Published in The Neuroscience of Attention Ed. by George Mangun, Oxford University Press (2012)
Summary and review of the above chapter
INTRODUCTION: The operation of the frontal eye field, as distinct from other brain regions, is suggested to be independent of current sensory inputs, thus functioning in purely top-down fashion, and having a unique role in the voluntary control of attention and gaze.
In vision only some incoming signals are selected for enhanced processing. Most of the focus of attention is at the centre of the visual gaze. However, this is not invariable, and attention can also be focused on the peripheral vision, without the gaze being shifted. This ability is called ‘covert’ attention.
In the mid 20th century, it was demonstrated that subjects could choose which part of a briefly flashed picture entered their perception. Spatial attention is seen as enhanced processing of the signals at a particular spatial location, and this may allow the perception of features that might otherwise go unnoticed.
Neuronal responses to attended stimuli, for instance in V4 neurons, are enhanced relative to ignored stimuli. Neuronal responses in V4 and the inferior temporal cortex have been shown to be enhanced just before saccades occur. V4 neurons are primed to respond to the immediate target of a saccade, and may also be involved in guiding the saccade. Some evidence suggests that covert attention might depend on the same circuits that guide these saccades. Thus eye movements may facilitate attention, and may hinder the detection of signals at other locations.
FRONTAL EYE FIELD (FEF)
The direction of attention and the build up to saccades may depend on a common neural processing system. An area of the prefrontal known as the frontal eye field (FEF) is thought to be involved in this processing, and is located between the anterior prefrontal and the motor cortex; that is between centres for cognition and for the organisation of movement. The FEF is well placed to guide saccades. It receives projections from most areas of the visual cortex, and it projects to the brain stem and midbrain areas involved with saccades. The FEF also feeds back to the visual cortex, and may thus influence visual representations. Neurons in the FEF, both visual and visuomovement neurons, have elevated responses to search targets.
The FEF thus appears to drive both saccade preparation and covert spatial attention. FEF neurons fire prior to a purposive saccade during learned behaviour suggesting a role in learned behaviour and voluntary production of saccades. The orientation of spatial attention is often goal-driven. In this case, the observer decides what is currently most relevant. Both visual and movement responsive neurons in the FEF were found to attend the location of spatial attention, and this neural activity is predictive of what the subject will detect.
There are connections between the FEF and both the superior colliculus and the lateral intraparietal, but some evidence suggests that it is the FEF that drives voluntary attention and saccade control. Another study demonstrated synchrony between the FEF and the visual cortex during covert attention, both involuntary and voluntary. The operation of the FEF, as distinct from the superior colliculus and the lateral intraparietal, is suggested to be independent of current sensory inputs, thus operating in a purely top-down fashion, and having a unique role in the voluntary control of attention and gaze.