17 Neuromechanics of Parkinson’s Disease

Basal Ganglia and Parkinson’s Disease

The process of aging in human beings has always been one of the chief focuses of medical interventions in society. For centuries, mankind has been looking for some sort of “fountain of youth”, and to this point we can say with some confidence that no such thing exists. As the human body ages, the potential for a host of different diseases increases. In current medical circles, no disease is as alarming or confusing as Parkinson’s disease. Parkinson’s disease attacks the brain similarly to the way cancer does, and many medical professionals are still baffled by exactly how this disease begins in the body. While Parkinson’s disease affects many areas of the brain, no area of the brain is as important to understanding the effects of Parkinson’s disease as the basal ganglia.

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Up until recently, the basal ganglia has been one of the most difficult areas of the brain to study due to its central positioning within the brain, multiple nuclei, and complicated role in brain function (Graybiel, 2000). Recent advances in brain imaging such as positive emission tomography (PET) and single photon emission computed tomography (SPECT) have helped scientists gain a better understanding of the basal ganglia. In a healthy adult brain, the basal ganglia carries out many functions involved with motor coordination, planning, and task specific decision making (Rocha et al., 2023). The basal ganglia is mainly responsible for sending dopaminergic signals to the premotor and motor cortex to initiate movement. However, Parkinson’s disease seriously impairs the basal ganglia’s ability to initiate signals.

Parkinson’s disease is characterized by tremors, muscle rigidity, difficulty planning and coordinating movements, and speech changes (Mayo Clinic, 2024). Patients with Parkinson’s disease will likely also experience depressive symptoms as a result of overall lower dopamine levels in the brain. Parkinson’s disease causes a protein called alpha-synuclein to uncontrollably build up into sticky clumps called Lewy bodies (Jellinger & Korczyn., 2023). Lewy bodies then attach to specific dopaminergic transmitters in the basal ganglia and alter the transmission of movement signals to the premotor and motor cortex. The impairment of basal ganglia functions causes a cascading, negative effect on the rest of the brain.

Medications to treat the symptoms of Parkinson’s disease do exist, however there currently is no known cure for the disease. Dopaminergic medications such as Levodopa have been shown to help patients manage symptoms of Parkinson’s, but much more research is needed in the area of prevention. Levodopa acts as a precursor to dopamine in the brain, while also calming down the overactive singals in the motor cortex (LeWitt & Fahn, 2016). Recently, methods of deep brain stimulation have shown promising results for the treatment of Parkinson’s disease. Inhibition of the subthalamic nucleus has been shown to suppress symptoms of Parkinsons disease in human patients (Benabid, 2003). However, deep brain stimulation can be very expesinve, up to and beyond $39,000 for a full round of treatment. Because of the expense, one of the most successful and cost effective interventions for individuals with Parkinson’s disease is a comprehensive exercise program to help maintain movement and motor control (Cleveland Clinic, 2022).

Parkinson’s Disease and Motor Control

While Parkinson’s is a neurodegenerative disease, most of its symptoms occur in the bodies of patients rather than in their brains. Parkinson’s affects the way the basal ganglia communicates with the motor and premotor cortices. Specifically, Lewy bodies in the basal ganglia drastically alter the amount and frequency of dopaminergic signals sent from the basal ganglia to different parts of the motor cortex (Blandini et al., 2000). The result of such haywire signals from the basal ganglia is an overproduction of signals from the premotor cortex–the area of the brain responsible for motor planning–which causes the motor cortex to send scattered, random impulses down the central nervous system (Konczak et al., 2009). These random impulses cause a host of problems for overall motor function, gait, and limb coordination.

Video above demonstrates the gait of Parkinson’s patients

Patients with Parkinson’s disease face a number of physical challenges, however one of the most concerning problems is an overall decline in proprioceptive abilities (Konczak et al., 2009). Simply put, proprioception is a human being’s ability to detect where their body is in space and coordinate movement without looking (Tuthill & Azim, 2018). Other common symptoms of Parkinson’s disease include delayed movement initiation, tremors at rest and while moving, slowed movements, joint rigidity, and postural instability (Mazzoni et al., 2012). These issues are a result of depleted dopaminergic signaling, a poorly functioning basal ganglia, and overall neural depletion. Issues with speech formation, particularly vowel sound creation have also been reported in Parkinson’s patients, though less common than physical symptoms.

Doctors traditionally prescribe Levodopa to patients with Parkinson’s disease as it boosts dopamine production and signaling in the brain. Levodopa helps minimize the physical symptoms of Parkinson’s disease, although it doesn’t slow disease progression and has limited effectiveness during the later stages of the disease’s progression (Hauser, 2009). Research has shown that people who exercise regularly are at a lower risk of developing Parkinson’s disease, and that patients dealing with the disease can use different forms of exercise as a therapeutic treatment for physical symptoms (Xu et al., 2019). It’s not clear exactly what causes Parkinsons disease, but evidence suggests that it’s mainly genetic and could be caused by exposure to industrial pesticides.

References

Benabid, A. L. (2003). Deep brain stimulation for Parkinson’s disease. Current opinion in neurobiology, 13(6), 696-706.

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Bloem, B. R., Okun, M. S., & Klein, C. (2021). Parkinson’s disease. The Lancet, 397(10291), 2284–2303. https://doi.org/10.1016/S0140-6736(21)00218-X

Cleveland Clinic. (2022, April 15). Parkinson’s disease: Causes, Symptoms, Stages,

Treatment, Support. Cleveland Clinic; Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/8525-parkinsons-disease-an-overview

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Hauser, R. A. (2009). Levodopa: Past, Present, and Future. European Neurology, 62(1), 1–8. https://doi.org/10.1159/000215875

‌Jellinger, K. A., & Korczyn, A. D. (2023). Are dementia with Lewy bodies and Parkinson’s

disease dementia the same disease?. Advances in Surgical and Medical Specialties, 489-524

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LeWitt, P. A., & Fahn, S. (2016). Levodopa therapy for Parkinson disease: a look backward and forward. Neurology, 86(14_supplement_1), S3-S12.

Mayo Clinic. (2024, September 27). Parkinson’s Disease. Mayo Clinic; Mayo Clinic.

https://www.mayoclinic.org/diseases-conditions/parkinsons-disease/symptoms-causes/syc-20376055

Mazzoni, P., Shabbott, B., & Cortes, J. C. (2012). Motor Control Abnormalities in Parkinson’s Disease. Cold Spring Harbor Perspectives in Medicine, 2(6), a009282–a009282. https://doi.org/10.1101/cshperspect.a009282

‌Rocha, G. S., Freire, M. A., Britto, A. M., Paiva, K. M., Oliveira, R. F., Fonseca, I. A., … & Cavalcanti, J. R. (2023). Basal ganglia for beginners: the basic concepts you need to know and their role in movement control. Frontiers in Systems Neuroscience, 17, 1242929.

Tuthill, J. C., & Azim, E. (2018). Proprioception. Current Biology, 28(5), R194–R203. https://doi.org/10.1016/j.cub.2018.01.064

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