Figure 11.

An alternative possible SC to motor command transformation. (A,B) As in Figure 10, the level of activity in the SC normally varies with eye position (ii), but here this variation is reflected in the computation of the SC's output signal (iii). Another difference is that the eye position signal in the SC is positively, rather than negatively, correlated with the movement field/site of activation, so that the number of spikes in the output is higher for more contralateral fixation positions. The combined eye amplitude-eye position signal derived from SC activity might be sufficient to guide the motor command (iv). (C,D) Microstimulation in the SC might serve to remove this eye position signal, by clamping the firing rate in a pattern dictated by the microstimulation train (ii). The output of the SC would then be the same across different eye positions (iii). The lack of an eye position component in the output signal would cause eye movements to vary with eye position (iv).