Gain control in reflex pathways

Summary form only given. A series of experiments was undertaken to determine the gain of the stretch reflex in decerebrate cats. Stretches are applied through a servo-controlled motor that receives length and velocity feedback which are adjusted so that it behaves like a spring of a particular stiffness. As the stiffness decreases the gain of the reflex increases until the stiffness is made much less than the intrinsic muscle stiffness. Under these conditions small brief pulses can elicit shortening of 1 mm or more and reflex forces that are larger than the force produced by the stretch itself. This suggests that the gain in the reflex is 1 or more at low frequencies. It is concluded that muscle control systems are adaptive and time-varying to accomplish the various tasks required by the organism. Although under some conditions the reflex gain is on the order of one, measurement of gain is compounded by a number of nonlinearities, and the value of these nonlinearities in various tasks remains to be determined