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NYU / Psychology / PSY 25 / What are the main motor structures and pathways?

What are the main motor structures and pathways?

What are the main motor structures and pathways?

Description

School: New York University
Department: Psychology
Course: Cognitive Neuroscience
Professor: Clay curtis
Term: Winter 2016
Tags: Cognitive Neuroscience, neuroscience, neural science, psychology nyu, and cog neuro
Cost: 25
Name: Motor Control I & II
Description: Both motor control lectures- very descriptive breakdown of everything!
Uploaded: 04/05/2016
7 Pages 128 Views 11 Unlocks
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3.1. Motor Control I


What are the main motor structures and pathways?



“Life’s aim is an act, not a thought.” -Charles Sherrington

The aim of all cognition is action.

What are the main motor structures and pathways? 

Motor pathway hierarchy

∙ The lowest level of the hierarchy is the spinal cord. The spinal cord is the point of  access between the nervous system and muscles(output signals). It’s also in charge of  reflexes.

∙ At the top of the hierarchy is the premotor and association areas in the cortex.  Processing within these regions is critical for planning an action based on an individual’s  current goals, perceptual input, and past experience.

Because the motor system is hierarchical, a lesion at any point in the hierarchy could have  different effects on movement.


What is basal ganglia?



Spinal Cord

Spinal cord neurons can generate simple sequences of actions without any external feedback.  These are reflexes. Reflexes are independent of higher processing.

Effector: A part of the body that can move. All forms of movement result from stimulation of  effectors. Muscles are affected by motor neurons:

∙ Alpha Motor Neurons are responsible for contractions by the release of acetylcholine.  They provide a physical basis for turning signals into movements by changing the length  and tension of the muscles. We also discuss several other topics like What is the meaning of neocolonialism?
Don't forget about the age old question of What is the meaning of hippocampus?

∙ Gamma motor neurons are responsible for sensing and regulating the length of the  muscle fibers

∙ Spinal Interneurons lie within the spinal cord and are innervated by afferent sensory  nerves (skin, muscles, joints). Signals to the muscles involve continual integration of  sensory feedback with the motor commands from higher centers.


What is brain machine interface?



If you want to learn more check out What is mutual marriage?

Muscles are often arranged in antagonistic pairs, one may serve to contract and the other  relaxes.

Pyramidal & Extrapyramidal Tracts

Pyramidal Tracts originate in the cortex and project all the way down to the spinal cord. ∙ Corticospinal tracts are responsible for voluntary skilled movement of the hands and  fingers.

Extrapyramidal Tracts project from the sub-cortex to the spinal cord.

∙ Causes involuntary reflexes and movement and influences regular movement as well.Don't forget about the age old question of What is planning?

Cerebellum

The cerebellum has an ipsilateral orientation because the input to and output tracts from the  cortex cross over to the contralateral side: Right side controls right, left side controls left. ∙ vestibulocerebellum: Balance and coordination of eye movements with body  movements. ex.vestibulo-ocular reflex (VOR) assures that the eyes stay fixed on an  object, regardless of body movements (like typing!)

∙ Spinocerebellum: Receives information from visual and auditory systems. Lesions here  can result in unsteady gait and lack of balance. Cells here are sensitive to the effects of  alcohol.

∙ Neocerebellum: Heavily connected to frontal and parietal lobes. Lesions here produce Ataxia which is the lack of voluntary control over voluntary muscle movements. Basal Ganglia

Caudate nucleus, putamen, substantia nigra, globus pallidus, subthalamic nucleus. ∙ Plays a role in motor control, specifically the selection and initiation of actions. Basal Ganglia as the gatekeeper. It inhibits irrelevant motion and lets through the most potent  stimulus.

∙ Huntington’s Disease: Causes excess movement. Basal Ganglia is no longer inhibiting  stimuli. Associated with the Indirect Pathway. The brakes are not working. o Indirect Pathway inhibits the Thalamus & cortical motor areas.(Inhibition of  inhibitory pathway just results in less control. Signals will get through that you  don't want to get through) Don't forget about the age old question of What is unemployed?

∙ Parkinson’s Disease: Too much inhibition causes loss of voluntary movement. The  basal ganglia is ALWAYS inhibiting (tremors while at rest). Associated with the Direct  Pathway. The brakes are always on.

o Hypokinesia: Reduced voluntary movement

o Bradykinesia: Slowness in movement

o Direct Pathway excites the thalamus. (Inhibition of an excitatory pathway is too  rigid. Nothing gets through.)

o Parkinson’s is linked with a loss of dopaminergic cells in the Substantia Nigra. Treatment usually involves L-Dopa injections, lesions to global pallidus or deep  brain stimulation.

o Patients w/ Parkinson’s diseases have difficulty shifting between concepts as  well as actions.

Direct & Indirect Pathways have different receptors that respond to Dopamine differently (D1 &  D2)

Primary Motor Cortex (M1)

M1 is located in the posterior part of the frontal lobe and receives input from nearly all regions  involved in motor control. M1 also has a crude somatotopic map.

∙ The representation of the effectors doesn't have to do with their size but rather how important they are to movement, and the level of control required for manipulating it. ex.fingers! If you want to learn more check out What are the calculate components of income statement?

Lesions to M1 typically result in hemiplegia which is the loss of motor control on one side of  the body.

Motor Execution vs. Planning

∙ Execution of motor movements only involves the motor cortex

∙ Planning a motor movement involves both M1 and the Supplementary Motor Area (SMA) ∙ Thinking about a motor movement only recruits SMA

If you apply TMS while someone is moving their fingers: 

TMS to M1: Result is a temporary loss of coordination. The next response is halted or incorrect. TMS to SMA: Subjects lose track of their movements. The goal was disrupted.’

Internally vs Externally Guided Movements

In the task, Internally guided movements are guided by memory, whereas the externally guided  movements are guided by a light.

Internally guided movements recruit SMA

Externally guided movements recruit PMC

3.2. Motor Control II

Apraxia Subtypes: (lesions to secondary motor areas)

∙ Apraxia is characterized by the inability to make skilled movements. Linking gestures to  meaningful actions. (NOT to be confused by Alexia or Ataxia).

1. Ideomotor Apraxia: The person has a sense of what the action is, but they cannot  execute that action. They have trouble with initiation. Ex. Hitting the hand on the head  when prompted with a comb. They understand that the comb is associated with the hair  but cannot make the proper action.

2. Ideational Apraxia: The concept of the action is impaired. They have difficulty  recognizing and executing such actions. ex. Brushing teeth with a hair brush.

Motor Hierarchy

∙ Premotor: Premotor region is responsible for planning and perceptual input. ∙ Motor: Takes the action plan and makes it happen.

Abstract Representation of Action

Action that is independent of a particular muscle group. Ex. Writing a word with multiple body  parts.

Trajectory Planning: How do we represent movements?

Trajectory-Based Representation: An action plan specifies the trajectory that will move the  limb across a certain distance, along a certain path.

Location Based Representation: Motor representation specifies the desired final position to  achieve movement goal.

Monkey Study on Trajectory Planning

Deafferentation: the interruption or destruction of the afferent connections of nerve cells,  performed in animal experiments to demonstrate the spontaneity of locomotor movement.  Results in a loss of sensory input. 

Deafferented monkeys got trained in a simple pointing experiment which would determine  whether trajectory based or location based planning seemed to be most valid. Because they  were deafferented, they did not know a force was being applied.

∙ The monkeys were tasked to point at a light in a dark room, however the catch was that  before they would be before the arm movement was made, an opposing force would  restrict the movement of the arm.

∙ The monkeys were NOT trained with the force. So if they were using a trajectory based  approach, the surprise force would’ve hindered their plan and they would have  undershot their target. ( The monkeys were not aware of the force. Had they known they  could’ve changed their motor plan upon noticing the force.)

∙ Results of this show that monkeys did not overshoot the goal so this supports location  based representations or endpoint control. 

Hierarchical Control of Action 

∙ Chunking movements together is possible (like memory can be chunked). ex. Asking someone to dance. The number of responses is big, but once accepted the arms and  legs act to stand up and dance. 

Neural Coding of Movement 

Motor Cortex 

Some neurons tended to have preferred directions. 

ex. Monkeys trained on a task to move their hand in the direction of a light stimulus. ∙ Population vectors tended to have better correlation with behavior than the analysis of  individual neurons. (Recording from a bunch of different cells and sum their signals  together. A population of neurons.) 

∙ Population vectors can also predict movement direction. Population vectors are already  curving towards the indicated direction before the movement is even made. So it doesn't  happen at the same time as the movement. 

Brain Machine Interface (BMI) 

Allows neural signals to be used to perform a desired action with the aid of a mechanical device  outside of the body. 

ex. Signals from neurons in motor cortex can be used to move a robotic arm. ∙ First done in rats (water/lever experiment). If they pushed a button, a lever would cause  the release of water. They turned a switch so that instead of the button the firing of the  neurons would control the lever. The rats picked up on the association and controlled it  without touching it. 

∙ Quadriplegic woman eating chocolate using a robotic arm. Patient M.N

Making BMI stable 

Recorded same neurons for 19 days, and actually the monkeys got better at doing the tasks  with the arm. Also when the target directions were changed, the monkeys were able to adapt to  the changes after some practice. Shows that motor cortex is plastic to some degree. 

Action Goals & Movement Plans 

Affordance Competition Hypothesis: At any given time we have multiple opportunities for  action that are defined by the environment. The opportunities for action compete against each  other, but only one action plan wins out. 

∙ Action selection and specification happen simultaneously and they continuously evolve. ∙ Action plans are eventually updated by environmental feedback and internal feedback &  drives. 

∙ One action wins is selected and executed. 

Evidence for AC Hypothesis 

Premotor cortex recording in monkeys. Repeated action plans are kept in mind until its clear  that one is selected. 

Representational Variation in terms of how motor areas represent action selection and  planning. Direct brain stimulation of dorsal premotor cortex and posterior parietal cortex has  different effects: 

Premotor Cortex 

∙ Stimulation evoked complex movements without conscious awareness or movement  intention. 

∙ Plays more of a role in execution 

Parietal Cortex 

∙ Stimulation evoked intention to move or perception of movement in absence of muscle  activity. With enough stimulation the patients would feel as if there was an actual  movement, even though there wasn't any muscle activity. ex. “i felt a desire to lick my  lips.” 

∙ Plays a role in intention. 

Repetition Suppression for Movements 

Repetition Suppression typically corresponds to less activation for repeated stimuli ∙ Participants shown small movie clips of both novel and repeated movements. They had  to see if the type of movement (kinematic) that was made was repeated/novel or if the  outcome of the movement was repeated/novel. ROI activation during this was measured. ∙ Less activation for repeated movements was found in left frontal cortex (execution) ∙ Less activation in right parietal cortex for repeated action goals. (Goals/Intentions) 

Mirror Neurons allow us to comprehend the actions that other people are doing. ∙ Same neural activity happens when we watch someone doing an action as when we are  doing the action. However it is not just about visual properties, it can also be aural or  something.

∙ signal goal oriented actions & understanding imitation. 

Mirror neurons & Expertise: Level of expertise impacts activation in mirror neurons. Example  of dancers. Viewing choreography caused activation in premotor and parietal areas. So mirror  neurons were activated for viewing choreography. 

How do we learn new motor skills? 

Sensorimotor Adaptation: When a learned skill is modified due to a change in the  environment. 

Ex. Throwing a ball normally vs. throwing a ball with Prism Glasses on. 

∙ The prism glasses distort the vision to one side so at first the there is a horizontal  displacement between the target and where the ball ends up but after a while the person  gets used to the change in visual input and begins to compensate for this deficit and  throws the ball at the target. When the glasses are removed they miss the target  because they are over compensating (after effect) but after a while they realize they no  longer have to. 

∙ People with damage to the cerebellum are not able to adapt to changes when they put  on the prism glasses. Suggests cerebellum plays a role in sensorimotor adaptation. 

Transcranial Direct Current Stimulation (Similar to but NOT the same as TMS) In the study TDCS was either applied to cerebellum or primary motor cortex, and the current  excites the neurons and helps along processing. In the experiment people had to make fast  reaching movements with a stylus. They had to practice these movements and then the  researchers rotated the visual input and they had to learn to adapt to the change in direction 

There was a double dissociation found between the two areas with respect to sensorimotor  adaptation. 

∙ Cerebellar stimulation resulted in faster learning of the movements. People were  making fewer errors. Suggests that cerebellum is important in the initial learning that  helps with the sensorimotor adaptation 

∙ Primary Motor Cortex stimulation resulted in stronger consolidation. The after effect of  the change in input lasted longer. Suggests that this is more involved in the retention  and consolidation of what is learned. 

Role of Dopamine in Motor Cortex 

There are dopaminergic projections in the brain from the Ventral Tegmental Area (VTA) in the  brainstem, to the Primary Motor Cortex that are necessary for acquiring new motor skills. **Projection tracts typically go from higher and lower brain regions as well as the spinal cord region. 

Rat study where rats had to pick up pieces of food with their paws (which is challenging for  them). Researchers lesioned the VTA in some rats, cutting off the dopamine projections and  then they were given an L-Dopa injection and others with the lesion were given a saline injection. 

Control(Sham) Rats = no lesion = no hindrance

Lesioned rats w/ L-Dopa injection = learned only with shot. 

Lesioned rates w/ saline injection = did not learn 

The sham rats learned the skill fine, but the lesioned rats did not improve unless they were  given the L-Dopa injection. So this suggests dopamine plays a key role in the learning of new  motor skills. 

Role of Cerebellum & Timing 

∙ Cerebellar lesions disrupt learning in the context of delay conditioning. ex. Air puff/eye  blink. They're trained to start blinking once they hear a tone since it had been paired with  a puff to the eye. But when rabbits are lesioned in the nucleus of the cerebellum, rabbits  blinked at the air puff but not at the tone. so they did not have an anticipatory response. 

∙ When cerebellum is lesioned in other areas, the anticipatory blink occurs but the timing  of the blink is off. So cerebellum must play a role in timing our movements. ∙ May generate sensory predictions of what it expects to happen given a specific  movement.

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