CEREBELLAR FUNCTION

CEREBELLAR FUNCTIONNBIO 401Robinson

Objectives:There are 6 signs of cerebellar damage. For each sign accurately describe:

1) what part of the cerebellum is damaged to cause that sign

2) the characteristics of that sign

3) for the motor learning deficit, the last sign we describe, the proposed mechanism by which the cerebellum learns new sensory-motor associations.

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

1) postural instability

vestibulocerebellum

Static (while standing) instability is evident when a patient cannot maintain a stable posture in some or several parts of her body (e.g., limbs, trunk, head, or eyes) while trying to stand still. When you ask such a patient to stand with her eyes closed and her arms raised, her body will sway and she will wave her arms. This is called the Romberg sign.

1) postural instability

vestibulocerebellum

Dynamic (moving) instability occurs when the patient has trouble holding a stable posture while walking. Such a patient will exhibit cerebellar ataxia, i.e., a staggering gait with feet placed widely apart, and a difficulty walking in a straight line. Cerebellar ataxia will make a patient's gait look like she is drunk.

Ataxic Gait - Simulated

Ataxic Gait - Real

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

Patients with this problem will be slow to start and stop movements. For example, when you ask such a patient to walk across the room, she will be slow to start and will have trouble stopping. In extreme cases someone else will need to stop her.

2) delayed movement start/stop

neocerebellum

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

neocerebellum

3) deficit in performing continuous, repetitive movements

Patients with this problem, called dysdiadochokinesis, have a hard time doing rapidly alternating movements. For example, in a commonly used diagnostic test, you can ask a patient to tap one hand on the other while rapidly alternating which surface of the target hand, palmar or dorsal, the patient taps. A patient with lateral cerebellar damage cannot do this task rapidly. She will not rotate the target hand completely and will not coordinate these rotations very well with the taps of the other hand.

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

4) movement dysmetria

Paleo- or neocerebellum

Dysmetria (wrong movement size) can occur in different movements after damage to any region of the cerebellum. Movements that are usually fast and accurate, such as rapid reaching or a rapid eye movement to a target, overshoot or undershoot their targets. A patient with cerebellar dysmetria may reach for something, overshoot, reach back, overshoot that movement and so on, so that her hand oscillates around the target.

Signs ofCerebellarDamage inLimb Movements

NORMAL

CEREBELLAR DAMAGE

(which side?)

Signs ofCerebellarDamage inLimb Movements

NORMAL

CEREBELLAR DAMAGE

(which side?)

Signs ofCerebellarDamage inLimb Movements

NORMAL

CEREBELLAR DAMAGE

(which side?)

Signs ofCerebellarDamage inLimb Movements

NORMAL

CEREBELLAR DAMAGE

(which side?)

Ataxic Arm Movement(On which side is the damage?)

Signs ofCerebellar Damagein Eye Movements

normal

bilateral cerebellar damage

Signs ofCerebellar Damagein Eye Movements

normal

bilateral cerebellar damage

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

Paleo- or neocerebellum

5) movement decomposition

A patient with a large cerebellar lesion cannot smoothly execute movements that require several simultaneous joint rotations. Such a patient will rotate one joint at a time in sequence.

Six signs of cerebellar damage

1) postural instability (static & dynamic)

2) delayed movement start/stop

3) deficit in performing continuous, repetitive movements

4) movement dysmetria

5) movement decomposition

6) motor learning deficit

6) motor learning deficit

Paleo- or neocerebellum

This apparent function of the cerebellum has attracted a great deal of attention from scientists because it represents a variety of learning, a phenomenon that everyone wants to understand in any form. We will discuss three examples in animals.

The Network of Neurons in the Cerebellar Cortex

(simple spikes) (complex spikes)

a b d u c e n sn u c le u s

la te r a lr e c tu s

m u sc le

m e d ia lv e s t ib u la r

n u c le i

h o r iz o n ta ls e m ic irc u la r

c a n a l

S c a r p a 'sg a n g lio n

+-

L E F T R IG H T

1

2

3

4

5

a c ce ss o r yo p t ic s y s te m

in fe r io ro l iv e

6

7

8

9

1 0

1 11 2

1 3

1 4

cerebe lla rfloccu lus

Proposed Mechanism for

VOR Adaptation

Surgical Method for CausingAdaptation of Saccade Size

HT HE

G = 0.50

HT HE

G = 1.00

HT HE

100 ms

G = E/T = 1.00

HT HE

G = 0.72

15°

A BACKWARD

HT HEG = 1.00

HT HE

G = 1.04

HT HE

G = 1.09

HT HE

G = 1.24

B FORWARD

Causing Adaptation of Saccade Size by Manipulating Target Movement

Saccade eye position record

EYE

PO SITION

1 0 °

7 °T A R -

G ETPO SITION

S T A R T O F

A D A P T A T IO N

1 0 °

7 °

E N D O F

A D A P T A T IO N

5

7

1 0

0 5 0 0 1 0 0 0 1 5 0 0

SA

CC

AD

ES

IZE

(deg

ree

s)

N U M B E R O F R IG H T W AR D S A C C AD E S

R IG H T W AR D (AD AP T E D )

L E F T W A R D (N O T A D A P T E D )

A B

C

Example of Saccade Adaptation Caused by Target Movement

the end