Interference between competing motor memories developed through learning with different limbs

Abstract

Learning from motor errors that occur across different limbs is essential for effective tool use, sports training and rehabilitation. To probe the neural organization of error-driven learning across limbs, we asked whether learning opposing visuomotor mappings with the two arms would interfere. Young right-handers first adapted to opposite visuomotor rotations A and B with different arms, and were then re-exposed to A 24 hours later. We observed that re-learning of A was never faster, nor were initial errors smaller than prior A learning, which would be expected if there was no interference from B. Rather, errors were greater than or similar to, and learning rate was slower than or comparable to previous A learning depending on the order in which the arms learned. This indicated robust interference between the motor memories of A and B when they were learned with different arms in close succession. We then proceeded to uncover that the order-dependent asymmetry in performance upon re-exposure resulted from asymmetric transfer of learning from the left arm to the right but not vice-versa, and that the observed interference was retrograde in nature. Such retrograde interference likely occurs because the two arms require the same neural resources for learning, a suggestion consistent with that of our past work showing impaired learning following left inferior parietal damage regardless of the arm used. These results thus point to a common neural basis for formation of new motor memories with different limbs, and hold significant implications for how newly formed motor memories interact.