[edit] Merging of Brain Areas
- What happens to a monkey’s representation of its fingers in brain if you suture two fingers of it? Explain the general principle, which is underlying that event.
- Receptive fields of the finger's representation merge after a few months
- → Clear border between receptive fields is lost
- → Unified single cortical area
- Altered experience → altered representation
- After a few weeks with unsutured fingers, the areas split again.
- Independent signal statistics needed for independent representations.
- Which effects can be observed in somatosensory cortex of rodent when either a whole row, a whole column, all but one, all whiskers are cut?
- Topographic map
- Barrel: Easily visible neuronal representation of whisker in brain
- One-to-one correspondance of whiskers to barrels
- Cut whole row/column
- Input to corresponding mapping is lost
- Representation of remaining whiskers takes over areas
- Cut all but one whisker
- Same process
- No gap remains
- Cut all whiskers
- Barrel field vanish
- Other areas take over this area
- What phenomenon can be observed in sensory motor cortex in violin players that learned playing at a young age?
- Intensive use of thumb & pinky
- Cortical representation of the thumb & pinky enlarged
- Larger response elicited by stimulation
[edit] Infarct
- Which effect does an infarct, which destroys some of a limbs representation, have on its representation. What can you do to influence this effect?
- Affected limb is hardly used
- → cortical representation of affected region + neighbor regions vanishes
- Motion rehabilitation
- Unaffected limb restrained
- Affected limb is trained
- Improvement remains even six months later
[edit] Phantom Limbs
- What is a phantom limb and how can this phenomenon be explained (name one hypothesis)?
- Definition, Occurrence
- Lost extremity that still can be felt
- Patients think they can still move it
- Sometimes it hurts painfully
- Occurs in 70-90% of amputees, probability increases with age
- Also appears in children which never had the respective extremity
- Explanations
- Psychological consequence of an amputation
- Neuromas firing inappropriately
- Severed nerve endings remained in stump
- Modifications of Penfield map (~homunculus)
- Touching of areas lying next to the amputed limp in the Penfield map
- → neighboring areas encroaches the area of the lost extremity
- Evidence by MEG experiments
- Imbalanced size of cortical representation contralateral to lesioned side
- At what age are phantom limbs very likely to be observed?
- Adulthood
- Probability increases with age
- Brain can not successfully unmask remapped connections
- Which methods have been tried to treat phantom limb pain?
- Ineffective
- Complete amputation of limb
- New phantoms
- Removal of neuromas
- Temporal relief
- Removal of thalamic and cortical areas
- Effective
- Body image
- Addresses the perceived body image
- A mirror is placed in such a way that the healthy limb is mirrored to the place where the amputed limb would be.
- Can even lead to whole disappearance of phantom
- Describe differences in cortical reorganization in subjects with or without phantom limb pain.
- Remapping hypothesis
- Tactile & proprioceptive input from tissue proximal to stump take over respective RFs of somatosensory cortex in subjects with phantom limb pain
- → Misinterpretation of input as belonging to phantom limb
- Depends on whether patient is able to integrate spontaneous activity in proximal tissue, commands sent to missing limb, and acitivity in neuromas.