Modulation of Human Muscle Spindle Discharge Figure 4. Examples of R-wave triggered discharge rate averages in pulse-wave modulated muscle spindles. Panels on the left (A–E) illustrate five afferents showing positive peak (excitatory response to the upbeat of pulse wave). Panels on the right (F–J) show five afferents displaying an initial negative peak (inhibitory effect). Discharge rate modulation is expressed as % difference from mean discharge rate. Time elapsed after R-wave is shown on the x-axis. Text box indicates the relative amount of variance explained by arterial pulsations (EV). Black thick lines represent averages. Gray thin lines show overlay of individual discharge rate traces in every cardiac cycle. doi:10.1371/journal.pone.0035091.g004 PLoS ONE | www.plosone.org 8 April 2012 | Volume 7 | Issue 4 | e35091