SUPPLEMENTARY EYE FIELD CONTRASTED WITH THE FRONTAL EYE FIELD DURING ACQUISITION OF CONDITIONAL OCULOMOTOR ASSOCIATIONS

1. The companion paper reported that a substantial proportion of cells in the supplementary eye field (SEF) of macaque monkeys show significant evolution of neuronal activity as subjects learn new and arbitrary stimulus-saccade associations. The purpose of the present study was to compare and contrast the activity of the SEF and the frontal eye field (FEF) during such conditional oculomotor learning. 2. In both SEF and FEF, we observed learning-dependent and learning-selective activity, defined as significant evolution of task-related activity as monkeys learned which of four saccades was instructed by a novel stimulus. By definition, in addition to changes as the monkeys learned the instructional significance of a novel instruction stimulus, learning-dependent activity also showed task-related modulation for trials instructed by familiar stimuli, whereas learning-selective activity did not. Of the 186 SEF neurons adequately tested, 81 (44%) showed one of these two categories of learning-related change. By contrast, of the 90 FEF neurons adequately tested, only 14 (16%) showed similar properties. This difference was highly statistically significant (chi(2) = 21.1; P < 0.001). 3. We also observed persistent differences in activity for trials with familiar versus novel instruction stimuli, which we termed learning-static effects. In some cases, the learning-static effect coexisted with learning-dependent or learning-selective changes in activity, although in others it did not. In the former cases, activity changed systematically during learning, but reached a level that differed from that for familiar stimuli instructing the same saccade. In the latter cases, the activity did not change significantly as the monkey learned new conditional oculomotor associations, but did show a significant difference depending upon whether a novel or familiar stimulus instructed a given saccade. Overall, 66 of 186 (35%) cells in the SEF and 17 of 90 (19%) cells in the FEF showed learning-static effects in one or more task periods. This difference was statistically significant (chi(2) = 7.9; P < 0.005). 4. The significant difference in the properties of SEF and FEF cells suggests a functional dissociation of the two areas during conditional oculomotor learning. In this respect, the FEF resembles the primary motor cortex, whereas the SEF resembles the premotor cortex.