Upper Motor Control

Question 1

Revise the organization of motor behavior (e.g. motor cortex, local circuits).

Answer 1

• Motor cortex involves expressions of the face and distal extremities
• Brainstem more about postural muscles

Question 2

Revise somatotopy in the spinal cord - which part receives signals from the motor cortex X brainstem? What kind of relationship - ipse X contra?

Answer 2

Lateral cortico-spinal tract = motor cortex, skill
- has crossing over, contralateral control
Medial white matter = brainstem, posture (stage setting)
- bilateral projections (with exceptions)

Question 3

How do we call the pathway that runs from cortex to spinal cord (2 names)? And what about cortex to brainstem?

Answer 3

• Lateral cortico-spinal tract = cortex-spine
  
  • Projects through Medullary pyramids -> also called Pyramidal tract
• Cortico-bulbar tract = cortex-motor nucleui in the brainstem

Question 4

What areas contribute with emotional signals to the motor pathway? What two parallel pathways do they form + their function?

Answer 4

Extrapyramidal projections
- Lateral = gestures, expressions recognizable as specific emotions e.g. face, postures

• Medial = control over the “settings” e.g. modulating threshold of laughting, crying

Question 5

Which two cortical structures are mainly concerned with motion? Describe their location.

Answer 5

Primary motor cortex
- precentral gyrus, spanning over inferior, middle, and superior frontal gyri
- spans over paracentral lobule

Premotor cortex
- in front of M1

Question 6

What two nuclei of the thalamus send projections to M1 and premotor c.? What other structures contribute?

Answer 6

• Ventral anterior nuclei
• Ventral lateral nuclei
  = VL/VA complex of the thalamus
• Other:
  
  • somatosensory cortex, “where” pathway of the vision (guidance of movement)

Question 7

What is interesting about a histological slice of M1 - layer, type of cells, their connections?

Answer 7

Brodmann’s area 4
Layer 5 - contains Betz cells (largest neurons of the cortex)
- gives rise to descending projections to the spinal cord and brainstem (BUT account to just small portion of it)
- seem to have monosynaptic connetions to alpha motor n. (most usually connect via interneurons)

Question 8

Why was precentral gyrus identified as PRIMARY motor cortex?

Answer 8

1. During first experiments they found out that when stimulating different parts of the precentral aspect yielded different thresholds for eliciting the movement
   => precentral gyrus had the lowest threshold (aka highest P of movement)
2. Seems to encode movements that are primarily connected to our body and its immediate space (e.g. putting something into our mouth)

Question 9

What is the somatotopy of M1? How is it different from S1 (3)?

Answer 9

BUT has Fractured somatotopy = less precise mapping than S1
- overlapping regions that belong to extensor and flexor muscles
- multiple representations of the same muscles e.g. 2 regions that move one digit
- no internal somatotopy e.g. wrist could be next a digit or elbow (homunculus IS MISLEADING)

Question 10

What is represented in M1(4)?

Answer 10

1. Movements, or movement intentions (NOT muscles)
2. Multiple dimensions of movement (force, direction, amplitude)
3. Movements that engage hand, lower face, hand-to-mouth coordination (maybe that’s why face and hand are mapped close together)
4. Skilled manual behavior in our space e.g. pulling something closer to inspect it in more detail

Lesion -> impairs “fractionated” movements of distal extremities or lower face

Question 11

Describe the experiment showing that M1 may encode intention to move rather than just the movement.

Answer 11

Experiment - micro-stimulating M1 region at different sites in rhersus monkeys BUT for a longer period than normally

Result - picture
- cross marks the start of the movement
-circle = end state
=> for all point the intention seemed to be to move the hand from distal position towards the face OR for different stimulation site e.g. trunk

Question 12

Can you recall this research?

Answer 12

Experiment: monkey is trained to move a joystick in specific directions -> a neuron was recorded when movement was executed

Result:
- rows = trials, lines = AP
- one neuron responded to a BROAD range of direction i.e. one neuron does NOT encode for single direction

Question 13

If each neuron could encode all kinds of directions - how does the brain decide what will be done?

Answer 13

It works on the basis of Population code = i.e. the final movement is an average vector of an assembly of firing neurons

Question 14

What may be the function of premotor cortex (it has slightly changed)? What are the subdivisions?

Answer 14

It used to be considered higher in hierarchy (e.g. planning the intension -> while M1 executes it) BUT since PM also has descending connections it seems unlikely

It probably includes a mosaic of essential movements (rough subdividion)
1. Medial premotor area (SSM)
2. Lateral premotor area

Question 15

What does the Medial premotor area include?

Answer 15

1. Medial premotor areas (SMA) = self-initiated movements
   - Emotional behavior(cingulate aspect)
   - organizing by-manual activities
   - Frontal eye field = orients eye movement e.g. turning eyes to contralateral side at our will

Question 16

How about the Lateral premotor area?

Answer 16

2. Lateral premotor areas
   - Movements guided by sensory or social interactions (e.g. Broca’s area)
   - Mirror motor neurons (encodes intention also in other people) => may give us understanding of social stuff (maybe movement-based interventions could help with social cognition in neurodevelopmental disorders)

Question 17

Name the division of brainstem pathways that gets info from vestibular system?
- what nuclei, spinal tract, function
- how is it different from the other one?

Answer 17

Primarily two divisions of cells:
1. Lateral and medial vestibulospinal tracts
- going from vestibular nuclei
- Lateral - ipselateral, extensor lower extremities
- Medial - bilateral, mainly cervical region
- BOTH part of the MEDIAL descending pathway
- Gets immediate feedback to adjust posture
- functions on the basis of PAST information
- e.g. sprinter stumbles -> has to continue with the race

Question 18

What’s the other brainstem motor pathway?
- where (rostral, caudal parts), function - how different?

Answer 18

2. Reticulospinal tract
   
   • going through the midline = Reticular formation (pons, medulla apects)
     
     • rostral part = modulation e.g. Ralphe nucleui
     • caudal part = coordination of lower motor n. output - some somatic, some visceral
   • bilateral supply to spinal cord n.
   • functions on the basis of ANTICIPATORY information -> adjustments of posture
     
     • e.g. a sprinter preparing to make an exposive action when “GO!” comes
       -> there must be connection to premotor c. and M1

Answer 19

Superior colliculus = motor structure that integrates sensory information
- input: vision, audition, sensorimotor
- output: reflexive motor action e.g. shift of our attention (saccadic eye movements, turning of head)

Question 20

Why does normal and fake smile look different?

Answer 20

They employ different motor pathway which results in a different output e.g. not having lines around the eyes

• Genuine emotional smile is motivated by Cingulate motor area
• While fake smile is executed by motor circuits in M1 and premotor c. - aka part of the pyramidal system

Question 21

What specific human skill could integrate both motor and emotional circuits?

Answer 21

Human speech - needs two components: vocalization and articulation