Fig. 1.

A: sequence of events in a typical trial of the serial-order task. Arrows indicate saccades, and dashed circles indicate direction of gaze. Monkeys had to make a saccade toward the red cross in the first trial phase, to the green hexagon during the second phase, and to the blue triangle during the third phase, irrespective of the objects' locations. The locations of the objects were subject to change between each trial phase and the next. Electrical stimulation (indicated during phase 3) occurred only on some trials and only during a single phase on a given trial. This might, with equal probability, be phase 1, 2, or 3. B: stimulation sites projected onto the frontal lobes in dorsal view. The area of the circle at each location is proportional to the number of sites studied during penetrations at that location (range: 1–6). PS, principal sulcus; AS, arcuate sulcus. C–E: for trial phases 1, 2, and 3, the fraction of trials on which the monkey made a saccade to the correct target rather than to either of the 2 incorrect targets. In each plot, there is 1 point for each stimulation site; x- and y-axes indicate trials on which electrical stimulation was or was not delivered during the corresponding phase, respectively.