plasticity and phantom limbs

Question 1

how is the palm of an owl monkey labelled?

Answer 1

D= distal
M= middle
P= proximal
P1,2,3,4= palm

Question 2

what happens to area 3b of a monkey when digit 3 of the monkey are amputated (mapping procedure carried out months after amputation)

Answer 2

there is no gap in the map
territory is invaded form either side by digit 2 and digit 4
remapping
shows that the adult cortex is able to remap

Question 3

what does nurturing of a litter cause when a rat has given birth

Answer 3

unusually high stimulation of the ventrum

Question 4

what would we expect to happen in the brain of a nurturing rat?

Answer 4

we would expect this excess of stimulation to lead to a remapping of the ventral area

there is a massive expansion of the representation of the ventrum (larger ventral area), increased magnification factor

Question 5

magnification factor and receptive fields in lactating rats

Answer 5

receptive field size is smaller in lactating rats: ventrum is now represented in finer spatial detail

magnification factor is increased

in adulthood we have mechanisms that control the relationship between magnification and receptive field size

Question 6

results when monkeys trained to contact rotating disk, causing excessive stimulation of the fingertip of digit 3

Answer 6

magnification increased in D3
receptive field size decreased in D3

Question 7

what does magnification factor of a body part represent in general?

Answer 7

receptor density
behavioural importance
training/ plasticity

Question 8

phantom limb

Answer 8

the illusion that an amputated or denervated limb can still be felt

Question 9

why do central circuits have no knowledge of what is happening to your body?

Answer 9

they simply decode the information being sent by the somatosensory cortex

Question 10

what happens if the hand nerve is electrically stimulated at the level of the elbow?

Answer 10

the afferents will be activated and send a signal to the somatosensory cortex

then activate the hand area of the primary somatosensory cortex

central circuits will interpret this as a sensation in the hand
(a phantom sensation)

Question 11

intraneural microstimulation (INMS) of the hand nerve in patients with denervation in the hand

Answer 11

patients felt a tingling in their hand (phantom sensations)
central perception circuits can be fooled into thinking the limb still has feeling as they still have a representation of the whole body

Question 12

microstimulation in the ex-leg zone of the VPL(thalamus) in leg amputees

Answer 12

elicited phantom sensations
shows teh ascending pathways are still active and can cause phantom limb

Question 13

how should it be possible to evoke phantom sensations

Answer 13

by stimulation of denervated areas:
nerve stimulation
subcortical stimulation

Question 14

patient VQ

Answer 14

When they touched different parts of VQ’s face with a cotton bud, her reported tingling in his phantom thumb (cheek), pinkie (lower lip), index (upper lip)
Map of phantom hand on VQs face
Plastic mechanisms have caused remapping of his primary somatosensory cortex

Question 15

results of electrophysiological recordings from the somatosensory cortex of a monkey, 12 years after cutting all the nerves that innervate a monkeys arm

Answer 15

Recordings from regions 3 and 4: normally represent the arm

found receptive fields on the chin

large remapping of primary somatosensory cortex, the arm is now sensitive to stimulation of the chin

They now have a doubling of face representation in their face cortex

no silent zone

All of arm area now contains a second representation of the face
So if we gently touch the chin we get activity in the regular face area, we also get activity in the x arm area
Central tactile circuits would interpret this as two touches