Neuroplasticity

Original Editor - Naomi O'Reilly

Top Contributors - Naomi O'Reilly, Evelin Milev, Tony Lowe, Ally Youssouf and Carlos Areia  

"Neurons that fire together wire together" - Hebbian theory

Introduction

It was once believed that the brain stopped developing after the first few years of life, it was thought that it was only during the early "critical period" as a young child that connections formed between the brains nerve cells which then remained fixed in place as we age. As such it was considered that only young brains were 'plastic' and thus able to form new connections. Because of this belief, scientists also thought that if a particular area of the adult brain was damaged, the nerve cells could not form new connections or regenerate, and the functions controlled by that area of the brain would be permanently lost.

In the book "Principle of Psychology" written over 100 years ago, William James presented the first theory of neuroplasticity, suggesting that the human brain is capable of reorganizing. It was not until 1948 when the term Neuroplasticity was first used by a Polish Neuroscientist named Jerzy Konorski, who suggested that over time neurons that had 'coincidental activation due to the vicinity to the firing neuron would after time create plastic changes in the brain'. [1] But it was not until the mid to latter half of the 20th century, following a wide range of research which showed that many aspects of the brain remain changeable even into adulthood, that the term Neuroplasticity came to prominence.

Neuroplasticity, also referred to as brain plasticity, is a term used to describe changes to the brain that happen throughout the lifespan in response to new experiences. Latest research shows that brain development and behaviour are guided by a basic genetic blueprint, in addition to a range of experiences and all that shapes the emerging brain[2]. Even prenatal events could be a factor in the modification of neuronal connections. This notion contrasted with the previous scientific consensus that the brain develops during a critical period in early childhood, then remains relatively unchangeable afterward.

Definitions

A wide range of definitions exist in relation to the term neuroplasticity, some of which look at noral development but others looking more specifically in relation to damage to the central nervous system.

'The ability of the brain to change in structure or function in response to experience'. [3] 

'The capacity of the nervous system for adaptation or regeneration after trauma' [4].

'The ability of the Central Nervous System to undergo structural and functional change in response to new experiences'. [5]

Overview

Information in the brain is transmitted from neuron to neuron through specialized connections called synapses. A synapse between two neurons is made up of presynaptic and postsynaptic terminals, which are separated by a synaptic cleft. The presynaptic terminal is filled with small vesicles containing chemical neurotransmitters, and the postsynaptic terminal consists of receptors specific for these neurochemicals. Neurons carry information in the form of an electrical impulse called an action potential that is initiated at the cell body and travels down the axon. At the synapse, an action potential causes the voltage-dependent release of neurotransmitter-filled vesicles, thereby converting an electrical impulse into a chemical signal. Neurotransmitters diffuse across the synaptic cleft, where they bind to receptors and generate an electrical signal in the postsynaptic neuron. The postsynaptic cell will then, in turn, fire an action potential if the sum of all its synapses reaches an electrical threshold for firing. Since a neuron can receive synapses from many different presynaptic cells, each cell is able to integrate information from varied sources before passing along the information in the form of an electrical code. The ability of neurons to modify the strength of existing synapses, as well as form new synaptic connections, is called neuroplasticity. Defined in this way, neuroplasticity includes changes in strength of mature synaptic connections, as well as the formation and elimination of synapses in adult and developing brains. This encompasses a vast field of research, and similar processes may also occur at peripheral synapses, where much of the pioneering studies on synaptic transmission first took place. In addition, neuroplasticity includes the regrowth (or sprouting) of new synaptic connections following central nervous system injury.

The human brain is now considered to be a highly dynamic and constantly reorganizing system capable of being shaped and reshaped across an entire lifespan. It is believed that every experience alters the brain’s organization at some level. Neuroplasticity refers to the lifelong capacity of the brain to change and rewire itself in response to the stimulation of learning and experience. Neurogenesis is the ability to create new neurons and connections between neurons throughout a lifetime. As we age, the rate of change in the brain, or neuroplasticity, declines but does not come to a halt. In addition, we now know that new neurons can appear in certain parts of the brain up until the day we die.

The more you engage neuroplasticity. As you practice and repeat each movement over and over, the new neural connections( new pathways) in your brain get stronger and stronger.

http://www.flintrehab.com/2015/neuroplasticity-after-stroke/

http://www.flintrehab.com/2016/repetition-can-heal-brain-faster-stroke-recovery/

Presentations 

  • Neuro Recovery & the Foundation for Rehabilitation - Neuroplasticity. Presentation by Jacqui Ancliffe, Senior Physiotherapist at the Royal Perth Hospital. (presentation slides)

Experience and brain plasticity

Changes in the brain can occur due to variety of stimulus. Kolb et al., state that there are three main types of plasticity that shape the developing brain:

  • Experience-independent plasticity is pretty much everything that happens with the brain during the prenatal developmental phase. Neuronal connections and brain formation are processes driven by complex genetic instructions. There is so much going on at this stage of brain development: neurons that fire together, make some structures stronger and parts of the brain more prominent than others, whereas those that do not sync very well together die out. And because all those neuronal losses could harm the brain the nature came up with a solution for that - overproduction of neurons. That is why due course of life we have most of our neurons when we are youngest and then gradually start loosing grey material.
  • Experience-expectant plasticity which is independent of external factories, helps the neurons to connect to each other independent of other processes. An example is the the formation of the retinal ganglion. Axons coming from the retina, initially are sending axonal branches for both eyes but in due course each branch has its own neurons. The axons of each branch fire together and create neuronal network independent of those in the other eye.
  • Experience-dependent plasticity can be seen throughout the life of every animal. Brain changes when different situations occur: moving to new territory, when learn problems or suffer from injury. Those are the daily challenges for all living creatures which could either increase or decrease synapse numbers and make some brain areas bigger than others.

Plasticity is hugely experience dependent event, especially experience which occur in early stages of life and is expected that this type of experience will have long-lasting effects. The plasticity of the brain in its whole complex manner can be summarised in one sentence: "Neurons that fire together, wire together".

Books

  • The Brain that Changes Itself 
    Dr.Doidge is a Canadian Psychiatrist, Psychologist, and best selling author of 'The Brain that Changes Itself' (2007). The book covers the field of neuroplasticity. Doidge does a great job of explaining the practical modern application for the field of Neuroplasticity. For people interested in neuroplasticity he gives us this list of words that we may come across that also relate to the field of neuroplasticity cognitive neurorehabilitation, neurorehabilitation, neurorehab, cognitive rehab, experience-based plasticity, neuroplasticity, neural plasticity, neuronal plasticity, brain plasticity, and plasticity.

Podcasts 

  • Imaging and Stimulating Brain Plasticity. Professor Heidi Johansen-Berg gives her inaugural lecture as head of the Plasticity Group at the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB).
    https://podcasts.ox.ac.uk/keywords/neuroplasticity

Video

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Recent Related Research (Pubmed)

Rehabilitation following spinal cord injury: how animal models can help our understanding of exercise-induced neuroplasticity.


References

  1. What is Neuroplasticity Cutting Edge Research Comprehensive Answers. History of Neuroplasticity. http://www.whatisneuroplasticity.com/history.php (accessed 1 March 2016).
  2. Kolb, B., et al. (2013). "Brain plasticity in the developing brain." Prog Brain Res 207: 35-64.
  3. The American Heritage Medical Dictionary. (2007). Retrieved March 10 2016 from http://medical-dictionary.thefreedictionary.com/neuroplasticity
  4. Mosby's Medical Dictionary, 8th edition. (2009). Retrieved March 10 2016 from http://medical-dictionary.thefreedictionary.com/neuroplasticity
  5. Klein JA, Jones TA. Principles of experience-dependent neural plasticity: Implications for rehabilitation after brain damage. J Speech Lang Hear Res. 2008;51:S225-239.
  6. Senatis. Neuroplasticity. Available from: https://www.youtube.com/watch?v=ELpfYCZa87g [last accessed 01/03/16]
  7. Khan Academy. Neuroplasticity. Available from: https://www.youtube.com/watch?v=ELpfYCZa87g [last accessed 01/03/16]
  8. Camilla Matuk. The Plastic Brain. Available from: https://www.youtube.com/watch?v=8Vo-rcVMgbI [last accessed 01/03/16]
  9. Donald Elger. Brain Based Learning Model. Available from: https://www.youtube.com/watch?v=VvZ-9ofM7Go [last accessed 01/03/16]
  10. Stress Free Life. The Phenomenon of Neuroplasticity. Available from: https://www.youtube.com/watch?v=rDTiZpPyqRk [last accessed 01/03/16]