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== Introduction to the Basal Ganglia ==
== Introduction to the Basal Ganglia ==
<blockquote>
[[File:Overview of the basal ganglia - Kenhub.png|alt=Overview of the basal ganglia (corpus striatum) - lateral view|300x300px|Overview of the basal ganglia (corpus striatum) - lateral view|thumb]]
The '''basal ganglia''' is group of subcortical nuclei within the brain that controls motor control, motor learning, executive functions, emotional behaviours, and play an important role in reward and reinforcement, addictive behaviours and habit formation.<ref name=":0" />  </blockquote>[[File:Overview of the basal ganglia - Kenhub.png|alt=Overview of the basal ganglia (corpus striatum) - lateral view|600x600px|Overview of the basal ganglia (corpus striatum) - lateral view|thumb]]The basal ganglia are located at the base of the forebrain.<ref>Yanagisawa N. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6117491/ Functions and dysfunctions of the basal ganglia in humans.] Proc Jpn Acad Ser B Phys Biol Sci. 2018;94(7):275-304. </ref> Disruption of the basal ganglia network leads to various movement disorders,<ref name=":0" /> such as [[Parkinson's]] and [[Huntington Disease|Huntington's Disease.]]
The '''basal ganglia''' are a group of subcortical nuclei, located at the base of the forebrain,<ref>Yanagisawa N. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6117491/ Functions and dysfunctions of the basal ganglia in humans.] Proc Jpn Acad Ser B Phys Biol Sci. 2018;94(7):275-304. </ref> that is primarily involved in motor control, as well as motor learning, executive functions and emotional behaviours. It also plays an important role in reward and reinforcement, addictive behaviours and habit formation.<ref name=":0">Lanciego JL, Luquin N, Obeso JA. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543080/ Functional neuroanatomy of the basal ganglia.] Cold Spring Harbor perspectives in medicine. 2012 Dec 1;2(12):a009621.</ref>
 
The classical basal ganglia model shows the connectivity between basal ganglia and [[Cerebral Cortex|cortex]] through two pathways with opposing effects for the proper execution of movement<ref name=":0">Lanciego JL, Luquin N, Obeso JA. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543080/ Functional neuroanatomy of the basal ganglia.] Cold Spring Harbor perspectives in medicine. 2012 Dec 1;2(12):a009621.</ref>.


This model has been modified to be viewed as multiple parallel loops and re-entering circuits whereby motor, associative, and limbic territories are engaged. These circuits deal mainly in the control of movement, behaviour, and emotions. These parallel circuits subserve the other functions of the basal ganglia engaging associative and limbic territories.<ref name=":0" />
Basal ganglia network dysfunction leads to various movement disorders,<ref name=":0" /> such as [[Parkinson's]] and [[Huntington Disease|Huntington's Disease.]]
== Structure ==
== Structure of the Basal Ganglia ==
[[File:PD Basal Ganglia etc.png|alt=A line diagram of the main structures of the basal ganglia|left|frameless]][[File:PD Basal ganglia .jpg|middle|frameless]]
[[File:PD Basal Ganglia etc.png|alt=A line diagram of the main structures of the basal ganglia|left|frameless|Basal ganglia.]][[File:PD Basal ganglia .jpg|middle|frameless]]
The largest component of the basal ganglia is the '''corpus striatum.''' The corpus striatum is made up of the '''caudate nucleus''' and '''lenticular nuclei''', which in turn is made up of the '''putamen''', '''globus pallidus externus''', and '''globus pallidus internus.''' The '''subthalamic nucleus''' (STN), and the '''substantia nigra''' (SN) are also components of the basal ganglia. These structures intricately synapse onto one another to promote or antagonize movement.<ref name=":1">Young CB, Sonne J. [https://www.ncbi.nlm.nih.gov/books/NBK537141/ Neuroanatomy, basal ganglia.] InStatPearls [Internet] 2018 Dec 28. StatPearls Publishing.</ref>


Divisions of the basal ganglia i.e. '''subcortical nuclei''':
The '''corpus striatum''' is the largest component of the basal ganglia'''.''' It contains the '''caudate nucleus''' and '''lenticular nuclei''', which is made up of the '''putamen''', '''globus pallidus externus''', and '''globus pallidus internus.''' The '''subthalamic nucleus''' (STN), and the '''substantia nigra''' (SN) are also components of the basal ganglia. These structures work together to promote or inhibit movement.<ref name=":1">Young CB, Sonne J. [https://www.ncbi.nlm.nih.gov/books/NBK537141/ Neuroanatomy, basal ganglia.] InStatPearls [Internet] 2018 Dec 28. StatPearls Publishing.</ref>[[File:Striatum.png|400x400px|thumb|Doral Corpus Striatum ]]
[[File:Striatum.png|400x400px|thumb|Doral Corpus Striatum ]]
* '''Corpus Striatum''': a heterogeneous structure with a volume of around 10 cm<sup>3</sup>. It receives afferent inputs from various cortical and subcortical structures and sends outputs to different basal ganglia nuclei.<ref name=":0" /> There are two main divisions in the corpus striatum:    
# '''Corpus Striatum'''- Has a volume of approximately 10 cm. It is a heterogeneous structure that receives afferents from several cortical and subcortical structures and projects to various basal ganglia nuclei.<ref name=":0" /> Within the striatum, there are two main divisions:    
** '''Dorsal Striatum''' (DS) (shown in red in the image): mostly involved in the control of conscious motor movements and executive functions. The dorsal striatum consists of the caudate nucleus and the putamen. The internal capsule is a white matter nerve tract in the dorsal striatum that separates the caudate nucleus from the putamen.    
#* '''Dorsal striatum''' (DS) see image, shown in red. Primarily involved in control over conscious motor movements and executive functions.  The dorsal striatum consists of the caudate nucleus and the putamen. A white matter nerve tract (the internal capsule) in the dorsal striatum separates the caudate nucleus and the putamen.    
** '''Ventral Striatum''': involved in the limbic functions of reward and aversion. It is made up of the nucleus accumbens and the olfactory tubercle.<ref name=":1" /> 
#* Ventral striatum, responsible for limbic functions of reward and aversion. Consists of nucleus accumbens and the olfactory tubercle.<ref name=":1" /> 
* Internal and external segments of the '''Globus Pallidus''': together, the globus pallidus and putamen form the lentiform (or lenticular) nucleus.<ref>Javed N, Cascella M. [https://www.ncbi.nlm.nih.gov/books/NBK557755/ Neuroanatomy, Globus Pallidus.] [Updated 2023 Feb 20]. In: StatPearls [Internet].</ref>
# Internal and External segments of '''Globus Pallidus''' (the globus pallidus and putamen were considered one structure, collectively referred to as the ''lentiform'' or ''lenticular'' nucleus until early 19th century<ref>Javed N, Cascella M. [https://www.ncbi.nlm.nih.gov/books/NBK557755/#:~:text=The%20globus%20pallidus%20lies%20at,control%20conscious%20and%20proprioceptive%20movements. Neuroanatomy, Globus Pallidus.] [Updated 2023 Feb 20]. In: StatPearls [Internet].</ref>).
* '''Subthalamic Nucleus''' (STN): a lens-shaped cell group that makes up a large part of the subthalamus.<ref>Basinger H, Joseph J. Neuroanatomy, Subthalamic Nucleus. [Updated 2022 Oct 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559002/</ref> 
# '''Subthalamic Nucleus''' (STN) -  a lens-shaped cell group that makes up the largest part of the subthalamus.<ref name=":0" /> 
* '''Substantia Nigra''' (SN) - (which means "black substance" in Latin): while the substantia nigra is located in the midbrain, it is considered part of the basal ganglia. This long nucleus has two parts: 1) pars compacta and 2) pars reticulata. Degeneration of the pars compacta decreases the amount of available dopamine.<ref>Jacobs LK, Sapers BL. [https://www.sciencedirect.com/science/article/pii/B9780443068980000335 Neurological Disease.] InPerioperative Medicine 2011 (pp. 343-359). Springer, London.</ref><br />
# '''Substantia Nigra''' (SN) - (“black substance” in Latin) is a long nucleus located in the midbrain but considered functionally a part of the BG because of its reciprocal connections with other brainstem nuclei. It consists of two components, the pars compacta and the pars reticulata, which have different connections and use different neurotransmitters. <ref>Jacobs LK, Sapers BL. [https://www.sciencedirect.com/science/article/pii/B9780443068980000335 Neurological Disease.] InPerioperative Medicine 2011 (pp. 343-359). Springer, London.</ref><br />
The two optional videos below provide further information on the structure and function of the basal ganglia:<div class="row">
The 2 videos below outline basal ganglia concepts.<div class="row">
   <div class="col-md-6"> {{#ev:youtube|OD2KPSGZ1No|250}} <div class="text-right"><ref>Neuroscientifically Challenged Basal ganglia . Available from:  https://www.youtube.com/watch?v=OD2KPSGZ1No [last accessed 14/01/2020]</ref></div></div>
   <div class="col-md-6"> {{#ev:youtube|OD2KPSGZ1No|250}} <div class="text-right"><ref>Neuroscientifically Challenged Basal ganglia . Available from:  https://www.youtube.com/watch?v=OD2KPSGZ1No [last accessed 14/01/2020]</ref></div></div>
   <div class="col-md-6"> {{#ev:youtube|mNc-6q6YAAw|250}} <div class="text-right"><ref>Armando Hasudungan. The Basal Ganglia Clinical Anatomy. Available from: https://www.youtube.com/watch?v=mNc-6q6YAAw [last accessed 05/01/2024]</ref></div></div>
   <div class="col-md-6"> {{#ev:youtube|mNc-6q6YAAw|250}} <div class="text-right"><ref>Armando Hasudungan. The Basal Ganglia Clinical Anatomy. Available from: https://www.youtube.com/watch?v=mNc-6q6YAAw [last accessed 05/01/2024]</ref></div></div>
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== Basal Ganglia - Recent Concepts ==
== Function of the Basal Ganglia  ==
The original functional organization of the basal ganglia was conceived as a loop, in which cortical afferent activity is dispatched to and modulated by the basal ganglia, which subsequently sends back a signal to the cortex to facilitate (or inhibit) motor activity. The basal ganglia were featured as a “go through” station within the motor loop. Current thinking now is that the basal ganglia has several loops, where cortical and subcortical projections interact with internal re-entry loops forming a complex network, ideally designed for selecting and inhibiting simultaneously occurring events and signals<ref name=":0" />.
 The classical basal ganglia model suggested that "information flows through the basal ganglia back to the cortex through two pathways with opposing effects for the proper execution of movement."<ref name=":02">Lanciego JL, Luquin N, Obeso JA. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3543080/ Functional neuroanatomy of the basal ganglia.] Cold Spring Harbor perspectives in medicine. 2012 Dec 1;2(12):a009621.</ref> In this "loop", cortical input is sent to the basal ganglia, where it is modified and then sent back to the cortex. As a result of this feedback, motor activity is either facilitated or inhibited.<ref name=":02" />  


Coronal slices that have been superimposed to include the involved basal ganglia structures. The' '''+'''' and ''''-'''<nowiki/>' signs at the point of the arrows indicate respectively whether the pathway has an excitatory or inhibitory effect. Green arrows refer to excitatory '''glutamatergic''' pathways, red arrows refer to inhibitory '''GABAergic''' pathways and turquoise arrows refer to '''dopaminergic''' pathways that are excitatory on the direct pathway and inhibitory on the indirect pathway. Note that dis-inhibitory pathways in effect are excitatory on the feedback to the cortex, while dis-dis-inhibitory pathways in effect are inhibitory.<ref name=":0" />
This model has been reviewed and updated. It is now believed that the basal ganglia have "multiple parallel loops and re-entering circuits whereby motor, associative, and limbic territories are engaged mainly in the control of movement, behaviour, and emotions."<ref name=":02" />
 
The following image illustrates various excitatory and inhibitory pathways from the basal ganglia to the cortex.<ref name=":0" />
[[File:Basal ganglia circuits.png|center|alt=This is a diagram of the flow of excitatory and inhibitory pathways through the basal ganglia.|frame|Basal ganglia circuits]]
[[File:Basal ganglia circuits.png|center|alt=This is a diagram of the flow of excitatory and inhibitory pathways through the basal ganglia.|frame|Basal ganglia circuits]]


== Pathophysiology ==
== Associated Conditions ==
The basal ganglia are particularly associated with movement disorders. Basal ganglia associated damage or dysfunction produces (1) tremors, (2) involuntary muscle movements, (3) abnormal increase in tone, (4) difficulty initiating movements, and (5) abnormal posture.  
Dysfunction of the basal ganglia is associated with specific movement disorders, and can cause issues such as (1) tremor, (2) involuntary muscle movements, (3) abnormal increase in tone, (4) difficulty initiating movements, and (5) abnormal posture. The following sections discuss movement disorders associated with basal ganglia dysfunction.<ref name=":1" />


Movement disorders comprise a variety of motor problems, not all of which are associated with dysfunction of the basal ganglia.<ref name=":1" />
=== Parkinson's ===
[[Parkinson's]] is the second most common neurodegenerative disorder. Its aetiology is multifactorial, with both genetic and environmental risk factors identified.<ref>Ben-Shlomo Y, Darweesh S, Llibre-Guerra J, Marras C, San Luciano M, Tanner C. The epidemiology of Parkinson's disease. The Lancet. 2024;403(10423):283-92.</ref> Parkinson's is characterised "by the progressive loss of dopaminergic neurons and the formation of Lewy bodies in the affected brain areas".<ref name=":3">Zhou, ZD, Yi LX, Wang DQ, Lim TM, Tan EK. [https://translationalneurodegeneration.biomedcentral.com/articles/10.1186/s40035-023-00378-6 Role of dopamine in the pathophysiology of Parkinson’s disease]. Transl Neurodegener. 2023;12(44). </ref> Because of the degeneration of dopaminergic neurons, there is less dopamine available in the substantia nigra and striatum, which causes various clinical signs of Parkinson's, such as:<ref name=":3" />


=== Parkinson's ===
* tremor
[[Parkinson's]] is the most notorious disease of the basal ganglia<ref name=":3">Alexander GE. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181806/#:~:text=Parkinson's%20disease%20(PD)%2C%20which,to%20characteristic%20motor%20disturbances%20that Biology of Parkinson's disease: pathogenesis and pathophysiology of a multisystem neurodegenerative disorder]. Dialogues Clin Neurosci. 2004;6(3):259-280. </ref>.
* postural instability
* [[bradykinesia]]
* muscle rigidity


'''Classic clinical symptoms include''':
=== Huntington's Disease ===
[[Huntington Disease|Huntington's disease]]<ref name=":4">Matz OC, Spocter M. The Effect of Huntington's Disease on the Basal Nuclei: A Review. Cureus. 2022;14(4):e24473.</ref> is a progressive, inherited neurodegenerative disease. It is associated with neuropsychiatric symptoms, movement disorders (usually chorea) and cognitive impairment / dementia.<ref name=":5">Stoker TB, Mason SL, Greenland JC, Holden ST, Santini H, Barker RA. [https://pn.bmj.com/content/practneurol/22/1/32.full.pdf Huntington's disease: diagnosis and management]. Pract Neurol. 2022 Feb;22(1):32-41. </ref><ref>Medina A, Mahjoub Y, Shaver L, Pringsheim T. [https://movementdisorders.onlinelibrary.wiley.com/doi/full/10.1002/mds.29228 Prevalence and incidence of Huntington's disease: an updated systematic review and meta-analysis]. Mov Disord. 2022 Dec;37(12):2327-35. </ref> Huntington's disease occurs in individuals with a CAG expansion in the huntingtin gene.<ref name=":5" />  There is neurodegeneration in many parts of the brain, the striatum<ref name=":5" /> and cortex are particularly affected.<ref name=":6">Kim A, Lalonde K, Truesdell A, Gomes Welter P, Brocardo PS, Rosenstock TR, Gil-Mohapel J. [https://www.mdpi.com/1422-0067/22/16/8363 New avenues for the treatment of Huntington's disease]. Int J Mol Sci. 2021 Aug 4;22(16):8363. </ref>  Symptoms usually start in individuals aged between 30-50 years. A key motor symptom is chorea (i.e. "brief, involuntary movements that generally affect the trunk, face, and arms"<ref name=":6" />). Chorea affects voluntary movements, ultimately affecting walking, speaking and swallowing.<ref name=":6" />


* [[Bradykinesia]]
Other motor signs include:<ref name=":6" />
* Resting tremor
* Postural instability
* Shuffling gait


* bradykinesia
* dystonia
* hyperreflexia
* decreased speed of eye saccades


This disease is a result of neurodegeneration of the SNpc [[Dopamine|dopaminergic]] neurons. Often found in the Parkinsonian striatum, alpha-synuclein protein aggregates form toxic Lewy bodies, which are inclusions within neurons. The substantia nigra, due to degeneration, loses its grossly visible dark pigmentation, a concomitant sign of dopamine biosynthesis dysfunction. This loss of dopamine depresses the nigrostriatal pathway<ref name=":3" />. With decreased dopaminergic input the striatum exerts less positive motor activity and more negative motor inhibition. This gives the characteristic hypokinetic dysfunction found in these patients.<ref name=":1" />
Cognitive impairments include:<ref name=":6" />


=== Huntington's Disease ===
* decreased executive function (difficulty with attention, concentration, multi-tasking, decision making)
[[Huntington Disease|Huntington's disease]]<ref name=":4">Matz OC, Spocter M. The Effect of Huntington's Disease on the Basal Nuclei: A Review. Cureus. 2022;14(4):e24473.</ref> is a hyperkinetic movement disorder. Its cause is a genetic defect manifesting as a CAG repeat on chromosome 4p on the HTT gene. This creates an abnormally long Huntington gene which leads to neuronal death in the caudate and the putamen. The indirect pathway is interrupted and leads to a hyperkinetic presentation.
* depression
* loss of memory
* decreased insight


Symptoms include
The most common psychiatric conditions are:<ref name=":6" />


* Involuntary movements (such as [[chorea]])
* depression
* Cognitive degeneration
* irritability
* Psychiatric dysfunction<ref name=":4" />
* increased impulsivity


=== Hemiballism ===
=== Hemiballism ===
Hemiballism<ref name=":5">Rocha Cabrero F, De Jesus O. Hemiballismus. [Updated 2023 Aug 23]. In: StatPearls [Internet].</ref> (from the Greek “to throw”) is used to describe hyperkinetic, involuntary, forceful movements of the ipsilateral arm and leg. Commonly a lesion in the contralateral subthalamic nuclei causes hemiballism. Given that the subthalamus is part of the indirect pathway this lesion reduces or eliminates indirect pathway signaling, leading to a relative overabundance of activity in the direct pathway. Such causes include [[stroke]], [[Overview of Traumatic Brain Injury|traumatic brain injury]], [[Motor Neurone Disease MND|amyotrophic lateral sclerosis]], nonketotic hyperglycemia, neoplasm, vascular malformation, and other causes.<ref name=":5" />
Hemiballism (from the verb “to throw” in Greek) is a rare movement disorder that causes "high amplitude movement of an entire limb or limbs on one side of the body."<ref name=":7">Hawley JS, Weiner WJ. Hemiballismus: current concepts and review. Parkinsonism Relat Disord. 2012 Feb;18(2):125-9.</ref> Hemiballism can be caused by several conditions, but acute cases are often associated with focal lesions in the contralateral basal ganglia and subthalamic nucleus lesion.<ref name=":7" /> Individuals with hemiballism tend to have a good prognosis.<ref name=":7" />


=== Tourette Syndrome ===
=== Tourette Syndrome ===
Tourette syndrome has been shown to have a significant neurological basal ganglia component which manifests as sudden, repetitive uncontrolled movements and vocalizations, called “tics.” These tics have been associated with dysfunction of the GABAergic projections from the striatum, leading to a relative increase in dopaminergic activity much like in hemiballism and Huntington’s disease<ref>Caligiore D, Mannella F, Arbib MA, Baldassarre G. Dysfunctions of the basal ganglia-cerebellar-thalamo-cortical system produce motor tics in Tourette syndrome. PLoS Comput Biol. 2017;13(3):e1005395. </ref>.
Tourette syndrome is a persistent neurodevelopmental condition associated with motor and phonic tics.<ref name=":2">Johnson KA, Worbe Y, Foote KD, Butson CR, Gunduz A, Okun MS. Tourette syndrome: clinical features, pathophysiology, and treatment. Lancet Neurol. 2023 Feb;22(2):147-58. </ref> While its pathophysiology is not fully understood, tics may be due to "inhibitory dysfunction within the sensorimotor cortico-basal ganglia network".<ref name=":2" /> Tourette syndrome can significantly impact quality of life, and treatment options are expanding.<ref name=":2" />
 
Additionally, parts of the basal ganglia play a key role in reward and reinforcement, addictive behaviours and habit formation. Pathophysiological processes underlying psychiatric disorders such as [[depression]] and obsessive-compulsive disorder (OCD) involve the basal ganglia and their connections with many other structures (particularly to the prefrontal cortex and the limbic system).<ref>Stathis P, Panourias IG, Themistocleous MS, Sakas DE. [https://www.ncbi.nlm.nih.gov/pubmed/17691350/ Connections of the basal ganglia with the limbic system: implications for neuromodulation therapies of anxiety and affective disorders]. InOperative Neuromodulation 2007 (pp. 575-586). Springer, Vienna. </ref> In terms of cognitive disorders, basal ganglia abnormalities have been found in individuals with [[schizophrenia]]<ref>Kéri S. [https://www.ncbi.nlm.nih.gov/m/pubmed/17854895/ Interactive memory systems and category learning in schizophrenia]. Neuroscience & Biobehavioral Reviews. 2008 Jan 1;32(2):206-18. </ref> and may explain the presence of  learning deficits associated with the disorder.<blockquote>[[Lacuna Infarcts ( Small Vessel Disease)|Silent Cerebral Infarcts]] - of interest a 2008 study found that approx. 5% of healthy middle-aged adults have microlesions in their basal ganglia. <ref>Das RR, Seshadri S, Beiser AS, Kelly-Hayes M, Au R, Himali JJ, Kase CS, Benjamin EJ, Polak JF, O'Donnell CJ, Yoshita M. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2712254/ Prevalence and correlates of silent cerebral infarcts in the Framingham offspring study.] Stroke. 2008 Nov 1;39(11):2929-35.</ref></blockquote>
 
== Physiotherapy Interventions ==
The importance and value of [[Exercise Physiology|exercise]] is becoming more and more apparent for a whole raft of health conditions. Recent evidence regarding exercise and basal ganglia impairments states:[[File:Exercise older person.jpg|right|frameless]]
# A 2016 study by Becker et al<ref>Niemann C, Godde B, Staudinger UM, Voelcker-Rehage C. Exercise-induced changes in basal ganglia volume and cognition in older adults. Neuroscience. 2014;281:147-163. </ref> into cognitive performance and basal ganglia changes concluded that physical activity, especially motor fitness level training, to be a promising tool causing structural changes in the basal ganglia and potential to diminish the cognitive decline in older adults and to support academic success in children and young adults.
# Exercise is beneficial and should be routinely prescribed in the management of Parkinson's (may aid in basal ganglia function)<ref name=":2" />.
# Exercise effects on basal ganglia damage:<ref name=":2">Petzinger GM, Fisher BE, Akopian G, Holschneider DP, Wood R, Walsh JP, Lund B, Meshul C, Vuckovic M, Jakowec MW. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3691073/ The role of exercise in facilitating basal ganglia function in Parkinson’s disease]. Neurodegenerative disease management. 2011 Apr;1(2):157-70. </ref>
#* The adult brain possesses a tremendous capacity for experience-dependent [[neuroplasticity]], even in the context of ageing and neurodegenerative disorders including Parkinson's, where the activation of neurotrophic factors may play a key role.
#* Animal models of [[Parkinson's Pharmacotherapy|dopamine]] depletion are beginning to reveal the underlying mechanisms by which exercise can remodel the brain through alteration in neuronal synaptic connections, especially dopaminergic and glutamatergic neurotransmission within the basal ganglia.
#Epidemiological studies, clinical observations, and animal research indicate that appropriately dosed physical activity and exercise may not only reduce the risk of developing Parkinson's in vulnerable populations but also benefit these patients by potentially protecting the residual nigrostriatal dopamine neurons or directly restoring the dysfunctional cortico-basal ganglia motor control circuit, and these benefits may be mediated by exercise-triggered production of endogenous neuroprotective molecules such as neurotrophic factors<ref>Hou L, Chen W, Liu X, Qiao D, Zhou FM. [https://www.frontiersin.org/articles/10.3389/fnagi.2017.00358/full Exercise-induced neuroprotection of the nigrostriatal dopamine system in Parkinson's disease]. Frontiers in aging neuroscience. 2017 Nov 3;9:358.</ref>.
#Exercise has been implicated in modulating dopamine and glutamate neurotransmission, altering synaptogenesis, and increasing cerebral blood flow. In addition, recent evidence supports that the type of exercise may have regional effects on brain circuitry, with skilled exercise differentially affecting frontal-striatal related circuits to a greater degree than pure aerobic exercise (with skilled exercise differentially affecting frontal related circuits more so than pure aerobic exercise). Thus proving that a combination of these exercises is very advantageous in prolonging the progression of Parkinson's<ref>Petzinger GM, Holschneider DP, Fisher BE, McEwen S, Kintz N, Halliday M, Toy W, Walsh JW, Beeler J, Jakowec MW. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4621077/ The effects of exercise on dopamine neurotransmission in Parkinson’s disease: targeting neuroplasticity to modulate basal ganglia circuitry.] Brain plasticity. 2015 Jan 1;1(1):29-39.</ref>.


== References ==
== References ==

Latest revision as of 03:36, 26 June 2024

Original Editor - Lucinda Hampton Top Contributors - Lucinda hampton, Lauren Heydenrych, Jess Bell, Kim Jackson, Tony Lowe, Stacy Schiurring, Joao Costa, Rucha Gadgil and Aminat Abolade
This article or area is currently under construction and may only be partially complete. Please come back soon to see the finished work! (26/06/2024)


Introduction to the Basal Ganglia[edit | edit source]

Overview of the basal ganglia (corpus striatum) - lateral view
Overview of the basal ganglia (corpus striatum) - lateral view

The basal ganglia are a group of subcortical nuclei, located at the base of the forebrain,[1] that is primarily involved in motor control, as well as motor learning, executive functions and emotional behaviours. It also plays an important role in reward and reinforcement, addictive behaviours and habit formation.[2]

Basal ganglia network dysfunction leads to various movement disorders,[2] such as Parkinson's and Huntington's Disease.

Structure of the Basal Ganglia[edit | edit source]

A line diagram of the main structures of the basal ganglia

PD Basal ganglia .jpg The corpus striatum is the largest component of the basal ganglia. It contains the caudate nucleus and lenticular nuclei, which is made up of the putamen, globus pallidus externus, and globus pallidus internus. The subthalamic nucleus (STN), and the substantia nigra (SN) are also components of the basal ganglia. These structures work together to promote or inhibit movement.[3]

Doral Corpus Striatum
  • Corpus Striatum: a heterogeneous structure with a volume of around 10 cm3. It receives afferent inputs from various cortical and subcortical structures and sends outputs to different basal ganglia nuclei.[2] There are two main divisions in the corpus striatum:  
    • Dorsal Striatum (DS) (shown in red in the image): mostly involved in the control of conscious motor movements and executive functions. The dorsal striatum consists of the caudate nucleus and the putamen. The internal capsule is a white matter nerve tract in the dorsal striatum that separates the caudate nucleus from the putamen.   
    • Ventral Striatum: involved in the limbic functions of reward and aversion. It is made up of the nucleus accumbens and the olfactory tubercle.[3] 
  • Internal and external segments of the Globus Pallidus: together, the globus pallidus and putamen form the lentiform (or lenticular) nucleus.[4]
  • Subthalamic Nucleus (STN): a lens-shaped cell group that makes up a large part of the subthalamus.[5] 
  • Substantia Nigra (SN) - (which means "black substance" in Latin): while the substantia nigra is located in the midbrain, it is considered part of the basal ganglia. This long nucleus has two parts: 1) pars compacta and 2) pars reticulata. Degeneration of the pars compacta decreases the amount of available dopamine.[6]

The two optional videos below provide further information on the structure and function of the basal ganglia:

[7]
[8]


Function of the Basal Ganglia[edit | edit source]

 The classical basal ganglia model suggested that "information flows through the basal ganglia back to the cortex through two pathways with opposing effects for the proper execution of movement."[9] In this "loop", cortical input is sent to the basal ganglia, where it is modified and then sent back to the cortex. As a result of this feedback, motor activity is either facilitated or inhibited.[9]

This model has been reviewed and updated. It is now believed that the basal ganglia have "multiple parallel loops and re-entering circuits whereby motor, associative, and limbic territories are engaged mainly in the control of movement, behaviour, and emotions."[9]

The following image illustrates various excitatory and inhibitory pathways from the basal ganglia to the cortex.[2]

This is a diagram of the flow of excitatory and inhibitory pathways through the basal ganglia.
Basal ganglia circuits

Associated Conditions[edit | edit source]

Dysfunction of the basal ganglia is associated with specific movement disorders, and can cause issues such as (1) tremor, (2) involuntary muscle movements, (3) abnormal increase in tone, (4) difficulty initiating movements, and (5) abnormal posture. The following sections discuss movement disorders associated with basal ganglia dysfunction.[3]

Parkinson's[edit | edit source]

Parkinson's is the second most common neurodegenerative disorder. Its aetiology is multifactorial, with both genetic and environmental risk factors identified.[10] Parkinson's is characterised "by the progressive loss of dopaminergic neurons and the formation of Lewy bodies in the affected brain areas".[11] Because of the degeneration of dopaminergic neurons, there is less dopamine available in the substantia nigra and striatum, which causes various clinical signs of Parkinson's, such as:[11]

Huntington's Disease[edit | edit source]

Huntington's disease[12] is a progressive, inherited neurodegenerative disease. It is associated with neuropsychiatric symptoms, movement disorders (usually chorea) and cognitive impairment / dementia.[13][14] Huntington's disease occurs in individuals with a CAG expansion in the huntingtin gene.[13] There is neurodegeneration in many parts of the brain, the striatum[13] and cortex are particularly affected.[15] Symptoms usually start in individuals aged between 30-50 years. A key motor symptom is chorea (i.e. "brief, involuntary movements that generally affect the trunk, face, and arms"[15]). Chorea affects voluntary movements, ultimately affecting walking, speaking and swallowing.[15]

Other motor signs include:[15]

  • bradykinesia
  • dystonia
  • hyperreflexia
  • decreased speed of eye saccades

Cognitive impairments include:[15]

  • decreased executive function (difficulty with attention, concentration, multi-tasking, decision making)
  • depression
  • loss of memory
  • decreased insight

The most common psychiatric conditions are:[15]

  • depression
  • irritability
  • increased impulsivity

Hemiballism[edit | edit source]

Hemiballism (from the verb “to throw” in Greek) is a rare movement disorder that causes "high amplitude movement of an entire limb or limbs on one side of the body."[16] Hemiballism can be caused by several conditions, but acute cases are often associated with focal lesions in the contralateral basal ganglia and subthalamic nucleus lesion.[16] Individuals with hemiballism tend to have a good prognosis.[16]

Tourette Syndrome[edit | edit source]

Tourette syndrome is a persistent neurodevelopmental condition associated with motor and phonic tics.[17] While its pathophysiology is not fully understood, tics may be due to "inhibitory dysfunction within the sensorimotor cortico-basal ganglia network".[17] Tourette syndrome can significantly impact quality of life, and treatment options are expanding.[17]

References[edit | edit source]

  1. ↑ Yanagisawa N. Functions and dysfunctions of the basal ganglia in humans. Proc Jpn Acad Ser B Phys Biol Sci. 2018;94(7):275-304.
  2. ↑ 2.0 2.1 2.2 2.3 Lanciego JL, Luquin N, Obeso JA. Functional neuroanatomy of the basal ganglia. Cold Spring Harbor perspectives in medicine. 2012 Dec 1;2(12):a009621.
  3. ↑ 3.0 3.1 3.2 Young CB, Sonne J. Neuroanatomy, basal ganglia. InStatPearls [Internet] 2018 Dec 28. StatPearls Publishing.
  4. ↑ Javed N, Cascella M. Neuroanatomy, Globus Pallidus. [Updated 2023 Feb 20]. In: StatPearls [Internet].
  5. ↑ Basinger H, Joseph J. Neuroanatomy, Subthalamic Nucleus. [Updated 2022 Oct 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559002/
  6. ↑ Jacobs LK, Sapers BL. Neurological Disease. InPerioperative Medicine 2011 (pp. 343-359). Springer, London.
  7. ↑ Neuroscientifically Challenged Basal ganglia . Available from: https://www.youtube.com/watch?v=OD2KPSGZ1No [last accessed 14/01/2020]
  8. ↑ Armando Hasudungan. The Basal Ganglia Clinical Anatomy. Available from: https://www.youtube.com/watch?v=mNc-6q6YAAw [last accessed 05/01/2024]
  9. ↑ 9.0 9.1 9.2 Lanciego JL, Luquin N, Obeso JA. Functional neuroanatomy of the basal ganglia. Cold Spring Harbor perspectives in medicine. 2012 Dec 1;2(12):a009621.
  10. ↑ Ben-Shlomo Y, Darweesh S, Llibre-Guerra J, Marras C, San Luciano M, Tanner C. The epidemiology of Parkinson's disease. The Lancet. 2024;403(10423):283-92.
  11. ↑ 11.0 11.1 Zhou, ZD, Yi LX, Wang DQ, Lim TM, Tan EK. Role of dopamine in the pathophysiology of Parkinson’s disease. Transl Neurodegener. 2023;12(44).
  12. ↑ Matz OC, Spocter M. The Effect of Huntington's Disease on the Basal Nuclei: A Review. Cureus. 2022;14(4):e24473.
  13. ↑ 13.0 13.1 13.2 Stoker TB, Mason SL, Greenland JC, Holden ST, Santini H, Barker RA. Huntington's disease: diagnosis and management. Pract Neurol. 2022 Feb;22(1):32-41.
  14. ↑ Medina A, Mahjoub Y, Shaver L, Pringsheim T. Prevalence and incidence of Huntington's disease: an updated systematic review and meta-analysis. Mov Disord. 2022 Dec;37(12):2327-35.
  15. ↑ 15.0 15.1 15.2 15.3 15.4 15.5 Kim A, Lalonde K, Truesdell A, Gomes Welter P, Brocardo PS, Rosenstock TR, Gil-Mohapel J. New avenues for the treatment of Huntington's disease. Int J Mol Sci. 2021 Aug 4;22(16):8363.
  16. ↑ 16.0 16.1 16.2 Hawley JS, Weiner WJ. Hemiballismus: current concepts and review. Parkinsonism Relat Disord. 2012 Feb;18(2):125-9.
  17. ↑ 17.0 17.1 17.2 Johnson KA, Worbe Y, Foote KD, Butson CR, Gunduz A, Okun MS. Tourette syndrome: clinical features, pathophysiology, and treatment. Lancet Neurol. 2023 Feb;22(2):147-58.
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