Figure 5.

Responses across all spindle afferents. Responses across an ensemble of nine type Ia afferents from the extensor digitorum, recorded from seven individuals during repetitive finger movement. All traces represent means across afferents, and the shaded colored areas represent ±1 SEM. Despite identical kinematic profiles across bias load conditions, the same effects of bias load on the ensemble of standardized (i.e., z-transformed) firing rates were observed as in the single afferent case (Fig. 3). Note that the EMG levels of the spindle-bearing muscle (extensor digitorum) during its stretch were not noticeably different between the no bias load and flexion-resistive bias load conditions (red vs blue traces), despite the difference in their corresponding ensemble firing rate signals (top), which is particularly clear during the initial periods of stretch (i.e., periods 5 and 6). In contrast to the extensor EMG, there is a difference in flexor EMG between the two conditions, and this difference is particularly apparent over periods 5 and 6.