The Basal Ganglia
Maryann Martone, Ph. D.
NEU257
2/22/2011
What are the basal ganglia?
• Depends on whom you’re talking to:
– Anatomical: Non-cortical nuclei in the
forebrain
• Caudate nucleus, putamen, nucleus
accumbens, amygdala, globus pallidus
– Functional: Richly interconnected set of
nuclei in the forebrain and midbrain
System View
• Dorsal Striatum
– Caudate nucleus
– Putamen
• Ventral Striatum
Striatum
– Nucleus Accumbens
– Olfactory Tubercle
• Globus Pallidus
– Internal segment
– External segment
– Ventral pallidum
Other Terms:
• Subthalamic nucleus
• Substantia nigra
Paleostriatum
– Pars compacta
– Pars reticulata
• Pedunculopontine
nucleus**
Archistriatum
Neostriatum
Where are the basal ganglia?
•Caudate Nucleus
•C shaped structure (“tail”)
•Lateral wall of lateral ventricle
•Head, body and tail
•Caudate nucleus
•Putamen
•Nucleus accumbens
•Internal capsule
•External capsule
•Extreme capsule
•claustrum
•Septum pellucidum
•Insular cortex
•Corpus callosum
•Caudate nucleus
•Putamen
•Globus pallidus external
•Globus pallidus internal
•Ventral pallidum
•Anterior commissure
•Substantia innominata
•Internal capsule
•Lentiform nucleus**
•Head, body, tail of caudate
• anterior and temporal horn of lateral ventricle
•Globus pallidus internal and external
•Internal capsule, anterior and posterior limbs
•Caudate nucleus (body and tail)
•Putamen
•Globus pallidus
•Subthalamic nucleus
•Substantia nigra
•Pars compacta
•Pars reticulata
•Globus pallidus
external
•Globus pallidus internal
•Subthalamic nucleus
•Substantia nigra
•Subthalamic nucleus
•Substantia nigra
•Ventral tegmental area
Rodent Brain
Globus pallidus and entopeduncular nucleus
vs.
Globus pallidus (external) and Globus pallidus
(internal)
“Chemical Neuroanatomy” was very important in
increasing our understanding of basal ganglia structures
•Use of different
histochemical and
immunocytochemical
stains revealed more
extensive striatal
structures than
previously thought
From Zhou et al., Nature Neuroscience, 4, 1224 - 1229
(2001)
•Also caused revised
views of basal ganglia
structures in nonmammals and pointed
to considerable
homologies between
birds, mammals and
reptiles
Functions of the basal ganglia
• Extrapyramidal motor system
• Motor planning, sequencing and learning
• Activity of striatal neurons is not sufficiently
explained by the stimuli presented or the
movements performed, but depends on certain
behavioral situations, certain conditions or
particularly types of trials
•
•
•
•
•
-sensory stimuli but only when the elicit movements
-instruction cues (go-no go)
-memory related cues
-reward (especially ventral striatum)
-self-initiated moves
• Basal ganglia distinguished from cerebellum by
connections with limbic system
Diseases of the Basal Ganglia
Parkinson’s:
•Akinesia
•Bradykinesia
•Resting tremor
•Rigidity
Huntington’s disease
•Chorea
•Psychiatric disturbances
•Dementia
Cytoarchitecture
•
•
•
Main neurotransmitter in basal
ganglia is GABA
95% of neurons in neostriatum are
medium spiny neurons (rodent)
– Contain GABA
– Principal neurons: project to
globus pallidus and SNpr
– Subpopulations are
distinguished by peptides,
neurotransmitter receptors
and connections
– Receive bulk of afferent input
Several populations of
interneurons
– aspiny
– ACh, GABA/parvalbumin,
GABA/calretinin;
GABA/NPY/NADPH/Somatost
atin
From Groves, Brain Res. 286: 109,
1983
The Neostriatal Mosaic
• Neostriatum divided
into two
compartments:
patch (striosome)
and matrix
• First described by
Ann Graybiel in
1978 using AChE
stain
• Not visible in Nissl
stains (“hidden
chemoarchitecture”)
• Define input/output
architecture of
neostriatum
From Holt et al., 1997, JCN
Connections
• Afferents (striatum):
–
–
–
–
Cerebral cortex (entire cortex)
Thalamus (intralaminar and midline nuclei)
Amygdala (basolateral nucleus)
Raphe, substantia nigra pars compacta, VTA
• Efferents (Gpi, VP, SNpr)
– Ventral tier nuclei of thalamus
– Superior colliculus
– Lateral habenular nucleus
All regions of cerebral cortex project to the basal
ganglia, but output of basal ganglia is directed towards
the frontal lobe, particularly pre-motor and
supplementary motor cortex
Basic Circuit of Basal Ganglia
Cerebral Cortex
Neostriatum
+
Gpi/SNpr
Gpe
+
+
VA/VL thalamus
Connections of afferents and within basal ganglia are largely non-reciprocal
Subth
Some numbers (rat)
•
•
•
•
2.8 million neurons in caudoputamen
46,000 neurons in Gpe
3200 neurons in Gpi
26,000 neurons in SNpr
– Oorschot (1996)
– Significant convergence of input from
striatum to target nuclei
Disinhibition
From Chevalier and Deniau, TINS 13:277, 1990
Direct vs
indirect
pathways
•Different
populations of
spiny neurons
•Enkephalin vs
substance P
•D1 vs D2
receptors
From Graybiel, A. Neural
Networks, Am J Psychiatry
158:21, January 2001
Facilitation vs inhibition of movement
Albin RL, Young AB, Penney JB. The functional anatomy of basal
ganglia disorders.Trends Neurosci. 1989 Oct;12(10):366-75.
Akinetic disorders: overactivity in the indirect pathway
•Dopamine increases activity in the direct pathway and decreases
activity in the indirect pathway
•Loss of dopamine decreases activity in the direct pathway and
increase activity in the indirect pathway
•Increased activity in the indirect pathway = increased activity in
the direct pathway = increased inhibition on thalamus
Hyperkinetic disorder: overactivity in the direct pathway
•Projections to the Gpe degenerate early in HD = removal of inhibition
= increased activity of indirect pathway
•Increased activity of indirect pathway = increased inhibition of
subthalamic nucleus = decreased excitatory drive on direct pathway =
decreased inhibition on thalamus
Inhibit
Hypokinetic
Releas
e
Hyperkinetic
Functional subdivisions
• Sensorimotor
– Putamen + globus
pallidus/SNpr
– SNpc
• Association
– Caudate nucleus + globus
pallidus/SNpr
– SNpc
• Limbic
– Nucleus accumbens +
ventral pallidum
– VTA
From Parent, TINS 13: 254, 1990
Neostriatal Mosaic and
Input/Output Organization
• Most inputs to the neostriatum terminate in a
patchy fashion (“matrisomes”)
• Input from a given cortical region terminates
over an extended anterior-posterior extent
• Functionally related cortical areas project to
the same patches
• Output neurons to a given efferent subregion
are also arranged in patches
• Neurons in patches project to both Gpi/SNpr
and GPe
Cortex
Neostriatum
Gpi/SNpr
“divergent-reconvergent
processing”
From Graybiel et al., The basal ganglia and adaptive motor control, Science, 265:
1826, 1994
Direct and Indirect Pathways