IIT Gandhinagar researchers find underlying limb-independent motor memories can help in stroke rehabilitation

Researchers at the Indian Institute of Technology (IIT) Gandhinagar have discovered that underlying limb-independent motor memories can help in stroke rehabilitation.

Probing how limb-independent memories are acquired, a team of researchers investigated both the algorithm used and the neural machinery causally associated with this process.

A study led by Prateek Mutha, an associate professor at IIT Gandhinagar, has also been published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) journal.

"Skilled actions, from a ballerina's pirouette to playing a ghamak on the sitar, are based on the ability to learn new movement patterns and to adapt them to new environments. This ability to learn, store, execute and continuously refine actions is broadly defined as motor learning and is driven by multiple neural mechanisms. Just as learning the list of prime ministers of India results in the formation of a memory that can be later recalled, motor learning also results in the formation of a 'motor memory' that subsequently enables superior movement performance," Mutha said. 

"Interestingly, motor learning comprises representations that are both limb-specific and limb-independent. Using a combination of behavioural experiments and computational modelling of healthy human participants learning of arm movements in a novel environment, we first found that effector-independent memories are forged through implicit learning, or learning without conscious realisation of how a skill is being learned. This mechanism contrasts, for instance, with learning using verbalisable or explicit processes such as those employed when learning a list of words," he added.

The four-member team then delivered high-definition cathodal transcranial direct current stimulation over a region of the brain called the posterior parietal cortex (PPC) in order to inhibit the underlying neural activity.

"We found that perturbing left but not right hemisphere PPC prior to learning blocked the implicit process and prevented the acquisition of the limb-independent memory. If the left PPC was perturbed after learning had been allowed to occur, the acquired memory was disrupted, and learning failed to generalise across effectors. This work thus established the PPC as an essential neural substrate for learning and storing effector-independent memories," he said.

According to Mutha, the work could potentially help physical therapists better strategise training of an unaffected limb when the affected limb cannot be engaged effectively during rehabilitation of stroke patients with significant weakness on one side of the body or the patients with other unilateral brain injuries.

"First, the fact that deficits in forming effector-independent memories are seen following left but not right hemisphere disruption, suggests that rehabilitation following left versus right hemisphere damage needs to be different. Second, if patients with left hemisphere damage, particularly in the PPC, fail to learn using implicit mechanisms, explicit strategies to accomplish the task goal may need to be provided to them in order to bring about improvements in their actions. Finally, the fact that learning can generalise from one effector to another, suggests that the 'unaffected' limb could be trained during rehabilitation to bring about performance gains on the affected side," he said.

The other members of the team included research scholars Adarsh Kumar, Gaurav Panthi and Rechu Divakar.