Mechanisms underlying interlimb transfer of visuomotor rotations

Abstract

We previously reported that opposite arm training improved the initial direction of dominant arm movements, whereas it only improved the final position accuracy of non-dominant arm movements. We now ask whether each controller accesses common, or separate, short-term memory resources. To address this question, we investigated interlimb transfer of learning for visuomotor rotations that were directed oppositely [clockwise (CW)/counterclockwise (CCW)] for the two arms. We expected that if information obtained by initial training was stored in the same short-term memory space for both arms, opposite arm training of a CW rotation would interfere with subsequent adaptation to a CCW rotation. All subjects first adapted to a 30° rotation (CW) in the visual display during reaching movements. Following this, they adapted to a 30° rotation in the opposite direction (CCW) with the other arm. In contrast to our previous findings for interlimb transfer of same direction rotations (CCW/CCW), no effects of opposite arm adaptation were indicated in the initial trials performed. This indicates that interlimb transfer is not obligatory, and suggests that short-term memory resources for the two limbs are independent. Through single trial analysis, we found that the direction and final position errors of the first trial of movement, following opposite arm training, were always the same as those of naive performance. This was true whether the opposite arm was trained with the same or the opposing rotation. When trained with the same rotation, transfer of learning did not occur until the second trial. These findings suggest that the selective use of opposite arm information is dependent on the first trial to probe current movement conditions. Interestingly, the final extent of adaptation appeared to be reduced by opposite arm training of opposing rotations. Thus, the extent of adaptation, but not initial information transfer, appears obligatorily affected by prior opposite arm adaptation. According to our findings, it is plausible that the initiation and the final extent of adaptation involve two independent neural processes. Theoretical implications of these findings are discussed.

Control of velocity and position in single joint movements

“…The idea that movement trajectory and final position are differentially controlled is also consistent with studies that have examined adaptation to novel forces (DiZio & Lackner, 1995;Lackner & DiZio, 1994) and visuomotor rotations (Sainburg & Wang, 2002;Wang & Sainburg, 2003. In the studies by Lackner and DiZio (DiZio & Lackner, 1995;Lackner & DiZio, 1994), participants reached to a target when adapting to Coriolis force fields, without any visual feedback.…”

“…This clearly suggests that trajectory and position seem to be differentially controlled. More recent studies investigating interlimb transfer of adaptation to visuomotor rotations have revealed similar distinctions in transfer of trajectory and final position information across limbs, thus lending further support to the idea that these features may be differentially encoded (Sainburg & Wang, 2002;Wang & Sainburg, 2003.…”

The extent of interlimb transfer following adaptation to a novel visuomotor condition does not depend on awareness of the condition

“…This modified access model extends the original access model by proposing that the properties of the controller used after initial memory formation will determine the nature of the information transferred across the limb systems. They further proposed that the two arm controllers have independent (short term) memory resources that can be accessed by their counterpart, based on a finding that adapting to two opposing visuomotor rotations simultaneously by the two arms neither facilitates nor interferes with interlimb transfer (Wang and Sainburg 2003). This idea has been confirmed by other studies, which demonstrated that adaptations to two opposing rotations can coexist in the sensorimotor system, one for each arm (Bock et al 2005;Galea and Miall 2006).…”

“…It is suggested that interlimb transfer occurs as a result of the executive decisions made by the motor control system, which occurs subconsciously, to determine whether to access and utilize the information that was obtained during initial learning with, and stored in the memory cache of, the opposite arm (Wang and Sainburg 2003).…”

The effects of a single bout of exercise on motor memory interference in the trained and untrained hemisphere

“…There are many studies available that looked at the effects of unilateral motor learning on bilateral performance changes using tasks such as visuomotor rotations (Sainburg and Wang, 2002;Taylor et al, 2011;Carroll et al, 2014;Wang and Sainburg, 2003) or ballistic type of movements (Carroll et al, 2013). Up until recently, no study ever looked at potential interference effects of unilateral motor learning.…”