The Plastic Brain

Today we would like to present you with the second of our series of guest bloggers. Allyson Mackey is a graduate student in the neuroscience program at UC-Berkeley. Enjoy!

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I was recently challenged by a colleague to come up with an example of a neuroscience finding that changed the way I live my life. I immediately thought of the now quite vast literature on neuroplasticity: the ability of our brains to change and adapt to new experiences. In this post, I’d like to propose that what we’ve learned about neuroplasticity so far can help us lead better lives, and that neuroplasticity research in the future will be poised to influence public policy issues ranging from health to education.  

I want to start by summarizing some exciting results from research on the structure and connectivity of brain cells, called neurons. Scientists have shown that experience can drive changes in the connections between neurons in as little as thirty seconds. Substantial changes in brain inputs, like the loss of a sense like vision or touch in a limb, can lead to remarkable compensatory re-organization in cortex. However, even subtle environmental changes can change brain structure. For example, giving rats interesting toys to play with, or allowing them to run more frequently on an exercise wheel, can lead to more connections between neurons in brain regions that are critical for learning, like the hippocampus. What is even more exciting is that cognitive enrichment and exercise can lead to neurogenesis, the creation of new neurons, in the hippocampus. The formation of new neurons was long thought to be impossible since, unlike other cells in your body, most neurons can’t divide to make more neurons after birth.

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Unfortunately, neuroplasticity is often called a double-edged sword. While positive environmental changes can lead to beneficial neural changes, the brain is also susceptible to negative environmental factors. One particularly relevant example is stress.  Chronic stress can prevent the birth of new neurons in the hippocampus, strengthen fear and anxiety circuits, and even effectively turn off brain regions responsible for attention and self-control. In summary, results from animal studies of neural plasticity suggest that our brains have the intrinsic ability to change in response to environmental demands both in adaptive ways, in response to cognitive stimulation and exercise, but also in maladaptive ways, in response to stress.

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While research studies on animals can tell us about basic neural processes, they may not be able to help us understand plasticity in brain networks that support higher cognitive skills. My research has focused on plasticity in fluid reasoning, the ability to solve novel problems. This ability is thought by many to be uniquely human. I was particularly interested in reasoning because it is highly predictive of academic success, so understanding its malleability may be relevant to education policy. Additionally, it has long been considered to be a genetically determined stable trait, much like eye color or height. However, there’s no reason to believe that the mechanisms of neural plasticity described above don’t apply to the brain regions involved in reasoning.

We designed a training program to improve reasoning ability in children ages 7 to 10. We also designed a training program targeted at cognitive speed, the ability to quickly process information and generate a response. Both reasoning and cognitive speed are critical cognitive skills that are measured by many intelligence assessments. We tested reasoning with a matrix reasoning task, and we assessed speed with a test that required children to transcribe a digit-symbol code as quickly as possible. We designed the training programs to be as similar as possible, including computerized and non-computerized games, as well as group and individual games, in both programs.

Matrix Reasoning Example (source)

Our game choices for the reasoning program were influenced by studies in our lab that have shown that one area at the very front of the brain (anterior prefrontal cortex) is most essential for solving reasoning problems. So, we chose games that we thought would engage this region most- games that involved comparing several ideas held in mind at the same time. We found that both programs improved the trained skill by over 30% after just 8 weeks. The gain in reasoning equated to a roughly 10-point gain in nonverbal IQ. Importantly, kids who participated in this study attended a school with historically low test scores. We plan to do additional research to see whether gains in reasoning lead to better academic outcomes. If so, then perhaps including cognitive training into curricula at struggling schools could lead to better student performance.

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Our study is not the only one to demonstrate that reasoning is malleable. Others have shown that practicing holding information in mind (working memory) can also lead to improvements in reasoning in both adults and children. It is still unknown how the brain changes to support reasoning gains, but several research groups are currently investigating these changes. Magnetic resonance imaging is the tool most often used to study neuroplasticity in humans. MRI allows us to see large-scale changes in the thickness of gray matter but doesn’t have the resolution to examine changes at the level of single cells. Similarly, we can observe changes in the activity of brain regions during cognitive tasks, but we still don’t know how the behavior of neurons has changed. So, while brain imaging methods give us a window in what mechanisms of plasticity might be at work in humans, we still rely on animal studies to discover the mechanisms in the first place.

Another important reason to understand plasticity at the cellular level is that it might actually help us learn better. Carol Dweck, a psychology professor at Stanford University, and her colleagues have shown that middle school students who learn about neurons and neural plasticity do better in school, presumably because they work harder to master tough material and don’t give up because they aren’t “smart” enough. The same is likely true for adults. If we believe that our brains are plastic, then we may be more likely to invest time and energy into learning new cognitive skills. Or, on the flip side, we may try harder to protect our brains from stress and mental inactivity.

References

1. Buonomano, D. V. and Merzenich, M. (1998). Cortical Plasticity: From Synapses to Maps. Annual Review of Neuroscience, 21: 149–186

2. Sapolsky, R. Why Zebras Don’t Get Ulcers: An Updated Guide to Stress, Stress Related Diseases, and Coping. 2nd Rev Ed, 1998. W. H. Freeman.

3. Mackey, A. P., Hill, S. S., Stone, S. I. and Bunge, S. A. (2011). Differential effects of reasoning and speed training in children. Developmental Science, 14: 582–590

4. Diamond, A. and Lee, L (2011). Interventions Shown to Aid Executive Function Development in Children 4 to 12 Years Old. Science, 33: 959-964

5. Klingberg, T. Training and plasticity of working memory (2010). Trends in Cognitive Science, 14(7): 317-324.

6. May, A. and Gaser, C. (2006). Magnetic-resonance based morphometry: a window intro structural plasticity of the brain. Current Opinions in Neurology. 19(4):407-411

7. Blackwell, L., Trzesniewski, K., & Dweck, C.S. (2007). Implicit Theories of Intelligence Predict Achievement Across an Adolescent Transition: A Longitudinal Study and an Intervention. Child Development, 78, 246-263

Allyson Mackey is a doctoral candidate in the Helen Wills Neuroscience Institute at UC Berkeley. Her research focuses on brain changes associated with fluid reasoning training in children and adults.