Biomedical subjects
M Schlag-Rey
Publications and source records attributed to M Schlag-Rey.
Direct projection from the supplementary eye field to the nucleus raphe interpositus.
Using WGA-HRP we have demonstrated that a direct projection links the supplementary eye field, but not the more caudal aspect of the supplementary motor area, to the brain stem omnipause region. Findings are discussed in relation to oculomotor control.
Does microstimulation evoke fixed-vector saccades by generating their vector or by specifying their goal?
Electrical stimulation was performed at several sites of the monkey's forebrain producing fixed-vector saccades when the eyes were steady. When the same stimulation was applied during or immediately after a spontaneous eye movement, the saccade trajectory was considerably modified: the eyes were driven, from wherever they were deviated by the spontaneous movement, to the point where the fixed-vector saccade would have brought them if the spontaneous movement had not occurred. This finding implies first, that saccades evoked from these sites are directed toward a goal and, a second, that the goal is defined with respect to an eye position sampled long in advance (before the spontaneous eye movement). This is consistent with the hypothesis that the electrical stimulation evoked the retinotopic representation of a target whose spatial coordinates were then computed at further stages to produce a saccade. Using the present paradigm, it may be possible to distinguish brain sites processing retinal error (at the visual stage) from those processing motor error (at the motor stage).
Evidence for a supplementary eye field.
Electrical microstimulation and unit recording were performed in dorsomedial frontal cortex of four alert monkeys to identify an oculomotor area whose existence had been postulated rostral to the supplementary motor area. Contraversive saccades were evoked from 129 sites by stimulation. Threshold currents were lower than 20 microA in half the tests. Response latencies were usually longer than 50 ms (minimum: 30 ms). Eye movements were occasionally accompanied by blinks, ear, or neck movements. The cortical area yielding these movements was at the superior edge of the frontal lobe just rostral to the region from which limb movements could be elicited. Depending on the site of stimulation, saccades varied between two extremes: from having rather uniform direction and size, to converging toward a goal defined in space. The transition between these extremes was gradual with no evidence that these two types were fundamentally different. From surface to depth of cortex, direction and amplitude of evoked saccades were similar or changed progressively. No clear systematization was found depending on location along rostrocaudal or mediolateral axes of the cortex. The dorsomedial oculomotor area mapped was approximately 7 mm long and 6 mm wide. Combined eye and head movements were elicited from one of ten sites stimulated when the head was unrestrained. In the other nine cases, saccades were not accompanied by head rotation, even when higher currents or longer stimulus trains were applied. Presaccadic unit activity was recorded from 62 cells. Each of these cells had a preferred direction that corresponded to the direction of the movement evoked by local microstimulation. Presaccadic activity occurred with self-initiated as well as visually triggered saccades. It often led self-initiated saccades by more than 300 ms. Recordings made with the head free showed that the firing could not be interpreted as due to attempted head movements. Many dorsomedial cortical neurons responded to photic stimuli, either phasically or tonically. Sustained responses (activation or inhibition) were observed during target fixation. Twenty-one presaccadic units showed tonic changes of activity with fixation. Justification is given for considering the cortical area studied as a supplementary eye field. It shares many common properties with the arcuate frontal eye field. Differences noted in this study include: longer latency of response to electrical stimulation, possibility to evoke saccades converging apparently toward a goal, and long-lead unit activity with spontaneous saccades.
Role of the central thalamus in gaze control.
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Unit activity related to spontaneous saccades in frontal dorsomedial cortex of monkey.
Single unit activity was studied in the dorsomedial edge of the frontal lobe, above the superior arcuate sulcus in three trained monkeys (Macaca nemestrina). Gaze and head movements were recorded with two magnetic search coils. Discharges preceding spontaneous eye movements in a preferred direction were consistently observed in light and in dark, in a limited cortical territory at the anterior border of the supplementary motor area. Microstimulation at these sites elicited saccades in the unit preferred direction. Five presaccadic units were studied head fixed and head free and showed the same saccade-related activity under both conditions. Preliminary data suggest that the area studied may be a supplementary eye field distinct from the arcuate frontal eye field.
Visuomotor functions of central thalamus in monkey. I. Unit activity related to spontaneous eye movements.
The region in and around the thalamic internal medullary lamina (IML) in the cat recently has been shown to contain neurons active with ocular saccades and responding to visual stimuli. In the present study, single-unit microelectrode recordings were made in the corresponding thalamic region of the alert monkey in order to determine whether neurons with similar properties existed. Our objective was to specify the functional characteristics of these thalamic cells in the monkey, since 1) cell populations in the central thalamus form an important link between brain stem structures, such as superior colliculus and paramedian pontine reticular formation, and cortical areas, such as frontal eye field and inferior parietal lobule; and 2) most neurophysiological information on these structures with regard to gaze mechanisms has been obtained in primates. In this first part of the study we report observations on 164 thalamic units whose activity was related to the performance of spontaneous eye movements, head fixed. The animals had been trained on a visual discrimination task but photic stimuli were used only for calibrating the eye-position recording and for inducing small saccades and smooth pursuit. The experiments were performed in dim red light and in total darkness. Three types of units were found: 67 saccadic burst units, 58 saccade pause-rebound units, and 39 eye-position units. Sixty-two of the burst units had a directional preference. Most of the on-directions were contraversive, and it was in such units that the lead time of firing before saccades was the longest (up to at least 400 ms). Some of the burst units had a movement field, others fired more intensively and with a longer lead time, depending on the eccentricity of the eye position reached in orbit. The five units with no directional preference were the ones showing the best relation of burst duration with saccade duration. Three types of pause-rebound units were distinguished, depending on whether the saccadic pause or the postsaccadic burst was the most conspicuous event or the pause occurred after saccade offset. The three types were called, respectively, omnipausers, omnirebound cells, and late pausers. Omnipausers and omnirebound cells had no directional preference but their typical firing patterns occurred very consistently with all saccades, even less than 2 degrees. In a few units, the rebound progressively faded away in total darkness. The relation of firing rate of eye-position units with eccentricity of the eyes in orbit was analyzed. Fluctuations in time and a hysteresis effect were found to affect this relation.(ABSTRACT TRUNCATED AT 400 WORDS)
Visuomotor functions of central thalamus in monkey. II. Unit activity related to visual events, targeting, and fixation.
In alert monkeys, single-unit responses to visual stimuli were recorded in the central thalamic region where eye movement-related activity has been observed (33). Usually, the stimuli were 1 degree annulus patterns of dim light presented at unpredictable locations on a tangent screen. The animals were trained on two tasks: one in which they delivered the stimulus themselves by pressing a panel that they had to release immediately when the stimulus shape changed to a square, and another one in which the stimulus was turned on by the experimenter and the monkeys were rewarded for fixating this target for a predetermined length of time. In both tasks, continuous stimulus fixation was required. Receptive fields were tested with and without a fixation point. Retinal coordinates of stimuli were obtained by subtracting eye-position coordinates from stimulus coordinates in space, the monkey's head being fixed. Unit responses in the cases where targeting occurred or did not occur were analyzed separately. Transient responses were observed in 63 units and sustained responses in 44 units. Among the 63 units responding transiently, 42 did so irrespective of targeting. Their receptive fields were very large, generally including the fovea, and predominantly contralateral when the fields were asymmetric. The responses of the other 21 units depended on the occurrence of targeting. They were called visually triggered eye movement-related responses (VTEM). VTEM units were further subdivided in 9 units active only with targeting and 12 units showing the classical phenomenon of "response enhancement" under this condition. VTEM units were contrasted to six units that were both passively visually responsive and bursting with saccades, either spontaneous or visually triggered. The latencies of passive visual and VTEM responses to stimulus onset were comprised between 77 and 135 ms in 80% of the units. VTEM units also fired prior to retargeting saccades. Presaccadic units active with spontaneous saccades also discharged with visually elicited saccades. The earliest sign of activation after stimulus onset eliciting a saccade appeared between 80 and 100 ms, that is, in the same range of latencies as passive visual and VTEM units. Sustained visual responses consisted of activation in 18 units and inactivation in 26 units. The occurrence of these patterns of firing was related to stimulus fixation. In the majority of cases, the changes in discharge frequency started before fixation was achieved by a targeting saccade. They terminated before fixation was broken by a saccade away from the stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)
Thalamic units firing upon refixation may be responsible for plasticity in visual cortex.
In alert cat and monkey, a unit type recorded in the region of the thalamic internal medullary lamina seems to provide the extraretinal signal postulated by Singer (1982) to explain the development of mature receptive field properties in cortical visual neurons. These thalamic units are silent (or silenced) during saccades in all directions; they discharge as soon as the eyes assume a new position. The abolition of this discharge by thalamic lesion, or conversely, its elicitation by electrical stimulation could respectively prevent or facilitate plastic changes in visual cortical areas of kittens.
Comparison of EOG and search coil techniques in long-term measurements of eye position in alert monkey and cat.
In cat and monkey a comparison was made of simultaneous records of eye movements obtained by the electro-oculographic and the magnetic search coil techniques. The major drawback of the electro-oculographic method is the slow d.c. drift, still present despite careful preparation of the electrodes. The d.c. level varies considerably with lighting conditions over long periods of time. In addition, the EOG picks up blink artifacts in monkey and other movement artifacts which are described in detail. The objective of this study was to document and evaluate the relative importance of these technical problems. Because of its simplicity and convenience the EOG method still has some applications in neurophysiological experiments. Its use requires the possibility of making frequent calibrations of gain and d.c. level.
Visuo-oculomotor properties of cells in the superior colliculus of the alert cat.
Visual responses and eye movement (EM) -related activities were studied in single units of the superior colliculus (SC) of alert cats. Spontaneous EMs were encouraged by training. Throughout the SC (i.e., in intermediate and deep layers as well as in superficial layers), units were found to respond well to visual stimuli. Strong and consistent responses could be elicited by very dim, low-contrast stationary stimuli. Visual responses varied from phasic to tonic; some units responded tonically to stationary stimuli in the center of the receptive field, and phasically to peripheral stimuli. Many cells responded more vigorously to moving than to stationary stimuli, but very few responded exclusively to stimulus movement. The vast majority of cells were directionally selective. A small number of units were sensitive to the absolute, as well as the retinal, position of visual stimuli. These cells were activated by visual stimuli which fell in the receptive field only if the cat's gaze was fixated on one half of the screen. It seems that these cells must receive information about both eye position and the retinal (receptive field) position of the stimulus. It is possible that they reflect coding of target location within a head (or body) frame of reference. EM-related units were of two types: (1) about 20% of the sample responded prior to spontaneous or visually-triggered EMs, and (2) another 10% (or more) responded with, but not before, EMs. Some cells in the second group discharge almost synchronously with EMs and, thus, cannot plausibly be said to respond to the movement of images across the retina. All cells in the first group were directionally selective. The percentage of EM-related cells in the deep layers of SC is lower in cat than in monkey. Possible reasons for such differences are discussed.
Visual responses of thalamic neurons depending on the direction of gaze and the position of targets in space.
Visual receptive field properties of neurons in the region of the thalamic internal medullary lamina were studied in alert cats while they fixated in various directions. In slightly more than 50% of the cells, the responsiveness of the cells was found to depend on the location of the stimulus with respect to the head-body axis (stimulus absolute position). A cell could ignore a stimulus outside its absolute field even if it was well placed within its receptive field. Three types of neurons were distinguished. Neurons with small central receptive fields were tonically activated when the animal fixated the stimulus in one half of the screen (usually contralateral). The firing rate of these cells was related to the stimulus absolute position measured along a preferred axis. Similarly, neurons with large receptive fields fired as a function of stimulus absolute position but stimulus fixation was not required. Neurons with eccentric fields responded to stimuli located in a target area defined in head-body coordinates. Such cells gave presaccadic bursts with eye movements terminating in the target area. The conclusion proposed is that neurons exist which code visual spatial information in a non-retinal frame of reference. This coding takes place at the time of stimulus presentation. Its role may be seen in the initiation of visually guided movements.
Visual and presaccadic neuronal activity in thalamic internal medullary lamina of cat: a study of targeting.
1. Visual responses and eye movement-related activities were studied in single neurons of the thalamic internal medullary lamina (IML) of alert cats. The animals faced a tangent screen on which stationary or moving spots of light were presented. Of 95 units, 26% discharged in relation to photic stimuli but not eye movement, 6% in relation to eye movement but not photic stimuli, and 68% in relation to both. These units were intermixed in the same region. 2. Visual responses varied from transient to sustained. IML units were not found particularly sensitive to stimulus movement when the eyes were fixed. Strong and consistent responses could be elicited by extremely dim and weakly contrasted stationary stimuli (e.g.) 3.4 mcd/m2, 2.6% of illumination background) binocularly viewed. Receptive fields (from 250 to 800 deg2) were determined, in absence of eye movements, by computing the position of effective stimuli relative to the point of fixation of the gaze. An area of greatest responsiveness in the receptive field of most units could be detected on the basis of either higher probability of response, minimum latency, greater number of spikes in initial transient burst, or stronger sustained activity. Whole fields or their areas of greatest responsiveness were located on the side toward which saccades were accompanied by increased firing of the unit. 3. On trials in which a delay occurred between stimulus presentation and the cat's targeting saccade, the majority of the units studied changed their activity twice: after the stimulus and before the eye movement. In 16 units, the presaccadic activation occurred only with targeting, not with spontaneous saccades. 4. These results suggest that cells in the IML region of the cat play a significant role in the control of visually elicited eye movements. The resemblance of these cells to the monkey's tectual cells is discussed and hypotheses are proposed a) to relate the receptive field characteristics to the targeting operation, and b) to account for the double activation--sensory and motor--of many IML cells.
Vusual responsiveness of eye-movement neurons in thalamic internal medullary lamina of cat.
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Neuronal activity before and during eye movements in thalamic internal medullary lamina of the cat.
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Neuronal activity correlated with eye movements in "nonspecific" thalamic nuclei.
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Unilateral visual neglect and thalamic intralaminar lesions in the cat.
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Induction of oculomotor responses from thalamic internal medullary lamina in the cat.
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