Lecture 11&12 - Map Plasticity and Pathologies

Question 1

What is a bad example of plasticity?

Answer 1

• Phantom Limbs: removal of sensory surface can lead to ongoing sensations from the surface

Question 2

What is PLP?

Answer 2

• Phantom Limb Pain
• Some stereotypical experiences that a lot of PL patients feel
• Pharmaco resistant

Question 3

What did Ramachandran do?

Answer 3

• Very small N group
• Strong spatial relationship between intact body and sensation of phantom limb
• Could touch someones face to make him feel his thumb due to the human plasticity map
• Got patients into MEG and used one hemisphere to act as a baseline and found a closeness within cortex that would have responded to the missing limb

Question 4

What happens when you look at a larger population?

Answer 4

• Sensations stable?: do you still feel it when i stroke face
• Are sensations modality specific?: Is it an itch/pain?

Question 5

Is there a relationship between PLP and remapping?

Answer 5

• Sig correlations between extent of remapping and intensity of phantom limp pain
• Stimulus on lip, on digit on hand
• Both hemispheres show different things: broken side = D2 & D4 increased in size and moved closer

Question 6

What is dystonia?

Answer 6

• Co-contraction of agonist/antagonist muscles
• Can happen genetically or if you over practise a particular sensation e.g musicians
• Lots of overlap in areas of digits

Question 7

How to track rehab of dystonia?

Answer 7

• Rehab = changed organisation of map NOT to normal, but textbook level normal
• Changes in experience are mirrored in the map

Question 8

What is mirror box therapy?

Answer 8

• Amputee places intact hand in box and put amput on other size
• Look at mirror and intact hand moves and visual stimulation catches and feeling of amputation falls = reduction in pain

Question 9

What is proprioception?

Answer 9

• Muscle and joint senses
• Patient IW lost fine touch and proprioception
• Has no body sense when eyes are closed
• Regained ability to walk and use limbs again

Question 10

What is the body schema?

Answer 10

• Body can be updated based on experience and is plastic

Question 11

Difference between top-down/bottom-up

Answer 11

• Bottom up: info comes from env
• Top down: info coming from areas of brain
• Bottom up is being altered by previous experiences of the world = multiple maps

Question 12

What are neurobiological substrates?

Answer 12

• Multiple maps that only occur in particular areas e.g found different states of motor system

Question 13

What happens when info from different modalities conflict? (Rubber hand exp)

Answer 13

• Rubber hand illusion: Visual info comes from hand & proprioception comes from real hand
• Visual and tactile input synchronised
• Paintbrush strokes real hand behind barrier
• Can feel touch in fake arm
• Ask ppts to indicate with other hand where hand in experiment is = adrift to rubber hand
• More adrift = correlates to how much you think the hand is yours

Question 14

To what degree is the rubber hand incorporated into the body schema? (Exp)

Answer 14

• Induced rubber hand illusion in MRI scanner
• Made brisk stabbing movements with sharp needle
• Subjects reported feelings of ownership over hand and anxiety when threatened

Question 15

What was the brain activity in the rubber hand exp?

Answer 15

• Pre-supplementary motor area activated when real hand threatened. Also activated for fake hand.
• Activity in insula and ACC was correlated with degree to which individuals thought fake hand was real

Question 16

What is consolidation?

Answer 16

• Mechanisms that act to stablise and enhance memories over time
• Memories do not have to be declarative/procedural
• Changes to cortical map structure are a kind of memory

Question 17

What does consolidation require?

Answer 17

• Requires a signal to ensure changes that are of significance
• Basal forebrain has been studied in cortical projection

Question 18

What is the signal for consolidation?

Answer 18

• Neurons in NBM use Ach as neurotransmitter
• Ach is also neuromodulator: regulates firing of larger groups of neurons

Question 19

How to link the NBM and Ach to map plasticity? (Exp)

Answer 19

• Lesion studies: remove NBM and cortex is starved of cholinergic input = no D2&4 expansion = map does not expand

Question 20

What is auditory cortex plasticity?

Answer 20

• Map of frequencies not map of body (A1)
  e.g looks like piano keyboard
• Performed on rodents

Question 21

What was the experimental design for rodents?

Answer 21

• Naive rat and manipulated rat: tone represented in A1 = manipulated artificial signal
• Can reshape auditory map: some could not identify other tones because of the way their maps changed.

Question 22

How does cholinergic input modulate the way that cortical neurons respond to sensory stimuli?

Answer 22

• Neural modulation shws env subtly changes mapping
• Retuning the receptive fields within the sensory cortex by giving them an overwhelming signal

Question 23

What is the role of NBM and map plasticity in naturalistic learning?

Answer 23

• When linking map plasticity and NBM activity = no real learning as no task performed by rats
• Link map changes, forebrain activity and changes in performance on an actual task
• Lesioned NBM = more specific

Question 24

How did they experiment plasticity in naturalistic learning?

Answer 24

• Trained rats to retrieve sugar pellets through a slit using a forepaw
• One group had NBM lesion, other group fake lesioned
• Real lesion = lower accuracy & longer to acquire reaching task skill
• Looking at cotor cortex, elicited forepaw movement = 30% increased in fake lesion compared to untrained rats
• NBM lesioned rats forepaw area = decreased 22% (even when trained)
• Links impairment of learning with disruption of plasticity

Question 25

What is the importance of ACh

Answer 25

- Linkage of NBM to ACh - Sensory input from env may signal HOW to learn - ACh determines WHAT we learn

Question 26

How to increase cognitive enhancement?

Answer 26

- Drugs made for other things but enhance normal people's conc & memory - Subtly changing electric charge and change how neurons fire e.g torpedo fish for headache relief in roman times & dude that connected murderers bodies to batteries in a theatre to make them move

Question 27

What did Fritsch and Hitzig do?

Answer 27

- Electrical stimulation of cortex can produce movements & Performed this on dog brains - Aided in development of functional localisation - Scalp could modulate human brain function e.g depression - Application of positive d-c current had a stimulating effect whereas a negative current inhibited - Mostly forgotten after Electroconvulsive Therapy

Question 28

What is modern day electrical stimulation?

Answer 28

- Transcranial electrical stimulation - Surface electrodes constant current stimulator: used as a modulator

Question 29

What was the meta-analysis for TES

Answer 29

- Not found to generate a significant effect on anything other than change Motot-evoked potentials (evaluates motor cortex) - Cheap, easy to apply - Very variable - Meta analysis was dodgy as authors decided to throw away a lot of data

Question 30

Why are TES effects so variable?

Answer 30

- Differences in cortical anatomy between ppts - Differences between electrode positioning between participants - State-dependent effects of cortical activity between ppts