Figure 6.

Motor unit firing patterns in decerebrate cat during crossed extension reflex and TVR trials. Top panel: muscle force; middle panel: instantaneous firing rate individual motor units recruited during the corresponding force trace (each color/row represents a separate motor unit); bottom panel: smoothed motor unit firing rates during the corresponding force trace. X-axis for all panels: elapsed time, relative to onset of vibration. Increasing preactivation force (mediated by the crossed extension reflex) led to increasing motor unit recruitment, as seen in left and right middle panels from t = −1:0 s. Vibration onset was marked primarily by further increases in motor unit recruitment and less so by increases in firing rate of previously recruited units. After vibration stops (at t = 3.5 s), persistent motor unit firing is evident, particularly in low-threshold units; a hallmark of motoneuron PICs.