Actions and Motor Control

Question 1

What are the different ways to study action/motor control?

Answer 1

Behavioural
Muscle Physiology
Electrophysiology
Neuroimaging/EEG

Question 2

How to use behavioural methods to study action/motor control?

What are the strengths/weaknesses?

Answer 2

• Use video or electronic recording equipment to record the position of body parts in space and time.
• Can measure speed, accuracy and kinematics (velocity, acceleration, etc.)
• Using this information, a model can be built of how the arm was moving in time.

Strengths: Allows us to systematically investigate the output of the action system. – how the motor control is implemented.

Weaknesses: Cannot tell us anything about the brain

Question 3

How is muscle physiology used to study action/motor control?

What are the strengths/weaknesses?

Answer 3

• Called electromyography
• Requires some electrodes attached to the skin (sometimes done with electrodes in the muscle, using with tiny needles)
• Can record activity of individual muscles or muscle fibers during action

Strengths: Allows an understanding of how muscles operate.

Weaknesses: Cannot tell us anything about the brain

Question 4

How is electrophysiology used to study action/motor control?

What are the strengths/weaknesses?

Answer 4

• Implant electrodes in brain and record activity of individual neurons directly from the motor cortex
• Can take a record of a number of neurons and measure their activity in real time

Strengths: Allows for excellent spatial and temporal resolution.

Weaknesses: cannot examine more than a miniscule percentage of the neurons at any one time. It’s very invasive and mostly used in animal studies

Question 5

What are the strengths/weaknesses of using neuroimaging/EEG to study action/motor control??

Answer 5

Strengths: Allows for a direct measure of activity in the human brain

Weaknesses: Many action processes take less than 2-4 seconds
Difficult to do the recording when a participant is moving and it’s hard to make many movements in a scanner environment!!!

Question 6

Where are muscles attached?

Answer 6

Muscles attach to the skeleton at the origin and insertion.

Question 7

What are muscles?

Answer 7

Muscles are collections of many muscle fibers.

Question 8

What do muscle spindles and Golgi tendon organs provide information about?

Answer 8

Muscle spindles and Golgi tendon organs provide proprioceptive information from the muscles. – Telling our brain sensory information related to movement, so our brain can adjust motor commands.

Question 9

How are muscles organised?

Answer 9

Muscles are organized into antagonistic pairs, with extensors extending the joint and flexors contract the joint.

Question 10

What happens at the neuromuscular junction?

Answer 10

• Motor neurons release neurotransmitters to cause muscle contraction at the neuromuscular junction.
• The neurotransmitter acetylcholine binds to ionotropic receptors, causing depolarization.
• If there is enough localized depolarization, voltage-gated ion channels will open.
• The rapid depolarization caused by the opening of voltage-gated ion channels causes the release of calcium.
• Calcium inside the muscle causes actin and myosin proteins to interact, which brings about a muscle contraction.
• Acetylcholinesterase removes the neurotransmitter and ends the contraction.

Question 11

What are the three types of motor behaviour?

Answer 11

Motor control
Motor learning
Motor development

Question 12

What is motor control?

Answer 12

An area of study primarily focusing on the principles of human skilled movement generated at a behavioural level of analysis.

(Looking at how movement is generated, both behaviourally and kinematically)

Question 13

What is motor learning?

Answer 13

A set of internal processes associated with practice or experience leading to relatively permanent changes in the capability of motor skill.

(Learning new motor skills and the steps involved, e.g., learning to ride a bike)

Question 14

What is motor development?

Answer 14

A field of study concerning the changes in motor behaviour occurring as a result of growth, maturation and experience.

(Looks at the development of motor control and motor learning, e.g., what happens in children, adulthood and old age in terms of our motor systems)

Question 15

What are the different levels of the hierarchical systems for motor control?

Answer 15

The information, in terms of signals transfers from the non-primary motor cortex down to the muscles.

Non-primary motor cortex: additional source of motor commands.

Primary motor cortex: initiates the motor commands.

Brainstem: integrates motor commands from higher levels of the brain and transmits them to the spinal cord.

Spinal cord: controls skeletal muscles in response to sensory information. Both reflex and voluntary movements.

Question 16

Explain the different levels of the hierarchical systems for motor control (starting from the outside)?

Answer 16

If we start from the peripheral aspect first:

First of all, we have the muscles that are attached to our skeleton that make movement possible.
Then we have the spinal cord which controls the muscles in response to sensory information it is receiving. It also houses some reflexes and voluntary movements.
Then we have the brainstem which integrates motor commands from higher cortical levels to transmit into the spinal cord.
Then we have the cortical areas which are the primary motor cortex which initiates the motor movement, and the non-primary motor cortex which adds more planning and additional sources of motor commands.

Question 17

What is the role of the spinal cord in low-level control?

Answer 17

• Crucial for controlling body movement
• Transfer the inputs to motor neurons
• Spinal reflexes = automatic responses
• For example, stretch reflex (i.e., the contraction that results when a muscle is stretched)
• Some aspects of locomotion (rhythmic, repetitive movements – swinging legs - are generated within the spinal cord)

Question 18

What is central pattern generator?

Answer 18

Neural circuitry responsible for generating rhythmic pattern of behaviour (walking)

Question 19

What are reflexes?

Answer 19

• Reflexes are simple movements coordinated by the spinal cord
• They are automatic (not controlled)

Question 20

How do reflexes work?

Answer 20

Proprioceptors detect a stretch and trigger a motor response to counteract the stretch

Question 21

What is proprioception?

Answer 21

Proprioception means we have some sensory receptors in our muscles that are informing the brain about the state of the muscles.
(Ask Elisa about this)

Question 22

How are some muscles directly controlled by the brain and what happens with all other muscles?

Answer 22

Some muscles are controlled directly by the brain:
The cranial motor nuclei of the brainstem send axons to directly innervate muscles of the head and neck. This is a direct pathway where the brain can immediately control muscles in your face e.g., eye movements, jaw movements and neck movements.

But for all the other muscles, the brain has to send commands to the spinal cord and then the spinal controls the muscles.

Question 23

What system is involved in all other muscles (apart from the face and neck)

Answer 23

The pyramidal system (or corticospinal system)

The spinal cord is involved in all other muscles (except from face and neck) because the information from the brain has to reach all the muscles in the body. This happens from the motor cortex down to the spinal cord using the ventral horn and then sending information to the nerve and to the muscles. This is called the pyramidal system or the corticospinal system.

Question 24

Explain the pyramidal system (or corticospinal system).

Answer 24

Neuronal cell bodies (of the motor neuron) within the cerebral cortex and their axons which pass through the brainstem forming the pyramidal tract of the spinal cord (corticospinal)

Decussation occurs in the medulla; the pyramidal tract from the right hemisphere crosses the midline to innervate the left spinal cord and vice versa.

Question 25

Which hemispheres control either side of the body?

Answer 25

The left side of the body is controlled by the right hemisphere. The signal is transmitted from the right motor cortex and the signal is transmitted on the right side until the medulla, where they cross and go down and innervate the muscles on the left side.

Question 26

Briefly summarise, where motor output comes from?

Answer 26

Motor output comes from the motor cortex (primary and non-primary motor cortices)
Projects through pyramidal tracts to spinal cord, where it synapses with peripheral motor neurones.

For all the muscles in our face, we have a direct interaction between the muscles and the brainstem. Pathways run parallel from cortex, basal ganglia and cerebellum via brainstem and spinal cord. These run outside the pyramidal tract called the extrapyramidal system

Question 27

What are the motor control systems in the cortex?

Answer 27

Primary motor cortex (M1)
Premotor cortex
Supplementary motor cortex

Question 28

What is the role of the primary motor cortex?

Answer 28

• Source of pyramidal tract neurones
• Planning, control, and execution of voluntary movements
  neurones
• The body parts are mapped in M1

Question 29

What is the role of the premotor cortex?

Answer 29

• Important in motor coordination

- Lesions cause impairments in stability of stance, gait and hand coordination

Question 30

What is the role of the supplementary motor cortex?

Answer 30

• Conception and initiation of movement

- Lesions cause deficits in voluntary movement or speech

Question 31

What is Transcranial Magnetic Stimulation (TMS)

Answer 31

It generates a magnetic pulse which changes the excitability of our cortex, it can change the level of action potential, the communication between neurons and can create excitation or a “virtual lesion” which will disappear after a couple of seconds. It’s been heavily used to look at motor evoked potential. We put the coil near the scalp, trigger the magnetic response and generate a fake movement (meaning you’ll involuntarily make a movement)

Question 32

What is the motor homunculus and how did we come to know about it?

Answer 32

Areas with more motor control or sensory input are larger in the homunculus – it looks distorted
Our brain needs to control all the muscles in our body, all the body parts are mapped in the primary motor cortex.
Similar to the sensory homunculus the motor homunculus also has a very large representation for our hands and fingertips (because we interact with our hands a lot).

We know about this organisation because past research used invasive recording of single neurons, nowadays we use something called TMS (transcranial magnetic stimulation).

Question 33

How accurate is the motor homunculus?

Answer 33

There are recent controversies of the motor homunculus…
• Newer research with longer stimulation of M1 suggests the map may be more complex than the homunculus
• Longer stimulation evokes complete movements, like moving the hand to the mouth and opening the mouth
There is no obvious population coding of direction with longer stimulation SO, WE NEED TO CONSIDER MUCH MORE COMPLICATED MOTOR REPRESENTATONS

Question 34

What are mirror neurons and what do they show?

Answer 34

Neurons active when performing an action or when observing another individual perform a similar action.

The mirror neuron system in the premotor cortex shows that we don’t just have the ability to move but we also have responses to watching the movement of someone. This seems to be the basic level of our social interactions with other people.

Question 35

Which motor control systems are outside the cortex?

Answer 35

These are at a subcortical level but still heavily involved in movement:
Basal Ganglia
Cerebellum

Question 36

What is the role of basal ganglia in motor control?

Answer 36

• The basal ganglia project to areas involved in motor control, cognition, and judgement.
• The basal ganglia initiate and maintain activity in the cortex.

Question 37

What are the components of the basal ganglia?

Answer 37

There are three components of the basal ganglia:
• Striatum (Caudate nucleus + Putamen nucleus)
• Globus Pallidus (the other nucleus)

Question 38

What other areas are functionally connected to the basal ganglia?

Answer 38

The subthalamic nucleus and the substantia nigra (another nucleus that is heavily connected to the basal ganglia) are functionally connected to the basal ganglia.

Question 39

What diseases are caused by the destruction of basal ganglia?

Answer 39

Many motor-related disorders

E.g., Parkinson’s Disease – a degenerative disorder

Question 40

What is Parkinsons disease caused by?

Answer 40

• Caused by progressive destruction of the dopaminergic neurons of the substantia nigra
• These neurons that are being destroyed deal with dopamine so there is a low level of dopamine in the brain

Question 41

How is Parkinsons disease treated?

Answer 41

• The realisation of dopamine’s involvement led to use of drugs which increase brain dopamine (patients are given drugs which increase the level of dopamine which can improve symptoms. But sometimes the drug doesn’t work)
• Surgical interventions and neural transplantation are under investigation as alternative therapies… (If the drugs don’t work, they can try deep brain stimulation which is essentially a pacemaker for controlling movement. Patients are getting an electrode inserted in the brain into the globus pallidus near the substantia nigra. By changing the amount of current transmitted, it is possible to change the activity of the neurons and reduce motor related symptoms such as tremors)

Question 42

What is the role of the cerebellum in motor control?

Answer 42

• Controls neural ‘programs’ for the execution of skilled movements
• Motor learning
• It sends excitatory connections to the brain and spinal cord.
• Cerebellum may provide fine-tune motor control.
• It combines sensory and motor information to predict where an object will be at some future point in time.

Question 43

What does injury to the cerebellum result in?

Answer 43

Injury to the cerebellum results in impairments to the coordination, accuracy, and timing of movements.

Question 44

Apart from motor control, what else is the cerebellum involved in?

Answer 44

The cerebellum sends projections to the frontal lobe and influences cognition, emotion, motivation and judgement.
Damage to the cerebellum impairs cognition, language perception, and grammar.
So, it’s much more than a motor control player

Question 45

Explain the Libets task and how it supports the idea that we don’t have free will?

Answer 45

In the task, participants are in front of a clock and there is a dot that is moving al around the clock. When the participants feel the urge to press the button, they press it. Meanwhile using EEG, the activity of the motor cortex is being recorded. At 0 there is the ‘movement onset’ which is when you do the movement but 200miliseconds before you make the action, there is a change of excitation in your motor cortex – so there is a period in which the activity of the motor cortex starts to increase, before you even think you have the urge to press the button. You can’t perceive this. It supports the idea that perhaps we don’t have a free will.