*4.1. Non-Human Primates Appear to Exhibit Limb Dominance*

In human beings, the construct of limb dominance or preference is well accepted; i.e., most people use their right arm for functional tasks, and a minority use the left arm. A select few people can use both arms equally well (ambidextrous). The question of whether monkeys have limb dominance remains a subject of scientific inquiry. In this analysis, there is asymmetry related to the *RP* of EMG data derived from the left and the right tail muscles. These results suggest that the long-tailed macaque (*Macaca fascicularis*) exhibits limb preference and/or dominance. This is also consistent with the observations of the veterinary staff involved with this project. Generally, limb dominance refers to the preferential use of one limb to perform functional tasks [51]. This asymmetry in the pre-lesion (normal control) period has implications for any analysis subsequent to the experimental TSCI. Conceptually, volitional motor control involves a two-circuit pathway; i.e., the upper motor neurons and the lower motor neurons of the corticospinal tracts. The upper motor neurons originate in the cortex, travel the internal capsule and pyramids, and terminate into the grey matter of the spinal cord. The lower motor neurons originate in the grey matter of the spinal cord, exit via the nerve roots and reach the muscles via the plexus and peripheral nerves. The data suggest that the neural network that controls the left and right neurophysiological circuit is not symmetrical. Therefore, it stands to reason that experimental TSCI will have different effects on the separate circuits. This is consistent with human disease, to the extent that a lesion in one part of the central nervous system may have different manifestations related to the limbs. As such, the effects of the lesion, from a neurological perspective, were analyzed in model 2 separately for both the left and the right side.
