Neuroplasticity in rehabilitation

A few weeks ago I attended a short presentation by Professor Meena Iyer from Missouri University. Her lecture was on the role of neuroplasticity in occupational therapy rehabilitation, although the principles of her talk apply across all of the allied health sciences. Here are the notes I took:

Plasticity: brain structure and function can be influenced throughout life by experiences i.e. it is flexible, and it has a clear age-dependant determinant, includes several morphological changes and many types of brain cells

Occurs under 2 primary conditions:

• Normal brain development within normal individuals: performance shapes plasticity
• As as adaptive mechanism to compensate for lost function and/or to maximise remaining functions in the event of brain injury

The environment and actions of an individual play a key role in influencing plasticity, but not as a result of desire

Is plasticity related to functional outcome?

Example of plasticity: the visual cortex is involved in the sense of touch in people who are blind (even if only blinded for a few days) i.e. the cells in the visual cortex take over the responsibility for “seeing” what the fingers feel. In addition, disrupting the visual cortex (with magnetic stimulation) has a negative impact on people’s ability to read braille. See PBS video – Changing your mind (2000). Scientific American Frontiers (www.pbs.org)

When areas of the brain are not stimulated (e.g. when the visual cortex isn’t stimulated in people who are blinded), those areas very soon take over other functions that were not necessarily related to their original function i.e. dormant pathways are activated

“It appears that in the blind, brains areas commonly associated with the processing of visual information are not rendered “silent” by visual deprivation but rather are recruited in a compensatory cross-modal manner” – Theoret, Merabet, Pascual-Leone (2004). J Physi Paris, 221

There are changes in:

• Dendritic morphology
• cortical maps
• Synaptic strength
• Neurogenesis
• Axonal trajectory
• Synpatic morphology
• Synaptogenesis
• Gene expression

The brain adapts in response to injury

When a nerve is injured, the areas of the brain responsible for movement and sensation of the injured part starts to change i.e. cortical reorganisation

Constraint induced therapy: impair the unaffected side so that the patient must use the affected side for function (accepted rehabilitation method, although original work had no control group, and no controlled study has been done since)

Promoting plasticity – principles of treatment

• Use it or lose it
• Use it and improve it
• Plasticity is experience specific
• Repetition matters (corollary: changes may not appear in the early stages of rehabilitation)
• Intensity (time) matters: continuous training over long periods is needed to change the neural substrate of behaviour
• Time matters: different forms of plasticity may occur at different times in recovery after an injury → plasticity may involve a sequence of phenomena
• Salience matters: activity should be meaningful to the person
• Age matters (change occurs more readily in younger people, so it’s important to build up “cognitive reserve’)
• Transference is possible: training in one area may enhance behaviour in related areas
• Interference can occur: some changes in plasticity may disrupt or limit certain behaviours or skills