One of the most intriguing characteristics of the brain is its ability to continually adapt to the experiences we have throughout our lives (physical, emotional, etc.). The remodeling of our brain implies changes at multiple levels, not only molecular or cellular but also functional.
Generally speaking, each experience will result in lasting increases or decreases in the strength of synaptic connections. The accumulation of such seemingly minor phenomena can lead to larger-scale modifications (physiological, morphological, structural, etc.). While very well described in the context of learning, plasticity is often perceived as the consequence of a long process rather than a single, immediate event.
Through the example of a joint injury, we will detail two short-term plasticity phenomena.
Immobilization 1
Immobilization after an injury may be advised or even required in some cases. Physiologically, spontaneous activity exists between motor brain regions when at rest. This low-intensity activity can indicate a functional connection between motor regions even in the absence of a stimulus and/or voluntary movement.
During a 48-hour immobilization period, spontaneous activity between the motor regions of the immobilized limb appears to disappear (see figure below), leading to a kind of functional disconnection with other motor brain regions. The persistence of immobilization and its plasticity, in addition to the muscular consequences (amyotrophy, etc.), helps explain the difficulty of rehabilitation upon resuming movement.
# Motor inhibition 2
Some injuries are associated with an inability to voluntarily contract the surrounding muscles. Documented under the term "Arthrogenic Muscle Inhibition", this reflex mechanism is, on the one hand, the result of an imbalance in the firing of motor neurons present in the gamma loop regulating muscle contraction.
On the other hand, motor inhibition appears to have a central origin, involving temporary or lasting cortical rearrangements, particularly in sensory and motor regions.
A rehabilitation perspective: motor imagery
Motor imagery is defined as the mental rehearsal of a motor action without physical execution. This mental practice is particularly interesting due to its ability to activate certain motor regions, making it a potential therapeutic tool. It was recently published in the context of immobilization. 3Motor imagery appears to be a useful technique during periods of inertia to limit detrimental effects on sensorimotor function. Regarding motor inhibition, only one recent study seems to have explored the promising effect of motor imagery. 4.
Clinically, its association within the Allyane method with...listening to low-frequency sounds have already raised awareness among healthcare professionals about using it to facilitate muscle recovery during rehabilitation.
Typhanie Dos Anjos – Head of Research, Allyane – PhD in Neuroscience
REFERENCES :
1. Newbold, DJ et al. Plasticity and Spontaneous Activity Pulses in Disused Human Brain Circuits. Neuron 107, 580-589.e6 (2020).
2. Lepley, AS & Lepley, LK Mechanisms of Arthrogenic Muscle Inhibition. Journal of Sports Rehabilitation 1–10 (2021) doi:10.1123/jsr.2020-0479.
3. Debarnot, U. et al. Motor imagery practice benefits during arm immobilization. Sci rep 11 (8928).
4. Oda, S. et al. Promising Effect of Visually-Assisted Motor Imagery Against Arthrogenic Muscle Inhibition – A Human Experimental Pain Study. J Pain Res 14, 285-295 (2021).