The discovery of structural and functional elements of motor behavior is one of the key issues in motor control. It is very likely that he kinds of units available in the spinal cord may constrain athe types and organization of descending controls, intermediate representations and sensorimotor transformations. Recently a new type of unit has been suggested, based on combined physiological and biomechanical data. This unit has been called a 'force- field primitive'. A force-field is a function that maps the forces generated ina the limb to the limb's configuration. The relationship between force-field primitives and other spinal mechanisms is not well understood. Primitives could represent general purpose promotor elements: the site of convergence of signals from descending, pattern generator and coordinating systems.. Alternatively, they could be elements associated exclusively with spina pattern generators. The types of force-field primitives corresponded closely to force-fields that could be measured during wiping, burning and flexion behaviors elicited in spinal frogs. It is thus clearly important to understand how force-field primitives are related to these reflex behaviors. To begin to relate force-field primitive descriptions to spinal pattern generators we propose the following; (1) We will record the kinematics, and electromyographic activity (EMG) of reflex behaviors and using accurate dynamic models we will relate these to the static force-field measurements and their EMGs recorded from tahe same behaviors. The reflex behaviors examined will be wiping, flexion withdrawal and aversive turning movements. (2) To examine interlimb coordination. (3) To address control and modulation of reflexes by descending systems, we will examine athe effects of bulbospinal control of afferents on the force-field structures, the EMGs and the kinematics in the wiping, flexion and turning behaviors. (4) Identified pathways associated with the turn and strike will be stimulated in reduced preparations to examine how these interact with the spinal reflex behaviors. The notion that a small number of 'primitives' may form a large part of the support of spinal behaviors, and, perhaps, descending control, is interesting for the following two reasons; First, it offers hope of a simple experimental understanding of spinal cored function. Second, it suggests that functional recovery from spinal injury may be possible in the future with only limited, but targeted, neural growth and connectivity. The experiments proposed will provide two critical sets of data to test this scheme of the organization of motor behavior; (1) a detailed understanding of the specific roles and organization of the force-field primitives in the known context of spinal behaviors, and (2) a description of how the force-field primitives in the known context of spinal behaviors, and (2) a description of how the force-field primitives used in spinal behaviors interact with de descending control.
| Kargo, William J; Ramakrishnan, Arun; Hart, Corey B et al. (2010) A simple experimentally based model using proprioceptive regulation of motor primitives captures adjusted trajectory formation in spinal frogs. J Neurophysiol 103:573-90 |
| Giszter, S F; Kargo, W J (2002) Separation and estimation of muscle spindle and tension receptor populations by vibration of the biceps muscle in the frog. Arch Ital Biol 140:283-94 |
| Kargo, W J; Giszter, S F (2000) Afferent roles in hindlimb wipe-reflex trajectories: free-limb kinematics and motor patterns. J Neurophysiol 83:1480-501 |
