A highly selective probe for fluorometric sensing of cyanide in an aqueous solution and its application in quantitative determination and living cell imaging.

A simple fluorescent probe (KS4) containing multiple reaction sites (phenolic -OH, imine and C = C bonds) is successfully synthesized and characterized using 1H NMR, 13C NMR, mass and single crystal XRD techniques. KS4 exhibits high selectivity towards CN- over a wide range of common anions in H2O:DMSO (1:1 v/v) leading to an amazing turn-on fluorescence at 505 nm via deprotonation of the phenolic -OH group. The limit of detection (1.3 µM) for CN- was much below the standard (1.9 µM) set by the World Health Organization (WHO). Stoichiometry of the interaction between KS4 and CN- was ascertained as 1:1 by the Job's plot method and the binding constant was determined to be 1.5x104 M-1. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) based theoretical insight has been appealed to understand the optical properties of KS4 before and after the addition of CN- ion. The probe shows respectable real-time applicability for qualitative detection of CN- in almond and cassava powder as well as quantification in real water samples with excellent recoveries (98.8 - 99.8%). In addition, KS4 is found to safe towards living HeLa cells and successfully applied to the detection of endogenous cyanide ions in HeLa cells.

How motivation and reward learning modulate selective attention.

Motivational stimuli such as rewards elicit adaptive responses and influence various cognitive functions. Notably, increasing evidence suggests that stimuli with particular motivational values can strongly shape perception and attention. These effects resemble both selective top-down and stimulus-driven attentional orienting, as they depend on internal states but arise without conscious will, yet they seem to reflect attentional systems that are functionally and anatomically distinct from those classically associated with frontoparietal cortical networks in the brain. Recent research in human and nonhuman primates has begun to reveal how reward can bias attentional selection, and where within the cognitive system the signals providing attentional priority are generated. This review aims at describing the different mechanisms sustaining motivational attention, their impact on different behavioral tasks, and current knowledge concerning the neural networks governing the integration of motivational influences on attentional behavior.

Community structure of terrestrial invertebrates inhabiting a tidal marsh islet in the Mediterranean Sea (Gulf of Gabes, Tunisia).

The composition of the terrestrial arthropod community of a tidal marsh islet in the Gulf of Gabes (Tunisia) was studied during two seasons (spring, autumn). The study was conducted on a small islet located in an area where the highest tidal excursions of the Mediterranean occur. Standard trapping methods (pitfall traps, mobile cages) were used to evaluate specie richness and abundance in different areas of the islet. Diversity indices were calculated for coleopterans and isopods alone. The structure of the arthropod community varied a great deal from one season to the other and differences were found when seaward areas were compared with landward ones. El Bessila presented a particularly rich beetle community whereas only few isopod species occurred. The moderately high diversity levels found for the beetle indicate the influence of the high tidal excursions in modelling the structure of the community.

Responses of neurons in macaque area V4 during memory-guided visual search.

In a typical scene with many different objects, attentional mechanisms are needed to select relevant objects for visual processing and control over behavior. To test the role of area V4 in the selection of objects based on non-spatial features, we recorded from V4 neurons in the monkey, using a visual search paradigm. A cue stimulus was presented at the center of gaze, followed by a blank delay period. After the delay, a two-stimulus array was presented extrafoveally, and the monkey was rewarded for detecting the target stimulus matching the cue. The array was composed of one 'good' stimulus (effective in driving the cell when presented alone) and one 'poor' stimulus (ineffective in driving the cell when presented alone). When the choice array was presented in the receptive field (RF) of the neuron, many cells showed suppressive interactions between the stimuli as well as strong attention effects. Within 150--200 ms of array onset, responses to the array were determined by the target stimulus. If the target was the good stimulus, the response to the array became equal to the response to the good stimulus presented alone. If the target was the poor stimulus, the response approached the response to that stimulus presented alone. Thus the influence of the nontarget stimulus was filtered out. These effects were reduced or eliminated when the poor stimulus was located outside the RF and, therefore, no longer competing for the cell's response. Overall, the results support a 'biased competition' model of attention, according to which objects in the visual field compete for representation in the cortex, and this competition is biased in favor of the behaviorally relevant object.

Learning increases stimulus salience in anterior inferior temporal cortex of the macaque.

With experience, an object can become behaviorally relevant and thereby quickly attract our interest when presented in a visual scene. A likely site of these learning effects is anterior inferior temporal (aIT) cortex, where neurons are thought to participate in the filtering of irrelevant information out of complex visual displays. We trained monkeys to saccade consistently to one of two pictures in an array, in return for a reward. The array was constructed by pairing two stimuli, one of which elicited a good response from the cell when presented alone ("good" stimulus) and the other of which elicited a poor response ("poor" stimulus). The activity of aIT cells was recorded while monkeys learned to saccade to either the good or poor stimulus in the array. We found that neuronal responses to the array were greater (before the saccade occurred) when training reinforced a saccade to the good stimulus than when training reinforced a saccade to the poor stimulus. This difference was not present on incorrect trials, i.e., when saccades to the incorrect stimulus were made. Thus the difference in activity was correlated with performance. The response difference grew over the course of the recording session, in parallel with the improvement in performance. The response difference was not preceded by a difference in the baseline activity of the cells, unlike what was found in studies of cued visual search and working memory in aIT cortex. Furthermore, we found similar effects in a version of the task in which any of 10 possible pairs of stimuli, prelearned before the recording session, could appear on a given trial, thereby precluding a working memory strategy. The results suggest that increasing the behavioral significance of a stimulus through training alters the neural representation of that stimulus in aIT cortex. As a result, neurons responding to features of the relevant stimulus may suppress neurons responding to features of irrelevant stimuli.

Volitional covert orienting to a peripheral cue does not suppress cue-induced inhibition of return.

Detection reaction time (RT) at an extrafoveal location can be increased by noninformative precues presented at that location or ipsilaterally to it. This cue-induced inhibition is called inhibition of return or ipsilateral inhibition. We measured detection RT to simple light targets at extrafoveal locations that could be designated for covert orienting by local or distant cues. We found that cue-induced inhibition cooccurred in an additive fashion with the direct effects of covert orienting, i.e., it detracted from facilitation at attended locations and increased the disadvantage for unattended locations. Thus, cue-induced inhibition cannot be suppressed by a volitional covert orienting to the cued location; the co-occurrence of different facilitatory and inhibitory effects confirms the simultaneous operation of multiple independent attentional mechanisms during covert orienting.

Serial attention mechanisms in visual search: a critical look at the evidence.

Until a few years ago, visual search tasks were of exclusive pertinence to psychophysicists and cognitive psychologists trying to understand the operating principles and computational constraints of visual perception and visual selective attention. In recent years, cognitive neuroscience, with its powerful tools, has started to explore more directly the neuronal mechanisms underlying search performance in humans and macaques, aiming at the same general goals. New observations from a number of cognitive neuroscience approaches are promising a near future of great excitement in this field of research. This article offers a critical review of some of these recent contributions and highlights some of the interpretational problems that they pose.

Possible recoding of visual space in covert orienting tasks.

Reaction time to lateralized light targets is longer if targets are preceded by light stimuli in the same visual hemifield compared to when they are preceded by light stimuli in the opposite visual hemifield. The effect is probably caused by interactions between implicit oculomotor tendencies and covert shifts of attention. We show here that a similar, but much smaller, ipsilateral RT inhibition can be observed when all stimuli are presented in a display completely lateralized to one hemifield, where ipsilateral and contralateral are defined with respect to the midpoint of the display. The persistence of ipsilateral inhibition with unilateral stimulus displays can be accounted for by a recoding of visual space predicated on the centering of covert attention on the display midpoint rather than on the fixation point. The recoding seems to affect the control of covert attention and perhaps oculomotor control as well.

Competitive mechanisms subserve attention in macaque areas V2 and V4.

It is well established that attention modulates visual processing in extrastriate cortex. However, the underlying neural mechanisms are unknown. A consistent observation is that attention has its greatest impact on neuronal responses when multiple stimuli appear together within a cell's receptive field. One way to explain this is to assume that multiple stimuli activate competing populations of neurons and that attention biases this competition in favor of the attended stimulus. In the absence of competing stimuli, there is no competition to be resolved. Accordingly, attention has a more limited effect on the neuronal response to a single stimulus. To test this interpretation, we measured the responses of neurons in macaque areas V2 and V4 using a behavioral paradigm that allowed us to isolate automatic sensory processing mechanisms from attentional effects. First, we measured each cell's response to a single stimulus presented alone inside the receptive field or paired with a second receptive field stimulus, while the monkey attended to a location outside the receptive field. Adding the second stimulus typically caused the neuron's response to move toward the response that was elicited by the second stimulus alone. Then, we directed the monkey's attention to one element of the pair. This drove the neuron's response toward the response elicited when the attended stimulus appeared alone. These findings are consistent with the idea that attention biases competitive interactions among neurons, causing them to respond primarily to the attended stimulus. A quantitative neural model of attention is proposed to account for these results.

Responses of neurons in inferior temporal cortex during memory-guided visual search.

Responses of neurons in inferior temporal cortex during memory-guided visual search. J. Neurophysiol. 80: 2918-2940, 1998. A typical scene will contain many different objects, few of which are relevant to behavior at any given moment. Thus attentional mechanisms are needed to select relevant objects for visual processing and control over behavior. We examined this role of attention in the inferior temporal cortex of macaque monkeys, using a visual search paradigm. While the monkey maintained fixation, a cue stimulus was presented at the center of gaze, followed by a blank delay period. After the delay, an array of two to five choice stimuli was presented extrafoveally, and the monkey was rewarded for detecting a target stimulus matching the cue. The behavioral response was a saccadic eye movement to the target in one version of the task and a lever release in another. The array was composed of one "good" stimulus (effective in driving the cell when presented alone) and one or more "poor" stimuli (ineffective in driving the cell when presented alone). Most cells showed higher delay activity after a good stimulus used as the cue than after a poor stimulus. The baseline activity of cells was also higher preceding a good cue, if the animal expected it to occur. This activity may depend on a top-down bias in favor of cells coding the relevant stimulus. When the choice array was presented, most cells showed suppressive interactions between the stimuli as well as strong attention effects. When the choice array was presented in the contralateral visual field, most cells initially responded the same, regardless of which stimulus was the target. However, within 150-200 ms of array onset, responses were determined by the target stimulus. If the target was the good stimulus, the response to the array became equal to the response to the good stimulus presented alone. If the target was a poor stimulus, the response approached the response to that stimulus presented alone. Thus the influence of the nontarget stimulus was eliminated. These effects occurred well in advance of the behavioral response. When the array was positioned with stimuli on opposite sides of the vertical meridian, the contralateral stimulus appeared to dominate the response, and this dominant effect could not be overcome by attention. Overall, the results support a "biased competition" model of attention, according to which 1) objects in the visual field compete for representation in the cortex, and 2) this competition is biased in favor of the behaviorally relevant object by virtue of "top-down" feedback from structures involved in working memory.

Neural mechanisms of spatial selective attention in areas V1, V2, and V4 of macaque visual cortex.

Many neurons in extrastriate visual cortex have large receptive fields, and this may lead to significant computational problems whenever multiple stimuli fall within a single field. Previous studies have suggested that when multiple stimuli fall within a cell's receptive field, they compete for the cell's response in a manner that can be biased in favor of attended stimuli. In the present study we examined this role of attention in areas V1, V2, and V4 of macaque monkeys with the use of a behavioral paradigm in which attention was directed to one of two stimulus locations. When two stimuli were presented simultaneously inside the cell's receptive field (which could be accomplished only in areas V2 and V4), we found that the cell's response was strongly influenced by which of the two stimuli was attended. The size of this attention effect was reduced when the attended and ignored stimuli were presented sequentially rather than simultaneously. In addition, the effects became very weak and inconsistent in these areas when only one of the two stimuli was located inside the receptive field. Attention thus modulated sensory responses primarily when two or more simultaneous stimuli competed for access to a neuron's receptive field. As in areas V2 and V4, attention did not modulate sensory responses in area V1 when only a single stimulus was inside the receptive field. In addition, the small receptive fields in this area precluded the simultaneous presentation of attended and ignored stimuli inside the receptive field, making it impossible to determine whether attention effects would be observed under the conditions that led to consistent attention effects in areas V2 and V4. Spontaneous firing rates in areas V2 and V4 were found to be 30-40% higher when attention was directed inside rather than outside the receptive field, even when no stimulus was present in the receptive field. Spontaneous firing rates also varied according to the particular location within the receptive field that was attended. These shifts in spontaneous activity may reflect a top-down signal that biases responses in favor of stimuli at the attended location.

Oculomotor activity and visual spatial attention.

Subjects made a horizontal or vertical saccade in response to a non-lateralized auditory stimulus. Simple manual reaction time (RT) for the detection of light targets at extrafoveal locations was modulated by the intention to make the saccade insofar as RT to targets presented at the saccadic goal location or in the hemifield containing that location was faster than RT to targets presented at the opposite, mirror-symmetric location. This RT difference was maximal prior to the beginning of the saccade and vanished after saccade termination, indicating that the effect was caused by the neural activity leading to the saccade rather than to the eye movement or the eye position per se. The results have implications for the understanding of the relations between visual spatial attention and oculomotor control, especially with regard to inhibitory phenomena arising from the non-correspondence between the line of sight and the focus of attention.

Neural mechanisms for stimulus selection in cortical areas of the macaque subserving object vision.

The present article reviews some recent work on the neuronal mechanisms underlying space-based and feature-based stimulus selection in the primate occipito-temporal pathway of cortical visual processing. Clear evidence demonstrates that activity in areas V4 and IT is high for a stimulus which is selected either for its position in space or for its features, while it is considerably suppressed for other, irrelevant stimuli. Data are discussed within a conceptual framework whereby objects in the visual field always compete for focal resources. According to task demands, any kind of input (objects of a certain category, objects with a certain form, color or motion, objects at a certain location) can be behaviorally relevant. A short-term description (working memory) of the currently relevant object properties controls competitive bias in the visual system, such that inputs matching that description are favored to the disadvantage of task-irrelevant inputs. This framework emphasizes a tight, causal link between memory signals and mechanisms for stimulus selection in visual cortex. In all cases gating of neural activity was constrained by spatial factors. In area V4, responses to an ignored stimulus in the receptive field of the recorded neuron were maximally suppressed when the monkey attended to a second stimulus located within the boundary of the same receptive field, while suppression was virtually absent when attention was directed to a second stimulus well outside the receptive field border. In IT cortex, suppressed responses depended on both the selected and ignored stimuli being within the hemifield contralateral to the recorded hemisphere, while suppression was much reduced when the stimuli were presented across the vertical midline. These spatial constraints on the occurrence of modulation of visual responses may reflect limitations imposed by the local pattern of reciprocal inhibitory connections, which are supposed to underlie competitive interactions among objects in the field, that is among object representations in cortex.

Do peripheral non-informative cues induce early facilitation of target detection?

It has been reported that simple reaction time (RT) to a peripheral visual target is faster if the target is presented within about 200 msec from the onset of a non-informative cue flashed at the same location, as compared with RT to a target presented at an uncued location. This period of facilitation is followed by a period of inhibition during which RT is longer if cue and target are shown at the same location or at different locations within the same hemifield, as opposed to contralateral cues and targets. Early facilitation has been explained by an automatic covert orienting towards the cue, while the following inhibition has been regarded as a consequence of such covert orienting. In a series of four experiments, we have investigated the dependency of these effects on the temporal and spatial relationships between cue and target. Normal, right-handed subjects responded to a target displayed for 16 msec simultaneously with, or following at stimulus-onset asynchronies (SOAs) of 60, 130, 300 or 900 msec, the onset of a non-informative cue. Both cues and targets could appear at random in one of four locations (Expts 1-3) or in one of two locations (Expt 4) disposed symmetrically across the fixation point along the horizontal meridian. Duration of the cue varied between experiments. In Expt 1 it was 16 msec. In Expt 2 the cue remained on view throughout the period of the SOA and terminated 300 msec after target onset. In the remaining two experiments cue duration was 130 msec. In the first experiment, at all cue-target SOAs RTs to target flashed either at the same location or in the same hemifield as the cue were significantly slower than RTs to contralateral cue-target combinations (RT inhibition). In the other experiments, there was no RT inhibition with targets in cued locations if the cue remained on during target presentation and outlasted target offset. Since at no SOA was RT to targets in cued locations shorter than RT to targets contralateral to cues, there was no direct evidence for facilitation. However, the facilitatory influence of these cues could be inferred from the fact that they countered and masked inhibition. RT to uncued targets ipsilateral to cues was consistently inhibited in all experimental conditions. These results show that at each cue-target SOA the consequences of a peripheral non-informative cue depend on whether or not the cue remains visible during target processing.(ABSTRACT TRUNCATED AT 400 WORDS)

A neural basis for visual search in inferior temporal cortex.

We often search for a face in a crowd or for a particular object in a cluttered environment. In this type of visual search, memory interacts with attention: the mediating neural mechanisms should include a stored representation of the object and a means for selecting that object from among others in the scene. Here we test whether neurons in inferior temporal cortex, an area known to be important for high-level visual processing, might provide these components. Monkeys were presented with a complex picture (the cue) to hold in memory during a delay period. The cue initiated activity that persisted through the delay among the neurons that were tuned to its features. The monkeys were then given 2-5 choice pictures and were required to make an eye movement to the one (the target) that matched the cue. About 90-120 milliseconds before the onset of the eye movement to the target, responses to non-targets were suppressed and the neuronal response was dominated by the target. The results suggest that inferior temporal cortex is involved in selecting the objects to which we attend and foveate.

Spontaneous Saccades and Gaze-Holding Ability in the Pigmented Rat. I. Effects of Inferior Olive Lesion.

We have studied the effects of lesion of the inferior olive on the spontaneous eye movements performed both in the light and dark in head restrained pigmented rats. The inferior olive lesion was made at least 1 month before study with 3-acetylpyridine and eye movements were recorded through a phase detection search coil apparatus. Following lesion, the spontaneous saccades performed in the dark present a postsaccadic drift which is made up of two components characterized by their different time courses, the first one being fast and the second one slow. The latter component is due to the leakage of the neural integrator and the former is mainly the consequence of a mismatch between the phasic and the tonic component of the ocular movement. In the light only the first component is present and then the eye maintains a steady position. After the lesion the saccades in the dark present a time constant of the slow component of the postsaccadic drift which is significantly reduced to approximately 600 - 900 ms from a value of 1600 - 4000 ms of the intact rats. This means that the integrity of the inferior olive is necessary to keep the time constant of the neural integrator within the physiological range. In the light, the amplitude of the postsaccadic drift depends on two factors. First, there is a mismatch between the phasic and the tonic components of the ocular movement, which are due to the pulse and the step of innervation of the extraocular muscles respectively. Different types of analysis have shown that the gain of the pulse to step transformation is about 0.77 at all saccadic amplitudes and eccentricities. Second, there is an increased leakiness of the neural integrator. Such a contribution increases linearly as a function of the eccentricity with a slope of 0.21. The main sequence of the saccades is not appreciably affected by the olivary lesion. Thus, the consequence of the inferior olive lesion may be interpreted as a general disruption of the integration process which, in physiological conditions, generates a proper and sustained oculomotor signal. More generally, it may be viewed as a loss of coordination between phasic and tonic motor commands.

Spontaneous Saccades and Gaze-Holding Ability in the Pigmented Rat. II. Effects of Localized Cerebellar Lesions.

We have studied the effects of the ablation of the cerebellar vermal area corresponding to lobules VI - VIII and of the flocculus - paraflocculus of both sides on the spontaneous eye movements performed in the light and in the dark in head-restrained pigmented rats. These effects have been compared with those already described for the inferior olive lesion. The cerebellar lesions were performed 1 week to 6 months in advance. Eye movements were recorded through a phase detection search coil apparatus. Following vermal topectomy, the main characteristics of the spontaneous saccades are unmodified. Following the ablation of the flocculus - paraflocculus there is no change in the saccadic main sequence. However, the spontaneous saccades in the dark present a postsaccadic drift made up of two components with different time courses, the first one being fast and the second one slow. The former is due in part to a mismatch between the phasic (the pulse) and the tonic (the step) components of the eye movements; the latter to the leakage of the neural integrator. In light only the first component is present and the eye maintains a steady position. The time constant of the neural integrator is considerably reduced to approximately 600 - 900 ms from a value of approximately 1600 - 4000 ms in the intact rats. The amplitude of the postsaccadic drift in the light depends on both the mismatch between the pulse and the step of innervation of the extraocular muscles and the increased leakiness of the neural integrator. The gain of the pulse to step transformation is reduced to approximately 0.79 at all saccadic amplitudes and eccentricities and such a reduction is due to a decreased step amplitude, while the pulse amplitude remains unchanged. The contribution of the leakage of the neural integrator to the postsaccadic drift in the light is a function of the eccentricity with a slope of 0.23. The deficits described after flocculus - paraflocculus ablation are also very similar to those described following inferior olive lesion from a quantitative point of view. The possible mechanisms of the visually activated olivocerebellar system in the control of saccadic performance and in maintaining its calibration are discussed.

Magnesium deficiency affects the pentylenetetrazol-induced convulsions in magnesium-deprived rats.

A group of 11 young albino rats was fed with a Mg2+ free diet. After a few days, the animals showed typical signs of Mg2+ deficiency, consisting in skin vasodilation, red conjunctiva and hair loss. Pentylenetetrazol (50 mg/kg i.p.) injected in these rats, 6 and 12 days after the beginning of the diet, elicited a more severe convulsive activity compared with that shown by a control group of 12 rats. These results suggest that a Mg2+ deficiency, though not necessarily responsible for the convulsive activity, may contribute to facilitate an epileptic episode or may lead to more severe convulsions. The possibility of a more powerful activation of the NMDA receptors in Mg2+ deficiency is discussed.

Saccadic Eye Movements and Gaze Holding in the Head-Restrained Pigmented Rat.

Spontaneous saccadic eye movements were recorded in seven head-restrained pigmented rats by means of a phase detection search coil system, both in the light and in the dark. In an illuminated environment, all the rats made numerous spontaneous saccades with an average amplitude of 13.2 deg (+/- 2.2 SD) and a maximal amplitude of 35 deg. In the dark, mean saccadic amplitude was significantly reduced to 9.2 deg (+/- 2.0 SD). Saccadic peak velocity increased linearly as a function of saccadic size, with no saturation at high amplitude values. In the light, peak velocity increase was 32.7 deg/s/deg (+/- 3.5 SD). This value is higher than that described in many other species including man and is similar to that of the monkey. Also saccadic duration increased linearly as a function of size at a rate of 1 ms/deg, which is closer to that of monkey than to that of other species including man. Both peak velocity and duration were not significantly different in the dark from those measured in the light. In the light, following a saccadic gaze shift, the rats were able to maintain a steady eye position for long periods, also at large orbital eccentricities. In the dark, on the contrary, the eye presented a drift towards the central position in the orbit. Such a drift had an exponential-like time course with a time constant of 1567 ms (+/- 829 SD), a value which is much shorter than that of cat and primates. This indicates that in the absence of a visual input, the rat has a poor gaze holding ability compared to other species.

Effects of ethanol and imidazobenzodiazepine Ro 15-4513 on spontaneous saccades of the pigmented rat.

The present study was aimed at investigating the alterations of the spontaneous saccadic eye movements of pigmented rats following ethanol administration. In addition we have studied the efficacy of the imidazobenzodiazepine Ro 15-4513 in reversing the effects of alcohol on saccades. The horizontal component of spontaneous eye movements was recorded by means of the magnetic field search coil technique on 11 head-restrained, pigmented rats. After the intraperitoneal injection of ethanol (1 g/kg) spontaneous saccades showed: i) a backward post-saccadic drift, with an exponential-like time course (time constant 100-150 ms); ii) a remarkable reduction of mean saccadic amplitude, up to 37% of control; iii) a significant decrease of peak velocity, which was reduced to about 80% of control. All these effects appeared and developed within a few minutes after the administration and were still present one hour later. When Ro 15-4513 (5 mg/kg) was injected i.p., 15 min after ethanol, the post-saccadic drift amplitude was immediately reduced and the drift was completely abolished within about 30 min. Mean saccadic amplitude returned to control values within a few minutes and was then steadily maintained for the following period examined (30 min). On the contrary, peak velocity showed only a slight tendency to recover which never was significant. When the same dose of Ro 15-4513 was injected alone there was no post-saccadic drift. However, mean saccadic amplitude increased, almost immediately, up to 160% of control. Its value showed a slight constant decrease in the following 30 min. Peak velocity was only slightly increased (up to 106% of control), but never was significantly different from control. Our results show that ethanol induces a remarkable impairment in the performance of spontaneous saccades. The imidazobenzodiazepine Ro 15-4513 is able to reverse completely only some of the alcohol-induced alterations, i.e. the post-saccadic drift and the reduction of saccadic amplitude, while it fails to counter efficiently the reduction of peak velocity. Ro 15-4513 exerts an intrinsic action, which is opposite to that of ethanol, on some of the saccadic parameters we have examined.