Bilateral Interference in Motor Performance in Homologous vs. Non-homologous Proximal and Distal Effectors

Abstract

Performance of bimanual motor actions requires coordinated and integrated bilateral communication, but in some bimanual tasks, neural interactions and crosstalk might cause bilateral interference. The level of interference probably depends on the proportions of bilateral interneurons connecting homologous areas of the motor cortex in the two hemispheres. The neuromuscular system for proximal muscles has a higher number of bilateral interneurons connecting homologous areas of the motor cortex compared to distal muscles. Based on the differences in neurophysiological organization for proximal vs. distal effectors in the upper extremities, the purpose of the present experiment was to evaluate how the level of bilateral interference depends on whether the bilateral interference task is performed with homologous or non-homologous effectors as the primary task. Fourteen participants first performed a unilateral primary motor task with the dominant arm with (1) proximal and (2) distal controlled joysticks. Performance in the unilateral condition with the dominant arm was compared to the same effector’s performance when two different bilateral interference tasks were performed simultaneously with the non-dominant arm. The two different bilateral interference tasks were subdivided into (1) homologous and (2) non-homologous effectors. The results showed a significant decrease in performance for both proximal and distal controlled joysticks, and this effect was independent of whether the bilateral interference tasks were introduced with homologous or non-homologous effectors. The overall performance decrease as a result of bilateral interference was larger for proximal compared to distal controlled joysticks. Furthermore, a proximal bilateral interference caused a larger performance decrement independent of whether the primary motor task was controlled by a proximal or distal joystick. A novel finding was that the distal joystick performance equally interfered with either homologous (distal bilateral interference) or non-homologous (proximal bilateral interference) interference tasks performed simultaneously. The results indicate that the proximal–distal distinction is an important organismic constraint on motor control and for understanding bilateral communication and interference in general and, in particular, how bilateral interference caused by homologous vs. non-homologous effectors impacts motor performance for proximal and distal effectors. The results seem to map neuroanatomical and neurophysiological differences for these effectors.

The influence of distal and proximal muscle activation on neural crosstalk

“…Although it is well documented that individuals are often more accurate when performing fine motor actions compared to gross motor actions [ 14 , 79 ], the current investigation may provide behavioral and neurophysiological evidence to account for these differences. Due to neuroanatomical differences between the neural organization of distal and proximal effectors (e.g., a distinct connection between brain and body, number of commissural fibers connecting muscles through the CC and spinal cord, the influence of uncrossed ventromedial corticospinal tracts and crossed lateral corticospinal tracts) [ 37 – 42 ], proximal effectors are likely influenced more by neural crosstalk than distal effectors [ 13 , 14 ]. Consistent with the possibility that proximal effectors are more susceptible to neural crosstalk, lower force harmonicity was observed for the non-dominant proximal effector than distal effector ( Fig 4 ).…”

“…It has been hypothesized that the influence of neural crosstalk on bimanual coordination is stronger for proximal effectors than for distal effectors [ 13 , 14 ]. The current investigation was designed to determine the effects of distal (FDI) and proximal (TBI) muscle activation on neural crosstalk when participants were required to produce a 1:2 multifrequency force pattern.…”

“…Significant EMG coherence in the Alpha band suggests a subcortical origin for neural crosstalk [ 11 , 50 ]. Other studies have also highlighted the contribution of the subcortical structures (e.g., cerebellum, basal ganglia, and spinal interneurons) and uncrossed corticospinal tracts to the performance of bimanual tasks specified by coupling temporal features [ 13 , 14 , 39 – 42 , 47 , 48 , 89 – 94 ]. The nature of the 1:2 bimanual coordination task requires the dominant effector to produce the actions twice as fast as the non-dominant effector.…”

“…Such work has used a variety of effectors (e.g., fingers, wrists, arms, shoulders) to examine coordination dynamics [ 3 , 12 ]. However, investigations directly comparing the coordination of distal and proximal effectors are less common [ 13 , 14 ].…”

“…Recent experiments comparing bimanual interference in proximal and distal effectors used a task that required participants to trace a sinewave pattern with their dominant proximal (shoulder and elbow) or distal (wrist and fingers) effector with a joystick while the non-dominant effector was inactive (unimanual control), produced a secondary movement task with distal effector, or produced secondary movement task with proximal effector [ 13 , 14 ]. Yet, the studies only assessed the performance of the dominant limb.…”