The Flexibility of the Mind

The genius of the scientific method is that it accepts no permanent solution. Skepticism is its solvent, for every theory is imperfect. Scientific facts are meaningful because they are ephemeral, because a new observation, a more honest observation, can always alter them.

-Jonah Lehrer

The power of science lies not in its ability dictate truth, but rather for the important stories that it tells that are relevant to our lives. Science is like a nebulous blob that is always rearranging and shifting, expanding to take in new observations. However, this isn’t always how science was viewed.

In the 19th century, positivism began to exert its influence over many of the time’s influential thinkers. This philosophy stated that the only true knowledge is scientific knowledge, knowledge gained through strict adherence to the scientific method based on empirical fact. This philosophy picked up steam especially because of the ideas that Darwin put forward in On the Origin of Species. Social Darwinists quickly jumped on this train, trying use Darwin’s work on natural selection to justify social programs such as eugenics. [12]

While positivism and social Darwinism suffered many attacks in the following years, this stanch scientific predestination took a hold on many people. Even today, many people believe the misinformed statement that Herbert Spencer phrased, which expressed the major of tenet of what he understood natural selection to be; the “survival of the fittest”. When asked why poor people can’t make it in the world, some people simply shrug their shoulders and say, “survival of the fittest.” And even after Freud uncovered the unconscious, pointing out the subjectivity of every inquiry, many people refuse to believe what they cannot see proved scientifically.

This prevailing environment is important to understand when discussing the importance of the human genome project and the discovery of neurogenesis on the brain and the shift in belief that this has caused. Many people believe that by studying the brain, scientists will close us into box. That we will be able to reduce the brain to mere, predictable parts; stripping the human mind of its importance and dignity.

When the human genome project first was presented, the idea was that it would place the blue print of our bodies into our hands. For the first time, we would have the keys to understand everything about ourselves. This quickly became realized as a pipe dream, when the sheer size of our genome was unleashed. In addition to its size, the fact that so much of our DNA was simply junk DNA caused confusion.

But perhaps the most unsettling realization that came from this project was the level of interaction between the environment and the genes. Different sequences can code for different things, in different places; there is no direct correlation between genome and product. Instead, there is chaos. An example used by Jonah Lehrer is particularly hard hitting. He discusses the fact that one would expect the highly complex cortex in the human, arguably one the world greatest engineering feats, to show an increased genetic input. But in fact, the genes that code for the human brain are roughly the same as those that code for the mouse brain. The most shocking conclusion to come from this is the chaos that it seems to suggest. From our view, everything seems to run smoothly, but on the cellular level, it is random movements and chaos which creates us. [12]

This seems to stand in direct defiance of the idea that everything can be quantitatively proven. For, if we can’t even understand how we think and process, how can we understand the world?

The second discovery is even more fascinating. For any years it was thought that we are born with the number of brain cells we will have, and that’s it. Anti-drug commercials used this idea to great affect in their ads (while it has now been shown that cannabinoids actually increase hippocampal neurogenesis [9]) and even bicycle helmet advocates appealed to it. Any research that came out in support of the idea that brains can create new neurons was ridiculed. The “irrefutable” evidence for the fact that neurons didn’t grow came from a study that was done in the 1980’s by Pasko Rakic of Yale. He realized that there had been no conclusive studies done to support the idea that neurons did not regenerate, so he went ahead to investigate the matter. [11]

In his experiment, Rakic injected the brains of 12 rhesus monkeys with radioactive thymidine. This allowed him to track the progress of the neurons in the brain. He then killed the monkeys at various stages, and searched for signs of new neurons. He did not find any. While this certainly didn’t prove neurogenesis didn’t happen, it convinced him and he even went on to write proofs on why it couldn’t.

However, there was a good deal of buried evidence that contradicted this. In 1962, Joseph Altman of MIT had published results using the same technique that Rakic had, that showed adult rats, cats, and guinea pigs brains all created new neurons. [10] In the 1970’s Michael Kaplan of University of New Mexico conducted an experiment using an electron microscope, where he was able to see neurons giving birth to new neurons in the mammalian brain. There was also the research done by Fernando Nottebohm, who did a series of experiments which showed that neurogenesis was necessary for song birds to learn to sing their songs. [11]

However, these men were forgotten until a young post-doc named Elizabeth Gould came across their results. She was working on the effect of stress on hippocampal neurons, which was known to decrease their numbers. However, one day she came across an anomaly in her research – the number of cells had increased. Thinking she had simply miscounted the cells, she went to the library for inspiration. It was here she found the work of these forgotten researchers, and realized she was not mistaken, and that the brain could actually heal itself. [12]

After 8 years of tedious and tough research, she had finally proven that neurogenesis does indeed occur. [5] [6] Since then, the field has been blown open. In 1992, Reynolds and Weiss were able to isolate neural stem cells in the brain from striatal tissue of adult mice. Since then, neural stem cells have been isolated from all over the brain, including areas were neurogenesis has not been seen to occur, such as the spinal cord.

The days of social Darwinism are over, and it is no longer justified saying that poor people are poor because they are weak and unfit. Rather, as Gould’s studies have shown that living in poverty and under stress stops the neurogenesis of hippocampal neurons. A study done by Gould and others showed that lack of sleep increased levels of glucocorticoids, which inhibit neurogenesis and can lead to the detrimental results associated with lack of sleep. [13]

It was once believed that depression was caused by a chemical imbalance in the brain, but as work by Castrèn as showed, it may be because of the change in the brains neural networks due to lack of neurogenesis. [3] A study done by Duran has shown that antidepressants increased neurogenesis in the adult rat brain. Although these studies are a far way from explaining depression, they do help explain it and offer a mechanism for reversing depression; increasing the brains own natural plasticity.

There have been studies done that have shown that exercise increases neurogenesis and helps stimulate memory and learning. [3] Gage from the Salk Institute for Biological Studies conducted a study where mice that exercised had better memory and increased adult neurogenesis. [16]

In fact, a doctor turned researcher, Jonas Frisén has already placed his eggs in that basket. He opened up a biotech company called NeuroNova, which uses neural stem cells and stimulates neurogenesis in them in the hope they will re-grow in place of the neural cells that have been destroyed, as the literature shows they might be able to. [2] They have a drug in trials now which regrow dopamine neurons in mice with Parkinson’s. [11]

However, the jury is still out. Adult neurogenesis is only thought to occur in two regions – the hippocampus and the olfactory bulb. [1] [14] The significance of growing new neurons in the hippocampus is fascinating, and could play a role in learning and memory. [7] The significance of neurogenesis in the olfactory bulb is less inspiring to some scientists, yet all the same, intriguing. The olfactory epithelium cells are known to be constantly replaced; one source for confusion of how smells are remembered. And while there are currently models for what adult neurogenesis in the hippocampus is useful for, there are no proven mechanisms. [8] There are three particularity prevalent models that suggest an effect of adult neurogenesis in the hippocampus; an increase of hippocampal memory capacity (Becker), the reduction of interference between new and older memories (Wiskott), and encoding time in memories (Aimone). However, these are simply models that have been proposed, and much more research must be done to probe the mechanism of action of adult neurogenesis. [8]

Still, the consequences of these discoveries are immense. They destroy the notion that science will box us into being “conscious automata”. Our genes do not determine us, as the human genome project and subsequent research has shown. Instead, the environment has been shown to have great importance in interacting with our genes. And neural plasticity has shown that the brain can and is always growing; healing itself, creating new synapses, and new neurons.

The power and plasticity of the brain have been shown by these recent and ongoing experiments, and are true in the sense that they support the theories we now accept. All that is left is to wait and see what new experiments have to say, and how they will change our understanding of the brain and its power.

Works Cited:

1. Adult Neurogenesis. (2008) Retrieved February 25, 2008, from Society for Neuroscience Web site: http://www.sfn.org/index.cfm?pagename=brainBriefings_adult_neurogenesis
2. Arias-Carrión et al. (2007) Adult neurogenesis and Parkinson's disease. CNS Neurol Disord Drug Targets. http://www.ncbi.nlm.nih.gov/pubmed/18045161?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
3. Castren E. (2005). Is mood chemistry?. Nat Rev Neurosci. http://www.ncbi.nlm.nih.gov/pubmed/15738959
4. Changing your mind. Retrieved February 25, 2008, from PBS-Scientific American Frontier Web site: http://www.pbs.org/saf/1101/resources/resources-2.htm
5. Gould E et al. (1999). Hippocampal neurogenesis in adult Old World primates. Proc Natl Acad Sci U S A. http://www.ncbi.nlm.nih.gov/pubmed/10220454
6. Gould E et al. (1999). Neurogenesis in the neocortex of adult primates. Science. http://www.ncbi.nlm.nih.gov/pubmed/10521353
7. Gould E et al. (1999). Learning enhances adult neurogenesis in the hippocampal formation. Nat Neurosci. http://www.ncbi.nlm.nih.gov/pubmed/10195219
8. James B. Aimone et al. (2007) Adult neurogenesis. Scholarpedia,. http://www.scholarpedia.org/article/Adult_neurogenesis
9. Jiang, W. et al. 2005. Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects. Journal of Clinical Investigation. http://www.jci.org/cgi/content/full/115/11/3104.
10. Kolata, G (1998). Studies Find Brain Grows New Cells . The New York Times, Retrieved 2/2008, from http://query.nytimes.com/gst/fullpage.html?res=9C07E4DC1239F934A25750C0A96E958260&sec=health&pagewanted=all
11. Lehrer , J (2006). The Reinvention of the Self. Seed Magazine, Retrieved 2/2008, from http://www.seedmagazine.com/news/2006/02/the_reinvention_of_the_self.php
12. Lehrer, J (2007). Proust was a neuroscientist. New York, New York: Houghton Mifflin .
13. Mirescu C et al. (2006). Sleep deprivation inhibits adult neurogenesis in the hippocampus by elevating glucocorticoids. Proc Natl Acad Sci U S A http://www.pnas.org/cgi/content/abstract/103/50/19170?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=neurogenesis+sleep&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
14. Neurogenesis. Retrieved February 25, 2008, from Wikipedia Web site: http://en.wikipedia.org/wiki/Neurogenesis
15. Neurogenesis. (2005) Retrieved February 25, 2008, from Wellesley College Biology Department Web site: http://www.wellesley.edu/Biology/Concepts/Html/neurogenesis.html
16. Reynolds, G (2007). Lobes of Steel . Retrieved February 25, 2008, from The New York Times Web site: http://www.nytimes.com/2007/08/19/sports/playmagazine/0819play-brain.html?_r=2&pagewanted=1&ref=playmagazine&oref=slogin