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MODULATION OF MOVEMENT: The Basal Ganglia - movement selection

Peter Wallén

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11-05

W. W. Norton

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Striatum

Inputs to the Basal ganglia/Striatum: •  Cortex •  Subst nigra compacta –

dopamin •  Thalamus

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Outputs from the Basal ganglia, via: •  Globus pallidus interna •  Substantia nigra reticulata to: •  Thalamus – Cortex •  Hjärnstam – Colliculus sup.

Neuronal circuitry in the Basal ganglia

Two different populations of Medium spiny neurons

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”Medium Spiny Neuron” in Putamen

Neurons in the striatum are active before movement initiation

Planning, Selection, Initiation and Adaptation of Motor Programs

Planning

Selection

Initiation

Central Motor Program

Muscle

Adaptation Sensory Feedback

Proprioception

Motor Cortex

Basal Ganglia

Motor Centers Cerebellum

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MOTOR INFRASTRUCTURE Neuronal networks that co-ordinate

different movements

Protective reflexes Swallowing CPG Respiratory CPG Locomotor CPGs Postural networks Chewing CPG

Express. of emotions Saccadic motor map Reaching

Selection Sequencing

timing

Neuronal circuitry in the Basal ganglia

Two different populations of Medium spiny neurons

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The Direct & Indirect pathways split in the Striatum

D1/SP and D2/ENK expressing neurons. Mixed population of projection neurons (MSNs), innervating the different targets.

Input to Medium Spiny Neurones (MSN – 95%)

•  From cortex on MSN spines (LTP/LTD)

•  From thalamus on dendritic shafts

•  Dopamine (SN, VTA) –  MSN direct loop D1 – SP

(netto exc.) –  MSN indirect loop D2 –

enkephalin (netto inhib.)

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down

up

Dopamine

+

Medium spiny neurons in striatum (input stage) • High threshold for activation

from cortex or thalamus • Filter function +/-

Cortex

Striatum MSN

Pallidal neurones (output stage) •  keep motor programs under

tonic inhibition

Thalamus

The direct loop through the Basal ganglia:

Initiates movement

Disinhibition - requires background activity!

Fig 18.6

Fig 18.8A

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The indirect loop through

the Basal ganglia: Stops movement

Fig 18.8B

Brainstem -

Center-surround organization of

direct and indirect pathways

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Cortex / pallium

Striatum

Pallidum

CPG CPG CPG

command command command

Thalamus

Sensory input

DA

locomotion posture saccades

Selection of behaviour

excitation (glut.) inhibition(GABA) DA-modulation

Fig 18.11

Hypokinesia: Parkinson

Hyperkinesia: Huntington

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Summary  points  –  The  Basal  Ganglia  

Ø  Inputs  to  Striatum,  from  cortex,  thalamus  and  SNc  (dopamine).    Ø  Outputs  from  GPi/SNr,  to  motor  command  centers.      Ø  Output  at  rest  is  tonic  inhibiDon.    Ø  Role  of  the  Basal  ganglia  in  motor  control:  1.  Motor  program  (CPG)  selec&on,  by  disinhibi&on  of  the  adequate  

motor  command  center  (direct  pathway).  2.  PrevenDng  acDvaDon  of  compeDng  motor  programs,  by  inhibiDon  

of  inadequate  command  centers  (indirect  pathway).