Attention and interlimb coordination : behavioural and neurophysiological processes

A conceptual and methodological framework has recently been developed from a blending of a traditional dual-task methodology and a dynamical perspective on coordination. Specifically, pattern stability has been shown to be a good predictor of VU) attentional demands (i.e., central cost) needed for maintaining coordination. One of the important assumptions is that the allocation of attentional resources can modify the coupling strength of interlimb coordination. Within this original framework that blends two different theoretical approaches with attention as an intervening variable modifying behavioural patterns, the present research further investigated at the behavioural and neurophysiological levels, the central cost of dynamical coordination patterns. Two experiments were carried out in the Phase 1 of the present research. The first examined whether previous findings obtained with bimanual coordination patterns could be extended to coordination patterns involving non-homologous limb combinations. Consistent with previous results, coordination stability and probe RT (i.e., a measure of attentional load) were found to co-vary. Furthermore, it was shown that temporal aspects of the coordination task were selectively modulated through attentional prioritisation without affecting the spatial aspects of the task (i.e., movement trajectories). Following evidence from Experiment 1 of dissociation between the temporal and spatial dimensions of interlimb coordination, the second experiment explored whether attentional focus could selectively modulate the spatial aspects of the interlimb coordination task without affecting the temporal coupling between the limbs. Experiment 2 showed that when the spatial aspects of the interlimb coordination task were prioritised not only the movement trajectories but also the temporal variability of the interlimb coordination task were modulated. Interestingly, attentional focus to the spatial dimension of interlimb coordination abolished the inherent performance asymmetries usually observed between the limbs (i.e., spontaneous performance differences between the left-hand and the right-hand and an ann and leg). Phase 2 of this research explored the neural correlates of dual-task performance involving an interlimb coordination and probe RT task. Single-pulse transcranial magnetic stimulation (TMS) was employed in a series of three experiments to specifically assess the excitability of corticospinal pathways during single- and dual-task performance. The first experiment examined the time course of corticospinal excitability of the tibialis anterior (TA) during the RT interval to a secondary task probe stimulus while simultaneously maintaining bimanual in-phase and anti-phase coordination modes. Although corticospinal excitability of the TA did not differ between the in-phase and anti-phase coordination modes, a large increase in corticospinal excitability was observed between single-task and dual-task performance. The second experiment examined whether the elevated corticospinal excitability during dual-task performance was a 'motor effect' reflecting increased cortical excitability associated :.vith the performance of the continuous bimanual coordination task or it whether reflected the concurrent performance of two tasks (i.e., a dual-task effect). The results showed that the elevation of corticospinal excitability was due, in part, to the production of bimanual movements. However, a further increase in corticospinal excitability also occurred in the dual-task condition. Thus, the increased corticospinalexcitability appeared to reflect a neural process related to the concurrent performance of two tasks. A final experiment tested whether the increased corticospinal excitability was a general signature of dual-task performance or specific to interactions within the motor cortex. Dual-task conditions involving either a primary motor task or a primary cognitive task (i.e., tone counting) combined with probe RT were compared. Results showed that increased corticospinal excitability was not a general effect of dual-task performance, but specific to dual-task situations involving motor tasks. Overall, the findings of the experiments conducted in this research exploring attention and coordination dynamics provided further support to the view that attentional allocation impacts on the coupling strength between the limbs and affects both the temporal and spatial dimensions of interlimb coordination. Furthermore, at the neural level, dual-task effects showed different neural manifestations for structural interference and capacity interference.