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Executive control requires controlling the initiation of movements, judging the consequences of actions, and adjusting performance accordingly. We have investigated the role of different areas in the frontal lobe in executive control expressed by macaque monkeys performing a saccade stop signal task. Certain neurons in the frontal eye field respond to visual stimuli, and others control the production of saccadic eye movements. Neurons in the supplementary eye field do not control directly the initiation of saccades but, instead, signal the production of errors, the anticipation and delivery of reinforcement, and the presence of response conflict. Neurons in the anterior cingulate cortex signal the production of errors and the anticipation and delivery of reinforcement, but not the presence of response conflict. Intracranial local field potentials in the anterior cingulate cortex of monkeys indicate that these medial frontal signals can contribute to event-related potentials related to performance monitoring. Electrical stimulation of the supplementary eye field improves performance in the task by elevating saccade latency. An interactive race model shows how interacting units produce behavior that can be described as the outcome of a race between independent processes and how conflict between gaze-holding and gaze-shifting neurons can be used to adjust performance. [ABSTRACT FROM AUTHOR]

It has been proposed that low-threshold Ca2+ (LT)-associated bursts in the lateral geniculate nucleus (LGN) of awake animals communicate significant or unexpected visual events to cortex. The present study investigated this hypothesis by examining the incidence of LT bursts in 146 cells recorded from the LGN of three macaque monkeys. Bursts were defined as clusters of two or more action potentials separated by not more than 4 ms and preceded by a > or = 100-ms quiescent interval. The incidence of bursts was examined in several intensive-training Go-NoGo and target selection tasks as well as in training-free tasks where natural scenes with both familiar and novel contents were shown. Our chief findings were as follows. 1) Bursts occur in the majority of cells under every condition tested, 2) burst incidence is very low (<1 burst every 10 s), 3) bursts occur in association with a receptive field stimulus on average only once every 23 times in 65% of cells tested, 4) cells responding with bursts to the stimulus also tended to exhibit higher levels of spontaneous bursting, 5) the presence of bursts did not depend on the novelty of the stimulus or its behavioral relevance. When the monkeys explored static natural scenes, 6) bursts were not correlated with short-term changes in the image sampled by the cell's receptive field during saccades. Burst incidence 7) did not increase when images were novel or when they evoked an emotional reaction, and 8) bursts did not decrease when images were familiar. 9) Bursts were not correlated with saccades in the dark, but 10) more spikes participated in bursts in the dark. Although these results confirm the occurrence of LT bursts in LGN cells of awake monkeys, they do not support the hypothesis that these bursts are a privileged means of transferring sensory information, that they signal unexpected or significant visual events, or that they are involved uniquely in the coding of natural scenes. [ABSTRACT FROM AUTHOR]

The latency and variability of latency of single-unit responses to identical visual stimulation were measured in the frontal eye field (FEF), supplementary eye field (SEF), and anterior cingulate cortex (ACC) of macaque monkeys performing visually guided saccades. The mean visual response latency was significantly shorter in FEF (64 ms) than in SEF (81 ms) or ACC (100 ms), and latency values determined by four methods agreed. The latency variability of the visual response was respectively less in FEF (21 ms) than in SEF (37 ms) or ACC (41 ms). Latency, variability of latency, and magnitude of the visual responses were correlated within FEF and SEF but not ACC. These characteristics of the visual response are consistent with the degree of convergence of visual afferents to these areas and constrain hypotheses about visual processing in the frontal lobe. [ABSTRACT FROM AUTHOR]