Neuroplasticity

Authored by Henry Strick van Linschoten

Neuroplasticity is a recently introduced term for structural or functional changes in the nervous system, or the capacity for such changes to occur in relation to experience or the environment. Whenever something is learned there are changes in the nervous system, and the possibilities for change are extensive: synaptic; non-synaptic; new synapses being made and breaking off; new neurons growing (“neurogenesis”) and neurons dying (“apoptosis”); dendritic spines (parts of neurons) changing shape. Learning, development and ontogeny, as applied to the nervous system, are synonyms of neuroplasticity.

Since humans are social animals an important part of human experience is interaction with other people (and animals). The possibility of neuroplasticity means that our nervous system can change as a result of our relationships. Much of our social behaviour is learned, and part of it is innate (e.g. the attachment behavioural system). Learning new social behaviour changes the brain, and developing a level and style of attachment security based on one’s contact with primary caregivers leads to changes, and leaves its “marks” in the brain. Internal and behavioural factors constantly interact with social, relational influences, and that this steers and shapes the detailed structure and functioning of the nervous system.

Synaptic plasticity in general is quite high. Synapses come and go, dendrites change shape and move around on a life-long basis. Some of the detailed synaptic changes which are the result of simple forms of learning have been traced in detail in animal experiments. There have also been a number of simple invertebrates where the impact on the nervous system of non-associative learning (a form of implicit learning) has been mapped in detail.

Neurogenesis peaks during the gestation period. In most mammals the great majority of neurons that they will have during life are present at birth. It used to be thought that after birth new neurons were not created, but that has turned out to be false. In mammals, including humans, neurons continue to be created on a small scale throughout life. It is currently thought that in most adult mammals new neurons are only added to parts of the olfactory bulb and the hippocampus. Neurons themselves do not reproduce; new neuron stem cells and progenitors are created in the subventricular zones, and in the subgranular zone, a part of the dentate gyrus of the hippocampus. where the precursors of neurons can be generated by mitosis, and develop into neurons (or glial cells). Once new neurons have been created, they must migrate (move around) to be connected to the rest of the nervous system. Neurogenesis and its extent is probably hormonally controlled.

It has also been established that in response to outside events it is possible for cortical maps (the locations in the cerebral cortex which are linked with specific parts of the body) to change substantially, e.g. when a finger is amputated.

The set of ideas associated with neuroplasticity are relevant for all areas of rehabilitation, after brain or limb damage, including stroke, for the prevention, treatment and cure of people with neurocognitive disorders (dementias), and in general for all teaching, counselling and therapy activity that has “learning” components. Names of some key people who investigated neuroplasticity in the last forty to fifty years are Bach-y-Rita (2012), Michael Merzenich and Doidge (2007).

Bell (2010a) sets out the view that the concept is redundant, and lists a number of meanings that may be intended by the term. Bell (2010b) gives a number of references showing that some of the ideas associated with neuroplasticity were known and discussed since the late 19th century. William James (1890) already used the word plasticity.

References

Bach-y-Rita, P. (2012). Traumatic Brain Injury: Comprehensive Neurological Rehabilitation (2nd edition).Hove, East Sussex: Psychology Press.

Bell, V. (2010a). Neuroplasticity is a dirty word. Available at www.mindhacks.com (accessed 31 December 2013).

Bell, V. (2010b). Neuroplasticity is not a new discovery. Available at www.mindhacks.com (accessed 31 December 2013).

Doidge, N. (2007). The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science. New York: Penguin.

James, W. (1890). The Principles of Psychology. New York: Dover Books.