Question

What interventions did Krakauer and colleagues use in order to make the brain "more plastic" and improve stroke recovery in the mice?

Answer 1

Krakauer and colleagues put forward a animal model by which it was demonstrated how neurorehabilitation and neural repair works in order to make the brain "more plastic" and improve stroke recovery in the mice. Animal and human studies have shown that important variables in learning and relearning motor skills and in changing neural architecture are the quantity, duration and intensity of training sessions. There is evidence to demonstrate that plasticity is “use-dependent” and intensive massed and repeated practice may be necessary to modify neural organization.

Rehabilitation, for patients, is fundamentally a process of relearning how to move to carry out their needs successfully. Motor learning theories have contributed to the way rehabilitation therapists work with people who have experienced a CVA and motor learning principles. have been applied to the functional retraining of clients with neurological impairments. There are four factors that contribute to motor learning: stages of learning, types of task, practice, and feedback. All four factors must be considered by clinicians when designing treatment programs for patients who have experienced a CVA. Practice and feedback are considered to be the two most important factors in skill acquisition.

(Xu et al. 2010) did an experiment with one month old mice. They taught the mice a task and then imaged their brains, at the level of individual dendrites. They showed that, within one hour of the training session, the mice that did well at the task (that is, had learnt it to some extent), had an increase in dendritic spines of about 10%. That is, the brain had undergone structural as well as functional changes. What‟s more, about 50% of the new spines were still there two weeks later and, for mice training for 16 days, 40% of the new spines were still there three months later. The authors conclude: „these data indicate that motor learning selectively stabilizes learning-induced new spines and destabilizes preexisting spines. The prolonged persistence of learning-induced synapses provides a potential cellular mechanism for the consolidation of lasting, presumably permanent, motor memories.‟ „Practice of novel, but not previously learned, tasks further promotes dendritic spine formation in adulthood‟ (Xu et al. 2010). Furthermore, they showed that different motor skills are encoded by different sets of synapses. Practice of novel, but not previously learned, tasks further promotes dendritic spine formation in adulthood. Their findings reveal that rapid, but long-lasting, synaptic reorganization is closely associated with motor learning. Krakauer stated that the study of how the brain rewires and regrows neurons after injury or to facilitate learning is one of the most exciting frontiers of neuroscience.

An experimental paradigm that is widely used to study motor learning involves having subjects hold the handle of a robotic arm and make planar reaching movements in a horizontal plane to visual targets displayed on a screen done by Shadmehr and Mussa-Ivaldi. When first exposed to the viscous curl field, subjects make skewed trajectories, but with practice are able to adapt to the force-field and again make smooth and nearly straight movements. When subjects are in this adapted state and the force-field is turned off, „after-effects‟ occur, with trajectories now skewed in the direction opposite to that seen during initial adaptation. The presence of after-effects is strong evidence that the central nervous system can alter motor commands to the arm to predict the effects of the force field and form a new mapping between limb state and muscle forces (internal model). Experiments indicate that internal models learned for one type of movement can generalize to other movements (Conditt). The importance of the concept of internal model to rehabilitation is that the model can be updated as the state of the limb changes. Thus rehabilitation needs to emphasize techniques that promote formation of appropriate internal models and not just repetition of movements and this concept was put forward by Krakauer in 2006. They examined the effects of the removal of visual feedback during movement on the learning of both stable and unstable dynamics in comparison with the case when both vision and proprioception are available. Subjects were able to learn to make smooth movements in both types of novel dynamics after learning with or without visual feedback. By examining the endpoint stiffness and force after learning it could be shown that subjects adapted to both types of dynamics in the same way whether they were provided with visual feedback of their trajectory or not. The main effects of visual feedback were to increase the success rate of movements, slightly straighten the path, and significantly reduce variability near the end of the movement. These findings suggest that visual feedback of the hand during movement is not necessary for the adaptation to either stable or unstable novel dynamics. Instead vision appears to be used to fine-tune corrections of hand trajectory at the end of reaching movements.