For quite some time now there has been considerable interest in the use of mirror therapy for the rehabilitation of motor function in stroke, specifically in the upper limb which has historically been a difficult area to rehabilitate mainly because it is much more complex than the lower limb (more on this in a future post).
Selected research surrounding mirror therapy in the past 10 years have statistically shown an improvement in function following 3-6 months post stroke (Thieme et al. 2012), but whether or not this form of therapy is superior to other forms of therapy, we still do not know. Furthermore, for a long time we could only speculate which neuronal pathways may be at work, until now.
Let me introduce you to a highly respected researcher I am totally in love with. If it weren’t for my wife, I would have probably flown halfway across the world by now to woo her.
In 2013, Dr. Soha Saleh and her talented research team at Rutger’s University in New Jersey conducted a randomised control trial (RCT) investigate the effective neuronal circuits and areas involved in patients with chronic stroke recognising virtual feedback. You can access this article here.
Using functional MRI, they were interested in testing their hypotheses as to which visuomotor systems and pathways are activated when an unaffected part of the hand moves, and which ones were activated when the mirrored feedback of the unaffected hand is presented. They also wanted to explore the relationship between level of hand function to the corresponding areas in the brain involved in their control.
The article itself is rather heavy on medical and statistical terminology but allow me to break it down into simpler terms.
In their experiment, she put 15 patients with chronic left and right hemiplegia, each with different areas of the brain affected by a stroke, through a fMRI machine and had them wearing special gloves that detected joint angles. She then showed them a virtual image of their own set of hands while they were lying in the fMRI machine and had them bend and extend their fingers on their unaffected hand first (experiment 1), followed by bending and extending fingers on their affected hand (experiment 2). Each experiment presented virtual feedback either of the same side as their moving hand, or the mirrored feedback of the moving hand.
Please excuse me, but at this point I will have you know that I am absolutely bursting with excitement, much like a schoolgirl who was about to go on her prom date. I will explain why in a moment.
They found that on the sides that when people moved their unaffected hand and were given direct feedback of that side virtually, that the frontoparietal region of the contralateral (opposite) side lit up. However the motion of the affected side with the same projection of direct visual feedback led to bilateral sensorimotor cortical and parietal activation, and contralateral insula and ipsilateral (same side) occipitotemporal cortex activation. The key message here is bilateral representation.
However, when these patients were given mirrored feedback, the ipsilesional somatosensory and motor areas of the cortex lit up. In other words, this means that when the person with a right sided stroke had been asked to move his left hand, the mirrored feedback of this hand that made it look like his right hand was moving, allowed his left cortex to engage when it would otherwise not, if no actual right hand movement was available to him. How fascinating!
In this paper, they also proposed the idea that given the two networks most strongly connected functionally – sensorimotor and somatosensory – in the response to mirrored feedback, that mirror therapy may have possibly be most beneficial to patients who are most impaired and have these two areas majorly affected.
From my point of view, this is particularly interesting to consider because it is this very group of patients who have the most difficulty with other forms of movement based therapies due to the reason that some degree of voluntary control is often required to get them started well enough for people to generally feel that it is worth practising. It’s almost like when you’re trying to hit a ball and if all you do is miss it over and over again because you have no movement to start with, all you want to do is just give up from a motivational point of view, which is going to impede your efforts to induce healthy neuroplasticity.
So what does this mean? I think possibly this stumbling block of having no or little voluntary control in the affected hand can somewhat be bypassed by using mirror therapy to access the cortical structures and induce functional neuronal changes directly in the brain, by tricking the brain into believing that actual movement through visualisation.
Of course, we need more research to prove this more thoroughly. But one thing’s for sure – we are getting closer to finding how this form of therapy can help selected groups of patients get better.
Resources: Saleh S, Adamovich SV and Tunik E. (2014). Mirrored Feedback in Chronic Stroke: Recruitment and Effective Connectivity of Ipsilesional Sensorimotor Networks. Neurorehabil Neural Repair 28 (4) 344-354. Retrieved from http://nnr.sagepub.com/content/early/2013/12/23/1545968313513074 Thieme H, Mehrholz J, Pohl M, Behrens J, Dohle C. (2012) Mirror therapy for improving motor function after stroke. Cochrane Database Syst Rev. 3:CD008449
