Supplementary eye field (SEF) is the name for the anatomical area of the dorsal medial frontal lobe of the primate cerebral cortex that is indirectly involved in the control of saccadic eye movements. Evidence for a supplementary eye field was first shown by Schlag, and Schlag-Rey. [1] Current research strives to explore the SEF's contribution to visual search and its role in visual salience. [2] [3] The SEF constitutes together with the frontal eye fields (FEF), the intraparietal sulcus (IPS), and the superior colliculus (SC) one of the most important brain areas involved in the generation and control of eye movements, particularly in the direction contralateral to their location. [2] [4] Its precise function is not yet fully known. [2] Neural recordings in the SEF show signals related to both vision and saccades somewhat like the frontal eye fields and superior colliculus, but currently most investigators think that the SEF has a special role in high level aspects of saccade control, like complex spatial transformations, [5] learned transformations, [6] and executive cognitive functions. [7] [8]
In 1874, David Ferrier, a Scottish neurologist first described the frontal eye fields (FEF). He noted that unilateral electrical stimulation of the frontal lobe of macaque monkeys caused "turning of the eyes and head to the opposite side" (Fig. 2). [9] The brain area allotted to the FEF by Ferrier's original map was actually quite large and also encompassed the area which we now call the SEF. A century's worth of experimental findings following Ferrier's work have led to shrinking the FEF's size. [10]
During the 1950s, surgical treatment of epileptic patients was being conducted. Neurosurgeons were removing lesions and other parts of the brain thought to be involved in causing the patient's seizures. Treatment of these epileptic patients lead to the discovery of many new brain areas by observant neurosurgeons concerned with the post-surgical implications of removing sections of the brain. Through electrical stimulation studies an area called the supplementary motor area (SMA) was observed and documented by the neurosurgeon Wilder Penfield in 1950. [11] [12] As Penfield had noted the induction of gaze shifts by stimulation of the rostral part of the SMA, another eye field's existence was postulated.
In 1987, the SEF was finally characterized by Schlag and Schlag-Rey as an area where low intensity electrical stimulation could evoke saccades, similar to the FEF. It was named as such to complement the SMA's name. [1]
The eye field originally defined by Ferrier's map of the frontal cortex extended medially to the dorsal surface of the brain (Fig. 2). [9] But the FEF proper has since shrunk into the rostral back of the arcuate sulcus (Fig. 1). [10] Experimenters have since established that the FEF and SEF are two separate and distinct brain areas responsible for saccade initiation through cerebral blood flow, and subdural electrode array studies. [11] [13] [14] [15]
In humans, the SEF is located in the rostral supplementary motor area (SMA). [16] It is located in Brodmann area 6 (BA6) which corresponds to area F7, the premotor cortex. [17] Based on single unit recording and microstimulation it has been established that the SEF is caudally contiguous with the parts of the SMA which represent orofacial, and forelimb movements. [1] [18]
The FEF is located in Brodmann area 8 which is just anterior to the premotor cortex (BA6) (Fig. 3). [19]
As opposed to the FEF, the SEF plays an indirect but executive role in saccade initiation. For example, the activity of SEF neurons is not sufficient to control saccade initiation in macaque monkeys performing stop signal go/no-go tasks. [3] In this kind of task a trained monkey is to make a particular response (in this case move its eyes, or produce a saccade) to a stimulus on a screen such as a flashing dot. For the go-task, the monkey is to look at the dot. But for the no-go task, the go signal will appear and be followed by the no-go signal, testing whether the saccade initiation can be inhibited. [20]
In other words, the SEF does not immediately or directly contribute to saccade initiation. But, the SEF is thought to improve saccade production by using prior knowledge of anticipated task requirements to influence saccadic eye movements. It does so by balancing gaze holding and gaze shifting actions, yielding a modest improvement in performance in stop signal tasks by delaying saccade initiation when necessary. [2] [3] It can be thought that the FEF does the driving part of saccade initiation, while the SEF acts as a backseat passenger, advising the driver as to what to do based on past insights. The SEF has recently been found to encode reward prediction error, suggesting that the SEF may actively evaluate decisions based on a value system on an occulomotor basis, independent of other brain regions. [21]
The visual system is sensitive to sudden change. [22] If something distracting occurs while a person is performing a task—reading a newspaper, for example—this immediately captures one's attention. [23] [24] [25] This sudden shift can be a distraction but it has been also thought to be a reflex of great importance as identifying and reacting to environmental changes quickly (when needed) can be imperative to survival. [24] [26] [27] [28] [29] Saccadic latency, the time delay between the appearance of a target and the initiation of a saccade, is an important parameter for learning which occulomotor neurons and structures of the brain play what specific roles in saccade initiation. [30] [31] There is much research being conducted on the role of SEF in determining visually salient objects and occurrences, using saccadic latency as the parameter of interest. [2] [26] [32] [33] [34]
SEF activity has been found to govern decisions in smooth pursuit but not the decision itself. [35]
The SEF responds to auditory stimuli as well as visual stimuli. [20] Visual responses from the SEF happen later and are much weaker than that observed in the FEF, though. SEF neurons also exhibit non-retinal modulation including anticipation and reward prediction. [3] [36]
The SEF was defined by the Schlags as a region where low currents (<50μA) evoke saccades. It is still found using this characterization as well as the known neighboring anatomy (Fig. 1). [1] [10]
SEF research is conducted mainly in monkey models. Typically trained rhesus macaque monkeys are used and surgically implanted with recording chambers. In this fashion, spike and local field potential (LFP) data can be acquired from SEF neurons, using microelectrodes in the recording chamber. Eye movements can also be monitored using eye-tracking camera equipment. [2]
Experiments obviously vary, but to give an example: the monkey might be made to partake in a color visual search task, sitting in front of a computer screen. The monkey would look at a point on the screen which would change from filled in to open at the same time which a colored point of "opposite" color appears on the screen. The monkey would be rewarded for looking at a new spot—"for making a single saccade"—within 2000 ms and then fixating on the spot for 500 ms. Varied tasks such as these are used and data is analyzed to determine the SEF's role in saccade initiation, visual saliency, etc. [2] [3]
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5.
A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. In contrast, in smooth-pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements.
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.
In neuroanatomy, the superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum or optic lobe. The adjective form tectal is commonly used for both structures.
The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.
The pars reticulata (SNpr) is a portion of the substantia nigra and is located lateral to the pars compacta. Most of the neurons that project out of the pars reticulata are inhibitory GABAergic neurons.
Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation, not only in humans, but also in animals with foveal vision. Microsaccade amplitudes vary from 2 to 120 arcminutes. The first empirical evidence for their existence was provided by Robert Darwin, the father of Charles Darwin.
In the scientific study of vision, smooth pursuit describes a type of eye movement in which the eyes remain fixated on a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit is asymmetric: most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making catch-up saccades. Most humans are also better at downward than upward pursuit. Pursuit is modified by ongoing visual feedback.
The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle frontal gyrus with the precentral gyrus, consisting of a frontal and parietal portion. The FEF is responsible for saccadic eye movements for the purpose of visual field perception and awareness, as well as for voluntary eye movement. The FEF communicates with extraocular muscles indirectly via the paramedian pontine reticular formation. Destruction of the FEF causes deviation of the eyes to the ipsilateral side.
The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and humans.
The supplementary motor area (SMA) is a part of the motor cortex of primates that contributes to the control of movement. It is located on the midline surface of the hemisphere just in front of the primary motor cortex leg representation. In monkeys, the SMA contains a rough map of the body. In humans, the body map is not apparent. Neurons in the SMA project directly to the spinal cord and may play a role in the direct control of movement. Possible functions attributed to the SMA include the postural stabilization of the body, the coordination of both sides of the body such as during bimanual action, the control of movements that are internally generated rather than triggered by sensory events, and the control of sequences of movements. All of these proposed functions remain hypotheses. The precise role or roles of the SMA is not yet known.
In cognitive neuroscience, visual modularity is an organizational concept concerning how vision works. The way in which the primate visual system operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
The dorsal attention network (DAN), also known anatomically as the dorsal frontoparietal network (D-FPN), is a large-scale brain network of the human brain that is primarily composed of the intraparietal sulcus (IPS) and frontal eye fields (FEF). It is named and most known for its role in voluntary orienting of visuospatial attention.
The primary gustatory cortex (GC) is a brain structure responsible for the perception of taste. It consists of two substructures: the anterior insula on the insular lobe and the frontal operculum on the inferior frontal gyrus of the frontal lobe. Because of its composition the primary gustatory cortex is sometimes referred to in literature as the AI/FO(Anterior Insula/Frontal Operculum). By using extracellular unit recording techniques, scientists have elucidated that neurons in the AI/FO respond to sweetness, saltiness, bitterness, and sourness, and they code the intensity of the taste stimulus.
Michael Steven Anthony Graziano is an American scientist and novelist who is currently a professor of Psychology and Neuroscience at Princeton University. His scientific research focuses on the brain basis of awareness. He has proposed the "attention schema" theory, an explanation of how, and for what adaptive advantage, brains attribute the property of awareness to themselves. His previous work focused on how the cerebral cortex monitors the space around the body and controls movement within that space. Notably he has suggested that the classical map of the body in motor cortex, the homunculus, is not correct and is better described as a map of complex actions that make up the behavioral repertoire. His publications on this topic have had a widespread impact among neuroscientists but have also generated controversy. His novels rely partly on his background in psychology and are known for surrealism or magic realism. Graziano also composes music including symphonies and string quartets.
The anti-saccade (AS) task is a way of measuring how well the frontal lobe of the brain can control the reflexive saccade, or eye movement. Saccadic eye movement is primarily controlled by the frontal cortex.
John Douglas (Doug) Crawford is a Canadian neuroscientist and the Scientific Director of the Connected Minds program. He is a professor at York University where he holds the York Research Chair in Visuomotor Neuroscience and the title of Distinguished Research Professor in Neuroscience.
Peter H. Schiller was a German-born neuroscientist. At the time of his death, he was a professor emeritus of Neuroscience in the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology (MIT). Schiller is well known for his work on the behavioral, neurophysiological and pharmacological studies of the primate visual and oculomotor systems.
Michael E. Goldberg, also known as Mickey Goldberg, is an American neuroscientist and David Mahoney Professor at Columbia University. He is known for his work on the mechanisms of the mammalian eye in relation to brain activity. He served as president of the Society for Neuroscience from 2009 to 2010.
The corollary discharge theory (CD) of motion perception helps understand how the brain can detect motion through the visual system, even though the body is not moving. When a signal is sent from the motor cortex of the brain to the eye muscles, a copy of that signal is sent through the brain as well. The brain does this in order to distinguish real movements in the visual world from our own body and eye movement. The original signal and copy signal are then believed to be compared somewhere in the brain. Such a structure has not yet been identified, but it is believed to be the Medial Superior Temporal Area (MST). The original signal and copy need to be compared in order to determine if the change in vision was caused by eye movement or movement in the world. If the two signals cancel then no motion is perceived, but if they do not cancel then the residual signal is perceived as motion in the real world. Without a corollary discharge signal, the world would seem to spin around every time the eyes moved. It is important to note that corollary discharge and efference copy are sometimes used synonymously, they were originally coined for much different applications, with corollary discharge being used in a much broader sense.