RAPID COMMUNICATION Frontal Eye Field Neurons Orthodromically Activated From the

Sommer, Marc A. and Robert H. Wurtz. Frontal eye field neu- proved by the Institute Animal Care and Use Committee and com-plied with Public Health Service Policy on the humane care androns orthodromically activated from the superior colliculus. J. Neu-rophysiol. 80: 3331–3333, 1998. Anatomical studies have shown use of laboratory animals. The FEF and SC were located anatomi-cally with magnetic resonance imaging and physiologically by re-that the frontal eye field (FEF) and superior colliculus (SC) of monkeys are reciprocally connected, and a physiological study cording from saccade-related neurons and by evoking saccades at described the signals sent from the FEF to the SC. Nothing is 50-mA threshold. Two tungsten microelectrodes for stimulation known, however, about the signals sent from the SC to the FEF. were implanted in the intermediate layers of the ipsilateral SC We physiologically identified and characterized FEF neurons that ( typically 1 was placed at 37 eccentricity and 1 between 10 and are likely to receive input from the SC. Fifty-two FEF neurons 307 eccentricity on the SC map, Robinson 1972) or one was moved were found that were orthodromically activated by electrical stimu- through the SC in a penetration (at 87 eccentricity). We recorded lation of the intermediate or deeper layers of the SC. All the neu- from single FEF neurons with conventional methods and attempted rons that we tested (n 34) discharged in response to visual to activate each with SC stimulation (single biphasic pulse, 0.15 stimulation. One-half also discharged when saccadic eye move- ms/phase, ¡600 mA/phase; Fig. 1A). ments were made. This provides the first direct evidence that the An FEF neuron was considered activated if it discharged consis-ascending pathway from SC to FEF might carry visual- and sac- tently (¢1/3 of stimulation trials) at about the same latency (vari