Suppression Of Reflexive Saccades Research Articles

The impact of the wake maintenance zone on attentional capacity, physiological drowsiness, and subjective task demands during sleep deprivation.

We aimed to investigate the impact of the Wake Maintenance Zone (WMZ) on measures of drowsiness, attention, and subjective performance under rested and sleep deprived conditions. We studied 23 healthy young adults (18 males; mean age=25.41±5.73years) during 40hr of total sleep deprivation under constant routine conditions. Participants completed assessments of physiological drowsiness (EEG-scored slow eye movements and microsleeps), sustained attention (PVT), and subjective task demands every two hours, and four-hourly ocular motor assessment of inhibitory control (inhibition of reflexive saccades on an anti-saccade task). Tests were analyzed relative to dim light melatonin onset (DLMO); the WMZ was defined as the 3hr prior to DLMO, and the preceding 3hr window was deemed the pre-WMZ. The WMZ did not mitigate the adverse impact of ~37hr sleep deprivation on drowsiness, sustained attention, response inhibition, and self-rated concentration and difficulty, relative to rested WMZ performance (~13hr of wakefulness). Compared to the pre-WMZ, though, the WMZ improved measures of sustained attention, and subjective concentration and task difficulty, during sleep deprivation. Cumulatively, these results expand on previous work by characterizing the beneficial effects of the WMZ on operationally-relevant indices of drowsiness, inhibitory attention control, and self-rated concentration and task difficulty relative to the pre-WMZ during sleep deprivation. These results may inform scheduling safety-critical tasks at more optimal circadian times to improve workplace performance and safety.

Eye Movements in Parkinson's Disease and Inherited Parkinsonian Syndromes.

Despite extensive research, the functions of the basal ganglia (BG) in movement control have not been fully understood. Eye movements, particularly saccades, are convenient indicators of BG function. Here, we review the main oculomotor findings reported in Parkinson’s disease (PD) and genetic parkinsonian syndromes. PD is a progressive, neurodegenerative disorder caused by dopaminergic cell loss within the substantia nigra pars compacta, resulting in depletion of striatal dopamine and subsequent increased inhibitory BG output from the internal globus pallidus and the substantia nigra pars reticulata. Eye movement abnormalities are common in PD: anomalies are more evident in voluntary than reflexive saccades in the initial stages, but visually guided saccades may also be involved at later stages. Saccadic hypometria (including abnormally fragmented saccades), reduced accuracy, and increased latency are among the most prominent deficits. PD patients show also unusually frequent and large square wave jerks and impaired inhibition of reflexive saccades when voluntary mirror saccades are required. Poor convergence ability and altered pursuit are common. Inherited parkinsonisms are a heterogeneous group of rare syndromes due to gene mutations causing symptoms resembling those of PD. Eye movement characteristics of some parkinsonisms have been studied. While sharing some PD features, each syndrome has a distinctive profile that could contribute to better define the clinical phenotype of parkinsonian disorders. Moreover, because the pathogenesis and the underlying neural circuit failure of inherited parkinsonisms are often well defined, they might offer a better prospect than idiopathic PD to understand the BG function.

Saccadic Abnormalities in Familial Parkinson's Disease Associated with -Synuclein (SNCA) Gene Mutation (PARK1) (P02.258)

Objective: To investigate saccadic characteristics of PARK1 and to compare them with those of other parkinsonian syndromes. Background Typical patterns of eye movement abnormalities have been described in both idiopathic (PD, CDB, LBD and MSA) and familial (PARK2 and PARK6) parkinsonian syndromes, providing not only useful diagnostic markers, but also insights in to the functions of the basal ganglia. Mutations in the SNCA gene are a rare cause of autosomal dominant early-onset Parkinson9s Diseases (PARK1); its gene product is the main component of Lewy bodies, the hallmark of parkinsonian neuronal degeneration. Design/Methods: Two symptomatic PARK1 patients were recorded during various saccadic paradigms: horizontal visually-guided saccades (VGS), anti-saccades, overlap, and memory-guided saccades (MGS) (10° and 18°). Data were statistically compared with those of 19 healthy controls. Results were related to findings reported in other parkinsonian syndromes. Results: Both patients showed saccadic abnormalities. VGS amplitude (10° p1:9.6±0.8°, p2:8.4±0.5° normal values (n.v.) 10.3±1.0° p Conclusions: PARK1 patients present peculiar abnormalities in both voluntary and reflexive saccades. Hypometric VGS, abnormal inhibition of reflexive saccades and staircase saccades have been described in other parkinsonian syndromes. The observation of slow VGS has never been reported in parkinsonian syndromes and may indicate the extension of the neuronal degeneration to other structures controlling saccade dynamics. The characteristic patterns of saccade abnormalities may help diagnosis as well as pointing to an understanding of the functions of the basal ganglia and how they become impaired in parkinsonian syndromes. Disclosure: Dr. Pretegiani has nothing to disclose. Dr. Leigh has nothing to disclose. Dr. Zee has received royalty payments from Oxford University Press. Dr. Federico has nothing to disclose. Dr. Piu has nothing to disclose. Dr. Rufa has nothing to disclose.

Saccade-Related beta-Band Desynchronization in the Subthalamic Nucleus of Parkinson Disease Patients during Successful Antisaccades and Error Trials (P01.196)

Objective: To investigate the saccade-related beta-band desynchronization (beta-SRD) recorded from deep brain stimulation (DBS) electrodes implanted in the subthalamic nucleus (STN) of Parkinson disease (PD) patients during successful antisaccades and error trials. Background The basal ganglia including the STN are involved in response selection by exerting or removing tonic inhibition in the thalamocortical loops and in the brainstem motor circuits. Beta-SRDs are thought to play a role in inhibition of unwanted movements and in execution of movements. Antisaccades require a strong inhibition of reflexive saccades towards the visual cue and a strong driving signal for voluntary saccades away from the visual cue. Whether beta-SRDs in the STN during successful antisaccades are different from those during error trials has not been studied. Design/Methods: Eighteen PD patients performed an antisaccade task 1 to 3 days after DBS surgery when the leads were externalized. Local field potentials were recorded from DBS electrodes implanted in the STN and electrooculography was used to measure saccades. We analyzed the power spectrum in each DBS contact pair using Morlet wavelets averaged on saccade onset. The incidence, latency, and duration of beta-SRDs during successful antisaccades were compared with those during errors trials. Results: The averaged incidence of errors was 36.3%. Mean latencies of saccades were longer during antisaccades (432.6 ± 170.6 ms (mean ± SD)) than during errors (309.5 ± 146.1 ms). Beta-SRDs were observed more often during antisaccades (24 of 31 STN) than during errors (7 of 31 STN; p Conclusions: Beta-SRDs were observed more frequently and were sustained for longer during successful antisaccades than during error trials. Those results suggest that beta-SRDs played a role in the suppression of unwanted saccades and in the successful execution of antisaccades. Disclosure: Dr. Yugeta has nothing to disclose. Dr. Hutchison has received personal compensation for activities with Medtronic Inc. as a speaker. Dr. Hutchison has received research support from Medtronic Inc. Dr. Chen has received personal compensation for activities with Allergan, Inc., Medtronic, Inc., Biovail, EMD Serono, Merz Pharma, the American Academy of Neurology, the Douglas Mental Health University Institute, Movement Disorders Society, the University of Pittsburg, Merz, CHIR, the Michael J. Fox Foundation for Parkinson9s Research, the Dystonia Medical Research Foundation, and has provided expert testimony and affidavit in welding related litigations. Dr. Chen has received research support from Medtronic, Inc.

The role of the frontal eye fields in the oculomotor inhibition of reflexive saccades: Evidence from lesion patients

The current study investigated the role of the frontal eye fields (FEF) in the suppression of an unwanted eye movement (‘oculomotor inhibition’). Oculomotor inhibition has generally been investigated using the antisaccade task, in which an eye movement to a task-relevant onset must be inhibited. Various lines of research have suggested that successful inhibition in the antisaccade task relies heavily on the FEF. Here, we tested whether the FEF are also involved in the oculomotor inhibition of reflexive saccades. To this end, we used the oculomotor capture task in which the to-be-inhibited element is task-irrelevant. Performance of four patients with lesions to the FEF was measured on both the antisaccade and oculomotor capture task. In both tasks, the majority of the patients made more erroneous eye movements to contralesional elements than to ipsilesional elements. One patient showed no deficits in the antisaccade task, which could be explained by the developmental origin of his lesion. While we confirm the role of the FEF in the inhibition of task-relevant elements, the current study also reveals that the FEF play a crucial role in the oculomotor inhibition of task-irrelevant elements.

Antisaccade generation is impaired after parietal lobe lesions

Antisaccades are directed away from visual targets. Impaired antisaccade generation has been attributed to frontal lobe damage. We studied antisaccades in patients with unilateral focal parietal lobe lesions. Normal subjects (N = 10) instructed to make 10° antisaccades opposite to a 100-ms target flash 10° to the right or left of center made antisaccades in 86.1% of trials. Patients (N = 13) made antisaccades contraversive to their lesions in 55.4% of trials and 50.5% of ipsiversive trials. In other trials, reflexive saccades occurred toward the target flash. Nine patients with imaged lesions overlapping in parietal lobe white matter showed subnormal antisaccade generation. Antisaccades provide a means of measuring voluntary saccade function of the parietal lobes independent of visual guidance. Impaired suppression of reflexive saccades and generation of antisaccades is attributed to disconnection of parietal lobe from frontal lobe ocular motor areas.

Control of Reflexive Saccades following Hemispherectomy

Individuals who have undergone hemispherectomy for treatment of intractable epilepsy offer a rare and valuable opportunity to examine the ability of a single cortical hemisphere to control oculomotor performance. We used peripheral auditory events to trigger saccades, thereby circumventing dense postsurgical hemianopia. In an antisaccade task, patients generated numerous unintended short-latency saccades toward contralesional auditory events, indicating pronounced limitations in the ability of a single hemicortex to exert normal inhibitory control over ipsilateral (i.e., contralesional) reflexive saccade generation. Despite reflexive errors, patients retained an ability to generate correct antisaccades in both directions. The prosaccade task revealed numerous contralesional express saccades, a robust contralesional gap effect, but the absence of both effects for ipsilesional saccades. These results indicate limits to the saccadic control capabilities following hemispherectomy: A single hemicortex can mediate antisaccades in both directions, but plasticity does not extend fully to the bilateral inhibition of reflexive saccades. We posit that these effects are due to altered control dynamics that reduce the responsivity of the superior colliculus on the intact side and facilitate the release of an auditory-evoked ocular grasp reflex into the blind hemifield that the intact hemicortex has difficulty suppressing.

Distinct Neural Correlates for Volitional Generation and Inhibition of Saccades

The antisaccade task has proven highly useful in basic and clinical neuroscience, and the neural structures involved are well documented. However, the cognitive and neural mechanisms that mediate task performance are not yet understood. An event-related fMRI study was designed to dissociate the neural correlates of two putative key functions, volitional saccade generation and inhibition of reflexive saccades, and to investigate their interaction. Nineteen healthy volunteers performed a task that required (a) to initiate saccades volitionally, either with or without a simultaneous demand to inhibit a reflexive saccade; and (b) to inhibit a reflexive saccade, either with or without a simultaneous demand to initiate a saccade volitionally. Analysis of blood oxygen level-dependent signal changes confirmed a major role of the frontal eye fields and the supplementary eye fields in volitional saccade generation. Inhibition-related activation of a specific fronto-parietal network was highly consistent with previous evidence involved in inhibitory processes. Unexpectedly, there was little evidence of specific brain activation during combined generation and inhibition demands, suggesting that the neural processing of generation and inhibition in antisaccades is independent to a large extent.

Effect of gabapentin on oculomotor control and parkinsonism in patients with progressive supranuclear palsy

The efficacy of gabapentin on motor, oculomotor and frontal lobe symptoms was evaluated in patients with progressive supranuclear palsy (PSP) in a pilot study. Fourteen patients were included and seven of them received gabapentin. Clinical evaluation and horizontal eye movement recordings were performed at inclusion and 5-weeks later. Motor score and saccade latency in the visually guided saccade (VGS) task were identical in the two groups. However, the error rate in the antisaccade task was significantly decreased in the gabapentin group. This preliminary study shows that gabapentin improves reflexive saccade inhibition in patients with PSP but does not improve the latency of VGSs.

Top-Down Control-Signal Dynamics in Anterior Cingulate and Prefrontal Cortex Neurons following Task Switching

The prefrontal cortex (PFC) and anterior cingulate cortex (ACC) have both been implicated in cognitive control, but their relative roles remain unclear. Here we recorded the activity of single neurons in both areas while monkeys performed a task that required them to switch between trials in which they had to look toward a flashed stimulus (prosaccades) and trials in which they had to look away from the stimulus (antisaccades). We found that ACC neurons had a higher level of task selectivity than PFC neurons during the preparatory period on trials immediately following a task switch. In ACC neurons, task selectivity was strongest after the task switch and declined throughout the task block, whereas task selectivity remained constant in the PFC. These results demonstrate that the ACC is recruited when cognitive demands increase and suggest a role for both areas in task maintenance and the implementation of top-down control.

Abnormal susceptibility to distracters hinders perception in early stage Parkinson's disease: a controlled study

BackgroundOne of the perceptual abnormalities observed in Parkinson's disease (PD) is a deficit in the suppression of reflexive saccades that are automatically triggered by the onset of a peripheral target. Impairment of substantia nigra function is thought to lead to this reduced ability to suppress reflexive saccades.MethodsThe present study examined whether this perceptual deficit is also present in early stage PD when using hardly noticeable task-irrelevant stimuli. Eleven non-demented de novo, untreated PD patients (mean age 57 yr, range 44 – 70) participated in the study as well as 12 age-matched controls. Performance on an 'oculomotor capture' task, in which in half of the trials an irrelevant stimulus with sudden onset was added to the display, was compared between patients and controls. Analysis of variance (ANOVA) was performed with group (patients/controls) and age (< 61 yrs/≥ 61 yrs) as independent factors and type of trial (control/distracter) as repeated measurements factor. The factor sex was used as covariate.ResultsWith respect to Reaction Time (RT), a significant interaction between group and condition was found. RTs increased under the 'irrelevant stimulus' condition in both groups, the patients exhibiting a significantly larger increase in RTs than the control group. Also, a significant interaction effect between group and condition for number of correct responses was found. The number of correct responses was reduced in the onset distracter condition, the reduction being larger in the patients. In the patient group, contrary to the control group, a higher age was associated with fewer correct responses at baseline and in the onset distracter condition, suggesting that perceptual functions in PD are highly susceptible to the effects of ageing. The increased reaction times and larger number of incorrect responses of the PD patients in the onset distracter condition may be related to impairments of substantia nigra function and lower brain stem.ConclusionThe capture task seems to be a sensitive instrument to detect early perceptual deficits in PD. The magnitude of the observed deficits suggests that perceptual functions in early stage PD are so substantially impaired that this may interfere with daily activities.

Mixing pro- and antisaccades in patients with parkinsonian syndromes

Prosaccades and antisaccades were investigated in three groups of patients with parkinsonian syndromes, Parkinson's disease, corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), and in a control group. Saccade tasks were performed in single-task blocks (i.e. either blocks of prosaccades or blocks of antisaccades) and in mixed-task blocks (i.e. in blocks of randomly interleaved pro- and antisaccades). Saccade latencies and directional errors (misdirected saccades) were analysed in each subject, and we concentrated more specifically on the comparison of error rates in single tasks and in repeated trials of mixed tasks (i.e. mixing costs). The performance of each group in single tasks was largely consistent with previous studies, with normal antisaccade error rates in Parkinson's disease and CBD patients and increased antisaccade error rates in PSP patients. In contrast, a double dissociation was observed in mixed tasks. Parkinson's disease and CBD patients showed a marked increase in prosaccade and antisaccade error rates in repeated trials of mixed tasks, illustrated by increased mixing costs, whereas PSP patients showed similar error rates in single and repeated trials of mixed tasks, i.e. normal mixing costs. These results demonstrate that: (i) antisaccade performances may be differentially affected in mixed tasks and single tasks; (ii) the region of the dorsolateral prefrontal cortex which is crucial for reflexive saccade inhibition does not seem to be involved in the additional processes required in mixed-task conditions; (iii) the study of interleaved pro- and antisaccades may increase the accuracy of the differential diagnosis between these parkinsonian syndromes.

Prepulse inhibition of the acoustic startle reflex and oculomotor control

Prepulse inhibition and the suppression of reflexive saccades on the antisaccade task are thought to tap inhibitory function. Reports of a lack of association between these measures suggest that they reflect different facets of inhibition. This study aimed to reexamine this relationship in a large sample and investigate the association of prepulse inhibition with oculomotor tasks that require inhibition of a reflexive saccade with lower concurrent processing demands than antisaccades, namely the oculomotor delayed response and fixation with distractors tasks. One hundred and seven healthy volunteers took part. Prepulse inhibition was uncorrelated with oculomotor performance. The error rate was highest for antisaccades, intermediate for the delayed response task, and lowest for fixation with distractors, and was correlated across tasks. These findings provide no evidence of a relationship between prepulse inhibition and oculomotor inhibition. Failure in suppressing reflexive saccades toward a peripheral target may represent a common inhibitory component underlying these oculomotor tasks.

Du noyau abducens à la mémoire spatiale : un parcours oculomoteur

Advances in our knowledge on eye movements over the last 25 years are reviewed, focusing on the author's experience. First, the advantages of binocular frontal vision, which is a common characteristic of all predator mammals, are compared to those of lateral vision, characterizing their preys. Binocular frontal vision implies a perfect parallelism of both eyes, which is ensured in the pons by means of the abducens nucleus, controlling abduction as well as adduction. The pathological example of the "one-and-a-half" syndrome, in which the abducens nucleus and the adjacent medial longitudinal fasciculus are simultaneously impaired, is described. The main brainstem syndromes involving vertical eye movements are also reviewed: in particular, the third nerve nucleus syndrome, in which both ipsilateral third nerve paralysis and contralateral superior rectus paralysis (with hypotropia) result from a unilateral third nerve nucleus lesion. A case of upbeat nystagmus (in the primary position of gaze) due to a small upper pontine lesion, probably affecting the ventral tegmental tract (VTT) is also reported. This is an opportunity to emphasize that, although a number of cases of upbeat nystagmus due to focal brainstem lesions affecting the upward vestibular pathway (UVP)--either at the upper pontine (VTT) or caudal medullary level--exist in the literature, no convincing cases with downbeat nystagmus (in the primary position of gaze) due to a focal brainstem lesion have been reported. Downbeat nystagmus could result from a UVP hyperactivity (secondary to a floccular lesion) and the notion that this pathway is physiologically predominant compared to the downward pathway, maybe due to gravity, is developed. A new hypothesis about the role of the caudal medulla in UVP is also proposed. Next, the cortical control of saccadic eye movements is reviewed, with a reminder that reflexive saccades are mainly triggered by the parietal eye field whereas intentional saccades depend upon the frontal eye field. The inhibition of reflexive saccades is mainly controlled by the dorsolateral frontal cortex (DLPFC), i.e. area 46 of Brodmann. A few examples of the use of saccades as a research tool and model in cognitive neurosciences are given. The use of memory-guided saccades allowed us to study spatial memory and led us to propose a relatively original conception of the cortical control of spatial memory in which the DLPFC, the parahippocampal cortex and the hippocampal formation could be involved successively according to specific periods of time. An experiment using functional magnetic resonance imaging in a paradigm studying decision is described, again with the involvement of the DLPFC in the decisional process. Lastly, the usefulness of eye movements in clinical neuro-ophthalmology at the bedside as well as in neurophysiological or even neuropsychological research in the laboratory is emphasized.

The Prefrontal Substrate of Reflexive Saccade Inhibition in Humans

Prefrontal dysfunction in neuropsychiatric disorders such as schizophrenia has been shown to impair inhibition of reflexive saccadic eye movements; however, it is unclear whether reflexive saccade inhibition can be attributed to a distinct subregion of the human prefrontal cortex. We tested 15 patients with acute unilateral ischemic lesions of the prefrontal cortex and 20 control subjects with an antisaccade task. Lesions were reconstructed using Talairach coordinates, and possible candidate regions for reflexive saccade inhibition were identified. Significantly increased antisaccade error rates were observed in patients with lesions affecting a region in mid-dorsolateral prefrontal cortex or the white matter between this region and the anterior portions of the internal capsule. Antisaccade error rates of patients with lesions outside this region were normal. These findings were largely independent of lesion volume, postlesion delay, and subject age. Our findings suggest that inhibition of reflexive saccades depends on a circumscribed subregion of the human dorsolateral prefrontal cortex. This region closely corresponds to Brodmann area 46 as defined by recent cytoarchitectonic studies. Increased antisaccade error rates in patients with prefrontal pathology may be explained by dysfunction of this region.

Eye movement control by the cerebral cortex

This review focuses on eye movement control by the cerebral cortex, mainly in humans. Data have emerged based on the important contribution of recent techniques such as transcranial magnetic stimulation and functional magnetic resonance imaging, which provide complementary results to those of the classical lesion and electrical stimulation studies. The location of the human frontal eye field and its role in pursuit eye movement control were recently detailed. Cumulative evidence for the role of the dorsolateral prefrontal cortex in unwanted reflexive saccade inhibition, short-term spatial memory and prediction suggests that this area controls decisional processes governing ocular motor behaviour. The organization of spatial memory in the dorsolateral prefrontal cortex (short-term), the parahippocampal cortex (medium-term) and the hippocampal formation (long-term) is also reviewed with the results of recent transcranial magnetic stimulation studies. The relatively complicated anatomy of the posterior parietal cortex in humans is briefly described followed by some additional results concerning the location of the parietal eye field - within the posterior half of the intraparietal sulcus - and its role in visuo-spatial integration and attention. The other areas involved in spatial attention are also examined in the light of several recent contributing reports. Lastly, there are also new functional magnetic resonance imaging findings concerning the posterior cingulate cortex, which appears to be mainly involved in the control of externally guided eye movements and attentional mechanisms. Many new findings on the organization of saccades and pursuit eye movements at the cortical level have recently been reported. Furthermore, eye movements are increasingly used as a tool to elucidate relatively complex neuropsychological processes such as attention, spatial memory, motivation and decisional processes, and a considerable number of reports dealing with these questions have been observed.

Event-related fMRI responses in the human frontal eye fields in a randomized pro- and antisaccade task.

We examined whether the frontal eye fields (FEF) are involved in the suppression of reflexive saccades. Simultaneous recording of horizontal eye movements and functional magnetic resonance imaging enabled us to perform a randomized pro- and antisaccade task and to sort blood oxygenation level dependent (BOLD) time series on the basis of task performance. Saccadic reaction time distributions were comparable across tasks indicating a similar effort in preprocessing of the saccades. Furthermore, we found similar BOLD activation in FEF during both correctly performed pro- and antisaccades. Frontal eye field activation started prior to target presentation and saccade generation. While we observed only few erroneous antisaccades, these were associated with a decrease in BOLD activity prior to target presentation, and increased BOLD activity after target presentation relative to correctly performed antisaccades. These findings are consistent with a role of the FEF in the suppression of reflexive saccades. The increase in activity after target presentation for antisaccade errors can only be indirectly linked to such a role but may also reflect activity related to the generation of a correction saccade. Frontal eye field BOLD activity may further represent general arousal, preparatory set, short-term memory, or salience-map related activity.

The frontal eye field is involved in spatial short-term memory but not in reflexive saccade inhibition.

Physiological studies in monkeys have shown that the frontal eye field (FEF) is involved in the preparation and triggering of purposive saccades. However, several questions of FEF function remain unclear: the role of the FEF in visual short-term memory, its ability to update its spatial map and its role in reflexive saccade inhibition. We have addressed these issues in a patient with a small acute ischemic lesion whose location corresponded very accurately to the region of the left FEF according to the most recent cerebral blood flow studies. An initial study was conducted on days 7 and 8 after the stroke, i.e., before substantial recovery. A first group of paradigms (smooth pursuit, simple saccade tasks) was performed to assess FEF dysfunction. In a second group of paradigms, (1) visual short-term memory was tested by means of memory-guided saccade paradigms with short and long delays (1 and 7 s), (2) spatial updating abilities were tested by a double-step saccade task and two memory-guided saccade tasks in which the central fixation point was displaced during the memorization delay, and (3) reflexive saccade inhibition was tested by the antisaccade task. Results show that the FEF is involved in short-term memorization of the parameters of the forthcoming memory-guided saccade encoded in oculocentric coordinates. Normal results in the antisaccade task suggest that the FEF is not involved in reflexive saccade inhibition.

Dopamine and impairment at the executive level

Patients with schizophrenia have an impairment in the inhibition of reflexive saccades, as a consequence of a functional impairment of the prefrontal cortex, which has not yet been encapsulated in terms of a formal model. A number of novel and testable hypotheses can be generated from the framework proposed by Findlay &amp; Walker that will stimulate further research. Their framework therefore marks an important step in the development of a comprehensive functional model of saccadic eye movements. Further advances will be assisted by (1) a recognition of important distinctions in the executive control of volitional saccades and (2) addressing the capacity for cross-model integration of spatial information in the generation of the spatial properties of saccadic eye movements.

Cortical control of saccades.

Saccadic eye movements are controlled by a cortical network composed of several oculomotor areas that are now accurately localized. Clinical and experimental studies have enabled us to understand their specific roles better. These areas are: (1) the parietal eye field (PEF) located in the intraparietal sulcus involved in visuospatial integration and in reflexive saccade triggering; (2) the frontal eye field (FEF), located in the precentral gyrus, involved in the preparation and the triggering of purposive saccades; and (3) the supplementary eye field (SEF) on the medial wall of the frontal lobe, probably involved in the temporal control of sequences of visually guided saccades and in eye-hand coordination. A putative cingulate eye field (CEF), located in the anterior cingulate cortex, would be involved in motivational modulation of voluntary saccades. Besides these motor areas, the dorsolateral prefrontal cortex (dlPFC) in the midfrontal gyrus is involved in reflexive saccade inhibition and visual short-term memory.