a general structure whose borders are binding. In spite of the similar general pattern of brain areas, however, each person has a unique brain. The prenatal differentiation level organizes the brain and creates a type of primary repertoire. The acquired change stage starts after birth—our experiences either weaken or reinforce, or alternatively, create or destroy the primary structural repertoire, though they do not cause prominent changes in the “big” anatomy—the one that can be seen with the naked eye.
Size Doesn’t Matter—the Brain Version
We belong to the subspecies—Homo sapiens sapiens (modern intelligent man, subspecies of Homo sapiens). Our species, the Homo sapiens, derived from the Homo erectus (the erect man) some two hundred thousand years ago along with the Homo neanderthalensis species, which was extinct some thirty thousand years ago. Neanderthals had bigger brain volume (1500 cubic centimeters), but the prefrontal area of their brain (where superior brain functions are formed) was significantly smaller than ours—a strategic disadvantage that tipped the scales in the neural survival battle.
Main Characteristics of Information Processing in the Brain
At the arena of assumptions regarding the manner of brain function, two polar approaches have been competing for a very long time. One is the “locating approach,” according to which each of the soul components is located in a specific brain area in which its neural correlate. According to the other approach, which is a polar alternative, thinking and memory functions are the result of the function of the whole brain, and the level of damage they suffer reflect the level of damage suffered by the whole brain.
There is truth in both approaches, but, separately, their explanatory power about the function of the brain is only partial.
Many brain researchers believe the human brain is more comparable to a Swiss pocketknife, which integrates various brain tools into various registers according to the “need of the hour” rather than a central, hierarchical processing system. Similarly, a functional pattern that has a greater explanatory power is a “functional systems pattern.”
This third pattern of function merges the two former approaches and polishes their rawness. It is based on the assumption that the brain is a collection of functional systems. To clarify this idea, we can t
ake the digestion system as an example. The stomach itself does not produce the digestion process, nor does the intestine, the pancreas, or the gall bladder as individual organs, but their mutual function and the interaction between these organs create digestion. In a similar way, our breathing relies on a combined operation of the breathing regulation system in the brainstem, the diaphragm, the intercostal muscles, and the lungs. The main complex functions of the soul are produce in a similar way- by the combined action of functional systems in the brain. Most mental functions, such as remembering, production of emotions, and dreaming, are products of complicated systems decentralized at various areas of the brain, and their reciprocal relations bring about the functions of the soul. Each of the components contributes its share to the big production. The functions of the soul do not reside within one of the structures that participate in their production; they reside in between them. Thoughts, like many other brain functions, are not born in specific brain areas but, rather, in between these areas.
The various functional systems integrate with each other modularly in order to perform designated tasks. The ensemble of neurons recruited for a specific task creates a designated register for the designated task in which the brain deals. The functional-units approach combines the two preceding approaches, and the synthesis creates a more reliable understanding of the reality.
The brain is like a musician with multiple instruments, and a mental task is like an accord—a sound composed of several subsounds. One can see brain function as a whole when all sounds merge into a single melody, or, when listening more carefully, one can distinguish between the sound of the harp and the sound of the cello and between the sound of the sitar and the sound of guitar—in other words, between the different functional systems that contribute to the specific brain function. When we perform a thinking task that requires concentration, accuracy, and timing, we act as a musical editor who can carefully select the musical soundtrack played in the halls of our skull.
