Children versus Adults
In the very first part of this discussion we claimed that neuroplasticity phenomenon can be observed for a whole life of an individual and always will adapt to new environment. However, another phenomenon, the phantom limb pain, seems contradicts the claim about beneficial ever lasting neuroplasticity.
For instance, children rarely experience chronic pain associated with Bp injury; in contrast, adults almost always develop it. According to literature, phantom limb pain is different from Bp injury; however, both may be related to inactivity of the limb. The brain requires getting visual evidence that its electrochemical commands are followed. When this visual test fails, the chronic (frequently unbearable) pain is developed. The are several theories as for this pain's origin: one is that the brain interprets absence of limb movement as a limb stuck into a position vitally threatening to the limb, and so generates pain signals. The second one is that absence of limb movement makes brain to enhance intensity of sent such signals which leads to pain feelings. Whatever the mechanism is, in Bp injuries functional recovery is associated with pain alleviation.
Pain experience and its intensity is also strongly correlated with cortical reorganization in animals (including humans). Yet, neither cortical reorganization, nor pain were shown to cause each other. More probably they both are dependent on another element which is related to absence of muscles activity or disorganized motor neurons regeneration (demonstrated in both children and adults). This absence of spinal cord plasticity (absence of directional motor neuron growth) often results in synkinesis (simultaneous innervations of proper and “foreign” muscle, e.g. diaphragm and hand). Though, immature children CNS is more plastic, for example in children with Bp injury, the injury site often develops in not dominant one. Also because nervous system is immature, it quite probable it may luck some pain or cortical reorganization trigger or it can be suppressed. It is interesting to note here that adults lack a number of reflexes young children have (Babinski, grasp, tonic neck, Moro, root, suck reflexes). Cortical reorganization is also associated with referred sensations (e.g. feeling face when hand is touched). Cortical reorganization is believed to be the evidence of plasticity of the brain, but not the sign of the recovery. However, restored motor activity causes re-reorganization of motor cortex backward to its normal state. There was also shown that proper pain anesthesia reverses cortical reorganization completely. Nevertheless, in adults, the surgery has to be performed as soon as possible due to massive lost of motor neurons, which restoration is both important for functional recovery and pain relive.
Several interesting approaches have been recently developed to teach an “old stubborn dog” (adult brain) new tricks – not to feel pain. They are: repetitive transcranial magnetic stimulation (rTMS) of motor cortex (series of 20 trains of 5 seconds’ duration of 55 second applied at a stimulation rate of 10 Hz and 80% of resting motor threshold intensity). Virtual reality game with tracking of eyes movement to generate virtual limb movement. Mirror use to simulate visual feedback. All three approaches allowed to alleviate pain in patients with Bp injuries.
The Source for the Background Image: ttp://arts.monash.edu.au/korean/klec/clipart/index.php?RollID=clipart001&FrameID=klec2003-c094
& http://www.learningrivers.com/WondersMetronome.html
Bilotkach Kateryna, UCI, BME 240, Spring-2009