Lecture 12

Question 1

BG components (4 main, 4 sub)

Answer 1

Striatum: caudate & putamen → INPUT ZONE
Pallidum: globus pallidus & substantia nigra pars reticulata → OUTPUT ZONE

• inhibitory GABAergic output
  Substantia nigra pars compacta
  Subthalamic nucleus

Question 2

BG input & output

Answer 2

INPUTS:
to caudate - from association cortices & FL eye movement motor areas
to putamen - from somatosensory cortices in PL, pMC, auditory & visual cortices

OUTPUTS:
to SC & thalamus, to PFC, PMC, pMC

Question 3

Links between BG & cerebral cortex

Answer 3

Corticostriatal pahtway - subcortical loop
Mirrors cortex functional organization
Striatum has “functional units” that reflect specialization of their cortical inputs

Question 4

Medium spiny neurons (MSN)

Answer 4

Input: Cortical neurons, local circuit neurons, dopaminergic neurons from substntia nigra, other MSNs, brainstem

Projections: inhibitory GABAergic
> caudate & putamen → globus pallidus & SNPR

Cortical input from 1000s of cortical neurons, synapses on dendrites spines
Local ciruit & thalamic neurons
> synapse on dendrite shafts

Question 5

BG path (fig.)

Answer 5

(see 12.5)

Question 6

BG links to saccades

Answer 6

Sontaneous tonic reticula activity supresses saccades
GABAergic MSNs reduce reticular activity
→ allow saccades!

(see 12.6 for caudate, SNPR and SC eye movements)

Question 7

BG direct pathway

Answer 7

Facilitate movement, release from tonic inhibition
Striatum INHIBITS global pallidus internal → decreased inhibition of VA/VL, EXCITATORY input to FC

Dopamine at D1 enhances direct

Question 8

BG indirect pathway

Answer 8

Inhibits movement, increases tonic inhibition
Striatum INHIBITS global pallidus external → decreased inhibition of subthalamic, INHIBITS thalamus, INHIBITS FC

Dopamine at D2 suppresses indirect

Question 9

Dopamine & BG pathways

Answer 9

D1 enhances direct
D2 enhances indirect

Overall decreases inhibitory output of BG

Question 10

Center surround organization

Answer 10

“Focused selection
Activation of some motor programs & suppression of competing motor programs

Co-activation”

Question 11

Huntington’s & BG

Answer 11

Caudate & putamen shrink
Globus pallidus external becomes more active
Reduces excitatory STN output to globus pallidus internal
INHIBITION reduced → to many movements involuntary

Hemiballismus: sudden hyperkinectic involuntary movement
> STN damage

Question 12

Muscimol & the indirect pathway

Answer 12

Muscimol is a GABA agonist
Decreases tonic SC inhibition
Leads to spontaneous, irrepressible saccades → mimics Huntington’s & hemiballismus

Question 13

Parkinson’s disease

Answer 13

3 signs: tremor at rest, rigidity, bradykinesia (slowness)
Motor problems, associated w/ dyskinesias
Degradation of substantia nigra pard compacta
Reduced dopamine → harder to start/ stop movement

Question 14

BG - non motor functions

Answer 14

Dorsolateral prefrontal loop: may regulate start/stop of cognitive processes

Limbic loop: may regulate mood transitions & emotional/motivated behavior
esp. ventral striatum