A Neural Correlate of Oculomotor Sequences

tremely skillful (accurate and quick) in performing learned sequences, not new sequences. Miyashita et al. (1996) found that learned hand movements were led by, and possibly guided by, saccadic eye movements that brought the gaze to the target in an anticipatory 2-1-1 Hongo Bunkyo-ku, Tokyo 113-8421 manner. That eye movement may guide hand movement was also suggested by human studies. Johansson et Japan al. (2001) asked human subjects to grasp an object and move it toward a target. Interestingly, a saccadic eye movement was often directed to a point in midair where Summary the object would travel by the subject's next action. These findings suggest that a learned action is acquired Complex learned motor sequences can be composed of a combination of a small number of elementary as a sequence of eye movements, as well as a sequence of hand movements. actions. To investigate how the brain represents such sequences, we devised an oculomotor sequence task If there is a learning mechanism for eye movements, it must be capable of overpowering the stimulus-bound in which the monkey had to choose the target solely by the sequential context, not by the current stimulus nature of eye movement. An effective way to test this capability would be to ask subjects to make different eye combination. We found that many neurons in the supplementary eye field (SEF) became active with a spe-movements under the identical environment, depending on the learned context. For this purpose, we trained two cific target direction (D neuron) or a specific target/ distractor combination (C neuron). Furthermore, such monkeys on an oculomotor sequence task (Figure 1) in which different sequences (" hypersets ") could be activity was often selective for one among several sequences that included the combination (S neuron). learned, each consisting of five saccades. Each saccade was a two-alternative forced choice response (" set "): These results suggest that the SEF contributes to the generation of saccades in many learned sequences. while the monkey was fixating on a central spot, two identical spots appeared simultaneously out of four positions. After the fixation point went off, the monkey had Introduction to make a saccade to one of the two spots that was designated to be the target (the other distractor) (Figure A learned action is often composed of sequential movements. Many experimental and theoretical studies have 1A). A unique feature of this task was that the target was …