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Frontal eye fields
The frontal eye fields (FEFs) are bilateral areas of the pre-frontal cortex in the primate and non-primate brain, involved in the programming of saccades - rapid movements of the eyes. They function as part of ocular motor systems within the brain to generate purposive and volitional eye movements. A long history of scientific research has accumulated of its complex structure, function and interconnections.

Research history
In the 19th century David Ferrier reported that electrical stimulation of an area of cortex in monkeys caused saccadic movements of the eye towards the contralateral - opposite - side. In 1931 Foerster investigated these bilateral areas and gave them the name ‘Frontal Eye Field’. The development of increasingly sophisticated measuring techniques aided extensive research into this area of the animal and non-human primate brain, leading to a burgeoning of detailed experimental data on the quality of activity in individual neurons and the oculo-motor networks they are part of. In the last few decades, a range of techniques have enabled the FEFs of the human brain to be studied, such as using event-related functional magnetic resonance imaging, to detect neural activity through blood oxygenation level distribution in the cerebral cortex during the anti-saccade task.

In order to attend to visual stimuli and efficiently act on this information, the most relevant part of the visual field must be processed on the fovea, the part of the retina that processes visual information with the highest acuity. Brain systems evolved to increase advantage in primates by adding cortical control to the phylogenetically older areas in the midbrain involved in saccade execution. Early studies detected a series of inhibitory and excitatory connections through oculo-motor neural networks; these produce fixation to a visual location, or eye movement in discrete steps. It was first thought low-level visual information controlled by separate systems within the brain were responsible for these separable aspects; it is now understood that the extensive network of cortical and sub-cortical structures involved in oculomotor activity overlap considerably. The FEF has ‘executive’ control within this system, overseeing sophisticated mechanisms of control.

Neurological patients who have damage to the FEF, unilaterally or bilaterally, have shown disruption to volitional control over other commands from ocular motor control areas, and impaired ability to generate endogenous saccades.

Location
In the human brain the FEF is located bilaterally in Brodmann Area 6 at the junction of the superior frontal sulcus and the precentral sulcus. In the non-primate brain the FEF is located in Brodmann Area 8, within the convexity of the arcuate sulcus. There has been ongoing debate regarding precise localisation of FEF in the human brain; the majority of research has involved experimentation on non-human primates, and the location of FEF identified in this population does not correspond exactly to human brain areas. Nevertheless, architectonic similarities are close enough to compare their functional organisation. Localisation of FEF is further complicated by variance in anatomical positions identified by different task requirements, and methods of measurement used to locate the FEF and investigate its function.

Function and neuroanatomy
Studies have shown FEF to play an important role in the control of both covert and overt visual attention. In the FEF, two types of voluntary movements are generated; smooth pursuit movements, and saccades, through a complex system of gaze holding and gaze shifting mechanisms, in conjunction with other prefrontal and motor association cortex areas involved in the performance of voluntary eye movements; supplementary eye field (SEF), cingulate eye field (CEF) and premotor eye field. Neurons with foveal receptive fields have been identified, and found to be active during both retinal and non-retinal stimulation. Movement-related neurons that initiate saccades, and fixation-related neurons that inhibit production of saccades, have been found throughout areas of the oculomotor system; in addition, the intraparietal sulcus (IPS) towards the posterior part of the brain, and particularly the superior colliculus (SC) in the midbrain, are involved in the generation and control of eye movements in the direction contralateral to the frontal eye fields' location. As well as higher order cortical and mid-brain areas, circuits connect with the brainstem and cerebellum. The major output of the FEF is to the SC in the midbrain and to premotor neurons in the reticular formation in the brainstem. Although much is known about its connections with other cortical and sub-cortical areas, less is known about the local cortical circuit. Neuroimaging studies of the FEF have shown most activity in rostral FEF regions when saccade eye movements are generated. Many neurons related to smooth-pursuit have been found in the caudal part of FEF, informed by interconnected cerebral areas of an oculomotor subsystem known as the cortical pursuit system. These have been found to integrate vestibular inputs and pursuit signals, enabling the visual eye field to be maintained on the fovea throughout movements of head and body. Thus, co-ordinated mechanisms incorporate body and eye movement information with visual information, enabling stable visual target maintenance.

A unique pattern of pursuit and vergence tracking signals have been found in FEF neurons, leading to three-dimensional motion velocity signals that have not been identified anywhere else in the visual system, which assist hand co-ordination for manipulating objects. Regions of the FEFs are adjacent to sensorimotor areas; this integration enables fine motor control and coordination. Other subtle functions of FEF link it to attention, and working memory. The FEF have a topographic structure that represents saccade targets in retinotopic coordinates. FEF neurons of macaque monkeys in experimental short-term memory tasks have shown maintenance of spatial information, regardless of the relevance of that information to the task, as well and demonstrated anticipatory activity in relation to target position; this is thought to contribute to object memory.

The SC, a sub-cortical region of the brain that receives direct visual information from the retina, generates reflexive, express saccades, which are very fast, and is responsible for the visual grasp reflex (VGR). This is the orientation system whereby we have our eye caught by, and fixate to, an exogenous stimulus, and mediation by the FEF exerts control over such saccades and head orienting. During early stages of brain maturation, young babies lack sufficient connections to frontal brain regions; voluntary control of eye movements matures throughout early years, and into middle childhood.

There is also evidence the FEF plays a role in purely sensory processing and that it belongs to a “fast brain” system through a superior colliculus – medial dorsal nucleus – FEF ascending pathway. In humans, its earliest activations in regard to visual stimuli occur at 45 ms with activations related to changes in visual stimuli within 45–60 ms; these are comparable with response times in the primary visual cortex.