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D Guitton

Publications and source records attributed to D Guitton.

At least 37 records · Page 2Linked to original sources
PubMed1993

Gaze-related activity of putative inhibitory burst neurons in the head-free cat.

1. Previous studies in the cat have demonstrated that output neurons of the superior collicular as well as brain stem omnipause neurons have discharges that are best correlated, not with the trajectory of the eye in the head but, with the trajectory of the visual axis in space (gaze = eye-in-head + head-in-space) during rapid orienting coordinated eye and head movements. In this study, we describe the gaze-related activity of cat premotor "inhibitory burst neurons" (IBNs) identified on the basis of their position relative to the abducens nucleus. 2. The firing behavior of IBNs was studied during 1) saccades made with the head stationary, 2) active orienting combined eye-head gaze shifts, and 3) passive movements of the head on the body. IBN discharges were well correlated with the duration and amplitude of saccades made when the head was stationary. In both head-free paradigms, the behavior of cat IBNs differed from that of previously described primate "saccade bursters". The duration of their burst was better correlated with gaze than saccade duration, and the total number of spikes in a burst was well correlated with gaze amplitude and generally poorly correlated with saccade amplitude. The behavior of cat IBNs also differed from that of previously described primate "gaze bursters". The slope of the relationship between the total number of spikes and gaze amplitude observed during head-free gaze shifts was significantly lower than that observed during head-fixed saccades. 3. These studies suggest that cat IBNs do not fit into the categories of gaze-bursters or saccade-bursters that have been described in primate studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Abducens Nerve↗
PubMed1992

Control of eye-head coordination during orienting gaze shifts.

Combined eye and head displacements are routinely used to orient the visual axis rapidly (gaze). Humans can use a wide variety of head movement strategies. However, in the cat, comparatively limited eye motility forces a more routine and stereotyped use of head motion. Nevertheless, the same general principles of gaze control may be applicable to humans, rhesus monkeys and cats. The gaze control system can be modeled using a feedback system in which an internally created, instantaneous, gaze motor error signal--equivalent to the distance between the target and the gaze position at that time--is used to drive both eye and head motor circuits. The visual axis is moved until this error equals zero. Recent studies suggest that the superior colliculus of the cat provides brainstem eye and head motor circuits with the gaze motor error signal; such studies have led to speculation that information on ongoing gaze motion is fed back to the superior colliculus. It is still uncertain whether comparable collicular and brainstem neuronal mechanisms control gaze in the monkey.

Animals↗
PubMed1991

Movement of neural activity on the superior colliculus motor map during gaze shifts.

The superior colliculus contains neurons that cause displacements of the visual axis (gaze shifts). These cells are arranged topographically in a motor map on which the vector (amplitude and direction) of the coded movement varies continuously with location. How this spatial representation becomes a temporal code (frequency and duration) in the motoneurons is unknown. During a gaze shift, a zone of neural activity moved continuously on the map from an initial location, defining the vector of the desired gaze shift, to a final "zero" position containing neurons that were active during fixation. Thus, the spatial-temporal transformation may be accomplished by control of gaze throughout the spatial trajectory of activity on the motor map.

Animals↗
PubMed1991

Control of orienting gaze shifts by the tectoreticulospinal system in the head-free cat. I. Identification, localization, and effects of behavior on sensory responses.

1. The input-output connectivity, in cat, of tectoreticular (TRNs) and tectoreticulospinal (TRSNs) neurons [together called TR(S)Ns] suggests a role for these cells in the sensorimotor transformations necessary for controlling orienting behavior. Multimodal sensory information converges directly onto these tectal neurons, and they project to several brain stem and spinal cord centers involved in the control of eye- and head-orienting movements. In this and the following two papers, we describe the sensorimotor discharges of antidromically identified TR(S)Ns. Here we describe the process of localizing and identifying them, characteristics of both their antidromic and sensory responses, and effects of behavioral context on these responses. 2. In 13 alert, chronically prepared cats, a total of 293 neurons were antidromically identified from either the predorsal bundle (PDB) immediately rostral to abducens nucleus or the ventromedial funiculus of the spinal cord at the level of the first cervical vertebra (C1). The cell bodies of all identified TR(S)Ns were confined to the intermediate and deep laminae of the superior colliculus (SC). The antidromic nature of the action potential evoked by stimulating either the PDB or C1 was verified by the use of a number of established criteria, including collision testing. 3. The mean antidromic latency from the PDB (TRNs + TRSNs) was 0.84 +/- 0.59 (SD) ms (n = 217). The conduction velocities of all cells activated by PDB stimulation ranged from 4 to 40 m/s. The mean latency from C1 (TRSNs) was 1.03 +/- 0.52 ms (SD) (n = 64), whereas conduction velocities ranged from 14 to 80 m/s. 4. One hundred thirty-eight TR(S)Ns were studied long enough to yield significant data regarding their involvement in visuomotor-orienting behavior. Ninety-eight percent (130/133) of the TR(S)Ns tested for visual responses could be induced to discharge action potentials in response to some form of visual stimulation. The other three neurons remained silent, even in response to the most provocative stimuli. These silent neurons nevertheless were shown to be depolarized by visual stimuli. TR(S)Ns were occasionally tested for auditory and somatosensory responses and some were multimodal. 5. TR(S)Ns had visual receptive fields that conformed to the retinotopic map of the visual field that is represented within the SC. Cells found in the lateral SC had receptive fields located in the lower visual field, whereas neurons that were situated medially had receptive fields in the upper visual field. Cells found in the rostral SC had small fields that included a representation of the area centralis.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗
PubMed1991

Control of orienting gaze shifts by the tectoreticulospinal system in the head-free cat. II. Sustained discharges during motor preparation and fixation.

1. We recorded from electrophysiologically identified output neurons of the superior colliculus (SC)--tectoreticular and tectoreticulospinal neurons [together called TR(S)Ns]--in the alert cat with head either unrestrained or immobilized. A cat actively exploring its visual surrounds typically makes a series of coordinated eye-head orienting movements that rapidly shift the visual axis from one point to another. These single-step shifts in gaze position (gaze = eye-in-space = eye-in-head + head-in-space) are separated by periods in which the visual axis remains stationary with respect to surrounding space. 2. Eighty-seven percent (86/99) of the TR(S)Ns studied during periods when the visual axis was stationary presented a sustained discharge, the intensity of which depended on the magnitude and direction of the vector drawn between current gaze position and the gaze position required to fixate a target of interest (gaze position error or GPE). The maximum sustained discharge recorded from each TR(S)N corresponded to a specific GPE vector and was correlated with the cell's position on the SC's retinotopically coded motor map. 3. The 86 TR(S)Ns could be divided into two classes. "Fixation TR(S)Ns" [fTR(S)Ns, n = 12] discharged maximally when the animal attentively fixated a target of interest, (i.e. GPE = 0 degrees). These neurons were located in the rostral SC and had visual receptive fields that included a representation of the area centralis. "Orientation TR(S)Ns" [oTR(S)Ns, n = 62] had visual receptive fields that excluded the area centralis and discharged for nonzero GPEs. The oTR(S)Ns were recorded more caudally on the SC's map. 4. For a given value of GPE, an ensemble of TR(S)Ns was active. When the cat changed its gaze position relative to a fixed target of interest, the zone of sustained activity shifted to a new collicular site. Thus, to maintain the maximum sustained discharge of a TR(S)N when target position was changed relative to the fixed body, it was necessary that gaze move to a new position that reestablished the preferred GPE. 5. The areal extent of GPEs for which a TR(S)N discharged defined a gaze position error field (GPEF) that was approximately coaligned with the cell's visual receptive field. The maximum sustained discharge occurred when GPE corresponded approximately to the center of the cell's GPEF. 6. The diameter of a TR(S)N's GPEF was related to the magnitude of that cell's optimal GPE. fTR(S)Ns had the smallest GPEFs, approximately 15-20 degrees; GPEF diameter was larger for oTR(S)Ns.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Control of orienting gaze shifts by the tectoreticulospinal system in the head-free cat. III. Spatiotemporal characteristics of phasic motor discharges.

1. In this paper we describe the movement-related discharges of tectoreticular and tectoreticulospinal neurons [together called TR (S) Ns] that were recorded in the superior colliculus (SC) of alert cats trained to generate orienting movements in various behavioral situations; the cats' heads were either completely unrestrained (head free) or immobilized (head fixed). TR (S) Ns are organized into a retinotopically coded motor map. These cells can be divided into two groups, fixation TR (S) Ns [f TR (S) Ns] and orientation TR (S) Ns [oTR(S)Ns], depending on whether they are located, respectively, within or outside the zero (or area centralis) representation of the motor map in the rostral SC. 2. oTR(S)Ns discharged phasic motor bursts immediately before the onset of gaze shifts in both the head-free and head-fixed conditions. Ninety-five percent of the oTR(S)Ns tested (62/65) increased their rate of discharge before a visually triggered gaze shift, the amplitude and direction of which matched the cell's preferred movement vector. For movements along the optimal direction, each cell produced a burst discharge for gaze shifts of all amplitudes equal to or greater than the optimum. Hence, oTR(S)Ns had no distal limit to their movement fields. The timing of the burst relative to the onset of the gaze shift, however, depended on gaze shift amplitude: each TR(S)N reached its peak discharge when the instantaneous position of the visual axis relative to the target (i.e., instantaneous gaze motor error) matched the cell's optimal vector, regardless of the overall amplitude of the movement. 3. The intensity of the movement-related burst discharge depended on the behavioral context. For the same vector, the movement-related increase in firing was greatest for visually triggered movements and less pronounced when the cat oriented to a predicted target, a condition in which only 76% of the cells tested (35/46) increased their discharge rate. The weakest movement-related discharges were associated with spontaneous gaze shifts. 4. For some oTR(S)Ns, the average firing frequency in the movement-related burst was correlated to the peak velocity of the movement trajectory in both head-fixed and head-free conditions. Typically, when the head was unrestrained, the correlation to peak gaze velocity was better than that to either peak eye or head velocity alone. 5. Gaze shifts triggered by a high-frequency train of collicular microstimulation had greater peak velocities than comparable amplitude movements elicited by a low-frequency train of stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Upper eyelid movements measured with a search coil during blinks and vertical saccades.

Upper eyelid movements were recorded in nine human subjects by mounting a miniature coil of wire directly on the eyelid and subjecting the search coil to a vertically directed alternating magnetic field. The metrics of blinks and lid movements accompanying saccades were described by "main sequence" relationships, linking maximum velocity to amplitude and duration to amplitude. In general, lid movements were faster than those reported previously in the literature, but there was considerable intersubject variability. On average, the main sequence relationships for blinks were independent of either starting lid position or whether the blinks were generated spontaneously, reflexively, or voluntarily. For the down phase of the average blink, both the maximum velocity and duration increased almost linearly with amplitude. The maximum velocity of the down phase was faster than that of the up phase. For lid movements accompanying vertical saccades, the maximum velocities in the up and down directions were similar and increased nonlinearly with amplitude, saturating at about 120 mm/sec (approximately 450 degrees/sec). Duration increased approximately linearly with amplitude. The down phases of blinks were much faster than those of saccade-related lid movements. By comparison, the maximum velocities of the up phase of blinks and of saccade-related lid movements were almost equal. The large intersubject variability suggests caution when using normative data to interpret abnormal lid motion for clinical purposes.

Adult↗
PubMed1990

Gaze-related activity of brainstem omnipause neurons during combined eye-head gaze shifts in the alert cat.

Studies undertaken in head-restrained animals have long implicated the omnipause neurons (OPNs) in the initiation of saccadic eye movements. These inhibitory neurons discharge tonically but cease firing just before and during saccades in all directions. By recording from OPNs in alert behaving head-unrestrained cats, we have demonstrated that the activity of these cells is related to the displacement of the visual axis in space (gaze), which is the sum of the eye movement relative to the head and head movement relative to space. OPNs were found to exhibit a complete cessation of discharge for a period equivalent to the duration of the gaze shift, and not to the duration of either the rapid eye movement or the head movement components. In large gaze shifts, OPNs were silent even when the eye was immobile in the orbit, as long as the gaze shift was not completed. The results of this study show that OPNs are controlled by neural elements that take into account the actual position of the visual axis relative to its final desired position irrespective of the trajectory of the eye in the orbit or of whether the head is moving or not.

Animals↗
PubMed1990

Gaze control in the cat: studies and modeling of the coupling between orienting eye and head movements in different behavioral tasks.

1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space = eye-relative-to-head + head-relative-to-space) by the use of a feedback circuit wherein an internally derived representation of gaze motor error drives both eye and head premotor circuits. In this paper we examine the effect of behavioral task on the individual and summed trajectories of horizontal eye- and head-orienting movements to gain more insight into how the eyes and head are coupled and controlled in different behavioral situations. 2. Cats whose heads were either restrained (head-fixed) or unrestrained (head-free) were trained to make orienting movements of any desired amplitude in a simple cat-and-mouse game we call the barrier paradigm. A rectangular opaque barrier was placed in front of the hungry animal who either oriented to a food target that was visible to one side of the barrier or oriented to a location on an edge of the barrier where it predicted the target would reappear from behind the barrier. 3. The dynamics (e.g., maximum velocity) and duration of eye- and head-orienting movements were affected by the task. Saccadic eye movements (head-fixed) elicited by the visible target attained greater velocity and had shorter durations than comparable amplitude saccades directed toward the predicted target. A similar observation has been made in human and monkey. In addition, when the head was unrestrained both the eye and head movements (and therefore gaze movements) were faster and shorter in the visible- compared with the predicted-target conditions. Nevertheless, the relative contributions of the eye and head to the overall gaze displacement remained task independent: i.e., the distance traveled by the eye and head movements was determined by the size of the gaze shift only. This relationship was maintained because the velocities of the eye and head movements covaried in the different behavioral situations. Gaze-velocity profiles also had characteristic shapes that were dependent on task. In the predicted-target condition these profiles tended to have flattened peaks, whereas when the target was visible the peaks were sharper. 4. Presentation of a visual cue (e.g., reappearance of food target) immediately before (less than 50 ms) the onset of a gaze shift to a predicted target triggered a midflight increase in first the eye- and, after approximately 20 ms, the head-movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Compensatory eye and head movements generated by the cat following stimulation-induced perturbations in gaze position.

It is thought that saccades are controlled by signals representing target and instantaneous eye positions coded with respect to the head. To determine the frame of reference relevant to gaze (= eye + head) control, we extended to the cat whose head is unrestrained the original study of Mays and Sparks (Mays and Sparks 1980). We stimulated the superior colliculus (SC) to perturb initial gaze position before the onset of a gaze shift made in the dark to a flashed target. Gaze shifts compensated for this perturbation and reached the target with normal accuracy, despite the absence of visual feedback. This result indicates that gaze shifts were coded in either a body-centered or spatial frame but we could not distinguish between these two alternatives because the cat's body was fixed.

Animals↗
PubMed1989

Fixation and orientation control by the tecto-reticulo-spinal system in the cat whose head is unrestrained.

The role of the tecto-reticular and tecto-reticulo-spinal neurons (here called TR(S)Ns) in gaze control is described. TR(S)Ns, located in the deeper layers of the cat superior colliculus (SC), project onto the eye and head premotor circuitry. TR(S)Ns located in the caudal SC had sustained and phasic discharges related to the control of gaze movements. The sustained discharge occurred when the visual axis was positioned at some vector quantity away from a target of interest. Each cell has its preferred vector corresponding to the cell's location on the collicular retinotopic map. This tonic discharge acted as a preamble to the phasic discharge and served to pre-excite the relevant oculomotor circuitry. The phasic discharge preceded gaze shifts whose direction and magnitude matched the preferred vector. The intensity of this discharge was correlated to the acceleration and velocity of the movement. TR(S)Ns situated in the rostral SC were maximally active when the cat fixated a target of interest. These neurons decreased their discharge rate during gaze shifts. Thus, TR(S)Ns provide both fixation and orientation signals to the eye and head premotor circuitry. A scheme is proposed where TR(S)Ns lie within a gaze feedback loop that controls eye and head movements via inputs to long lead burst neurons and omnipause neurons.

Animals↗
PubMed1988

Changing patterns of eye-head coordination during 6 h of optically reversed vision.

1) This study investigates the early development of adaptive changes in oculomotor function associated with coordinated eye-head tracking of the optically reversed image of an earth-fixed target seen through horizontally reversing dove prism goggles attached to the skull. 2) Two tasks comprised a) fixation of a single target during head rotation which causes the seen target's image to move in the direction of head motion by an amount exactly equal to the head movement itself (the 1-Target task), and b) change of gaze onto a displaced target with head free to move (2-Target task). 3) The 1-Target task requires the eyes to move in a direction opposite to that of the normal vestibulo-ocular reflex (VOR). The 2-Target task is identical, except that reorientation onto the new target calls for an initial saccadic eye movement in a direction opposite to that of the ensuing head movement, which is contrary to the normal pattern of eye-head coordination during gaze shifts. 4) Eye (EOG) and head (potentiometer) movements were continuously recorded (0-250 Hz) in an apparatus which permitted sudden, unexpected, electromagnetic braking of the head movement, either just before or during the intended manoeuvre. 5) Early adaptive strategies employed reduction of VOR gain, rearrangement of timing, amplitude and shape of "catch-up" saccades and the introduction of centrally programmed eye movements uncovered by the braking manoeuvres. 6) All of these phenomena were detectable in an initial series of 60 trials, in which the total exposure to visual-vestibular conflict was less than 30 s. They became more systematized and more marked after 6 h of active reversed vision experience. 7) Specifically, mean VOR gain, measured within the first 80 ms of head movement (deemed free of visuomotor influence), became markedly attenuated (25% in the first test series; 66% after 6 h of active vision-reversed exercise). In addition (not included in the above percentages) there were numerous occasions of complete absence of measurable VOR during head rotation, in both the first and final test series. 8) In the 1-Target task, the latency of the first "catch-up" saccade (re onset of head movement) tended to offset residual VOR by becoming shortened to the point of synchrony with head movement onset. This saccade (not present in control tests) continued to occur on those occasions when the head was unpredictably prevented from moving, and when head movements were made in the dark.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1987

Gaze control in humans: eye-head coordination during orienting movements to targets within and beyond the oculomotor range.

Gaze, the direction of the visual axis in space, is the sum of the eye position relative to the head (E) plus head position relative to space (H). In the old explanation, which we call the oculocentric motor strategy, of how a rapid orienting gaze shift is controlled, it is assumed that 1) a saccadic eye movement is programmed with an amplitude equal to the target's offset angle, 2) this eye movement is programmed without reference to whether a head movement is planned, 3) if the head turns simultaneously the saccade is reduced in size by an amount equal to the head's contribution, and 4) the saccade is attenuated by the vestibuloocular reflex (VOR) slow phase. Humans have an oculomotor range (OMR) of about +/- 55 degrees. The use of the oculocentric motor strategy to acquire targets lying beyond the OMR requires programming saccades that cannot be made physically. We have studied in normal human subjects rapid horizontal gaze shifts to visible and remembered targets situated within and beyond the OMR at offsets ranging from 30 to 160 degrees. Heads were attached to an apparatus that permitted short unexpected perturbations of the head trajectory. The acceleration and deceleration phases of the head perturbation could be timed to occur at different points in the eye movement. 4. Single-step rapid gaze shifts of all sizes up to at least 160 degrees (the limit studied) could be accomplished with the classic single-eye saccade and an accompanying saccadelike head movement. In gaze shifts less than approximately 45 degrees, when head motion was prevented totally by the brake, the eye attained the target. For larger target eccentricities the gaze shift was interrupted by the brake and the average eye saccade amplitude was approximately 45 degrees, well short of the OMR. Thus saccadic eye movement amplitude was neurally, not mechanically, limited. When the head's motion was not perturbed by the brake, the eye saccade amplitude was a function of head velocity: for a given target offset, the faster the head the smaller the saccade. For gaze shifts to targets beyond the OMR and when head velocity was low, the eye frequently attained the 45 degrees position limit and remained there, immobile, until gaze attained the target.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1986

Presaccadic burst discharges of tecto-reticulo-spinal neurons in the alert head-free and -fixed cat.

Tecto-reticulo-spinal neurons (TRSNs) discharge high frequency bursts of action potentials prior to visually triggered gaze shifts made in the head-fixed (eye only moves) or head-free (eye and head move together) conditions. These high-frequency presaccadic bursts are weak or absent when the cat generates gaze shifts to non-visible remembered targets. TRSNs remain silent during spontaneously generated gaze shifts. The visually triggered gaze shifts, that are preceded by TRSN bursts are faster than gaze shifts directed at non-visible targets.

Action Potentials↗
PubMed1986

Visual, vestibular and voluntary contributions to human head stabilization.

We have investigated the ability of humans to stabilize their heads in space and assessed the influence of mental set and the relative importance of visual and vestibular cues. Ten normal subjects and 3 patients with bilateral vestibular loss were studied. Subjects were fixed firmly to the chair of a turntable facing a screen on which was projected a target spot. A 'gunsight' spot generated by a small projector fixed to the head provided feedback of head position. Four conditions were studied (1) Gunsight (GU): subjects were instructed to stabilize the head in space by superimposing the 'gunsight' spot on the fixed target spot while chair position was displaced according to a random pattern with a bandwidth from 0-1 Hz. (2) Imagined gunsight (IGU): identical to condition 1 except that the subject was blindfolded and so had to imagine the target position. (3) Mental arithmetic (MA): subjects did mental arithmetic while the chair was displaced. (4) Visual tracking (VT): subjects were instructed to track the target spot with the 'gunsight' spot while the chair was fixed and the target spot driven to follow the chair displacement trajectory used in conditions 1, 2 and 3. In GU normal subjects stabilized their head position extremely well (mean HEAD/CHAIR gain = 0.81). Significant stabilization was present in IGU although the gain (mean gain = 0.61) was reduced compared to GU. There was very little stabilization in MA (mean gain = 0.12). In VT, subjects tracked the target with about the same gain (mean gain = 0.68) as in IGU. By comparison, the vestibular patients could not perform IGU, for which their performance (mean gain = 0.08) was similar to MA (mean gain = 0.06). In GU (mean gain = 0.54), their performance was attributable to visual tracking (mean gain in VT = 0.50). For the frequency bandwidth in which subjects were tested, the results show that: When subjects were distracted by mental arithmetic, the contribution to head stability of the short latency cervico-collic (CCR) and vestibulo-collic (VCR) reflexes is negligible. As expected, vision plays an important role in stabilizing the head. Equally important are long latency stabilizing mechanisms whose onset times (140 ms) are shorter, but still comparable to that of vision. The latter mechanisms are of vestibular origin and their influence is under voluntary control so as to permit augmenting head stability compared to what it would be if vision acted alone.

Adult↗
PubMed1985

Tectospinal neurons in the cat have discharges coding gaze position error.

Tectospinal neurons (TSNs) in the caudal superior colliculus of the alert behaving cat have a sustained discharge that depends on the magnitude and direction of the vector between a food target and the visual axis. Each TSN has its 'optimal' vector for which it will be activated at a maximum discharge rate independent of whether the animal's head is free or fixed. The discharge is not due to prolonged stimulation of a TSN's receptive field since the discharge persists even when the target is not visible.

Animals↗
PubMed1985

Frontal lobe lesions in man cause difficulties in suppressing reflexive glances and in generating goal-directed saccades.

The frontal eye field (FEF) and superior colliculus (SC) are thought to form two parallel systems for generating saccadic eye movements. The SC is thought classically to mediate reflex-like orienting movements. Thus it can be hypothesized that the FEF exerts a higher level control on a visual grasp reflex. To test this hypothesis we have studied the saccades of patients who have had discrete unilateral removals of frontal lobe tissue for the relief of intractable epilepsy. The responses of these patients were compared to those of normal subjects and patients with unilateral temporal lobe removals. Two tasks were used. In the first task the subject was instructed to look in the direction of a visual cue that appeared unexpectedly 12 degrees to the left or right of a central fixation point (FP), in order to identify a patterned target that appeared 200 ms or more later. In the second "anti-saccade" task the subject was required to look not at the location of the cue but in the opposite direction, an equal distance from FP where after 200 ms or more the patterned target appeared. Three major observations have emerged from the present study. Most frontal patients, with lesions involving both the dorsolateral and mesial cortex had long term difficulties in suppressing disallowed glances to visual stimuli that suddenly appeared in peripheral vision. In such patients, saccades that were eventually directed away from the cue and towards the target were nearly always triggered by the appearance of the target itself irrespective of whether or not the "anti-saccade" was preceded by a disallowed glance. Those eye movements away from the cue were only rarely generated spontaneously across the blank screen during the cue-target time interval. The latency of these visually-triggered saccades was very short (80-140 ms) compared to that of the correct saccades (170-200 ms) to the cue when the cue and target were on the same side, thereby suggesting that the structures removed in these patients normally trigger saccades after considerable computations have already been performed. The results support the view that the frontal lobes, particularly the dorsolateral region which contains the FEF and possibly the supplementary motor area contribute to the generation of complex saccadic eye-movement behaviour. More specifically, they appear to aid in suppressing unwanted reflex-like oculomotor activity and in triggering the appropriate volitional movements when the goal for the movement is known but not yet visible.

Adult↗