According to the Center for Disease Control and Prevention, approximately 795,000 individuals have a stroke in the United States each year, and out of this alarming large population, nearly 80 percent experience motor dysfunction and impairments. As the diagnoses rates of both acute and chronic stroke symptoms continue to increase globally, reform of existing therapies and search for new methods of neurorehabilitation have long been in the call for. The greater population often overlook or do not appreciate the vast interconnectedness of neural pathways that construct the privilege of motor abilities. Motor functions depend on a wide array of ascending and descending pathways including sensory and proprioceptive devices, and the immensely complex engagement of higher brain regions such as the premotor and primary cortex along with the cerebellum and each of their distinctly different upper motor neuron activity. On an extensively micro molecular level understanding of the nervous system’s control of motor capabilities, each of these regions depend on specific neurotransmitters and their respective receptors to initiate a cascade of events that work to activate motor abilities and visual-spatial awareness. Acetylcholine and their respective ionotropic (nicotinic acetylcholine receptors) and G-coupled protein receptor (muscarinic acetylcholine receptors), work to construct a mural of peripheral activity at neuromuscular junctions in order to facilitate distal and proximal extremity muscular functions. Additionally, glutamate and its respective receptors NMDAR (N-methyl-D-aspartate) and AMPAR (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) habituate a variety of locations in the upper regions of the brain and heavily contribute to the upper motor neuron functions. When injuries to the central nervous system occur as a response to the extremities of stroke effects, a number of inhibitions to previously stated pathways and their molecular components that influence symptoms of motor impairments occur. Classical training-based interventions such as physical, occupational, or language therapy as well as novel multimodal approaches like, e.g., mirror therapy or music-based therapy, have all been shown to enhance functional recovery, albeit to variable degrees.2 Though it has been shown that physical therapies have been successful in functionally reorganizing motor functions in stroke patients most significant improvements occur in the first few weeks post-stroke, often reaching a relative plateau after 3 months with less significant recovery subsequently.2 The imitations of physical methods of enhancing motor impairments has pushed physician and neurophysiological researchers, alike, to seek out new approaches to combat symptoms of motor dysfunction. One effective mechanism has been the practice of non-invasive brain stimulation techniques like transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (TDCS) which can be used to modulate neural plasticity, in which motor improvements upon TMS-evoked inactivation of contralesional M1 can be observed in the first week post-stroke in patients with mild motor deficits.2 These methods rely heavily on the concept of central nervous system stimulation in which certain regions of the brain that specifically regulate the mechanisms of motor abilities are excited in order to induce forms of positive neuroplasticity. Codependently, these forms of neurorehabilitation have been combined with methods of physical therapies to form a comorbid conditioning in the attempt to generate more successful outcomes.
In addition to the array of methods that primarily concentrate on the stimulation of central nervous system components, research such as that of Vincent Chen and his colleague’s amaze the world of neurobiology by proposing the influence of stimulating peripheral sensory and proprioceptive receptors in order to elicit a form of mirror and feedforward mechanisms to perhaps enhance motor functions. In this study subjects received electrical intervention twice a week for eight weeks and finished all assessment sessions including follow-up. The electrical signal group received 40-minute sensory level electrical stimulus prior to motor training and the control group received sham-electrical signaling instead.1 Though this research remains in the infancy stage, it has shown remarkable outcomes in which they reported an increase in corticomuscular activity in beta band which suggested that during motor relearning, the motor cortex has stronger connectivity between the central nervous system and muscles at the periphery.1 Research in neurophysiology calls for pioneers such as those aforementioned in order to further advance universal understanding of methods that could combat not just impairments induced by stroke but, ultimately, all forms of neurologic motor impediments.
Works Cited
Chen, Vincent; Chou, Li-Wei; Fregni, Felipe; Kao, Chung-Lan; Pan, Li-Ling; Tsai, Mei-Wun; Wei, Shun-Hwa; Yang, Wen-Wen. (2018). Effects of 8-Week Sensory Electrical stimulation combined with motor training on EEG-EMG Coherence and Motor Function in Individuals with Stroke, Scientific Reports.
Grefkes, C., Fink, G.R. Recovery from Stroke: Current Concepts and Future perspectives. Neurol. Res. Pract. 2, 17 (2020). https://doi.org/10.1186/s42466-020-00060-6
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