W4L2 - Using knowledge of brain body interactions

Question 1

What is target muscle reinnervation?

Answer 1

Targeted muscle reinnervation

• During amputation surgery
  
  • Nerves for missing muscles are reattached to existing muscles to prevent neuroma
• After some time
  
  • Nerves activate new muscles when attempting ‘old’ function
  • EMG generated in re-innervated muscle detect by prosthetic and used to make ‘natural’ movement

Question 2

What is quadriplegia? What did prosthetics demonstrate?

Answer 2

Quadriplegia

No signal going through spinal cord and muscles

Prosthetic

• Microelectrode planted over M1, where electrode is ued to map M1
• Electircal signal to computer
• Showed that motor cortex is still able to function over a decade after loss of descending motor outputs

Question 3

Aflalo (2015): Other than M1, where else could electrodes be implanted to enable movement control?

What is the issue?

Answer 3

PPC (Think) + M1 (Move)

Issue

No feedback – there is no sensation arising back from the arm etc (eggshell)

Question 4

What is somatosensory feedback.

Answer 4

Somatosensory Feedback

• Sensation of body and its movements
  
  • Different sense occur via different receptors located on nerve endings
    
    • Free nerve endings: Pain, warmth, cold
    • Merkel’s disk: Light Touch
    • Pacinian corpuscles: deep pressure
    • Hair follicle receptor: hair movement

Question 5

How does somatosensory feedback work

Answer 5

• Receptors open Na+ channels in axons, causing action potientials (diff forms of stimuli, diff receptors > electrical signals)
• Sensation sent to brain via. spinal nerves which have different characteristics for different receptors
  
  • Dermatome: Area of body each spinal nerve innervates

Question 6

How does sensory information reach the brain?

Answer 6

• Receptors > Spinal cord > Somatosensory cortex (behind M1)
  
  • Signal coming down from M1 > Medulla > Contralateral side
  • Signal coming up from left index fingers > Medulla > Contralateral hemisphere
  • Hence, this information coming back up through the sensory system also comes back up to the medulla and crosses over to the contralateral side

Question 7

How is somatosensory cortex organised? How is it different from M1

Answer 7

Somatotropic organization

• All the information about sensation from the face come in right next to the region of the motor cortex that corresponds to the face.

Difference

• You feel tooth pain but you can’t move your teeth
• You have lots of sensory information from the genitals but not much control over it.

Question 8

Other than somatosensory cortex, where is information sent to? What happens if there is damage to one region

Answer 8

Somatosensory information is also sent to insular, which is also involved in emotions

• Feather = Nice
• Hard harshake = Unpleasant

Damage to one region can cause separation of emotional content versus sensation

Question 9

When sensory nerves are damaged, what can be useful and why? What are some criticisms

Answer 9

Microarrays placed over somatosensory cortex

• Mimics natural biology
• Adaption or learning (e..g picking up egg)

Critics

• Some scientists argue that sensory feedback not essential with visual feedback and practice

Question 10

What is efference copy? What is the advantage?

Answer 10

Efference Copy (corollary discharge)

• Copy of the motor command sent to sensory regions (instead of muscles)
  
  • Enables planned movement to be compared with actual movement
  • Enables sense of self-generated movement

Question 11

Explain why when we copy someone’s force, it gets stronger? How does it relate to tickle

Answer 11

Efference Copy

• We pay more attention to externally generated information than internally generated sensations
  
  • Wwhen we do it to ourselves, we know that we are about to get a push.
  • So if you push someone else you think that you’re not doing it as hard as it feels to them

Since we know the tickle is coming, it doesn’t work

Question 12

What are the 2 kinds of tickles?

Answer 12

Tickle

• Light feather touch “itch type”
  
  • Somatosensory and ACC
• Deeper laughter provoking type

Anterior supplementary motor cortex activated when laughing

Question 13

Self-tickle with delay. What are the results?

Answer 13

If there is a delay between thinking and action, one can self-tickle

• If you move a joystick and the feather attached to another device will tickle you, but is there is no delay between your movement and the feather tickling you, then you don’t find it too ticklish because you are doing it
• If you move the joystick and there is a 100ms delay with tickling you, you find it more ticklish. If the delay goes up to 200ms, it gets even more ticklish and it is about as ticklish as when someone else tickles you

Question 14

Explain the link between tickle and schizophrenia

Answer 14

• Schizophrenia may result from faulty efference copies of speech and movement (maybe thought)
• If one doesn’t recognise it as self-generated it is natural to assume someone said something
  
  • Not much difference in tickle rating when tickle is self-generated versus externally-generated in patients with auditory hallucinations presents or absent