Modulation of Human Muscle Spindle Discharge Figure 3. Phase-locking and resetting of ongoing muscle spindle discharge. For further details see text and legend of Fig. 2. doi:10.1371/journal.pone.0035091.g003 By contrast, the third phase locking mechanism in spontane- ously active afferents was based on inhibition by the upstroke of the pulse wave (Fig. 3C). After being silenced for about 150 ms, approximately 250 ms after the R-wave the afferent resumed its firing with two phase-locked spikes. The following spikes showed considerable jitter and phase locking was not maintained. PLoS ONE | www.plosone.org 6 April 2012 | Volume 7 | Issue 4 | e35091