Neuromechanical simulation

Abstract

The importance of the interaction between the body and the brain for the control of behavior has been recognized in recent years with the advent of neuromechanics, a field in which the coupling between neural and biomechanical processes is an explicit focus. A major tool used in neuromechanics is simulation, which connects computational models of neural circuits to models of an animal's body situated in a virtual physical world. This connection closes the feedback loop that links the brain, the body, and the world through sensory stimuli, muscle contractions, and body movement. Neuromechanical simulations enable investigators to explore the dynamical relationships between the brain, the body, and the world in ways that are difficult or impossible through experiment alone. Studies in a variety of animals have permitted the analysis of extremely complex and dynamic neuromechanical systems, they have demonstrated that the nervous system functions synergistically with the mechanical properties of the body, they have examined hypotheses that are difficult to test experimentally, and they have explored the role of sensory feedback in controlling complex mechanical systems with many degrees of freedom. Each of these studies confronts a common set of questions: (i) how to abstract key features of the body, the world and the CNS in a useful model, (ii) how to ground model parameters in experimental reality, (iii) how to optimize the model and identify points of sensitivity and insensitivity, and (iv) how to share neuromechanical models for examination, testing, and extension by others.

Keywords: behavior; biomechanics; computational model; motor control; movement; sensorimotor integration; sensory feedback.

Figure 1

A block diagram illustrating the organization of the fly flight model, showing the five distinct models (Controller, Rigid Body Dynamics, Aerodynamics, Environment, and Sensory Systems) and the signals that pass between them (in italics).

Figure 2

Simulated locust kick and jump. (A) Neural circuit, with flexor (red) and extensor (green) motor neurons, inhibitory (gold) neurons, flexor command (lavender) neuron, the flexor and extensor muscles, and the tendon lock mechanism that prevents premature extension. (B) Jump motor program. Top: flexor (red), extensor (green), and inhibitory motor neurons (gold); 2nd: Flexor muscle tension; 3rd: Extensor muscle tension; Bottom: longitudinal (blue) and vertical (green) distance moved. (C) The kick immediately before (left) and 5 ms later (right). (D) The jump immediately before (left) and 25 ms later (right) as the feet leave the ground. Adapted from Cofer et al., .

Figure 3

Illustrative diagram of the neuromechanical system of the cat hind leg; details differ from those presented in the four papers reviewed. 1. Swing/stance CPG. 2. Stance and Swing INs excite Motor INs. 3. Motor INs excite overlapping pools of Motor Neurons. 4. Motor Neurons excite leg muscles. 5, 6. Muscle spindle Ia and II afferents provide excitatory feedback to Motor Neurons, Motor INs, and Stance/Swing INs, and cross inhibition of antagonists. 7, 8. Ankle extensor afferents inhibit and hip extensor afferents excite Swing CPG elements to promote stance–swing transition.