Distinct Motor Plans Form and Retrieve Distinct Motor Memories for Physically Identical Movements

Abstract

We can adapt movements to a novel dynamic environment (e.g., tool use, microgravity, and perturbation) by acquiring an internal model of the dynamics. Although multiple environments can be learned simultaneously if each environment is experienced with different limb movement kinematics, it is controversial as to whether multiple internal models for a particular movement can be learned and flexibly retrieved according to behavioral contexts. Here, we address this issue by using a novel visuomotor task. While participants reached to each of two targets located at a clockwise or counter-clockwise position, a gradually increasing visual rotation was applied in the clockwise or counter-clockwise direction, respectively, to the on-screen cursor representing the unseen hand position. This procedure implicitly led participants to perform physically identical pointing movements irrespective of their intentions (i.e., movement plans) to move their hand toward two distinct visual targets. Surprisingly, if each identical movement was executed according to a distinct movement plan, participants could readily adapt these movements to two opposing force fields simultaneously. The results demonstrate that multiple motor memories can be learned and flexibly retrieved, even for physically identical movements, according to distinct motor plans in a visual space.

Formation of model-free motor memories during motor adaptation depends on perturbation schedule

“…Limited transfer of learning was also observed between rhythmic and discrete movements (Ikegami et al 2010). In addition, distinct motor plans or distinct tools are also associated with limited interference between two opposing perturbations (Cothros et al 2009;Hirashima and Nozaki 2012). Overall, these studies suggest that transfer or interference between motor memories requires a common neural representation.…”

A cognitive framework for explaining serial processing and sequence execution strategies

“…The required movement representations may develop at various levels of processing, and these representations differ to the extent that movement details are pre-specified. Consequently, a particular movement series can be produced using various alternative internal models (Hirashima & Nozaki, 2012). This flexibility to change to another processing strategy-i.e., another execution modewas recognized long ago (e.g., Wickelgren, 1969).…”

Vestibular benefits to task savings in motor adaptation

“…Associating each task with a different context by adding static visual (Gandolfo et al 1996) or haptic cues (Cothros et al 2008) does not improve recall of the memory. However, if tasks are distinguished by dynamic sensorimotor contextual cues, there is evidence for learning and storage of multiple internal models (Hirashima and Nozaki 2012;Howard et al 2008Howard et al , 2010Howard et al , 2012Malone et al 2011;Nozaki et al 2006). For example, when unimanual and bimanual tasks are linked to opposing force fields, interference is reduced in the arm that is involved in both tasks (Nozaki et al 2006).…”

“…Likewise, different limb configurations, such as wrist postures (Gandolfo et al 1996) or starting hand positions (Hwang et al 2006a), can aid in learning. Recently, different targets in the visual domain (Hirashima and Nozaki 2012) or different cueing premovements (Howard et al 2012) also were discovered to provide sufficient sensorimotor context to permit parallel learning of opposing force fields.…”