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Basal Ganglia
Principles of neural sciences 5th ed.
The human brain: an introduction to its functional anatomy 6th ed.
林 永 煬國立陽明大學 腦科學研究所
Basal ganglia and surrounding structures, as seen in an axial section
Basal ganglia and surrounding structures, as seen in coronal sections
The compact (SNc) and reticular (SNr) parts of the substantia nigra
Terminology associated with the basal ganglia
Parasagittal section showing how the striatum got its name
Three-dimensional reconstruction of the striatum and globus pallidus inside a translucent CNS
Striopallidal fibers: from putamen to globus pallidus (pallidum)
Corticostriate fibers: from cerebral cortex to putamen, caudate nucleus, or nucleus accumbens
Pallidothalamic fibers: from globus pallidus to thalamus
Nigrostriatal fibers: from substantia nigra to striatum
Nigroreticular fibers: from substantia nigra to reticular formation
Thalamostriate fibers: from intralaminar nuclei to striatum
Basal ganglia circuitry
Corticostriate inputs: Afferents from cortex to striatum and subthalamic nucleus
Excitatory (glutamate) connections
Output projections: Efferents leaving from globus pallidus (GPi) and substantia nigra (SNr) to thalamus
Inhibitory (r-aminobutyric acid [GABA]) connections
Thalamocortical projections: Excitatory (glutamate) connections
Principal inputs to and outputs from the basal ganglia
Cortical functions related to basal ganglia circuitry
Movement
Cognition
Emotion
Motivation
Parallel loops through the basal ganglia
Cortical functions related to basal ganglia circuitry
Motor functions: sensorimotor cortex putamen GP thalamus motor/premotor/supplementary motor areas
Cognitive functions: association cortex caudate nucleus GPi-SNr thalamus prefrontal areas
Emotion/motivation: amygdala/hippocampus/limbic cortex ventral striatum (nucleus accumbens) ventral pallidum thalamus (dorsomedial nucleus) temporal/ hippocampus/limbic cortex
Major connections of the striatum
Medial (A) and lateral (B) views of the left striatum showing the somatotopic representation of body parts
Chemical compartmentalization of the striatum
P=putamen, CN=caudate nucleus, IC=internal capsule, A=nucleus accumbens
Acetylcholinesterase (AChE)-rich background (matrix) with embedded AChE-poor regions (striosomes *)
P
A
CN
IC
*
Caudate nucleus stained for enkephalin
Caudate nucleus stained for AChE
High enkephalin levels are found in the peripheries of striosomes.
*
Case presentation
A 25-year-old woman with dramatic change in cognition, motivation, and self-care.
Contrast-enhanced computed tomography scans of a 25-year-old woman with dramatic change in cognition, motivation, and self-care.
Acute stage 8 months later
Major connections of the external segment of the globus pallidus (GPe)
Afferents to GPi and SNr
Efferents from GPi and SNr
GPi and SNr receive inhibitory inputs from striatum, and excitatory inputs from STN.
GPi and SNr provide output from basal ganglia.
Subthalamic fasciculus interconnecting STN and GPi
Major connections of STN
STN provides a powerful excitatory input to GPi and SNr.
Major inputs to STN arise not only from GP but also from cerebral cortex.
Different sectors of STN deal with motor, cognitive, affective functions.
Abnormalities of movement due to basal ganglia disorders
Hyperkinetic disorders: tremor, chorea, athetosis, ballismus, hemiballismus
Disturbance of muscle tone: dystonia
Huntington’s disease
Parkinson’s disease
Hemiballismus
s/s: wild flailing movements of one arm and leg
Lesion location in contralateral STN
Most often seen in older people with a stroke involving a ganglionic branch of posterior cerebral artery
Video show
Contrast-enhanced mass in left STN of a 65 y/o male HIV-positive patient with unintentional, forceful flinging movements of right limbs.
Longitudinal slice of a normal brain
Huntington’s disease
s/s: involuntary choreiform movements, alterations of mood or cognitive function dementia and personality change
Symptom onset at age of 30 – 50 years
Inherited in an autosomal dominant pattern, with a defective gene at short arm of chromosome 4
Pathomechanism: striatal (esp. caudate nucleus) and cortical degeneration
Video show
MRI scan in a 29 y/o man with Huntington's disease
MRI scan in a normal individual
Dorsal-ventral degeneration gradient (red > blue)
Parkinson’s disease
s/s: tremor rigidity (increased muscle tone) slow movements (bradykinesia, hypokinesia) stooped posture
Pathomechanism: degeneration of substantia nigra (esp. SNc, pigmented nigral cells)
The midbrain of a patient with Parkinson's disease, showing loss of pigmentation in the compact part of the substantia nigra (*)
A model for movement control by basal ganglia(through excitatory (green) and inhibitory (red) interactions)
Direct pathway Indirect pathway
Loss of excitatory STN projections(e.g. hemiballismus)
Dopamine excites direct pathway, but inhibits indirect pathway.
Loss of dopamine neurons from SNc causes a reduced thalamic and cortical output. (e.g. PD)
Increased blood flow in the supplementary motor area (S) and premotor cortex (P) of Parkinson's disease patients during movement following treatment with levo-dopa
Parkinson’s disease following unilateral pallidotomy
Improvement in bradykinesia and rigidity Increase in cerebral blood flow on PET