I came across a very interesting article today with regards to stroke, and the impact cerebral plasticity has on rehabilitative techniques (see http://www.theguardian.com/science/2015/feb/08/robert-mccrum-lucky-survivor-stroke-treatment-revolution?CMP=twt_gu). It’s an area that I have read quite a bit on, and so this blog will aspire to give a brief overview of different forms of rehabilitation, and the reasoning behind them. The focus will be on motor function, rather than the cognitive impairments that can accompany a stroke.
Firstly, a stroke occurs when the blood flow to a particular brain area is disrupted (Murphy & Corbett, 2009). This allows cells to die off, which negatively affects the functioning of that cerebral region, i.e. an infarct to the hand knob of the motor cortex could lead to an impairment of hand movement. Strokes can be caused by a burst aneurysm or a blood clot blocking a blood vessel. This website (http://www.stroke.org/) will answer a wide range of questions regarding the causes and consequences of stroke. This blog will be discussing one of the most notable and debilitating effects of stroke: motor impairment.
Robert McCrum speaks of the difference in the rehabilitation environment between today and 30 years ago, when he first came into contact with it. He uses words like “dynamic” to describe the attitudes and approaches of stroke recovery nowadays. He attributes the growing knowledge surrounding cerebral plasticity to this new optimism. Cerebral plasticity refers to the structural change of the brain in order to accommodate changing demands (Lövdén, Wenger, Märtensson, Lindenberger & Bäckman, 2013). This is often depicted as the “rewiring” of neural connections, and appears to be fundamental for learning and re-learning, in the case of rehabilitation (Kleim & Jones, 2008). Although the concept can seem complex and daunting, it is actually a simple enough idea; the brain creates a compensatory pathway or method to carry out a task to the best of the individual’s (new) ability. It’s the same principle as finding an obstruction preventing you from taking the easy route on the highway to your destination, and choosing to drive down the smaller, less-taken roads to reach it.
Physical rehabilitation has been employed in cases of stroke for quite a long time. One might believe that this is simply to strengthen the muscles that have wasted away, and has nothing to do with the neural mechanisms of motor function. But why have the muscles diminished in the first place? In the majority of cases, lesions to the motor cortex destroy the motor neurons responsible for stimulating said muscles which leads to a gradual depletion of tone and strength. Physical rehabilitation attempts to stimulate the motor regions, in order to excite the motor areas responsible for the impairment in functioning (Liepert, Miltner, Bauder, Sommer, Dettmers, Taub & Weiller,1998). This will allow a reorganization of the (now) redundant anatomical circuits and allow neuronal populations to change their physiological relationships with other neuronal ensembles (Linazasoro, 2006). Physical rehabilitation for stroke is largely concerned with muscle strengthening and physical conditioning, with advancements in technology introducing us to an era of robot-assisted movement training (Teixeira-Salmela, Olney, Nadeau & Brouwer, 1999; Lum, Burgar, Shor, Majmunder & Van der Loos, 2002). Imaging studies have demonstrated plastic changes to the neural networks involved in movement, coinciding with marked motor improvement (Hodics, Cohen & Cramer, 2006).
While neural plasticity’s place in physical rehabilitation is interesting, even more fascinating is it’s role in rehabilitative interventions which employ mental/motor imagery to aid recovery. Mental imagery can be defined as a process in which individuals can actively relive sensations (visual, auditory, tactile, etc) without the need for external stimuli (Jackson, Lafleur, Malouin, Richards & Doyon, 2001). Motor imagery is described as the internal reproduction of the representation of a specific action, without the execution of movement (Jackson et al., 2001). A notable example of the reasoning behind the use of mental imagery in motor rehabilitation comes from Pascaul-Leone and colleagues (1995) study. This investigation incorporated three groups: (i). the physical group, which involved physically practicing playing a piano piece over a period of time, (ii). the mental group, which involved mentally imagining playing the same piano piece over the same period of time, and (iii). a control group. The results revealed that both the mental and physical group showed a marked improvement in their fine finger motor skills, when compared to controls. It also demonstrated that structural changes to the motor cortex pertaining to the fingers, in both the physical and mental group. This suggests that these neural networks were recruited for the learning of the motor task, and that mental practice can appropriately access and modulate those connections (Pascaul-Leone et al., 1995). This study recruited healthy individuals, but it lays a foundation for the use of mental/motor imagery in stroke rehabilitation.
Stroke research has used the evidence of mental/motor imagery recruiting the same cortical motor areas in order to function, as an argument for its place in rehabilitation. Researchers have suggested that imagery of movement can stimulate the redistribution of active connections between parallel motor regions, and thus, improve recovery of motor function (Dijkerman, Ietswaart, Johnson & MacWalter, 2004). This form of rehabilitation involves techniques such as mentally rehearsing an action over a set period of time, and mentally practicing an action just prior to actually engaging in said movement. However, these methods have been met with mixed results. It should be noted that these studies can be confounded by a number of factors, that could lead to results determining whether the rehabilitation is effective or not. These include patients’ inability to engage in mental imagery (as lesions may disrupt neural networks involved in these processes), small sample sizes, heterogeneity in participants’ characteristics and outcome measures (Sharma, Pomeroy & Baron, 2006). Within the number of studies that provide evidence for mental/motor imagery’s positive impact on motor recovery, there have been reports that improvement in motor function is specific to the mentally rehearsed tasks (Dijkerman et al., 2004). This is less than optimal, as treatment generalizability is exceedingly important within rehabilitative techniques. Nonetheless, mental/motor imagery as a form of rehabilitation is an area that researchers should strive to engage in; even to use it as a complimentary add-on to physical rehabilitation. This type of intervention is ideal, as it requires little supervision, is cost-effective and easily accessible (Braun, Kleynen, Schols, Beurskens & Wade, 2008).
Stroke is a highly prevalent and disabling event, and thus, it is no surprise that there is a variety of rehabilitation programmes being researched and developed to combat it’s harsh impact on motor performance. It is important to be aware of cerebral plasticity’s role in these rehabilitative interventions, as it is the reorganization of neural connections that stroke researchers are targeting. It should also be noted that due to the nature of stroke, the research into stroke rehabilitation has wider implications for other neurological disorders; these often provide a basis for treatments for neurodegenerative disorders affecting the motor system, such as Parkinson’s Disease, or for motor impairments resulting from traumatic brain injuries. In addition to the research’s practical significance, neural plasticity is a fascinating concept; the ability of the brain to pave new pathways and build new bridges in order to engage in learning or re-learning processes. It’s certainly an area worth keeping an eye on, and hopefully, the coming years will find these rehabilitative techniques to make progress in leaps and bounds.
References
Braun, S., Kleynen, M., Schols, J., Schack, T., Beurskens, A., & Wade, D. (2008). Using mental practice in stroke rehabilitation: a framework. Clinical Rehabilitation, 22(7), 579-591.
Dijkerman, H. C., Ietswaart, M., Johnston, M., & MacWalter, R. S. (2004). Does motor imagery training improve hand function in chronic stroke patients? A pilot study. Clinical rehabilitation, 18(5), 538-549.
Hodics, T., Cohen, L. G., & Cramer, S. C. (2006). Functional imaging of intervention effects in stroke motor rehabilitation. Archives of physical medicine and rehabilitation, 87(12), 36-42.
Jackson, P. L., Lafleur, M. F., Malouin, F., Richards, C., & Doyon, J. (2001). Potential role of mental practice using motor imagery in neurologic rehabilitation. Archives of physical medicine and rehabilitation, 82(8), 1133- 1141.
Kleim, J. A., & Jones, T. A. (2008). Principles of experience-dependent neural plasticity: implications for rehabilitation after brain damage. Journal of Speech, Language, and Hearing Research, 51(1), S225-S239.
Liepert, J., Miltner, W. H. R., Bauder, H., Sommer, M., Dettmers, C., Taub, E., & Weiller, C. (1998). Motor cortex plasticity during constraint-induced movement therapy in stroke patients. Neuroscience letters, 250(1), 5-8.
Linazasoro, G. (2006). Plasticity in PD: from compensatory usefulness to negative aberrant behaviours. Focus Parkinson Dis, 18, 5-9.
Lövdén, M., Wenger, E., Mårtensson, J., Lindenberger, U., & Bäckman, L. (2013). Structural brain plasticity in adult learning and development. Neuroscience & Biobehavioral Reviews, 37(9), 2296-2310.
Lum, P. S., Burgar, C. G., Shor, P. C., Majmundar, M., & Van der Loos, M. (2002). Robot-assisted movement training compared with conventional therapy techniques for the rehabilitation of upper-limb motor function after stroke.Archives of physical medicine and rehabilitation, 83(7), 952-959.
Murphy, T. H., & Corbett, D. (2009). Plasticity during stroke recovery: from synapse to behaviour. Nature Reviews Neuroscience, 10(12), 861-872.
Pascual-Leone, A., Dang, N., Cohen, L. G., Brasil-Neto, J. P., Cammarota, A., & Hallett, M. (1995). Modulation of muscle responses evoked by transcranial magnetic stimulation during the acquisition of new fine motor skills. Journal of neurophysiology, 74, 1037-1037.
Sharma, N., Pomeroy, V. M., & Baron, J. C. (2006). Motor imagery a backdoor to the motor system after stroke?. Stroke, 37(7), 1941-1952.
Teixeira-Salmela, L. F., Olney, S. J., Nadeau, S., & Brouwer, B. (1999). Muscle strengthening and physical conditioning to reduce impairment and disability in chronic stroke survivors. Archives of physical medicine and rehabilitation, 80(10), 1211-1218.
Brain Nerd 