University of California, Davis, California 95616, USA, and Brandeis University, Waltham, Massachusetts, USA
The primary functions of spinal locomotor central pattern generators
(CPGs) are to provide oscillatory motor commands to individual
joints or segments and to control the precise timing of those
commands across all joints or segments for efficient, coordinated
locomotor behavior. Our ability to understand the neuronal mechanisms
underlying intersegmental coordination has been hampered by
the complexity of propriospinal interconnectivity and the paucity
of quantitative data on the magnitude and timing of those connections.
Theoretical approaches have therefore been employed to discover
general roles by which CPG-like oscillator systems must be constructed
to produce appropriate coordinated locomotor behavior; the locomotor
CPG is represented as a network of oscillators, where each oscillator
generates local motor output and interoscillator coupling provides
intersegmental coordination. Mathematical analysis of such coupled
oscillator systems has provided a number of experimentally testable
predictions regarding the link between coupling and coordination.
Application of these network-level predictions to the results
of electrophysiological experiments has required data analysis
methods that can relate the behavior of the
in vitro spinal
cord to the variables employed by the mathematical model. Hence,
our most recent work has focused on developing analytic tools
for quantifying the changes in locomotor output that result
form experimental manipulations of the propriospinal system
in terms of frequency, intersegmental phase, and intersegmental
correlation. Results of recent experiments can now be used to
put further constraints on the allowable kinds of intersegmental
coupling provided by mathematical modeling of the system.
