Control of Movement

Question 1

The Basal Ganglia

Answer 1

A group of nuclei which are central to control of movement

Question 2

Movement disorders

Answer 2

A diverse array of neurological illness that results in disorderd control of movement

Question 3

Efference copy

Answer 3

A prediction of expected movement outcome which is generated at the same time as the movement signal and which is compared with the actual movement outcome.

Question 4

How is the movement control processed?

Answer 4

It is processed at different levels

Question 5

Describe the basal ganglia as a multiple relay system

Answer 5

It takes a massive input from multiple cortical and brainstem regions, and outputs to selected parts of the same areas for focussed function.

Question 6

What is just as important as motor functions of the basal ganglia?

Answer 6

Non-motor processing

Question 7

What are the circuits of the multiple relay system of the basal ganglia?

Answer 7

• Motor circuit
• Associative circuit
• Limbic circuit

Question 8

How is the basal ganglia divided anatomically?

Answer 8

The basal ganglia is segregated anatomically and between the circuits but also further subdivided anatomically so the circuit will project to different basal ganglia nuclei that are all connected.

Question 9

What is the main output from the basal ganglia?

Answer 9

Inhibitory - so less movement

Increase the activity of the basal ganglia then there is less movement.

Question 10

Why is the function of the basal ganglia important?

Answer 10

It is important to link the emotional and cognitive function as sometimes the importance of not doing something.

Question 11

What are the two pathways in the basal ganglia?

Answer 11

• Direct go pathway

- Indirect stop pathway

Question 12

What neurotransmitter affects the two pathways of the basal ganglia?

Answer 12

Dopamine produced by the substantia nigra

Question 13

Direct Go Pathway

Answer 13

Inhibiting the inhibitory output nucleus hence promoting movement - decreased output activity from basal ganglia so increased movement

Question 14

Indirect Stop Pathway

Answer 14

Excitatory onto inhibitory nucleus hence making less movement happen = increased output activity from basal ganglia so decreased movement.

Question 15

What neurons input into the basal ganglia?

Answer 15

The striatum - medium spiny neurons

Question 16

Substantia nigra

Answer 16

Part of the brain producing dopamine

Question 17

Which part of the brain is damaged in Parkinson’s Disease?

Answer 17

Substantia nigra

Question 18

Describe the motor circuit

Answer 18

• Motor cortex releases signals to the putamen which if increasing movement will cause the release of dopamine from the substantia nigra and then distributes to basal ganglia and other regions including thalamus

Question 19

The rate (Alexander and Delong) model

Answer 19

• Changes in firing rate (of output nuclei) determine the rate of thalamic inhibition and therefore amount of movement possible
• If increased firing rate, then the basal ganglia goes up there is inhibition of movement.

Question 20

Parkinson’s Disease

Answer 20

• Long term degenerative disorder of the CNS that mainly affects the motor system.
• Clinically dominated by a lack of movement = bradykinesia
• The substania nigra degenerates so not enough dopamine.
• Inhibitory output of the basal ganglia so inhibits motor cotex stopping movement

Question 21

Bradykinesia

Answer 21

Decreased bodily movement

Question 22

Hemiballismus

Answer 22

• Involuntary flinging movement to one side of the body due to subthalamic nucleus stroke
• Excessive inhibition of the inhibitory output nucleus causing hyperkinesia as the thalamus and motor cortex are not stopped

Question 23

Hyperkinesia

Answer 23

Increase in muscular activity that results in excessive normal movements

Question 24

Function of the sub thalamic nucleus

Answer 24

Key regulator in preventing movement - if it doesn’t exist then there is no inhibition of thalamus and motor cortex

Question 25

Clinical problems with the rate model

Answer 25

- Patients with movement disorders have been treated with lesions in parts of the brain to identify treatment - Results are unexpected as lesioning thalamus does not promote akinesia - lesioning the GPi does not cause dyskinesia

Question 26

What have animal models with Parkinson's shown about the function of the basal ganglia?

Answer 26

It is not the level of BG output but the pattern that is important.

Question 27

What did deep brain stimulation surgery show about neurons in Parkinson's disease?

Answer 27

Showed that there is a particular frequency at which the nerve cells fire around 20-30 hz (beta frequency). In PD, the beta frequency is high reducing movement rather than increased firing to the region.

Question 28

How is neuron frequency recorded in humans?

Answer 28

- Usually carried out in disorder patients to see how the frequency differs - In a normal situation, there are a lot of different frequencies of firing in different nerve cell populations. - Differential frequency firing allows the carrying of lots of information in the multiple patterns of firing. - In Parkinson's everything is synchronised and reduces the information processing and transfer.

Question 29

What evidence is there that beta activity is high in individuals with Parkinson's?

Answer 29

- Levodopa medication suppresses beta activity and reduces the synchronised firing - ON frequency falls when on medication. This results in greater movement when the beta activity is suppressed. - Deep brain stimulation surgery can also suppress beta frequencies shown improve movement - Direct stimulation of the STN at beta band frequencies worsened Parkinson's - Dopamine treatment will improve movement as in PD, there is a reduction of dopamine so no movement.

Question 30

What is moving?

Answer 30

The change from one (stable) sensory state to another (stable) sensory state.

Question 31

Steps for moving state changes

Answer 31

1. Turn down beta power 2. The basal ganglia will get ready to destabilise the state to allows for new sensory state 3. Stabilise the beta power will increase again

Question 32

How does the brain work from Bayes to Free energy

Answer 32

- The brain has a system that allows us to build internal models of the world. Therefore, we know how the world is meant to work and how the body is meant to interact with the world - Needs to be a mechanism that turn up/down the particular state in order to allow the maintainence of a state or transition into a new state - There are two possibilities: to stay in the current state or move

Question 33

What does the brain do when the body does not move?

Answer 33

Turn up the strength of the current sensory state keeping a static essentially high beta activity that prevents movement from happening

Question 34

What does the brain do when the body needs to move?

Answer 34

Beta activity is reduced which will turn down the strength of the current sensory state and allows a new prediction to emerge

Question 35

What is the systemic approach to motor control?

Answer 35

All of the different areas that feed information in order for motor control

Question 36

Sensory neuropathy

Answer 36

Loss of joint position sense and sensation sense - no damage to the brain but loss of sensory feedback coming in.

Question 37

How does the brain check that the input received is correct?

Answer 37

Sends a signal to the cerebellum that receives sensation information from the body and makes sure it is the expected response.

Question 38

What happens if there is damage to the cerebellum?

Answer 38

Results in the person being unsteady and uncoordinated, the comparison cannot take place so the brain isn't able to adapt to errors that occur in movement

Question 39

Cerebrellar disorders

Answer 39

Person cannot learn to walk normally and adapt to new situations

Question 40

Why do people with parkinsons have trouble going through doors?

Answer 40

The idea from switching from one sensory state to another means they are stuck in a synchonous state due to high beta activity that prevents from changing state

Question 41

Tourette's Syndrome

Answer 41

Chronically low beta activity so the sensory state is unstable meaning that movement is present in an uncensored way