The basal ganglia are a group of subcortical nuclei that receive input from the cortex and project to the cortex via the thalamus. They consist of the striatum, globus pallidus, substantia nigra, and subthalamic nucleus. The basal ganglia influence motor control and posture through direct and indirect pathways and receive modulatory input from the substantia nigra. Diseases of the basal ganglia result in movement disorders like Parkinson's disease and Huntington's disease.

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Basal Ganglia
• Basal ganglia are a group of deep subcortical
nuclei located at the base of forebrain. They are
primarily involved in control of posture and
movement.
• Basal Ganglia Consist of Four Nuclei
– striatum
• caudate and putamen
– globus pallidus –G.externus, G. internus
– substantia nigra – Pars compacta, Pars reticulata.
– subthalamus

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*They receive inputs mainly from cortex and project to the
cortex via thalamus.
* Basal ganglia via their cortical connections project principal
to brainstem areas that give rise to all extrapyramidal
tracts.
*Therefore, basal ganglia mainly influence extrapyramidal
functions.
*Lesion of basal ganglia produces abnormal movements
and severe deficits in control of posture.
INTRODUCTION

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Inputs.
• The main inputs to basal ganglia come from
cerebral cortex
• Basal ganglia also receive inputs from
thalamus, dorsal raphe nucleus, and
pedunculopontine region of the brainstem.
• Most afferent information enters basal ganglia
via striatum (caudate nucleus and putamen).
ganglia.

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The afferent fibers are:
1.Corticostriate projection: Basal ganglia receive afferents
from all parts of cerebral cortex via corticostriate projection.
• Putamen receives input mainly from the sensory motor
cortex and caudate nucleus receives inputs from
remainder of the cortex.
2. Thalamostriate projection: The centromedian nucleus of
thalamus projects to the striatum via thalamostriate
projections.
3. Raphestriate projection: Striatum also receives input from
dorsal raphe nucleus.
4. Pedunculostriate projection: Pedunculopontine nucleus of
brainstem projects to basal

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The basal ganglia are the
principle subcortical components
of a family of parallel circuits
linking the thalamus with the
cerebral cortex
Figure 57-11
Figure 57-12

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Motor Loop
The main feature of input and output of basal ganglia is that
cerebral cortex projects to striatum, striatum projects to
internal segment of globus pallidus, globus pallidus projects
to thalamus, which projects back to the cortex, completing
the motor loop.
Motor loop forms two major neuronal circuits through basal
ganglia: putamen circuit and
caudate circuit.

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Caudate extends into all lobes
of the cortex and receives a
large input from association
areas of the cortex
Mostly projects to globus
pallidus, no fibers to sub-
thalamus or substantia
nigra
Most motor actions occur as a
result of a sequence of thoughts.
Caudate circuit may play a role
in the cognitive control of motor
functions
Caudate Circuit
Figure 57-12

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Putamen Circuit
Mostly from
premotor and
supplemental
motor cortex to
putamen then
back to motor
cortex. May
play a role
in the
execution
of motor
movement
Figure 57-11

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Connections within NUCLEI of Basal Ganglia
Major connections within the basal ganglia are as follows :
1. Nigrostriatal projection: The pars compacta portion of substantia nigra
projects to striatum. The nigrostriatal projection is dopaminergic.
Degeneration of this system produces parkinsonism.
2. Striatonigral projection: Striatum also projects to substantia nigra. The
striatonigral projection is inhibitory and neurotransmitter secreted in this
pathway is GABA. Degeneration of this pathway produces Huntington’s
disease.
3. Projection from subthalamic nucleus to globus pallidus internus:
Subthalamic nucleus projects to internal segment of globus pallidus.
This projection is excitatory.

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Connections within basal ganglia
Figure 57-14

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Neural Pathways through Basal Ganglia
The inputs, interconnections, and outputs constitute two important neural pathways through the
basal ganglia that are involved in control of motor activities: the direct pathway and the indirect
pathway.
Direct Pathway
Cortex projects to striatum. Striatum projects to globus pallidus internus, which projects to thalamus
and thalamus in turn projects to motor cortex.
1. The projection of cortex to striatum is excitatory (glutaminergic).
2. Projection of striatum to globus pallidus internus is inhibitory (GABAergic), and projection from
globus pallidus internus to the thalamus is inhibitory (GABAergic).
3. Thus, stimulation of striatum results in stimulation of thalamus by disinhibition. The direct
pathway is stimulated during movement. Usually, neurons in the striatum have less resting
background activity.
• During movement, they are activated by inputs from cortex and thalamus.
• Activation of striatum inhibits globus pallidus internus.
• However, pallidal neurons themselves are inhibitory to thalamus.
• Therefore, activation of striatum finally excites the thalamic neurons.
Consequently, the target neurons in the motor cortex are stimulated via thalamocortical projection

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Indirect Pathway
This involves connection from striatum to the external segment of globus pallidus, which projects to
subthalamic nucleus. Subthalamic nucleus projects to internal segment of the globus pallidus,
which in turn projects to thalamus
1. In this pathway, striatum inhibits globus pallidus externus, which inhibits subthalamic nucleus.
2. Subthalamic nucleus activates globus pallidus internus.
3. Therefore, stimulation of striatum activates globus pallidus internus through this indirect
pathway.
4. The final output of striatum through this indirect pathway is inhibitory (as globus pallidus internus
activation inhibits thalamocortical projections).

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Modulation by Nigrostriatal Projections
The direct and indirect pathways have opposite
effects. Normally, there is a balance between
these two pathways. Alteration of activity in either
of the pathways leads to imbalance in motor
output from basal ganglia. Therefore, in basal
ganglia disorders, both hypokinetic and
hyperkinetic features are observed.

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1.Another important connection of these pathways is the
nigrostriatal projections.
• The dopaminergic projections from pars compacta of
substantia nigra to the striatum appear to have an
excitatory influence on the direct pathway and inhibitory
influence on the indirect pathway.
• It also modulates the input from cortex to the striatum.
2. Therefore, projection from substantia nigra to striatum is
important physiologically.
3. The neurons in the striatum are cholinergic.
4. In striatum, the ratio of acetylcholine and dopamine keeps
the striatal neurons active. Alteration in this Ach-DA ratio
results in abnormalities in motor activities.

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Motor Function of the Basal Ganglia
• Control of complex patterns of motor activity
– writing.
– using scissors.
– throwing balls.
– shoveling dirt.
– some aspects of vocalization.

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1.The neurons of basal ganglia are observed to discharge
before the movement begins. This indicates that basal ganglia
are involved in planning and programming of motor activities.
2. Basal ganglia control posture.
• Basal ganglia-thalamic-cortical projection to brainstem
influences descending pathways that control posture.
• Diseases of basal ganglia result in profound postural
abnormalities.
3. Basal ganglia inhibit stretch reflexes by stimulation of
caudate nucleus.
.
FUNCTIONS OF BASAL GANGLIA

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4. Neostriatum regulates subconscious gross movements.
5. Basal ganglia also play a role in cognitive functions.
• This is especially performed by the caudate nucleus
through its connections with the frontal portion of the
neocortex.
• Lesion of caudate nucleus results in deficit in
performance based on learning.

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6. Lesion of head of the left caudate nucleus is
associated with dysarthric aphasia (difficulty in
articulating words).
7. Globus pallidus provides inputs for appropriate
muscle tone for skilled movements.
8. Substantia nigra is the center for coordination
of impulses essential for skilled movements.
9. Basal ganglia controls associated movements
that occur automatically and normally with
various body movements.

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Parkinson’s Disease
With age, there is progressive loss of dopamine and dopamine receptors
in the basal ganglia. When this process is accentuated, parkinsonism
results.
Causes
1. Idiopathic: The cause of degeneration of dopaminergic neurons is not
exactly known.
2. Drugs: phenothiazine, D2 receptor blockers, etc.
3. MPP: It has been recently described that methylphenyl-pyridinium
(MPP) concentration in the brain of parkinsonism is high. MPP is
formed from methyl-phenyltetrahydropyridinum (MPTP) by the action of
monoamine oxidase B (MAO-B) enzyme. MPP rapidly accumulates in
the neurons of basal ganglia and destroys them
DYSFUNCTIONS OF BASAL GANGLIA

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Features
Both hypokinetic and hyperkinetic movements are observed in parkinsonism.
Hypokinetic Movements
1. Akinesia: Akinesia is defined as difficulty in initiating movements and
decreased spontaneous movements.
2. Bradykinesia: Bradykinesia is defined as slowness of movement.
• All activities are grossly reduced and slowed. Difficulty in tying shoelaces
and buttoning is frequently observed.
3. Decreased associated movements: Examples of associated movements
are swinging of the arms during walking or the facial expressions during
speaking.
• expressionless face or mask face (facial immobility).
4. Serpentine stare: Frequency of spontaneous blinking of eyes decreases
producing a serpentine stare.

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Hyperkinetic Movements
1. Rigidity: Rigidity of parkinsonism is different from
spasticity that occurs in UMN paralysis.
• In rigidity, the motor neuron discharge is increased in
both agonists and antagonists.
• Therefore, the limbs offer resistance to passive
bending throughout the movement (lead pipe rigidity).
• Sometimes, cogwheel rigidity (series of catches
during passive movement) is also seen.
• However, the clasp-knife spasticity (sudden loss of
resistance while moving a rigid limb) of UMN paralysis is
never seen.

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2. Tremor: Tremor occurs due to regular alternating
contractions of antagonist muscles,
• Typically, tremor is observed only at rest.
• Once the patient initiates the movement, tremor
disappears. This is described as resting tremor.
3. Festinant gait: The patient walks in an attitude, as if
he is trying to catch the center of gravity. Usually, he
bends forward but does not fall, instead takes short and
shuffling steps.
4. Micrographia: Combination of tremor, rigidity and
bradykinesia results in small, tremulous, difficult
handwriting, called micrographia

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Festinant Gait

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Management
DIAGNOSIS functional dopaminergic imaging by SPECT, in
which uptake of striatal dopaminergic marker particularly in
posterior putamen is reduced.
Dopamine transporter (DaT) imaging by using radiolabeled
ligand binding to dopaminergic terminals.
Treatment
1. Replacement of dopamine: Dopamine cannot cross the
blood–brainbarrier.Therefore,Levodopa
(L-dopa), a precursor of dopamine that easily crosses blood–
brain barrier, is the drug of choice for parkinsonism. It also
helps repair dopamine deficiency.
• Dopamine receptor agonists: Dopamine agonists like

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2. Anticholinergics: Though Parkinson’s disease occurs
due to dopamine deficiency in the striatum, the
alteration in the ratio of dopamine to acetylcholine plays
an important role.
• Therefore, injection of anticholinergics that
decreases acetylcholine concentration in the basal
ganglia and reestablishes acetylcholine dopamine ratio
improves the symptoms.
3. MAO-B Inhibitors: Deprenyl is the drug of choice.
Deprenyl inhibits monoamine oxidase B and therefore,
prevents formation of MPP from MPTP.
• Selegiline, a MAO-B inhibitor.

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4. Transplantation of adrenal medulla: Transplantation
of adrenal medulla from one of the adrenal glands of the
patient into his basal ganglia helps in regenerating the
dopaminergic neurons.
5. Implantation of fetal basal ganglia: Implantation of
tissue from the basal ganglia of fetuses into the basal
ganglia of the patient improves the condition.
6. Transplantation of glomus cells: Recently, for
treatment of parkinsonism, glomus cells from carotid body
are isolated and transplanted into basal ganglia. Glomus
cell releases dopamine locally. This has been found to be
encouraging.

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Lesions of Basal Ganglia
• Globus pallidus
– athetosis - spontaneous writing movements of the
hand, arm, neck, and face.
• Putamen
– chorea - flicking movements of the hands, face, and
shoulders
• Substantia nigra
– Parkinson disease - rigidity, tremor and akinesia
– loss of dopaminergic input from substantia nigra to the
caudate and putamen

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• Subthalamus
– hemiballismus - sudden flailing movements of
the entire limb.
• Caudate nucleus and putamen
– Huntington chorea - loss of GABA containing
neurons to globus pallidus and substantia nigra.
Lesions of Basal Ganglia (cont’d)

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The disease occurs due to degeneration of GABAergic
striatonigral pathway.
• GABAergic and cholinergic neurons are lost in the
striatum.
Age: Disease usually starts between the age of 30 and 40
years and progresses uniformly till death that usually
occurs within 10–15 years. Disease has three important
features: chorea, dementia, and slurred speech.
HUNTINGTON’S DISEASE

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Features
Chorea: Chorea is defined as rapid involuntary and
dancing movements. The chorea is called as Huntington’s
chorea. It is believed that loss of GABAergic neurons in the
striatum removes its inhibitory influence on the globus
pallidus, which reduces the activities in the thalamic
nucleus that results in chorea.
Dementia: due to progressive loss of cholinergic neurons
in the cerebral cortex.
Slurring speech
.

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Treatment
no definite treatment of Huntington’s chorea. The disease is
progressively fatal. Drugs are used to reduce the symptoms.
Tetrabenazine has been used recently to reduce the
choreiform movements. It reversibly binds with vesicular
monoamine transporter (VMAT) and inhibits the uptake of
monoamine into synaptic vesicles. It also acts as dopamine
receptor antagonist.
Tetrabenazine is used in other movement disorders such as
dyskinesia

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Ballism
Ballism is defined as involuntary movements that are
flailing, intense, and violent in nature. Usually, it occurs
suddenly. Ballism occurs when the subthalamic nucleus is
damaged.
Athetosis
Athetosis is defined as continuous but slow writhing
movements. It occurs due to damage to striatum.
OTHER DYSFUNCTIONS