Direct and indirect assessment of gamma-motor firing patterns.

The study of the patterns of gamma-motor activity which accompany natural contractions has been long and difficult, and has not as yet led to general agreement. In this review we have simplified matters by considering the case of locomotion in the cat only, and we have avoided discussion of the various hypotheses which have been advanced to provide general schemes of gamma control for a wide range of movements. The development of the subject is shown to depend very much on devising ingenious methods applicable to reduced and intact animals. Direct recording from gamma-motoneurones has only been possible in reduced preparations, whereas indirect assessment of gamma activity from spindle afferent recordings was used in these and in intact animals. At this point in time, we still have no direct recordings from gamma-motoneurones in normally behaving animals, but those obtained in decerebrate animals show distinct patterns of modulation for static and dynamic types with particular temporal relation to the stepping movements. The spindle recordings in intact animals potentially provide the most important information, and the problems of interpretation, which have previously caused difficulties, are beginning to be solved through the insights obtained from the reduced preparations.