Human neuroimaging has revealed a specific network of brain regions—the default-mode network (DMN)—that reduces its activity during goal-directed behavior. So far, evidence for a similar network in monkeys is mainly indirect, since, except for one positron emission tomography study, it is all based on functional connectivity analysis rather than activity increases during passive task states. Here, we tested whether a consistent DMN exists in monkeys using its defining property. We performed a meta-analysis of functional magnetic resonance imaging data collected in 10 awake monkeys to reveal areas in which activity consistently decreases when task demands shift from passive tasks to externally oriented processing. We observed task-related spatially specific deactivations across 15 experiments, implying in the monkey a functional equivalent of the human DMN. We revealed by resting-state connectivity that prefrontal and medial parietal regions, including areas 9/46d and 31, respectively, constitute the DMN core, being functionally connected to all other DMN areas. We also detected two distinct subsystems composed of DMN areas with stronger functional connections between each other. These clusters included areas 24/32, 8b, and TPOC and areas 23, v23, and PGm, respectively. Such a pattern of functional connectivity largely fits, but is not completely consistent with anatomical tract tracing data in monkeys. Also, analysis of afferent and efferent connections between DMN areas suggests a multisynaptic network structure. Like humans, monkeys increase activity during passive epochs in heteromodal and limbic association regions, suggesting that they also default to internal modes of processing when not actively interacting with the environment.

The frontal eye field (FEF) has long been regarded as a cortical area critically involved in the execution of voluntary saccadic eye movements. However, recent studies have suggested that the FEF may also play a role in orienting attention. To address this issue, we reversibly inactivated the FEF using multiple microinjections of muscimol, a GABA_Aagonist, in two macaque monkeys performing visually guided saccades to a single target. The effects of FEF inactivation were also studied in a covert visual search task that required monkeys to search for a target presented among several distractors without making any eye movements.As expected, inactivating the FEF caused spatially selective deficits in executing visually guided saccades, but it also altered the ability to detect a visual target presented among distractors when no eye movements were permitted. These results allow us to conclude definitively to an involvement of the FEF in both oculomotor and attentional functions. Comparison of the present results with a similar experiment conducted in the lateral intraparietal cortex area revealed qualitatively different deficits, suggesting that the two areas may make distinct contributions to selective attention processes.

We investigated the contribution of the lateral intraparietal area (LIP) to the selection of saccadic eye movement targets and to saccade execution using muscimol-induced reversible inactivation and compared those effects with inactivation of the adjacent ventral intraparietal area (VIP) and with sham injections of saline into LIP. Three types of tasks were used: saccades to single visual or memorized targets, saccades to synchronous and asynchronous bilateral targets, and visual search of a target among distractors. LIP inactivation failed to produce deficits in the latency or accuracy of saccades to single targets, but it dramatically reduced the frequency of contralateral saccades in the presence of bilateral targets, and it increased search time for a contralateral target during serial visual search. In the latter task, the observed deficits might reflect either an ispilateral bias in saccadic search strategy or an attentional impairment in locating a target among flanking distractors within the contralateral field. No effects were observed on any of these tasks after VIP inactivation. These results suggest that one important contribution of LIP to oculomotor behavior is the selection of targets for saccades in the context of competing visual stimuli.