The Root of Thought (15 page)

In 2003, Alvarez-Buylla’s lab published papers about the human brain injected with BrdU. He was able to determine that the area next to the human ventricle was slightly different from the mouse, with an extra space between the dividing cells and the ventricular wall (see
Figure 9.1
). Cells divide in adult humans as well, and the dividing cells are astrocytes in humans. He was unable to see a migratory stream to the olfactory bulb. The human brain has tiny pockets of ventricular fluid throughout the brain, and it’s possible that the olfactory bulb can take care of its own division without the main ventricular area. After we reach adulthood, our brain cells are not unchanging—they constantly divide to deal with our environment.

FIGURE 9.1 Astrocytes dividing by the ventricle, with cilia reaching up and floating like seaweed in the ventricular fluid (top). The astrocytes (dark cells) reach into the fluid and swing long arms to cling to blood vessels.

Reprinted from
Cell Stem Cell
, Vol. 3, Issue 3, Mirzadeh, Z., Merkle, F.T., Soriano-Navarro, M., Garcia-Verdugo, J.M., and Alvarez-Buylla, A. “Neural Stem Cells Confer Unique Pinwheel Architecture to the Ventricular Surface in Neurogenic Regions of the Adult Brain,” p. 274, Copyright (2008), with permission from Elsevier.

However, in researchers’ lust for the search of neurons, they have determined that our cortex remains the same after we reach adulthood. The cortex, the area of our high-level thinking, does not form new neurons after adulthood. In primates and specifically humans, the cortex contains the majority of accessible conscious information in the brain. If new neurons can be formed in the olfactory bulb and hippocampus and neurons are supposedly responsible for our thoughts, why can’t new neurons form in the cortex? This was a depressing fact for many researchers and had been believed since 1911, when Ramón y Cajal looked exhaustively at cortical neurons.

However, astrocytes divide in the human cortex throughout our lifespan.

Cell division in the adult cortex was known for some time by many in the field, but new neurons never noticed. Therefore, the research was discarded and swept under the rug. Without neurons, what was the point? The field is called “adult neurogenesis” after all. But Alvarez-Buylla’s revelation that the dividing cells are astrocytes had been lost. Now that glia, and more specifically, astrocytes are known to communicate and tell neurons what to do, and they are the new cells dividing in the adult in subcortical areas that need fast neuronal communication, and are the cells dividing
in the cortex
as well, studies of “adult gliogenesis” are coming to light.

Cortical gliogenesis in adult humans was proven in a study published in 2006. Researchers from Sweden in collaboration with researchers from the United States and Australia used an ingenious technique to investigate cell division in adult humans. They were able to take advantage of the radioactive material that enters into brain cells as they divide, similar to how thymidine is visualized. During nuclear weapons testing aboveground between the mid-1950s and the nuclear test ban treaty in 1963, massive amounts of heavy carbon were launched into the atmosphere. By studying the brains of people who gave their organs to science and had lived during this period of time, researchers were able to look at cells that divided and incorporated the heavy carbon. There was extensive cell division. These dividing cells were then examined for whether they were neurons or glia. None of the cells became neurons. The dividing cells were glia.

They followed these studies by injecting BrdU into the bloodstream of patients dying of various forms of cancers of the body—similarly to the method used by Alvarez-Buylla. They found exactly the same result as the heavy carbon studies—constant glial growth occurs in the cortex, but no new neurons are formed.

Studies of this nature are primarily used to show that cortical neurogenesis is a phenomenon restricted to development around the birth. However, the idea of new astrocytes constantly turned over in the area of our brain being responsible for higher thought is astounding.

The formation of new astrocytes in the cortex throughout our adult life must contribute to the thoughts of human beings. This idea—combined with the knowledge of calcium wave communication and regulation of transmitters in astrocytes—leads to the theory that astrocytes are the root of thought and they can turn over constantly to keep our brains in top working order. When this constant turnover is disrupted, we begin to understand the problems that can arise. Further studies on glia illuminate the responsibility of astrocytes for the wonders of our thoughts and the causes of catastrophic disruptions to the fluid orb of will that is our brain. Strict neuronal focus in brain research cannot even begin to understand how and why we function and how to cure our most horrific brain diseases. The fact that new astrocytes continue to divide into adulthood means they attempt to form new space for the storage of information to expand thinking abilities, just as a weight lifter works his muscles to get stronger so that he can lift even greater weights. Mental exercise might be how we achieve higher intelligence and store more information. Monotonous neurons, only 10 percent of the brain and incapable of regeneration, are simply thoroughfares maintained by astrocytes to be used for the purpose of long-distance communication.

Everyone knows that learning and education increases intelligence, but where does the intelligence go? It is a definite possibility that it is stored in astrocytes that can regenerate throughout life. Is it possible that these newly regenerated astrocytes in the cortex are replacing ones that aren’t performing up to task? And in lower areas of the brain, such as the hippocampus and olfactory bulb, astrocytes can sprout into neurons to provide a fast link to glial centers when a new nugget of important information enters our environment and needs to be processed and stored by cortical astrocyte centers.

Many organs in the body create new cells throughout life—the blood, the liver, and skin. The seeming solid and unregenerative ability of the brain is due to the focus of research on neurons and not glia in the last 100 years. Cajal performed exhaustive studies of neuronal cells after his standoff with Golgi at the Nobel Prize lectures in an attempt to find some semblance of regenerative ability in the cortex. He found nothing. Alvarez-Buylla’s experiments in deeper brain regions are beginning to challenge these views. Combined with the experiments that showed astrocytes communicate with themselves and neurons, we can get a grasp on the fantastic research that will soon arise in the twenty-first century when glia are no longer neglected and relegated to secondary status. The avenues to research astrocytes are numerous, and hopefully, future astrocyte research will bring to light the causes and cures for many brain diseases.

If one remembers the old Cliff Claven theory that alcohol kills brain cells, but we use only 10 percent of our brain so it was okay to kill brain cells, we were killing off the weakest. Drinking was like the survival of the fittest in the brain. The cells remaining were the strongest, so drinking heavily increased the efficiency of our thoughts. Well, it is apparent now that the 10 percent of neurons are not what we need to worry about. The health of our brain hinges on astrocyte cell division. Our brain is like a jungle, full of life and constantly growing until we die. Evidence exists for the possibility of how we control that growth, how the growth is stunted, and what happens when it is out of control.

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Hope and promise reside in glia, and now the knowledge of astrocytes as our adult stem cells gives researchers an avenue to pursue an understanding of the fundamental mysteries of the mind. The brain can be seen as a verdant entity throughout our life—constantly growing to replenish deserted areas and wastelands. It is not a static place like the moon, a rock knocked around by the bombardments of space, as previously thought, but it is like the Earth in every sense, packed with growth and changing constantly. In the cortex, this growth is the domain of the astrocytes. Neurons remain hardwired except when the astrocyte turnover becomes great enough that it requires the population to sprout a new neuron, especially in areas solidifying new memories. They are paths for quick action in our extremities and to bring and take new information from glial centers. An astrocyte controls its entire environment in the cortex and communicates with other astrocytes in the manner of calcium waves. It is a cohesive and fluid unit capable of storing complex information and recording time, but not controlled by space.

The astrocyte can be seen evolutionarily as the extension of the single cell at the start of life—it must maintain itself through interactions in the species and eventual reproduction. The neuron has evolved as the fast-acting tool at the beck of the astrocyte’s will. The growth of astrocytes in areas responsible for memory controls how we survive as living beings; the astrocyte determines if something should be avoided or challenged. They are the reason we exist—our essence—and how we think is the result of our existence.

A lot has been made of synapses at neuronal connections. Synapses sprout after birth and then become more hardwired into young adulthood. However, the synapses sprout only after the peak growth of astrocytes at birth, indicating that astrocytes determine synaptogenesis.
Astrocytes can process the information that the neurons bring in from the environment through the monitoring of synapses. The amount of neural synapses is astrocyte dependent. As we age, when the less useful synapses are eliminated, the astrocyte must have a hand in this process. In children of abuse, it is believed that the synaptic elimination process is accelerated; there are less sprouts, and therefore, children do not develop properly. However, what happens to the astrocytes after the abuse is likely the key to understanding the streamlined neurons. The astrocytes take in the potent information in a heightened situation, good or bad, and then eliminate some of the synapses, streamlining the neuron—like a city removing freeway exits to help traffic move more rapidly.

Theoretically, the same would occur to a human raised in an environment that doesn’t stimulate his senses. This person would develop less synaptic complexity. Because of these studies and with the revelation that children with Down’s Syndrome have less synaptic complexity, it is believed that more synapses equates to higher intelligence and that to achieve more synapses is to bombard your child with as many positive learning apparatuses as possible. However, the synapses are not what need to be stimulated; it is the astrocytes. Astrocyte growth is not dependent on synapse amount. But synaptic growth and elimination is dependent on the health and growth of astrocytes.

This is the reasoning behind giving children so many things to play with, such as Baby Einstein, Legos, Transformers, He-Man figurines, Sesame Street, Cabbage Patch Kids, and Dora the Explorer. Using objects that are manipulated by the hands is important, because our hands make us distinct from other animals. Sensory interaction can create a mind that fosters neuronal connections. This is why children need to play with toys. However, the importance of glial stimulation as neuronal impulses reach the brain is paramount.