Posts Tagged ‘neurons’

How the Cognitive Reserve Works

December 22, 2017

There have been many previous healthy memory posts informing its readers that there are people who die with brains filled with amyloid plaque and neurofibrillary tangles, but who never exhibited any of the cognitive or behavioral symptoms of Alzheimer’s. About one-third of the people who die without cognitive problems have had the plaques and tangles that define Alzheimer’s Disease. It is believed that intellectual stimulation builds this cognitive reserve. HM has advanced the notion that it is specifically Daniel Kahneman’s System 2 processing that largely builds this cognitive reserve.

The question is what is the cause or causes of this cognitive reserve? Jeremy Herskowitz at the University of Alabama at Birmingham and his colleagues studied brain samples from 41 people. They had either beta-amyloid plaques but not symptoms, plaques and symptoms, or no plaques or symptoms. The team took close-up pictures of the samples, then used software to trace the physical shape of the brain cells and their connections or synapses. This technique allowed the team to visualize the first neuron of a pair that make up a synapse. This neuron sends out small buds known as spines which connect with projections from other neurons. Each synapse exists where a spine links to a projection. The spines of people who were Alzheimer’s resistant were longer than those from the other groups (Annals of Neurology, dos.org/cgfx).

Synapses are where signals pass from one neuron to another. Herskowitz says “the longer spines might make the synapse more effective in this role. Or new spines might be growing outwards to generate more synapses to replace those destroyed by plaques and tangles.” Herskowitz goes on to say,”It’s possible that the spines are reaching out to maintain the synaptic connections. They are putting themselves out there to catch a new one.”

Michael Valenzuela at the University of Sydney says that this finding may not be the only explanation. Brain imaging studies suggest that people who are resistant to Alzheimer’s may compensate for damage by using different parts of their brain. It should also be noted that these explanations are not mutually exclusive. They could both be operative.

The news here is that we have reasonable explanations as to what accounts for this cognitive reserve. However, it has long be expected that this cognitive reserve is built by cognitive activity. HM further postulates that it is System 2 processing of Kahneman’s ilk that is primarily responsible for the cognitive reserve.

So live a healthy lifestyle, stay cognitively engaged, and foster growth mindsets for a health memory.

This post is based on an article by Claire Wilson titled “Elongating your brain cells could ward off Alzheimer’s in the News & Technology section of the 25 November 2017 issue of the New Scientist.

© Douglas Griffith and healthymemory.wordpress.com, 2017. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

The Adult Brain Makes New Neurons and Effortful Learning Keeps Them Alive

October 19, 2014

The title of this blog post is the same title as an article in Current Directions in Psychological Science 2014 23:311 (DOI: 10.1177/0963721414540167) by Tracey J. Shors of Rutgers University.. The healthymemory blog has posted many pieces emphasizing that new neurons continue to be developed until we die. The hippocampus produces thousands of new neurons each day. Unfortunately a significant number of them die and do so within just a few weeks after their birth. So the critical question is how to save these neurons from an untimely death.

As the title states the answer is effortful learning. Although the cited research did not involve human subjects, two important facts need to be remembered. It is difficult and expensive to conduct similar research with humans. And findings from the vast majority of research using non-human subjects do generalize to population of humans.

It has been noted many times in the healthymemory blog that physical exercise facilitates neurogenssis. However, many of these new cells do not survive. It takes effortful learning for there to be a lasting preferential effect on the survival of these new neurons.

Fortunately Dr. Shors concluded the article with a discussion of the relevance of these findings for humans. Here are four recommendations:

  1. spacing trials of training or learning over longer periods of time. (which has been discussed in previous healthymemory blog posts).

  2. Self-testing (which has been mentioned on previous healthymemory blog posts).

  3. varying the conditions of training or learning

  4. interleaving different topics and/or skills within the same training session.

The fourth item on interleaving different topics or skills might sound like a contradiction of the many healthymemory blog posts warning against the dangers of multi-tasking. The difference here is the time laps between switching. Here the time laps are substantially longer than those commonly done in multi-tasking.

The four recommendations provide vice on how to do new learning. The two important points for the survival of new neurons are:

  1. Learn new knowledge of skills.

  2. The learning should be effortful, requiring mental effort.

What is Neuroplasticity and How Does It Work?

March 15, 2014

Neuroplasticity is the ability of the brain to change its structure in response to experience.”1

What follows is a brief synopsis as to how this change is accomplished. We have an average of ten thousand connections linking an average neuron to other neurons. Given that there a hundred billion neurons, there are hundreds of trillions of synaptic linkages. Moreover there are trillions of glial cells supporting the effort. One type of glial cell is the oligodendrocyte. When we develop skills after many hours of practice the oligodendrocytes produce myelin. Mylein is a fatty sheath that coils around the neuron’s axon that sends signals to other neurons. When myelin is present, the speed of the action potential down the axon is 100 times faster. Myelin also decreases the time for recovery before the next firing, the refractory period. This refractory period is 30 times shorter. So the enhanced functoning of a myleinated circuit is 3,000 (30 times 100) faster than a non-myleinated circuit. This provides the basis for the phenomena performances we sometimes see.

Synaptogenesis is the process by which synapses are created or strengthened. Myleinogenesis the process by which these circuits become much faster. In addition to these two ways in which the brain changes as the result of experience there is neurogenesis. Neurogenesis occurs throughout the entire life span and involves the differentiation of neuro stem cells into fully mature neurons in the brain. This process may take from two to three months in contrast to the more rapid synaptogenesis that occurs within minutes to hours and becomes consolidated over days or weeks. Studies have identified this more slowly occurring neurogenesis in the hippocampal region, but it is expected that this will be found in other areas in the future. Of course, the hippocampus is important for its central role in memory. Research has also shown that physical exercise benefits hippocampal growth (see the healthymemory blog post, “To Improve Your Memory, Build Your Hippocakmpus.”)

Epigenesis is the process by which experience alters the regulation of gene expression by way of changing the various molecules (histones and methyl) on the chromosome. Understand that genes themselves are not changed. Rather the way that information is read out from the genes is changed. This is how experience and genetics interact.

SNAG is the acronym to explain how these processes result in neuroplasticity. SNAG stands for stimulating neural activation and growth. Add to this the expression that neurons that fire together , wire together. That’s how we learn, but this is also the basis for remembering. Neurons that have not fired together for a long time, can result in that memory circuit being difficult to find. The memory is likely still available, but not currently accessible. That’s why healthy memory recommends revisiting old memory circuits. When you can’t remember something, sometimes it is good not to look it up, but to keep trying to remember. Even if this attempt fails, your nonconscious mind is apt to keep looking for it, and it might suddently pop into memory hours or even days later.

Remember to use your mind to control, exercise, and grow neural circuits. This is the fundamental means of keeping a memory healthy.

1Siegel, D. J. (2012). Pocket Guide to Interpersonal Neurobiology. New York: Norton & Company. This blog post is based primarily on this reference.

© Douglas Griffith and healthymemory.wordpress.com, 2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.