Movements occur not in isolation but in a coordinated manner: to catch a flying ball we must move our eyes, head, and body into position and finally reach with our arms. While substantial progress has been made in the understanding of the brain regions that are related to the individual movements, little is known about the mechanism within the brain for this coordination. In experiments this year, we have found neurons in the monkey superior colliculus, which lies on the roof of the brainstem, that may act to coordinate several types of movements. We recorded from neurons that lie near the rostral pole of the superior colliculus and that increase their activity in relation to small rapid or saccadic eye movements that direct the eye from one region of the visual field to another. We found that these neurons increased their activity before saccades to small changes of target location (less than a few degrees of visual angle) when that change in position moved the target into the contralateral visual field but decreased their activity when the saccade was either larger or directed to the ipsilateral visual field. Each neuron increased its discharge maximally for a given change in target position. For small position changes, the neuron discharge increased, but a saccade was frequently not made at all. Thus the neuron's activity was more closely related to the required change in eye position to bring the fovea on to the target, rather than to the generation of the saccade itself. This made these rostral neurons in the superior colliculus very similar to other saccade related neurons in the caudal superior colliculus that are referred to as buildup neurons: both increase their discharge rate when the desired target is in the contralateral visual field and this activity can occur whether or not a saccade is made. If these neurons convey a motor error signal rather than the signal that is specific for a saccadic eye movement, then they ought to increase their discharge before other types of eye movements as well. One of these other movements, smooth pursuit eye movements that keep the fovea on a moving target, can also be generated by small target errors, and we next determined whether these superior colliculus neurons are related to such pursuit movements. They are. The activity of the rostral neurons increased with pursuit to the contralateral side and decreased with such pursuit to the ipsilateral side. Electrical stimulation of the caudal superior colliculus alters the generation of saccadic eye movements, and if the rostral superior colliculus is related to pursuit as well as saccades such stimulation should alter pursuit as well. We found that stimulation during pursuit alters the eye speed: it increased the speed of the pursuit toward the contralateral side and decreased it for pursuit toward the ipsilateral side. This effect of stimulation is very similar to that seen for the effects of electrical stimulation in cerebral cortical areas whose relation to pursuit generation has been well established. Thus, a strong case can be made that the activity in the rostral superior colliculus is related to both the generation of saccades and pursuit. This in turn suggests that these neurons in the superior colliculus are conveying a signal of motor error not a signal that a specific movement be made. Other neurons in the superior colliculus and elsewhere are charged with the task of specifying how the motor error is to be reduced to bring the target on to the fovea such as the saccade related burst neurons that are also in the superior colliculus. The mechanism for coordination of movement within the brain would be to first to establish a motor error signal and then to use this same signal for multiple movements to reduce that error. While we have studied this issue specifically in relation to eye movements, similar mechanisms may be used to coordinate eye and skeletal movements as well.