Cerebellum Ataxia Incoordination/ rapid alternating John H. - - PDF document

1

Cerebellum

John H. Martin, Ph.D. Center for Neurobiology & Behavior Columbia University

Cerebellar Signs

Ataxia Hypometria & Response delays Incoordination/ rapid alternating movements (disdiadocho- kinesia) PNS Fig. 42-16

Research Points to Several Key Cerebellar Functions

• Comparison of intent and action (ie.,

errors) and generates corrective signals

• Motor learning and adaptation
• Plays a role in automating and
• ptimizing behavior
• Motor cognition and general cognition &

emotions (new evidence; controversial)

Goal: Cerebellar function

• Overview of motor system hierarchy
• Cerebellar anatomy
• Principal pathways out of the cerebellum--

How the cerebellum impacts the motor pathways

• Experimental approaches to reveal:

– Motor learning – Mental processes underlying movement control – Role in cognition and emotions

Motor Hierarchy

Exerts influence at all levels Intent Actual

1° Som sensory

Cerebellar Functional Anatomy

2

Cerebellar Cortex Deep Cerebellar Nuclei: Dentate Interposed Fastigial PNS Fig. 42-1

Input-output Organization

Cerebellar cortex Fastigial Interposed Dendate Deep Cerebellar Nuclei: Vestibular nuclei Cortex Nuclei Output

Extrinsic inputs: mossy fiber climbing fiber

+

• +

+

NTA Fig. 13-2,4 IVth vent Vermis Intermediate hem. Spinocerebellum:

Vermis Intermediate hem.

Spinocerebellum (Vermis + Intermed. Hem) Control of limbs and trunk Lateral hem. Cerebrocerebellum:

Lateral hem.

Cerebrocerebellum (Lateral hemisphere) Planning of movement+ Floculo-nodular lobe Vestibulo-cerebellum (Floculo-nodular lobe) Control of eye & head movements Balance

Cerebellar divisions

NTA Fig. 13-1

Cerebellar Cortex

Inputs Output Interneurons Climbing fibers

• from Inferior olive

Mossy fibers Purkinje neurons Stellate neurons Granule neurons Basket neurons Golgi neurons

Molecular Purkinje Granular

NTA Fig. 13-11 Parallel fiber input to cerebellar cortex With inhibitory circuits Inhibition reduces size of active Purkinje neurons = Lateral inhibition Output more focused; more precise Without inhibitory circuits

Functional divisions of cerebellar cortex --> Deep nuclei

PNS Fig. 42-2

3

Functional divisions of cerebellar cortex --> Deep nuclei

Vermis Intermediate hem Cerebrocerebellum Lateral hemisphere Spinocerebellum Vestibulo- cerebellum Floculo-nodular lobe Cerebrocerebellum Lateral hemisphere Dentate Intermediate hemisphere

Inter posed

To lateral sysetms Spinocerebellum Vermis Fastigial To medial sysetms To frontal motor areas

Motor Planning +++ Motor execution

Vestibulo- cerebellum To vestibular nuclei

Eye mvt & balance PNS Fig. 42-3 NTA Fig. 13-1

Medial & lateral systems

Interposed nuclei Fastigial Vestibulocerebellum via vestibular nuclei NTA Fig. 10-2 Intermediate and Lateral Hemispheres Vermis & Vestibulocerebellum Cerebellar cortex & Deep nuclei Brain stem nuclei Thalamus and Cortical motor areas Bilateral Ipsilateral Brain stem nuclei Planning and limb control Axial control PNS Fig. 42-10, 12

Functions of the Cerebellum

• Motor learning/adaptation
• Non-motor functions:

– Active tactile exploration – Higher brain functions (cerebellar cognitive- affective syndrome)

Motor Learning

Before Prisms After Before Prisms After PNS Fig. 42-15

Non-motor Function

Passive stimulation Discriminate roughness Manipulate only Manipulate + discriminate PNS Fig. 42-14

4

Cerebellar Motor Functions

• Implemented via lateral and medial pathways,

especially the corticospinal tract

• Incorporated into motor programs via frontal motor

areas (SMA, premotor cortex…)

• Becomes part of motor strategy via prefrontal cortex

Cerebellar Cognitive Affective Disorder

• Lesions of the posterior cortex and vermis
• Impairment of executive functions

– Planning, verbal fluency, abstract reasoning

• Difficulties with spatial cognition

– Visuo-spatial organization, visual memory

• Personality changes

– Blunting of affect, inappropriate behaviors

• Language disorders

– Agrammatism

Conclusions

• Cerebellar lesions produce

– Incoordination & errors not weakness – Lose ability to anticipate errors – Lose ability to correct

• Motor learning

– Requires sensory awareness – Implemented via the descending cortical and brain stem pathways

• Cognitive and emotional disturbances

– Anatomical connections to prefrontal and cingulate cortex (via thalamus)

• No single function

– Clearly mostly motor; learning, optimizes – Functions may apply to cognitive and emotional behaviors