You may have heard about this idea of “Neuroplasticity” or the brain’s ability to change itself. The word and idea have been popularized by many authors and two of my favorite books on the subject are by the psychiatrist Norman Doidge (“The Brain’s Way of Healing” and “The Brain That Changes Itself”). Through these books and others, I have been introduced to the idea of the malleability of the brain and nervous system especially in relation to brain injuries (e.g. a stroke or trauma to the head).
However, neuroplasticity is not just a phenomenon confined to the domain of brain injury and recovery. We know that the brain changes in people with chronic pain (see: Moseley and Butler’s work in the books “Explain Pain” and “The Graded Motor Imagery Handbook“). Furthermore, the brain reorganizes in response to immobility, as I recently learned in one of my classes: the representation in the brain for one’s ankle is reduced after just 4-6 weeks of ankle immobilization!1 (each of our body parts has a “map” in the brain for sensory and motor information from that body part; as I’ve written about before: Maps).
I recently read an interesting paper about the neuroplastic changes following ACL surgery.2 Proposed mechanisms for these changes are via altered sensory input (ie., loss of mechanoreceptors at the knee and joint effusion) and motor output (e.g., change in joint loading due to pain, instability, etc.) which lead to reduced activation of both sensory and motor “knee areas” in the brain. One repercussion of this altered input/output may be an increase stimulus intensity needed to get a contraction of the quadriceps muscles (i.e., does VMO or quadriceps insufficiency ring a bell for anyone working with ACL rehabilitation patients?!). Another change may be the increased reliance on other sensory systems (visual and spatial systems).
This paper compared brain activity in individuals who had undergone ACL reconstruction vs. matched controls while performing a knee flexion and extension task. Results seemed to support the idea of neuroplastic changes in individuals who had undergone ACL reconstructive surgery. In these individuals (compared with the matched controls) there was an increase in activation in brain areas associated with visual and somatosensory processing (lingual gyrus and secondary somatosensory cortex) and in the motor cortex corresponding with the surgically repaired ACL (possibly due to reduced motor cortex excitability).2
What does this mean for ACL rehabilitation? Well, as the authors of the study propose, it may be beneficial to utilize certain tactics to reduce the reliance on visual information and retrain the functional use of somatosensory and proprioceptive information (e.g., via blindfolding and/or biofeedback). Additionally, it is important to be aware of these changes as we work with individuals post ACL reconstruction in order to fully address their impairments and return them to function. We can’t just retrain the body (i.e., muscles, ACL graft, joint structures), we must retrain the brain!
(The branching of this Joshua tree reminds me of how our brains are constantly adapting to new stimuli)
1- Liepert, J, Tegenthoff, M, & Malin, JP. (1995). Changes of cortical motor area size during immobilization. Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control, 97(6), 382-386.