Motor Learning Interference Is Proportional to Occlusion of LTP-Like Plasticity

Abstract

Learning interference occurs when learning something new causes forgetting of an older memory (retrograde interference) or when learning a new task disrupts learning of a second subsequent task (anterograde interference). This phenomenon, described in cognitive, sensory and motor domains, limits our ability to learn multiple tasks in close succession. It has been suggested that the source of interference is competition of neural resources, although the neuronal mechanisms are unknown. Learning induces long-term potentiation (LTP) that can ultimately limit the ability to induce further LTP, a phenomenon known as occlusion. In humans we quantified the magnitude of occlusion of anodal transcranial direct current stimulation (A-tDCS)-induced increased excitability after learning a skill task as an index of the amount of LTP-like plasticity used. We found that retention of a newly acquired skill, as reflected by performance in the second day of practice, is proportional to the magnitude of occlusion. Moreover, the degree of behavioral interference was correlated with the magnitude of occlusion. Individuals with larger occlusion after learning the first skill were (1) more resilient to retrograde interference and (2) experienced larger anterograde interference when training a second task, as expressed by decreased performance of the learned skill in the second day of practice. This effect was not observed if sufficient time elapsed between training the 2 skills and LTP-like occlusion was not present. These findings suggest competition of LTP-like plasticity is a factor that limits the ability to remember multiple tasks trained in close succession.

Consensus Paper: Probing Homeostatic Plasticity of Human Cortex With Non-invasive Transcranial Brain Stimulation

“…More recent work suggests that observation of a motor training task is sufficient to prevent subsequent induction of LTP-like PAS effects [89] and that the temporary occlusion of LTP-like plasticity after motor learning is likely to be a mechanism necessary for successful skill retention (Cantarero et al, 2013a;Cantarero et al, 2013b). Retention for a simple motor task after learning was proportional to the magnitude of LTP occlusion during a subsequent NTBS protocol and that the amount of occlusion was predictive of resilience against interference of subsequent learning [90,91]. Interestingly, the effect of motor learning as a 'primer' depends on the learning phase: the observed homeostatic effects on subsequent PAS protocols were only observed when 'priming' involved training a novel motor task, while 'priming' with a well-practiced task did not significantly modulate subsequent PAS [79].…”

Deep Breathing Practice Facilitates Retention of Newly Learned Motor Skills

“…This is non-trivial because benefits seen shortly after learning do not always translate to the longer term34, and the effects at these two time frames can indeed be the opposite depending on activity during the intervening period163536. This finding is also important because delayed retention tests are often better signatures of actual learning than short-term changes in performance.…”

Electrifying the motor engram: effects of tDCS on motor learning and control

“…Support for this idea stems from the impact of tDCS on motor learning, for which LTP is essential (Rioult-Pedotti et al, 2000) and from detailed neurophysiological study in animals (Fritsch et al, 2010) and in humans (Cantarero et al, 2013a, 2013b). However, the LTP model does not account for the simple effect of tDCS on motor behaviors independently of any learning process, nor does it account for the effect of cathodal stimulation on motor learning or control.…”