Written by Reina Stewart and Alannah Verville | July 30th, 2019
What is Neural Plasticity?
The human body consists of a central nervous system (CNS) and a peripheral nervous system
(PNS) [5]. Nerve cells, or neurons, are the building blocks of these systems. The CNS includes
the brain and the spinal cord, whereas the PNS is made up of all the neurons in the rest of the
body [5]. Neurons in the CNS analyze information, while the sensory and motor neurons in the
PNS bring information to and from the CNS, respectively [5]. Throughout life, these connections
are subject to change and this is due to neural plasticity, which may be defined as “the capacity
of the nervous system to modify itself, functionally and structurally, in response to experience
and injury” [12]. Neural pathways can strengthen and fade, and new connections can be
established [12]. Neural plasticity is directed by our cognitive, sensory, and behavioural
experiences [6]. When repeated, changes in our actions, thoughts, and emotions influence the
structure and function of the brain [6]. In this way, neural plasticity is experience-dependant.
Without neural plasticity we would not be able to grow, learn new things, improve our skills, or
recover from injury. So, neural plasticity is an important part of everyone’s life. There are
various principles of neural plasticity that are directly related to rehabilitation and we will
discuss four of them [6].
What are the principles of experience-dependant neural plasticity?
“Use it or lose it”
When neural pathways are not used to perform tasks for an extended period of time, they begin to break down [6]. This occurrence has been demonstrated through various experiments, such as the following (ethically questionable) studies:
Preventing kittens from using one of their eyes resulted in a decrease in the number of neurons that respond to light stimuli in the visual area of the brain [3]
Restricting young rats from moving lead to incomplete development of neurons in the area of the brain that helps to coordinate voluntary movement [9]
When deprived of sensory information, it is not uncommon for degraded neural pathways to be taken over by other brain areas so that different functions can be carried out [6]. For example:
Visual brain areas of individuals who are blind were activated while they used their hands [11]
Auditory brain areas of people who are deaf were activated in response to visual stimuli [2]
These phenomena are relevant to rehabilitation for a couple of reasons. First, brain areas that remain deactivated because they are not being used can promote additional loss of function [6]. For instance, individuals who experience a stroke may lose some functional ability in one of their arms [7]. As a result, they may not use their affected arm as often and this non-use may weaken their arm even further [7]. Also, recovery of various skills and abilities may be facilitated through the adoption of new functions by different brain regions [6]
“Use it and improve it”
While brain function can be compromised due to a lack of use after injury, neural plasticity may also be activated in specific brain areas by way of proper training [6]. Enhanced sensory and motor abilities that develop due to extended training occur with immense neural plasticity in the cerebral cortex of animals [6]. This complex brain region processes sensory and motor information and allows us to carry out an extensive array of behaviours and cognitions [1]. Rehabilitation efforts may also lead to comparable changes within the brain [6].
Research findings show that rich experiences can improve performance and increase neural plasticity following brain damage [6]. For example, after a group of rats with damage in sensory and motor brain regions engaged in several weeks of obstacle course training, they experienced greater behavioural function and increased plasticity in comparison to rats who performed less complex exercises [4]. The effects of various post-injury treatments have also been optimized through rehabilitative training [Johansson, 2000 as cited in 6].
The main point here is that it is important to maintain use of body areas that have been affected by a neurological disorder or trauma in order to sustain and improve function [6]. In other words “use it and improve it”.
“Specificity”
In order to achieve a task-specific adaptation in the body, training must be relevant to the desired skill [6]. Research findings show that participants who are trained to repeat a skilled movement are much more successful in achieving neural changes in comparison to those who performed unskilled movements [6]. For example, the results of one study showed that people who practiced making specific and skillful ankle movements experienced activation in certain CNS regions, but this did not occur in those who repeated unskilled ankle movements [10]. Not only does the training have to be specific to produce the desired effect, it also has to be challenging [6]. Additionally, it is important to note that improving one type of skill may not result in the development of another. For example, exercises that are meant to enhance swallowing ability after stroke do not necessarily promote speech production (Huang, Carr, & Cao, 2002). The core message of this principle is that we must perform the task that we want to improve [6].
“Repetition Matters”
The principle of repetition highlights the importance of persistence. The brain requires consistent repetition of a skill in order to successfully rewire itself and promote healing [6]. In order to achieve long-term neural changes along with enhanced functional ability, most skills must be practiced over and over [6]. Through repetition, neural changes and improved abilities may be protected against future deterioration in the absence of practice [8].
At the Neuromotion Centre for Rehabilitation, this principle is put into practice. MyndMove is a non-invasive electrical stimulation technique where the participant engages in many repetitions of a specific task while simultaneously experiencing tiny bursts of electricity to the muscles, causing the muscles to contract and send signals to the brain. Based on the concept of neural plasticity, this reinforces neural pathways to become stronger.
References
[1] Budd, J., & Kisvarday, Z. F. (2015). Wiring principles of cerebral cortex. S.l.: Frontiers Media SA.
[2] Finney, E. M., Fine, I., & Dobkins, K. R. (2001). Visual stimuli activate auditory cortex in the deaf. Nature Neuro- science, 4, 1171–1173. Huang, J., Carr, T. H., & Cao, Y. (2002). Comparing cortical activations for silent and overt speech using event-related fMRI. Human Brain Mapping, 15, 39–53.
[3] Hubel, D. H., & Wiesel, T. N. (1965). Binocular interaction in striate cortex of kittens reared with artificial squint. Journal of Neurophysiology, 28, 1041–1059.
[4] Jones, T. A., Chu, C. J., Grande, L. A., & Gregory, A. D. (1999). Motor skills training enhances lesion-induced structural plasticity in the motor cortex of adult rats. Journal of Neuroscience, 19, 10153–10163
[5] Khan Academy. (n.d.). Overview of neuron structure and function. Retrieved from https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/a/overview-of-neuron-structure-and-function
[6] Kleim, J. A., Jones, T. A. (2008). Principles of experience-dependent neural plasticity: Implications for rehabilitation after brain damage. Journal of Speech, Language, and Hearing Research, 51, 225-239.
[7] Kwakkel, G., Veerbeek, J. M., van Wegen, E. E., & Wolf, S. L. (2015). Constraint-induced movement therapy after stroke. The Lancet. Neurology, 14(2), 224–234. doi:10.1016/S1474-4422(14)70160-7
[8] Monfils, M. H., Plautz, E. J., & Kleim, J. A. (2005). In search of the motor engram: Motor map plasticity as a mechanism for encoding motor experience. Neuroscientist, 11, 471–483 doi:10.1177/1073858405278015
[9] Pascual, R., Hervias, M. C., Toha, M. E., Valero, A., & Figueroa, H. R. (1998). Purkinje cell impairment induced by early movement restriction. Biology of the Neonate, 73, 47–51.
[10] Perez, M. A., Lungholt, B. K. S., Nyborg, K., & Nielsen, J. B. (2004). Motor skill training induces changes in the excitability of the leg cortical area in healthy humans. Experimental Brain Research, 159(2), 197-205. doi:10.1007/s00221-004-1947-5
[11] Sadato, N., Pascual-Leone, A., Grafman, J., Ibanez, V., Deiber, M. P., Dold, G., Hallet, M. (1996). Activation of the primary visual cortex by Braille reading in blind subjects. Nature, 380, 526–528.
[12] von Bernhardi R., Bernhardi L.E., Eugenín J. (2017) What is Neural Plasticity?. In: von Bernhardi R., Eugenín J., Muller K. (eds) The Plastic Brain. Advances in Experimental Medicine and Biology, vol 1015. Springer, Cham