Cortical Reorganisation

Question 0

PMC stimulation

Answer 0

Causes muscle movement on the contralateral side

Brain projects via spinal cord

Question 1

How are neurons organised?

Answer 1

Topographically

Question 2

PSC activation

Answer 2

Sensitive to touch, topographic, homunculus

Question 3

Cortical Map

Kwan et al (78)

Answer 3

Not perfect!

Question 4

Cortical maps are

Answer 4

Dynamic
Modified by experience
Reorganise according to brain injury/body changes
Plasticity is the basis for learning and recovery

Question 5

Long term potentiation

Answer 5

Long lasting enhancement of signal transmission between two neurons
Ability to change strength of chemical synapses

Question 6

Cortical remapping

Merzenich et al

Answer 6

Ex1: monkey, amputated middle finger. Areas remapped in PMC after a few weeks, representation was overtaken by neighbouring fingers.

Ex2: monkey made to rest 2x digits on a rotating disk for rewards. After a few weeks, cortical representations became enlarged: cortical maps respond to peripheral changes

Question 7

Cortical remapping

Pons et al (91)

Answer 7

Amputated monkey hand
Over taken by face in adult macaque
Cut sensory forearm nerves: remapped into neck
Cortical remapping

Question 8

Cortical remapping

Humans: Giraux et al (01)

Answer 8

CD had both hands amputated
Later given hand transplants
fMRI studied reorganisation (6m before amputation and transplant, 2/4/6m after)
Shift in hand related activity back to classical PMC&PSC location

Question 9

Cortical remapping

Humans: Farne et al (02)

Answer 9

CD 5m after graft, tactile sensation recovered quickly
But tactile perception of the face extinguished the hand
Effect disappeared after an extra 6m

Question 10

Phantom limbs

Mitchell (71)

Answer 10

Amputated limb feels present, feel pain and cramp.

Aware of illusion. 98% experience discomfort immediately after limb loss. Usually wears off.

Question 11

Phantom limbs
Ramachandran & Hirstein (98)
VQ

Answer 11

VQ 17yrs, car accident, lost forearm
Phantom hand just below stump.
Stolen face with cotton bud, shut eyes - parts of the face mapped onto the phantom limb. Stable 1w later.

Question 12

Phantom limbs
Ramachandran & Hirstein (98)
DS

Answer 12

Motorcycle accident, arm amputated 1yr later
Stimulation of ipsilateral face
Over 6m, thumb took over face.
Separate map of hand on shoulder.

Question 13

Phantom pain

Flor et al

Answer 13

Onset can be immediate or years later
Long or short lasting
70% of phantom limbs are still painful 25yrs later
Changes could be central/peripheral cause of pain

Question 14

Phantom pain

Harris (99)

Answer 14

Control theory

Brain continues to send commands to phantom limb, efferent copies monitored, negative feedback on movement but not from limb.
Pain - large error, expected sensory consequences falter.

Question 15

Mechanisms of the phantom limb

Unmasking

Answer 15

Between the thalamus and sensory cortex
Hand inhibits face connections in hand

More prominent connections cause inhibition in suppressed connections in normal body. Previously latent neurons become active, synapses become unmasked.

Question 16

Mechanisms of the phantom limb

Thalamus level

Answer 16

New connections made at thalamus level.

Face over takes existing hand neurons and converting them.