Methods for estimating the numbers of motor neurons in man
Abstract
Some motor system diseases are associated with losses of motor neurons in the spinal cord, brainstem and sometimes the pyramidal tract neurons in the motor cortex. For two decades methods for estimating the numbers of motor units supplying various muscles have been applied and, despite some physiological and technical limitations, have provided powerful tools for estimating the severity and courses of these diseases. Presently, new methods including 'hands-off' automated techniques have been used to estimate motor unit numbers. These methods greatly simplify the application of motor unit estimates while at the same time improving their accuracy and reproducibility. These and other new methods for estimating motor unit numbers, their physiological and technical basis and the potential pitfalls of these and older techniques will be covered. As well, applications of these techniques to the study of aging and various motor system diseases will be shown.