Aphasia 2b - Plasticity

Aphasia 2b - Plasticity

1. Raymer et al. (08)

   • 1. Timing of treatment delivery
   • 2. Use it or lose it
   • 3. Generalisation (trans of treat fx)
   • 4. Intensity of treatment

2. Kleim & Jones (08): 10 Principles of Neuroplasticity

   • See Isobel's summary sheet...
   • 1. Use it or lose it: Neurological functions which aren't utilsed may decline
     • Evidence to support the use of language skills to maintain them
     • Cortical neurons reduced in vis cortex for kittens deprived of light
     • Other sensory modalities may take over
       • fMRI revealed blind Pat, visual cortex active in tactile task, e.g. braile
     • Tube feeding and neural circuitry in swallowing (Robbins et al 07)
   • 2. Use it and improve it: Training in a specific function is likely to improve that function
     • N. Plastcitiy is basis of all learning
     • Therapy is valid
     • See Raymer et al. (07)
     • Housing animals in complex environments post injury can improve functional recovery
     • Acrobatic training, vs normal exercise in rats (post lesion) shown to enhance synaptic pasticity in contralateral hemishere
   • 3. Specificity: Training to drive plasticity in a linguistic area (believed to have regional specificity), needs to be specific to that area - the nature of the experience drives the pasticity
     • Don't expect generalisation to always occur! But training in one modality may change a limited subset of neural circuitry involved in another
     • Humans trained to make skilled ankle movements vs those trained to repeat unskilled movements exhibited better cortico-spinal excitability
       • Rates to CATE / Transference.
       • Reach and grab tasks in rats = denritic growth in motor cortex (contra lat to trained limb) but only suble fx on ipsilateral cortex
   • 4. Repetition matters: In order for plastic changes to resist decay, training must go beyond the acquisition of skill - repetition beyond where might appear necessary.
     • Keep going!
     • Rats on skilled reaching task: demo beh changes quickly, however synapse number, strength and map reorganisation does not alter until several days of practise
   • 5. Intensity matters: In order for neuroplastic changes to occur training needs to be provided over an intense period. However, too much training can overuse impaired extemities
     • Boghal et al (03): Intense training over a short period approx 8 hours / week for 11 weeks was more effective than training over a longer period, approx 2 hrs / wk for 22 weeks
     • Get an app!
       • Don't overdo it
     • Animals trains to perform 400 reaches / day vs 60 / day showed an increase in synapse numbers
       • Extreme use during early vulnerable period unwise: Forcing rats to rely on impaired forelimb frst 7 days after smot cort lesion, exaggerated tissue loss & worsened outcomes (compared to rats allowed both limbs)
   • 6. Time matters: Different changes occur at diff times during taining
     • Therapy should be delivered within particularly sensitive time windows ideally - acute post injury period
       • But any therapy is better than no therapy
       • However, starting too soon may result in lack of retention
     • Motor skill training: Gene expression first, synapse formation, map reorganisation
     • Raymer et al (2007) – aphasia treatment initiated in the chronic phase resulted in major functional improvements (from meta-analysis), but the greatest improvements occurred when therapy started in the acute post-injury period.
     • Further research needed to know how time windows in rats relate to humans
   • 7. Salience matters: Emotional stimulus used in training are likely to induce greater N.P. changes
     • If it doesn't mean anything, they won't remember it
     • Animals that received a reward of food after hearing a musical tone showed greater representation of this tone in auditory cortex - tone without reward does not alter topography aud maps
       • There is a neural system that mediates saliency - engaging this is critical for driving experience dependent NP - ACETYLCHOLINE agonists
       • Rats will also repeatedly engage in rehabilitative reaching if it earns them food treats.
   • 8. Age matters: Map reorganisation, synaptogenesis and E.D. Synaptic potentiation all dcrease with age
     • Older people are likely to take longer for neuro pl. changes to occurr
     • Older rats show less NEUROGENESIS (prod of new neurons) after ischaemic insult than young ones.
   • 9. Transference: Plasticity within one set of NEURAL CIRCUITS can transfer to another
     • See Thomson et al. (03) and Kiran's discussion CATE, Complexity Account of Theraputic Efficacy
     • Stimulation of pharynx post stroke enhanced cortical representation and improved swallowing
     • Exercise may also increase this - elevates NEUROTROPHIC FACTORS
   • 10. Interference: N.P Changes resulting from training in some areas can actually interfere with achieving NP changes in other areas
     • Functional compensations vs. bad habits
       • Over-reliance on unaffected modalities
     • 'learned non-use': Training in use of inpsilesional limb (in rats) resulted in decreased use of impaired limb

3. NEURALPLASTICITY: Adaptive capcity of CNS. Brain can alter structure and function in response to internal & external pressures thorughout life

   • Belived to be basis of learning in intact brain
   • Brain encodes experience and leans new beh.
   • Driven by changes in beh, sensory and cognitive exp
   • RECOVERY: Takes several forms (Brant et al. 97)
     • Restoration
       • Beh level: Perform task in same manner as before
       • Neur level: Restored function within area of cortex previously damaged by stroke.
       • E.g. after thrombolysis
     • Reorganisation
       • Neur level: of neural substrate to lang functions
       • Either ipsilaterally or contralaterally
         • Homologous regions of right hemisphere
         • Dominant hem. lang. areas - especially perilesional
     • Compensation
       • Beh. Level: Use of new strategy to perform a tast
       • Neur. Level: Diff neural tissue takes over function lost
     • Habituation
     • Restiution

4. RECOVERY / PROGNOSIS - dependent on:

   • Size of lesion
   • Age
   • Gender - women may be more health concous
   • Handedness - lefties perhaps more distributed representation
   • Education level - although correlates w lifestyle
   • SITE of lesion (most important factor)
   • Amount of arcuate fasciculus in R.H. (See Forkel et al. 2014)
   • Single and group case studies have demonstrated improvements in language recovery after many years post-stroke, Hickin et al 2002).

5. Complexity Account of Treatment Efficacy (CATE) (Thompson et al., 2003): The more complex the item that is trained, the more likely it is to be generalised

   • Puts learning hierarcy into debate
     • Complexity hierarchy based on typicality
   • True for: sentence production, naming and child phonology
   • See Kiran (2007)
   • Relates to literature in adult second language learning

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