Association Between Cross-Limb Transfer and Practice Organization.

Although the importance of practice has been evidenced in early studies of cross-limb transfer, the association between cross-limb transfer and practice organization remains unknown. The two primary means of organizing practice are constant practice (CP) and variable practice (VP). When the same generalized motor program governs the motor responses, VP produces better transfer than CP. Thus, we hypothesized that VP would generate a higher cross-limb transfer level than CP. We assigned 40 participants to CP or VP groups and conducted an experiment consisting of three phases: pre-test, practice, and transfer test. At pre-test, all participants practiced eight trials of a sequence key-pressing task with the non-dominant hand (NDH). After the pre-test, all participants performed a practice phase of 72 trials with the dominant hand, but CP and VP groups underwent their different practice schedules (CP or VP) such that the CP group practiced a sequence key-pressing task in one sequence, and the VP group practiced four different sequences randomly. On the transfer test all partcipants completed eight trials with the NDH 24 hours after the practice phase. The CP group showed better performance than the VP group on the transfer test, and we concluded that the effects of practice organization in cross-limb transfer are distinct from intra- and inter-task transfer such that the specificity of practice explained the benefits of CG.

Association Between the Catechol-O-Methyltransferase (COMT) Val158Met Polymorphism and Manual Performance Asymmetries.

Within the cognitive domain, neuroscience and cognitive psychology researchers have investigated the relationship between handedness and cognitive skills. However, there have been few studies of the three-way association between manual asymmetry, its genetic components, and cognition even though this line of research could further an understanding of asymmetry. One enzyme involved in cognitive functions related to the dopaminergic system and to the prefrontal cortex is the catechol-O-methyltransferase (COMT), and it has a trimodal activity distribution in the human population due to its functional polymorphism known as Val158Met. This study investigated whether this COMT polymorphism is associated with asymmetries in the performance of a manual dexterity task. Forty-two right-handed undergraduate students ( Mage = 25.12, SD = 5.84; 15 women, 27 men) performed two trials each of place and remove conditions of the Grooved Pegboard Test with each hand (right and left), counterbalancing the order of the initial or starting hand. We calculated the mean time to perform the task for both hands on both trials and found, as hypothesized, that the Met/Met group gave a more asymmetrical performance than the Val/Met group under the place condition because dopamine levels reduced flexible behavior for the Val/Met group. We suspect that the place condition requires greater interhemispheric connectivity, as it requires a greater cognitive flexibility, and highly asymmetrical individuals are said to be less flexible. The findings of this study suggest a significant association between the COMT polymorphism and manual asymmetry in healthy populations.