Abstract
Handedness is one of the most recognized lateralized behavior in humans. Usually, it is associated with manual superiority regarding performance proficiency. For instance, more than 90% of the human population is considered more skilled with the right hand, which is controlled by the left hemisphere, than with the left. However, during the performance of bimanual tasks, the two hands usually assume asymmetric roles, with one hand acting on objects while the other provides support, stabilizing the object. Traditionally, the role of the two hands is viewed as fixed. However, several studies support an alternate view with flexible assignments for the two hands depending on the task. The supporting role of the hand depends on a closed loop pathway based on proprioceptive inputs from the periphery. The circuit’s efferent arm courses through the dorsal corticospinal tract (dCST) in rodents and terminate on spinal cord interneurons which modulate the excitability of motoneurons in the ventral horn. In the present work, we developed an experimental model of unilateral lesion targeting the cervical dCST with microinjections of the vasoconstrictor endothelin-1 (ET-1) to evaluate the degree of flexibility of forelimb assignment during a food manipulation task. Our results show that just 3 days after unilateral corticospinal tract (CST) injury in the cervical region, rats display severe motor impairment of the ipsilateral forepaw together with a remarkable reversal of motor assignment between the forelimbs.
Highlights
Given its widespread occurrence across vertebrates, lateralization of CNS structure and function is thought to be associated with a positive selective advantage (Rogers and Andrew, 2002; Rogers et al, 2004; Duboc et al, 2015)
We found the baseline performance of the test with the preferred paw (PP) is significantly higher than with the NPP for both the sham (PP = 9.33 ± 0.33, NPP = 6.00 ± 0.52, t(10) = 5.42, p = 0.0003) and the lesion (PP = 9.67 ± 0.56, NPP = 5.17 ± 0.48, t(10) = 6.130, p = 0.0001) groups
A two-way repeated measures analysis of variance (ANOVA) was conducted to evaluate the effect of group and days after surgery (3, 7, 14) on the number of pellets retrieved in the Montoya test with the PP (Figure 3)
Summary
Given its widespread occurrence across vertebrates, lateralization of CNS structure and function is thought to be associated with a positive selective advantage (Rogers and Andrew, 2002; Rogers et al, 2004; Duboc et al, 2015). Lateralization may increase brain efficiency by reducing interference between potentially competing processes, such as limb coordination during bimanual tasks (Rogers et al, 2004). The traditional view of motor control holds that the left-hemisphere is specialized for skilled hand movements and the performance of the. Suggests that each arm/hemisphere is specialized for controlling different movement features during bimanual interaction (Haaland and Harrington, 1989; Sainburg, 2002). The nondominant arm excels in impedance control, characterized by corrective, feedback elements, while the dominant arm excels in tasks requiring precise coordination of limb dynamics, which rely on predictive, feedforward elements (Wang and Sainburg, 2007)
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