FIGURE 3.

Comparison of the effects of PIC on cat motoneuron discharge

Comparison of the effects of PICs on cat motoneuron discharge (A) (modified from (29)) and their presumed effects on human motor unit discharge (B) (Heckman CJ, Thompson CK, unpublished data). A: the red trace shows a firing pattern in response to a triangular-shaped pattern of injected current (black trace) in a cat motoneuron lacking a strong PIC. The green trace was recorded in response to the same input from a cat motoneuron with a strong PIC. Note the acceleration in firing induced by the rapid amplification of the PIC, followed by saturation. The arrows at onset and offset indicate the hysteresis (offset at lower input level than onset for the PIC motoneuron). B: the firing patterns from seven human motor units recorded during a volitionally generated, torque output in isometric conditions. The similarity between the cat and human data is striking. The blue and orange traces have arrows to indicate the onset-offset hysteresis. Images from Ref. 29 are used with permission from Journal of Neurophysiology.