One of the central questions in the field of motor control is to understand how our motor goals are translated into actions. The Bizzi laboratory has elaborated a theoretical and experimental framework that describes the way in which the central nervous system transforms planned movements into muscle activations. Among the techniques used by the lab are behavioral training, cortical recording from single neurons, electromyographic (EMG) recording of muscle activity, microstimulation, cellular inactivation, kinematic measurement of movements in three dimensions, functional imaging, and computational modeling. Experimental models include frogs (including spinalized and spinal cord-isolated preparations), rats, cats, rhesus monkeys, and humans (both patients and normal subjects). The Bizzi lab is part of the Department of Brain and Cognitive Sciences at MIT, and is affiliated with the McGovern Institute for Brain Research.
modular motor control
In the natural world some complex systems are discrete combinatorial systems - they utilize a finite number of discrete elements to create larger structures. The genetic code, language and perceptual phenomena are examples of systems in which discrete elements and a set of rules can generate a large number of meaningful entities that are quite distinct from those of their elements. A question of considerable importance is whether this fundamental characteristic of language and genetics is also a feature of the vertebrate motor system. In the last few years, my colleagues and I have asked this question: are there simple units (motor primitives) that can be flexibly combined to accomplish a variety of motor tasks? We have addressed this fundamental and long-standing question in experiments that utilize spinalized frogs (Bizzi et al., 1991; Giszter et al., 1993), rats (Tresch and Bizzi, 1999), and currently monkeys (d'Avella et al., in preparation). With an array of approaches such as microstimulation of the spinal cord (Mussa-Ivaldi et al., 1994), NMDA iontophoresis (Saltiel et al., 2001), cutaneous stimulation of the hindlimb (Tresch et al., 1999) and vestibular activation (d'Avella and Bizzi, 1998), we have provided evidence for a modular organization of the frog's and rat's spinal cord.
The idea of control of movements based on motor primitives is also of significance to studies of motor learning. The problem of adaptation to a new environment can be framed as one of finding an activation parameter for each primitive such that the sum of their actions results in a force field which approximates the dynamics of the environment (Mussa-Ivaldi and Bizzi, 2000). To better understand the neural basis of such motor adaptation, we have recorded cellular activity from the frontal cortical areas of the primate. We have identified populations of neurons that exhibit learning-dependent plasticity in primary motor cortex (Li et al., 2001), the supplementary motor area (Padoa-Schioppa et al., 2002, 2004), and the dorsal and ventral premotor areas (Xiao et al., 2006). These data suggest multiple cortical motor areas are involved in learning to move in novel environments.
motor recovery after stroke
How patients with stroke re-learn movements through practice (motor recovery) and how they learn to recombine these movements into novel, unpracticed movements (motor generalization) is poorly understood and is central to progress in neurorehabilitation. Our work provides evidence that movements trained in a virtual environment performed by patients with stroke can be generalized to similar real world tasks and to certain types of untrained tasks, producing gains in real world function (Holden et al., 2001, 2005). This potential for recovery still exists after conventional therapy has been discontinued. This method is ideally suited for telemedicine-enabled application in patients with impaired mobility or in underserved areas.
General correspondence should be addressed to:
Bizzi Lab, 46-6189
43 Vassar Street
Cambridge MA 02139
phone: (617) 253-5687
fax: (617) 258-5342