Abstract
Here, we investigate the role of sensory feedback in gait generation and transition by using a three-dimensional, neuro-musculo-mechanical model of a salamander with realistic physical parameters. Activation of limb and axial muscles were driven by neural output patterns obtained from a central pattern generator (CPG) which is composed of simulated spiking neurons with adaptation. The CPG consists of a body-CPG and four limb-CPGs that are interconnected via synapses both ipsilaterally and contralaterally. We use the model both with and without sensory modulation and four different combinations of ipsilateral and contralateral coupling between the limb-CPGs. We found that the proprioceptive sensory inputs are essential in obtaining a coordinated lateral sequence walking gait (walking). The sensory feedback includes the signals coming from the stretch receptor like intraspinal neurons located in the girdle regions and the limb stretch receptors residing in the hip and scapula regions of the salamander. On the other hand, walking trot gait (trotting) is more under central (CPG) influence compared to that of the peripheral or sensory feedback. We found that the gait transition from walking to trotting can be induced by increased activity of the descending drive coming from the mesencephalic locomotor region and is helped by the sensory inputs at the hip and scapula regions detecting the late stance phase. More neurophysiological experiments are required to identify the precise type of mechanoreceptors in the salamander and the neural mechanisms mediating the sensory modulation.
Highlights
Locomotion is an integral part of a whole range of animal behaviors such as searching for food or a place to rest and for escaping predators or other life threatening situations
The neuro-musculo-skeletal (NMS) model was supplemented with proprioceptive sensory feedback via stretch receptor like neurons residing along the body and angle detectors for hip and scapula joints
Different strengths for the inhibitory connections among the four limb-central pattern generator (CPG) were systematically analyzed and the resulting activity patterns for the two major limb muscles are shown in the Figure 4
Summary
Locomotion is an integral part of a whole range of animal behaviors such as searching for food or a place to rest and for escaping predators or other life threatening situations. A symmetry can be seen along the body axis and the body makes S-shaped standing waves coordinated with the movements of the limbs (Hildebrand, 1976; Frolich and Biewener, 1992; Ashley-Ross, 1994a). This coordination is such that it allows the salamander to increase its stride length utilizing its sprawling posture (Roos, 1964; Daan and Belterman, 1968). Even though these gait patterns have been well characterized and observed in intact salamanders, underlying mechanisms behind gait generation and transitions are still not properly understood
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