Subthreshold microstimulation in frontal eye fields updates spatial memories

The brain's sensitivity to self-generated movements is critical for behavior, and relies on accurate internal representations of movements that have been made. In the present study, we stimulated neurons below saccade threshold in the frontal eye fields of monkeys performing an oculomotor delayed response task. Stimulation during, but not before, the memory period caused small but consistent displacements of memory-guided saccade endpoints. This displacement was in the opposite direction of the saccade that was evoked by stronger stimulation at the same site, suggesting that weak stimulation induced an internal saccade signal without evoking an actual movement. Consistent with this idea, the stimulation effect was nearly absent on a task where an animal was trained to ignore self-generated eye movements. These findings support a role for the frontal eye fields in accounting for self-generated movements, and indicate that corollary discharge signals can be manipulated independent of motor output.