Action Flashcards
What is action
Change in the environment
3 types of actions
Somatic:
Autonomic
Actions internal to the CNS
Example of somatic action
Skeletal muscles: move limbs
Example of autonomic action
Smooth muscles: change blood pressure, digest food
Cardiac muscles: heartbeat
Endocrine glands: secrete hormones
Exocrine glands: secrete sweat, saliva, etc..
Actions internal to the CNS
Update memory, switch tasks, etc…
Update path you take to school → update your address in your memory → action in brain
Problem solved by action
How to effect change in the world
Importance of action
Necessary to achieve goals (eat, drink, reproduce, survive, etc…)
Challenge of action
The inverse problem: determining what actions to take in order to achieve goals
Working from the goal backwards
We are hungry (goal) → have to figure out what actions to take to get there
Where is supplementary motor cortex located relative to primary motor cortex and premotor cortex
rostral to primary motor cortex and dorsal to premotor cortex
Motor system hierarchy
Start off with a high level goal and work your way down to which specific muscles to activate → opposite from perception
What does the motor equivalence writing task show
pattern/form of strokes were mostly the same between conditions
Using the same upper levels of hierarchy and replacing the lower ones
Inverse model of motor control explained
Current position & desired position → motor commands
Start with goals then determine what to do to end up there
Used to create a motor plans
Do we usually do the inverse model or the forward model first
Use the inverse to formulate plan then use the forward model to evaluate it
Forward models of motor control explained
Current position & motor commands → predicted position
Given where my hand is now and the muscle movements I’m going to take → where is my hand going to end up
Used to evaluate motor plans and/or actions
Know what the results should be and compare that to what actually happened
Explain how the inverse and forward model connect and provide the steps
Start with a desired behaviour and use the inverse model to get a motor command
A copy of that motor command gets send to a forward model which takes motor command and current state to predict what will happen
Can compare what actual happened to what we predicted
What is an efferent copy
internal copy of a motor command
What is feedforward control and an example
Motor command sent to muscle
Faster, but less accurate
Uses inverse model
Have a desired state and come up with a motor common send it to the muscles and hope that it works
Removing hand from hot pot or throwing a ball
What is feedback control and an example
Motor command sent to muscle
Actual state compared to desired state
Adjustments made based on errors
Catching a ball
Picking up a coffee cup
Slower, but more accurate
Uses inverse and forward model
Does the feedback control have feedforward within it
Yes
Compares what happens to what we wanted to happen
Does feedforward control use inverse or forward model
Inverse
Does feedback control use inverse or forward model
Both
What is the function of the premotor cortex
Involved in selecting goals and planning actions at a conceptual level
- want to quench thirst so we need to drink from a cup
involved in motor planning
Particularly when plans are driven by external stimuli → picking up a cup to quench thirst
What area is involved in the highest level of motor planning
premotor cortex
What is motor planning
Planning of voluntary actions begins at a conceptual level based on goals
What is the readiness potential and its use
Planning in premotor cortex (contralateral hemisphere) occurs before voluntary movement
activation precedes awareness
You could guess what hand someone will move before it does by looking at which hemisphere is activated
How can we plan for multiple actions
We can come up with an initial motor plan for both actions if we aren’t sure what we are going to do yet
Planning for multiple actions experiment
Spatial cues: Monkey is cued with two possible targets (red & blue)
Memory period: Cues are removed, monkey seems to prepare both actions → remembers both
Color cue: Monkey is cued with actual target, and now prepares single action → you will be doing red action
Go signal: Monkey initiates action
Monkey brain shows activation for both motor plans
Function of mirror neurons
neurons in premotor cortex represent actions at a conceptual level → represents abstract idea of breaking a peanut
Mirro neuron experiment
Record a money performing different tasks with a peanut: Breaking a peanut, Watching and hearing someone else break a peanut, Watching someone else break a peanut, Hearing someone else break a peanut
Neuron fire in all cases because thee neurons represent the abstract idea of breaking a peanut
Function of supplementary motor cortex
Involved in selecting goals and planning actions at a conceptual level
Particularly when plans involve internally generated sequences of actions
- tying shoes
- Playing a song on the piano
- dancing
- pitching a baseball
Results from recording SMA neuron during different motor sequences
Fires in anticipation of a particular sequence → push turn pull sequence but not the push pull turn sequence
fire before a particular action in a particular sequence → fires before the push action in the pull, push, turn sequence
This neuron fires before the third action in every sequence
Learned vs cued sequences when SMA is inhibited
Unable to perform learned sequences from memory without SMA
Without the SMA the animal could perform the action when it was told which action to perform at each step
Function of primary motor cortex
represents directional movements of body parts, not specific muscle actions
Move arm forward
Difference between SMA and premotor cortex
SMA handles learned sequences of action
Premotor cortex handles cued sequences
Where do signals from motor cortex travel
Signals from motor cortex travel directly to lower motor neurons and lower circuit neurons in brainstem and spinal cord → synapse on other side of the body
Where is the primary motor strip located
back of frontal lobe –> pre central gyrus
How are motor and somatosensory maps similar
Each hemisphere of cortex controls the contralateral side of the body
Bottom of body is represented at the top
cortical magnification is shown in both
What part of the cortex is involved in directional selectivity
Primary motor cortex
Is directional selectivity based on a visual cue
No, it is about the direction of movement
Explain what a tuning curve for directional selectivity represents
Plot average response rate for different angles of movement for a single neuron
It is quite broad –> → doesn’t only fire to movement in 180 degree direction
How do we create a population vector from tuning curves and what do the length and direction of the lines mean
Record two neurons, which each have a tuning curve → combine the representation
Direction of vector is determined by preferred direction
Length represents how much it is firing
When we add them together, the resulting vector points in the direction the animal moves
What does a population vector do
Accurately represents actual movement direction for multiple neurons by adding up the individual vectors
Is the motor cortex involved in planning
Still plans for directional movement a bit
Do population vectors represent motor plans?
Yes
If a cue is presented to the animal, After 100 or 200 ms the population vector starts to form in motor cortex → animal hasn’t move yet
The direction of the population vector predicts the direction of the forthcoming movement
Function of basal ganglia
Motor intentions
Help to select, initiate, and
inhibit movements through
cortico-basal ganglia-
thalamocortical loops
Critical to dopamine-based reinforcement learning (learning when to act from
reward)
What kinds of control do the cortico-basal ganglia-thalamocortical loops participate in
Participate in motor control, cognitive control, and emotional control
Path of cortico-basal ganglia-thalamocortical loops
Start in the cortex, pass through the basal ganglia, then the thalamus and back to the cortex
Direct pathway in cortico-basal ganglia-
thalamocortical loops
- Cortex
- Striatum
- Globus pallidus pars interna (GPi)/Substantia nigra pars reticulata (SNr)
- Thalamus
- Cortex
Indirect pathway in cortico-basal ganglia-
thalamocortical loops
Cortex
Striatum
Globus pallidus pars externa (GPe )
Subthalamic nucleus (STN)
Globus pallidus pars interna (GP i)/Substantia nigra pars reticulata (SNr)
Thalamus
Cortex
Baseline activation in cortico-basal ganglia-
thalamocortical loops
Before the direct or indirect systems are engaged, the GPi/SNr have high tonic (baseline) activity, inhibiting thalamus → thalamus has little output to cortex
What pathway does action initiation use in cortico-basal ganglia-thalamocortical loops
Direct pathway
What pathway does action inhibition use in cortico-basal ganglia-thalamocortical loops
Indirect pathway
Action initiation steps in cortico-basal ganglia-thalamocortical loops
Direct pathway:
- Motor plan forms in motor cortex
- Motor cortex excites striatum
- Striatum inhibits GPi/SNr → lowers their tonic firing rate
- GP/SN disinhibits thalamus → less inhibition
- Thalamus excites cortex → increases activity of motor cortex until it generates the action
This aids selection and initiation of action
How do we determine if we are going to activate the indirect or the direct pathway of the cortico-basal ganglia-thalamocortical loops
Reinforcement learning
Action inhibition steps in cortico-basal ganglia-thalamocortical loops
Indirect pathway:
1. Motor cortex excites striatum
2. Struatum inhibits GPe
3. GPe disinhibits STN
4. STN excites GPi/SNr
5. GPi/SNr reinhibits thalamus
6. Thalamus tells motor cortex “not yet”
More steps in indirect pathway make it slower to act than direct pathway
Happens when you need to wait for a go signal
How does reinforcement learning work in the cortico-basal ganglia-thalamocortical loops
Unexpected rewards generate dopamine signals from the substantia nigra pars compacta (SNc) to the striatum
Dopamine release excites the direct pathway (via D1 receptors) and inhibits the indirect pathway (via D 2 receptors)
This allows modification of behavior based on reward → more based on something that is better than expected
What happens when you damage the cerebellum
movement isn’t as smooth/coordinated
Does the cerebellum have white matter and grey matter
What about sulk and gyri
yes
Grey matter on the outside
What types of cells are found in the cerebellum
Granule cells: 50 billion (¾ of all neurons in the brain)
Purkinje cells: 200 000 inputs per cell → lots of dendrites -> lots of connections
Function of cerebellum
Critical to performing movements in a smooth and coordinated way
How is the cerebellum involved in motor coordination
Uses forward model to predict results of motor commands (implement feedback control)
Uses differences between actual results and predicted results for:
Online error correction → tweak it as we go
Motor learning → next time it will be better from the beginning
Feedback control to make movements better
How does the cerebellum compare our actual actions to our predicted actions
Motor command in primary motor cortex gets sent to spinal cord so that you can execute it → efferent copy of command goes to cerebellum
Something happens from taking the action and meanwhile the cerebellum uses forward model to predict what should happen next
These two things are compared → if there is an error → it gets sent back through the thalamus to primary motor cortex to make adjustments
Is feedback control fast and is it accurate
Feedback takes time
The faster you go, the less time you have for feedback → Less feedback leads to greater error
This implies a speed/accuracy tradeoff
What does Fitts’s law describe
describes the speed/accuracy trade off for pointing motions
What does the T, a , b , w, and D represent
Time, T, for pointing motion depends on:
Distance to target, D
Width of target, W
Initiation time for limb, a
Relative pace of limb, b
If you want to reach the target in less time what would happen to W
target would have to be wider –> less accurate
If you want to reach a narrower target what would happen to T
T would increase –> less speed
What would happen if you increased D in fits law. What about decreased D
increased D would be faster and decreased D would be slower
How is the cerebellum involved in cognitive coordination
adding numbers in your head, figuring out your next move in chess playing chest
Where do primary motor cortex axons go to?
Axons from primary motor cortex synapse directly on lower motor neurons and local circuit neurons → crosses over
Can the spinal cord generate movements on its own?
yes
What is a lower motor neuron
cell body in spinal cord and axons travel out to the muscles
What is local circuit neuron
in spinal cord but doesn’t synapse on muscle → figures out which muscles are going to be active
Is the brain involved in the patellar reflex
No
What is the flexor withdrawal reflex circuit used for
Shifting weight if you step on something sharp
Is conscious control (inhibition) of a flexion reflex possible:
Yes, if the intention not to respond was prepared in advance, so that a signal could be sent to the reflex pathway in the spinal cord before the stimulus occurred, thus inhibiting the reflex when the stimulus did occur
What are central pattern generators
Local circuits in spinal cord:
Can control complex movements → walking
Can respond to environmental changes
Do not require higher-level input
Still need brain to tell you when to start
Central pattern generators experiment explained
Movement is still possible following resection (cut) of the spinal cord before the hind legs → no signals from brain getting to hind legs
Circuitry exists within the spinal cord to move the legs
How are muscles activated
Lower motor neurons synapse directly on muscle fibers
Release of neurotransmitter causes muscle fibers to contract
What are muscle spindles
Muscle spindles (sensory cells) detect changes in muscle length and send them back to spinal cord via dorsal root ganglia
Does one axon only innovate one muscle fibre
One signal axon can innervate many muscle fibres → cause them to contract
For limbs with finer motor control, each motor neuron innervates fewer muscle fibers → leads to cortical magnification
How is multi unit recording done in an awake animal
Electrodes implanted in brain and a mount is on the head → plug into the mount
record the brain activity of the animal
What is intracellular electrical recording
Electrode into individual neurons → in vitro
Voltage clamp/Current clamp
Patch clamp
What is extracellular recording and single unit vs multi-electrode recording
Electrode adjacent to individual neurons
Records field potentials
Single-unit recording → record from a single neurons
Multi-electrode recording → record from lots of neurons simultaneously
How is the spatial and temporal resolution for single unit or multiunit recording:
Great spatial resolution →
Because you are recording from a single neuron
Great temporal resolution → when activity occurs
Challenges to single unit or multiunit recording
How to find “right” neurons
How does this neuron relate to other 100 billion neurons?
What are some of the larger considerations of animal experimentation
Pain and suffering
Lack of consent
Killing living creatures
Interspecies differences (Fruit fly, Mouse, Macaque)
Benefit to humanity
Necessity for knowledge
Example of a brain-machine interface
Reach and grapes by people with tetraplegia using neurally controlled robotic arm
How do we use brain machine interfaces
Two microelectrode arrays are implanted into the left motor cortex (in motor strip) to detect neuron signals
Neuron signals pass to connectors, attached to the skull (mount)
Amplified signals are passed to a Brain-machine interface which interprets them and passes them onto the arm
Interface operates robotic arm in real time
How do we decode the primary motor cortex activity to use it for the brain-machine interface
Can learn the relationship between pattern of neural activity and intended action → use this to convert the motor intentions into commands for the robotic arm
