The Root of Thought (5 page)

American surgeon Walter Freeman (1895–1972) performed the lobotomies throughout the United States from the 1930s to the 1950s. The van that he traveled in was called the lobotomobile. Mental patients who were difficult to deal with were given the procedure. Freeman was educated at Yale and Penn and was not an amateur. He firmly believed in the benefits of the surgery with many notable patients including Rosemary Kennedy. The results of these tragic surgeries were the understanding that much of higher-level thinking resides in the cortex. With the advent of pharmaceutical treatments for psychiatric disease, his lobotomies thankfully went out of vogue.

But it was the work of American-born Canadian surgeon Wilder Penfield in the 1950s that showed areas of the cortex might be responsible for different functions of thought. Penfield learned under Sherrington and became a master of electrophysiology.

In the 1940s, it was shown that by cutting axons traversing from the right to left hemisphere, seizures could be reduced. While the surgery was being performed, the human patients were put under only local anesthesia applied in the scalp. Touching the brain is not painful because no sensory nerve endings reside there. The patients could talk to the experimenter and he could talk to them. The surgeon stuck electrodes into different areas of the brain as mapped by ablation and previous electrical studies and asked patients to perform functions. Ironically, by stimulating areas electrically, the surgeon could block them from doing certain things such as saying words or moving an arm. Patients could think about a function, but they were unable to perform it. Although this was the opposite of what they expected—hoping to induce action through electrical stimulation, it did reveal that areas of the cortex were important for many levels of thought.

Further work into the idea of localization of thought was performed by Roger Sperry (1913–1994) in the 1960s. Using epileptic patients who had their hemispheres separated by the surgery, he covered one eye and had patients perform tasks that would not be noticed by the hemisphere of the brain opposite the eye. He was able to determine that each brain
hemisphere has a different consciousness. This is where we get the terms on whether we are a right-brained person or a left-brained person, as the right brain was more associated with emotion and abstract thought, whereas the left brain had more concrete mapping of linguistic properties. Although it is not true that each brain area is responsible for only one aspect of the duality of personality, Sperry would win the Nobel Prize for his work.

The cell-based root of thought has eluded us. We might know certain elements about how we think, but nothing has validated the Neuron Doctrine’s notion that the neuron is the seat of our intelligence and thought. Thought is intertwined with the ability to imagine and create. The illuminating studies on neurons for their understanding of its electrical properties remain unsatisfactory in their explanation of how we think.

As pre-electrical Swiss scientist Albrecht von Haller (1708–1777) stated a decade before the time of Franklin’s experiments in his
Dissertation on the Sensible and Irritable Parts of Animals
, “the nervous fluid must have 6 essential properties. 1) That it be highly moveable. 2) That not only must it be moveable, but that it must be capable of being set in motion only by the will and force of the soul and not by the help of the heart. 3) That it must be a fluid element, and very rapid in movement. 4) That it must be very subtle, so as not to be seen by a microscope. 5) That it must have a particular affinity for the nerves. 6) That it be colorless, odorless, tasteless, and without perceptible heat.”

Haller was elucidating principles on which the agent of nervous action could be defined, and specifically, motor nerve action. Looking back, all these criteria fit nicely with electricity except number 2. The neuron undoubtedly conducts electricity, but what spurs it to action—other neurons in a billion-cell complex circuit? Neural conductance is rapid, can travel long distances, can cause muscular contractions and animal action, and it communicates sensory input to the brain. All cells have an electrical potential, but neural structure allows the current to travel long distances in an “all-or-nothing” manner. However, glial cells in the brain exhibit activity in more subtle and elegant mechanisms than neural electrical depolarization. Cajal did not have techniques available to understand glial function, and the Neuron Doctrine prevented glial research with new techniques only until recently. These cells have properties that are more likely to be initiators and masseuses of nervous action, the will of controllable ability.

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If you look at a tulip, you wouldn’t think it was an armadillo. Similarly, looking at a neuron, you wouldn’t think it was glia. But you might look at a whale and think it’s a fish, until you look at it closely and realize it has no gills and breathes through lungs. Then, you have a problem. Through genetic testing and excavations by paleontologists, we now know it likely originated as a land animal that took back to the sea and is related to hoofed animals like the horse. But before genetic testing and evolutionary biology, classification was based on appearance. This remains true for cellular classification.

Glial cells include Schwann cells, Müller cells, epithelial cells, ependymal cells, oligodendricytes, tanycytes, microglia, and astrocytes—all function as differently from each other as they do from neurons.

Students of scientific fields always claim that learning new terms in the field is like learning a new language. Just as the meaning of an English word can change over time (such as plane, buck, mouse, and gay), the meaning of a scientific label can change after its function is understood.

As functions of cells are understood, the labels have remained. Glia are capable of signaling and communicating, but they will always be referred to as glia (glue). Virchow’s “glue” label sticks because it was originally believed that a neuron was the only cell able to signal and communicate. As we can see by the confusing nature of the “planet” Pluto, it is difficult to unclassify the classified. Neuron comes from the Greek for sinew or tendon, and synapse is Greek for clasp, although they all sound like they were coined by an extraterrestrial techno group. The word tomato’s origins come from the Aztec dialect of Nahautl in central Mexico, but almost everybody, including the author, doesn’t know whether it should be called a fruit or a vegetable.

Of course, things change over time, and that is why the terms “glia” and “neuron” are preferable to some uniform naming procedure that modern biology and astronomy try to force upon us. And really, who knows glia means “glue” anyway? Our brains like to create.

In evolutionary biology, it is not completely understood why life started. It is believed that carbon excluded sodium in the ocean at some point, thus creating a cell. Energy was then required to maintain the electrical gradient created by electrolyte exclusion. Eventually cells aggregated with other cells and worked together for energy. Then plants and animals split, with animals evolving so some of the cells were sensory units that knew where to find the food. Then, more defined motor cellular units developed to help the animal move more efficiently to attain the food.

Neurons are the cells that developed for sensory and motor function and have their roots in the evolutionary reflex to procreate and get food. The higher-level thoughts of imagination and creation could have evolved separately and maybe even before the neuron.

The classical neuron, as described by Cajal, is actually best represented by the cell located in the cerebellum first discovered by Jan Purkinje (1787–1869). The Purkinje cells of this area located in the posterior base of the brain have amazing aesthetic structure. The dendrites look like an elaborate magnolia tree. The cell body is a perfect bulb like a teardrop. And the axons are so long, they extend out of the cerebellum into the pons, a structure next to the medulla at the base of the brain.

However, many other types of neurons exist with different characteristics. Functionally, they are mainly classified based on what connections they make: sensory neurons, motor neurons, and interneurons. In the patellar reflex or “knee jerk” reflex described by Sherrington in the early twentieth century, the tap of the patellar tendon of the knee causes sensory firing to the spinal cord, and the connection of motor neurons there creates contractions in your quadriceps, which causes the leg to jerk. No one who was tapped on the knee would argue that they controlled the reflex with their thoughts.

Because of this reflex, people who rashly respond to something without thinking are derogatorily told not to have a “knee-jerk” reaction and to think before they talk. Someone who punches another person in the face for being called a “sheep lover” is likely not thinking before acting and having a “knee-jerk” reaction. Similarly, if someone’s father says he
hates the St. Louis Cardinals, and then his child says he hates the St. Louis Cardinals, too, the kid is probably not thinking about why he hates the St. Louis Cardinals (although this may be a reasonable sentiment) and just copying an authority figure. This is another “knee-jerk” reaction. These reactions are completely neuronal and an occurrence by which nothing happens between the sensory stimulus and motor output.

Sensory neurons are stimulated by the receptors that correspond to our five senses. For instance, the sensory neurons in our tongue respond to different molecules and pH levels in food to tell us whether we taste something sweet, sour, salty, bitter, or one recently discovered by Japanese researchers in the last five years, umami, which is a savory, meat-like flavor.

In our ears, minute hair cell receptors at the end of our cochlea respond to sound vibrations. In our eyes, rods and cones are stimulated by photons and converted into electrical neural signals. Our skin has receptors for temperature and vibration. Our ever-changing nose is constantly turning over neurons and glia in response to the ever-changing nature of smell. The nose is especially interesting because in lower-life forms, the olfactory bulb is more prominent in size ratio to the rest of the brain.

Motor neurons stimulate muscular action. But what is between? When someone tells you to use your noodle, what do you use?

Although the term glia and its first drawings were likely contributed by Rudolph Virchow in 1846, Heinrich Müller (1820–1864)—no relation to Johannes, the great advisor—was the first to describe a retinal glia cell in 1851. The cells are known to modulate signaling in the retina. They can signal to themselves as well. Not knowing what to call them because they seem to be a completely different functional unit than neuronal ganglion cells extending out from the eye into the brain, researchers have classified them as glia and they are called Müller cells.

Müller is often overlooked in favor of Virchow, although Virchow’s publication of his 1846 work didn’t happen until 1853, two years after Müller’s. And Müller’s drawings and description were much more intricate. In fact, Virchow got the best of Müller around this time professionally as well. Virchow sided with the revolutionaries in Berlin from 1848 to 1849, eventually losing his chair at the university due to his politics. The University of Würzburg pounced on the opportunity to have Virchow chair its department and chose him over the likely candidate Müller. Müller spent half a year in a sanitarium because of the slight.

The next major glial cell was discovered in the peripheral nervous system by Theodore Schwann. Schwann was also a student of Johannes Müller. If neurons are the highways, then Schwann cells are the construction workers in the peripheral nervous system. The function of these cells is so different from Müller cells that it is amazing they are both called glia. They are about as related as Henrich and Johannes Müller. Schwann had no clue about the function of the cells, only that they were associated with axons in the periphery.

The myelin on axons was not understood until the advent of the high-powered electron microscope in the mid-twentieth century. The electron microscope allowed researchers to see subcellular structures clearly for the first time. It was then that the wrapping twists of myelinating Schwann cells could be seen and the notion of axons secreting the myelin themselves debunked. Schwann cells myelinate the axons which extend out to the muscles so they are able quickly conduct electrical impulses. Schwann cells release the fatty myelin from their cell body and swirl it around a group of axons like a butcher wrapping up some sausages. Umami-flavored sausages.

In the central nervous system, the construction workers that myelinate the axons are called the oligodendricytes. Cajal’s Argentine student Pío del Río Hortega first described this cell. Smaller than Schwann cells, oligodendrocytes abundantly reside in the white matter of the brain and wrap myelin around fibers.

Other glial cells that line structures such as the ventricles and blood vesicles in the brain are called ependymal cells, endothelial cells, and tanycytes. These cells are the military defense of the brain. Ependymal cells seem to help cerebral spinal fluid flow with extending filipodia and lining the walls. Epithelial cells line blood vesicles and the retina. Epithelial cells have the important task of not allowing any contaminant from the blood to invade the brain. Tanycytes also separate the CSF and the blood with tight junctions.