HISTORICAL RESEARCH ___________________________

The brain has been associated with limb movement since at least the 4th century BC, when Hippocrates noted that injuries to one side of the head typically resulted in motor deficits on the opposite side of the body. Many centuries later, René Descartes attempted to make sense of the nerves interconnecting brain and muscle, and their role in the production of limb movement. He presumed that tiny filaments within the nerves (themselves supposed to be tubes) could open and close valves that would regulate the flow of "animal spirits". The drawing included in the banner of each page was Descartes' effort to explain the reflex withdrawal of a limb from a painful stimulus. He proposed that the stimulus sets in motion the animal spirits in nerves running to the ventricles of the brain. Valves within the ventricles would open, releasing the spirits into nerves running to the muscle. Inflation of the muscles would cause the limb to withdraw.

Descartes imagined that voluntary movements were controlled in a similar fashion. The figure to the right, published in 1662 in De Homine suggests how voluntary movements might be guided by vision. Light striking the retina would cause visual information to be conducted into the brain via hollow optic nerves. The limb would then be set in motion by a chain of events similar to that of reflex movements. Descartes further imagined that the pineal body , by virtue of its singular, midline representation in the brain, acted as an interface between the soul and the complex system of valves which regulated the flow of animal spirits.
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In the several centuries since Descartes, we have gained an increasingly detailed understanding of the mechanisms by which the brain exerts its influence over the muscles of the limbs. However, if our understanding of the mystery of these mechanisms has increased, so too has our appreciation of their complexity. Ironically, we know now that sensory and motor information is indeed propagated within hollow, fluid-filled tubes. However, the mechanisms are far more complex than Descartes imagined, involving not hydraulics, but complex electro-chemical cascades.

A pivotal point in our understanding of these motor systems came approximately 130 years ago through experiments conducted by the Germans Eduard Hitzig and Gustav Fritsch, and by British neurologist David Ferrier. These researchers noted that limb movements occurred when electrical stimuli were applied to an area toward the front of the brains of experimental animals. Ferrier's drawing of effective stimulus sites on the brain of a monkey is shown to the left. Subsequently this area became known as the primary motor cortex . We know now that it sends movement command signals directly to the spinal cord. Similar, but higher resolution maps were constructed from human neurosurgical patients by the American neurosurgeon Wilder Penfield. A well-known version of this map is shown in the figure to the right.


( From Finger (1994). The Origins of Neurosciences. Oxford University Press. )
David Ferrier
(1843-1928).		 Wilder Penfield
(1891-1976).
 

Primary motor cortex is reciprocally interconnected with numerous other cortical areas. In addition, most of the cerebral cortex is further interconnected with the cerebellum and basal ganglia, two other brain structures having important motor function. One aspect of my research involves studying the detailed representation of movement or muscle activity that is expressed by the signals recorded from each of these motor signals. In other experiments we examine the connections among the different areas, and attempt to relate this network of connections to the signals they produce. Finally, in an applied area of my research, we record the brain's natural control signals and attempt to extract information from them that could be used to control an external device like a computer or a robotic arm.
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(click to see movie of the SARCOS high performance humanoid robot catching a ball)

The SARCOS "DB" robot is among the most advanced humanoid robots ever built. It has 30 degrees of freedom that include multiple joints in all four limbs, the neck, and eyes. It has binocular vision that allows it to locate and track moving objects. On the left, DB is shown catching a ball. To be successful, the robot must detect the ball, predict its trajectory, and plan and execute a movement to intercept it. On the right, DB demonstrates 3-ball cascade juggling. Grasping and releasing the balls would have been far too complex, so the robot used funnels to catch the balls. Visual feedback and trajectory planning was too slow, so the movements of the hands were pre-programmed. Consequently, the robot was unable to compensate for any slight variation in the trajectories of the balls, and could juggle for only a few seconds. Bruce Tiemann has little to worry about for the moment...

(click to see movie of the SARCOS high performance humanoid robot juggling 3 balls)
The Feinberg School of Medicine, Department of Physiology, Northwestern University
Website modified on October 29, 2009