Neural Basis of Movement
LECTURE 1: INTRODUCTION TO SENSORY-MOTOR SYSTEMS AND METHODS
Movement
• All of our intentional interaction with environment is through movement
• Understanding of movement control gives insight into hoe the nervous system works
Human movement is special
• Hands
o we are uniquely able to hold and manipulate objects
o we strong and opposable thumbs
o we have flexible and powerful grip
o we have evolved to be tool users
o tool use has allowed us to be general specialists
• Planning (spectrum of abilities)
o we are able to resist immediate responses
o we are better able to plan ahead
o we are better at using flexible rules
Interesting psychological aspects of movement
• Sensory
o we are almost totally unable to move if we lose sensation (dead leg)
• Learning and memory
o we never forget to ride a bike
o we can control our bodies through development
• Action-perception (motor-sensory) interactions
o can understand what tools are and the affordances of different objects
o the motor system is involved in action observation and understanding
o we hold multiple action plans simultaneously and change our minds
• Motor cognition and social interaction
o moto system much more involved in cognition than initially thought
Different learning systems
• Cortex – learning relationships
• Basal Ganglia – reinforcement learning
• Cerebellum – learning through error corrections
Motor Psychophysics
• Traditional ‘sensory’ psychophysics
o vary the stimulus (complexity) -> record simple psychological
responses
▪ pupil size change in response to luminance
• Motor psychophysics
o keep the stimulus simple -> look for regular features of complex movements (complex movement
underlying a simple action)
• Planning choices
o CNS must make decisions in almost every movement
,Motor planning
Planning choices
Motor invariants
• Humans show highly stereotyped trajectories for eye and
arm movements
• Path – sequence of positions of the hand in space
• Velocity – time sequence along a path
• Movements are chosen so as to minimise some cost
o the cost of a movement is specified
o movements are chosen so as to minimise cost
• Examples (all produce similar outcomes)
o Minimum Jerk Model (Flash & Hogan, 1985)
▪ smoothness of trajectory
o Miniumum Torque Change Model (Uno et al, 1989)
▪ rate change of torques (force at a joint)
o Minimum variance theory (Harris & Wolpert, 1998)
▪ minimise variance at the end of movement – more accurate and consistent with less variation
Motor learning and memory
• Sequence learning has revealed important information
regarding motor learning and memory:
o The interaction between implicit and explicit
processes
o The role of sleep
o Interference
o Consolidation
o Probabilistic learning
,Animals’ nervous system
• The reason animals have a nervous system is to act and move
• Thought is but action confined to brain (Jackson, 1835-1911)
• Memory, cognition, sensory processing, they’re there for a reason and that reason is action (Wolpert, 2010)
Neuron types
Inputs
Integration
Outputs
• A typical neuron
o The human brain has approximately
100 billion neurons and 100 trillion synapses
Action potentials
• Brief voltage sensitive change in permeability
• Fast change in Na+ permeability
• Slower change in K+ permeability
Synapse
• Pre-synaptic action potentials increase membrane potential
• Influx of Ca++
• Release of vesicle contents (neurotransmitter)
• Binding to post-synaptic receptors
• Generation of post-synaptic potentials (PSPs)
The Neuromuscular Junction (special synapse)
• NMJ is the complex synapse between nerve & muscle
• Specialised nerves called ‘Alpha’ motor neurons connect to muscles
• It is specialised but has features typical of all synapses
• Alpha neurons innervate between the nervous system and the musculature
• When action potentials arrive it allows a big uptake (strong response) due to the
large surface area
1. presynaptic axon & terminal
2. postsynaptic membrane
3. synaptic vesicle
A motor unit is a single motor neuron, along
4. acetylcholine receptors
with all of the muscle fibres it innervates
Motor unit
A motor pool is a collection of motor units
When an action potential reaches the NMJ there
is a twitch
a) slow response
b) quicker response
c) maximum effort
a. caused by:
i. increased rate of
responding
ii. use of more motor
units
, Muscle structure
Size principle: under load, motor units are
recruited from smallest to largest. In
practice, this means that slow-twitch, low-
force, fatigue-resistant muscle fibres are
activated before fast-twitch, high-force, less
fatigue-resistant muscle fibres
Slow twitch fibres – Type I (can maintain force for a while)
Fast twitch fibres – Type II (cannot maintain force for a long time)
Summary
• Movement allows us to interact with the world and is the reason we have brains
• Nerves are electro-chemical signalling devices
• Motor neurons innervate muscle fibres and reside in the spinal cord
• Motor neurons excite muscle fibres at the neuromuscular junction (NMJ)
• A motor unit is a single motor neuron, along with all of the muscle fibres it innervates
• There are fast and slow twitch fibres that are recruited according to the size principle
Recording and measuring nerve activity
• Single neurons – rare in humans
o can record peripheral nerves and occasionally during brain surgery
• Can easily record electrical discharge of single muscles through the skin (EMG)
• Can record electrical discharge of large populations of neurons through the scalp (EEG and MEG)
• Can detect some chemical signals – calcium, neurotransmitters – with PET imaging or invasive methods
Electromyography (EMG)
Surface EMG- put electrodes on the skin
Wire EMG – high quality, invasive
record signals between electrrodes, can record individual motor units
can see how you recruit muscles
Recording from the brain
• Non-invasive
o Electroencephalography (EEG)
o Magnetoencephalography (MEG)
o fMRI, PET, fNIRS
LECTURE 1: INTRODUCTION TO SENSORY-MOTOR SYSTEMS AND METHODS
Movement
• All of our intentional interaction with environment is through movement
• Understanding of movement control gives insight into hoe the nervous system works
Human movement is special
• Hands
o we are uniquely able to hold and manipulate objects
o we strong and opposable thumbs
o we have flexible and powerful grip
o we have evolved to be tool users
o tool use has allowed us to be general specialists
• Planning (spectrum of abilities)
o we are able to resist immediate responses
o we are better able to plan ahead
o we are better at using flexible rules
Interesting psychological aspects of movement
• Sensory
o we are almost totally unable to move if we lose sensation (dead leg)
• Learning and memory
o we never forget to ride a bike
o we can control our bodies through development
• Action-perception (motor-sensory) interactions
o can understand what tools are and the affordances of different objects
o the motor system is involved in action observation and understanding
o we hold multiple action plans simultaneously and change our minds
• Motor cognition and social interaction
o moto system much more involved in cognition than initially thought
Different learning systems
• Cortex – learning relationships
• Basal Ganglia – reinforcement learning
• Cerebellum – learning through error corrections
Motor Psychophysics
• Traditional ‘sensory’ psychophysics
o vary the stimulus (complexity) -> record simple psychological
responses
▪ pupil size change in response to luminance
• Motor psychophysics
o keep the stimulus simple -> look for regular features of complex movements (complex movement
underlying a simple action)
• Planning choices
o CNS must make decisions in almost every movement
,Motor planning
Planning choices
Motor invariants
• Humans show highly stereotyped trajectories for eye and
arm movements
• Path – sequence of positions of the hand in space
• Velocity – time sequence along a path
• Movements are chosen so as to minimise some cost
o the cost of a movement is specified
o movements are chosen so as to minimise cost
• Examples (all produce similar outcomes)
o Minimum Jerk Model (Flash & Hogan, 1985)
▪ smoothness of trajectory
o Miniumum Torque Change Model (Uno et al, 1989)
▪ rate change of torques (force at a joint)
o Minimum variance theory (Harris & Wolpert, 1998)
▪ minimise variance at the end of movement – more accurate and consistent with less variation
Motor learning and memory
• Sequence learning has revealed important information
regarding motor learning and memory:
o The interaction between implicit and explicit
processes
o The role of sleep
o Interference
o Consolidation
o Probabilistic learning
,Animals’ nervous system
• The reason animals have a nervous system is to act and move
• Thought is but action confined to brain (Jackson, 1835-1911)
• Memory, cognition, sensory processing, they’re there for a reason and that reason is action (Wolpert, 2010)
Neuron types
Inputs
Integration
Outputs
• A typical neuron
o The human brain has approximately
100 billion neurons and 100 trillion synapses
Action potentials
• Brief voltage sensitive change in permeability
• Fast change in Na+ permeability
• Slower change in K+ permeability
Synapse
• Pre-synaptic action potentials increase membrane potential
• Influx of Ca++
• Release of vesicle contents (neurotransmitter)
• Binding to post-synaptic receptors
• Generation of post-synaptic potentials (PSPs)
The Neuromuscular Junction (special synapse)
• NMJ is the complex synapse between nerve & muscle
• Specialised nerves called ‘Alpha’ motor neurons connect to muscles
• It is specialised but has features typical of all synapses
• Alpha neurons innervate between the nervous system and the musculature
• When action potentials arrive it allows a big uptake (strong response) due to the
large surface area
1. presynaptic axon & terminal
2. postsynaptic membrane
3. synaptic vesicle
A motor unit is a single motor neuron, along
4. acetylcholine receptors
with all of the muscle fibres it innervates
Motor unit
A motor pool is a collection of motor units
When an action potential reaches the NMJ there
is a twitch
a) slow response
b) quicker response
c) maximum effort
a. caused by:
i. increased rate of
responding
ii. use of more motor
units
, Muscle structure
Size principle: under load, motor units are
recruited from smallest to largest. In
practice, this means that slow-twitch, low-
force, fatigue-resistant muscle fibres are
activated before fast-twitch, high-force, less
fatigue-resistant muscle fibres
Slow twitch fibres – Type I (can maintain force for a while)
Fast twitch fibres – Type II (cannot maintain force for a long time)
Summary
• Movement allows us to interact with the world and is the reason we have brains
• Nerves are electro-chemical signalling devices
• Motor neurons innervate muscle fibres and reside in the spinal cord
• Motor neurons excite muscle fibres at the neuromuscular junction (NMJ)
• A motor unit is a single motor neuron, along with all of the muscle fibres it innervates
• There are fast and slow twitch fibres that are recruited according to the size principle
Recording and measuring nerve activity
• Single neurons – rare in humans
o can record peripheral nerves and occasionally during brain surgery
• Can easily record electrical discharge of single muscles through the skin (EMG)
• Can record electrical discharge of large populations of neurons through the scalp (EEG and MEG)
• Can detect some chemical signals – calcium, neurotransmitters – with PET imaging or invasive methods
Electromyography (EMG)
Surface EMG- put electrodes on the skin
Wire EMG – high quality, invasive
record signals between electrrodes, can record individual motor units
can see how you recruit muscles
Recording from the brain
• Non-invasive
o Electroencephalography (EEG)
o Magnetoencephalography (MEG)
o fMRI, PET, fNIRS
