After-effects of preceding movement on dynamic responses of spindle primary afferents during passive muscle lengthening in the cat.

After-effects of preceding movement on the activity of primary spindle afferents of de-efferented cat hindlimb muscles were examined during the dynamic phases of slow linear test movements. These dynamic after-effects were compared with the static after-effects observed in the spindle activity during steady-state of the parent muscle and with hysteresis after-effects of the muscle proper. According to their pattern, the dynamic phases of the spindle and muscle reactions can be divided into two parts. During the first part (at the beginning of movement), both spindle responses and muscle state (either length or load depending on the mode of the test movement) strongly depended on the previous history of movement, being completely independent of the direction of preceding movement in the second part of the dynamic phase. These two parts were treated in terms of interaction of the movement-dependent after-effects in muscles and muscle spindle afferents. These findings allowed us to suppose that, during rather slow single-joint movements, the spindle afferents from the passive antagonist muscles can provide signals free from the effects of preceding movement.