The Mysterious Connections between Neurons
Quote: “Neural Darwinism proposes that the brain gets around this problem by randomly creating new synapses to continually renew its potential for learning, while eliminating the synapses that aren’t useful” (Seung 90).
Background: Neural Darwinism is a Darwinian theory to explain how synapses are created, eliminated, and developed. Synapses are essential for neurons to communicate and connect to each other. This approach to synapse development is known as a random process where neurons randomly create synapses and are able to communicate. The process of “survival of the fittest” is used to develop the strong synapses and eliminate the weak synapses between neurons (Seung 88). Cell assemblies or synaptic chains can then be created for the strong synapse connections. This idea concerns the question of memory storage. As a result, the synapses that can store memories and information are strengthened and developed but the ones that are less used and weak are eliminated, mostly because these synapses cannot store memories. Natural selection is able to coordinate the correct synapse connections that neurons need. The reasons as to why certain synapses are developed and others eliminated still remains unclear.
Figure 1: On the right is Charles Darwin. On the left is Gerald Edelman, one of the researchers who developed the neural Darwinism theory.
Introduction: The topic of Neural Darwinism is of great interest to me because of the association with Darwin’s theory of evolution. Although some people do not believe in evolution, Darwin has demonstrated several pieces of evidence and thorough explanations for his theory. With this, I believe in natural selection and the theory of evolution as it explains the certain physical characteristics humans and other animals have. I am a fan of his work and research for the explanations he has given to the world around us. In addition, I am a fan of his work because he was able to formulate his theory of evolution when he visited the Galapagos Islands, and island owned by my home country Ecuador. The idea of Neural Darwinism with memory is a plausible reason as to why there are connections between certain types of neurons. Millions of neurons inhabit human brains, and the connections and synapses between them is truly complex; Neural Darwinism is able provide a simple solution as to why these connections exist. This rule of thumb that strong connections develop and weak connections are eliminated is common sense. If it works for other physical characteristics, then there’s a great chance that it can work for neurons. I believe this reason for synapse creation and elimination is a simple and clear cut explanation depicting the complex nature of the neurons and synapses.
Research: There is much study being done concerning this topic. For example, in the paper, Behavioral and neural Darwinism: selectionist function and mechanism in adaptive behavior dynamics, research went into studying how behavior adapts to mutations in the nervous systems of organisms. Essentially a link between behavior and the synaptic modifications in groups of neurons was researched. There has also been research into if neural Darwinism is actually Darwinism. In the paper Artificial Life by Terry Van Belle, Belle discusses how some models of natural selection deal with genetic algorithms, and neural Darwinism does not deal with this. In addition, “individuals of neural Darwinism do not replicate…and [they ultimate reduce] to a random search” (Belle). On the other hand, “other models of natural selection “have the capacity [to replicate and] explore new solutions over time” (Belle). Research into neural Darwinism has changed the idea that the brain is a rigid and fixed mode. With neural Darwinism, the brain is thought of as a “more biological and powerful notion of ‘experiential selection’” that is shaped through experience, such as trial and error stages (Sacks). Moreover, neural Darwinism is also being studied in olfactory system as to how this concept is applicable in the olfactory system. Since neural Darwinism occurs in the brain, this topic is very broad and complex as to what the effects of neural Darwinism may be. Furthermore, students have written papers asking the question about the relationship between neural Darwinism and free will, if there is one. Even with the amount of research done on this topic, there still lie many unanswered questions than will only be solved through further and profound research.
Figure 2: Simplistic figure of the human brain.
As I explained earlier, the reason some connections between neurons are strengthen and other weakened remains unsolved. This idea of neural Darwinism to explain how neurons are able to connect and communicate remains as a theory. Millions of neurons inhabit the brain, and the connections made in the early stages of a baby between these neurons remain complex. As in the book Connectome states, “It’s an important challenge for connectomics to reveal the exact conditions under which a new synapse survives or is eliminated” (Seung 89). Using connectomics and neural Darwinism, a reason as to why brains sometimes fail to store information is given; the connections do not exist. These connections do not only exist from neuron to neuron but from neuronal group to neuronal group.
Figure 3: Millions of neurons inhabit a human’s brain.
The unanswered questions revolving around neural Darwinism may never be solved unless connectomics and neuroscience do not advance. Neural Darwinism operates at neuron level and the research at this level is still in its beginning stage and new and better technology is created and will be created to actually visualize what neurons are exactly doing throughout the lifespan of a human. The visual images on the website eyewire.org, are able to show neurons at a basic level, but there is still much left out such as actual synapses between the neurons. As neuroscience continues to be a complex science making progress, the unresolved issues concerning the connections between neurons and neuronal groups will be addressed. More enhanced technology to see a human’s Connectome and neurons inhabiting inside will allow neuroscientist to physically see and research how neurons behave at early and later stages of human lives.
Figure 4. Here are three pictures of neurons at a child’s birth, at 7 years old, and at 15 years old. As the baby grows and develops, neurons become more complex and create more connections between themselves.
The built of a human’s Connectome or that of a mouse will also lead to a better understanding of neurons to each other. Connections and communication via synapses will be studied more as it is easier to understand with the whole Connectome in perspective. Whether the connection between neurons is made randomly or systematically on demand will be a step closer to understanding the brain’s complexity.
Figure 5: The human Connectome is a project to one day visualize and image the connections between neurons.
My idea as to the question why some neuron connections are strengthened and others weakened lies in the evolutionary approach of random selection and trial and error. Neurons are starting out and beginning to grow in babies, and with such a great number of them, confusion may result. Connections begin everywhere between two neurons at high speed, but a connection between two neurons starts out as weak. As a connection is used more and more in a baby growing up, the connection stays, powering up and strengthening the connection. Although, if the connection is not used, weakening of the connection results because the brain decides the connection is not very useful and inefficient when a better connection can occur.
Figure 6: The connection between two neurons occurs in the space between the axon and dendrite, called the synapse. The creation of a synapse between two neurons allows for communication.
Belle, Terry Van. "MIT Press Journals - Artificial Life - Abstract." MIT Press Journals - Artificial Life - Abstract. N.p., 30 Apr. 2010. Web. 08 Aug. 2012. <http://www.mitpressjournals.org/doi/abs/10.1162/artl.1918.104.22.168>.
Mcdowell, JJ. "Behavioral and Neural Darwinism: Selectionist Function and Mechanism in Adaptive Behavior Dynamics." National Center for Biotechnology Information. U.S. National Library of Medicine, May 2010. Web. 08 Aug. 2012. <http://www.ncbi.nlm.nih.gov/pubmed/19941941>.
Sacks, Oliver. "In the River of Consciousness." N.p., 15 Jan. 2004. Web. 08 Aug. 2012. <http://heavysideindustries.com/>.
Seung, Sebastian. Connectome: How the Brain's Wiring Makes Us Who We Are. Boston: Houghton Mifflin Harcourt, 2012. Print.