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