Spontaneous Saccadic Eye Movements Research Articles

Spontaneous modulations of high-frequency cortical activity

ObjectiveWe clarified the clinical and mechanistic significance of physiological modulations of high-frequency broadband cortical activity associated with spontaneous saccadic eye movements during a resting state. MethodsWe studied 30 patients who underwent epilepsy surgery following extraoperative electrocorticography and electrooculography recordings. We determined whether high-gamma activity at 70–110 Hz preceding saccade onset would predict upcoming ocular behaviors. We assessed how accurately the model incorporating saccade-related high-gamma modulations would localize the primary visual cortex defined by electrical stimulation. ResultsThe dynamic atlas demonstrated transient high-gamma suppression in the striatal cortex before saccade onset and high-gamma augmentation subsequently involving the widespread posterior brain regions. More intense striatal high-gamma suppression predicted the upcoming saccade directed to the ipsilateral side and lasting longer in duration. The bagged-tree-ensemble model demonstrated that intense saccade-related high-gamma modulations localized the visual cortex with an accuracy of 95%. ConclusionsWe successfully animated the neural dynamics supporting saccadic suppression, a principal mechanism minimizing the perception of blurred vision during rapid eye movements. The primary visual cortex per se may prepare actively in advance for massive image motion expected during upcoming prolonged saccades. SignificanceMeasuring saccade-related electrocorticographic signals may help localize the visual cortex and avoid misperceiving physiological high-frequency activity as epileptogenic.

Spontaneous Ocular Scanning of Visual Symmetry Is Similar During Classification and Evaluation Tasks.

Visual symmetry perception and symmetry preference have been studied extensively. However, less is known about how people spontaneously scan symmetrical stimuli with their eyes. We thus examined spontaneous saccadic eye movements when participants (N = 20) observed patterns with horizontal or vertical mirror reflection. We found that participants tend to make saccades along the axis of reflection and that this oculomotor behaviour was similar during objective classification and subjective evaluation tasks. The axis-scanning behaviour generates a dynamic sequence of novel symmetrical images from a single static stimulus. This could aid symmetry perception and evaluation by enhancing the neural response to symmetry.

How does number magnitude influence temporal and spatial parameters of eye movements?

The influence of numerical processing on individuals' behavior is now well documented. The spatial representation of numbers on a left-to-right mental line (i.e., SNARC effect) has been shown to have sensorimotor consequences, the majority of studies being mainly concerned with its impact on the response times. Its impact on the motor programming stage remains less documented, although swiping movement amplitudes have recently been shown to be modulated by number magnitude. Regarding saccadic eye movements, the few available studies have not provided clear-cut conclusions. They showed that spatial-numerical associations modulated ocular drifts, but not the amplitude of memory-guided saccades. Because these studies held saccadic coordinates constant, which might have masked potential numerical effects, we examined whether spontaneous saccadic eye movements (with no saccadic target) could reflect numerical effects. Participants were asked to look either to the left or to the right side of an empty screen to estimate the magnitude (< or > 5) of a centrally presented digit. Latency data confirmed the presence of the classical SNARC and distance effects. More critically, saccade amplitude reflected a numerical effect: participants' saccades were longer for digits far from the standard (1 and 9) and were shorter for digits close to it (4 and 6). Our results suggest that beyond response times, kinematic parameters also offer valuable information for the understanding of the link between numerical cognition and motor programming.

NCMP-04. OPSOCLONUS-MYOCLONUS SYNDROME ASSOCIATED WITH CONTACTIN-ASSOCIATED PROTEIN-LIKE 2 AUTOANTIBODY IN THE SETTING OF NON-SMALL CELL LUNG CARCINOMA

Abstract INTRODUCTION Opsoclonus–myoclonus syndrome (OMS) is a rare neurological disorder characterized by spontaneous multidirectional saccadic eye movements, myoclonus, and ataxia. It is suspected to be an autoimmune mediated process precipitated by a paraneoplastic or infectious trigger. Among the pediatric population, OMS is often associated with neuroblastoma and anti-Hu antibody. Paraneoplastic syndromes in adults manifesting as OMS are most commonly described in breast, gynecological and small cell lung cancer with associated anti-neuronal antibodies (ANNA-2; anti-Ri). We describe the first case of OMS associated with lung adenocarcinoma and Contactin-associated protein-like 2 (Caspr2) antibody. CASE REPORT: A 46-year-old-woman with history of limited small cell lung cancer (SCLC) status-post chemotherapy with cisplatin and etoposide and prophylactic whole brain radiation, presented with new onset gait instability, nausea, vomiting, vertigo, and opsoclonus. Two months prior to her presentation, a chest computed topography (CT) revealed no evidence of recurrent disease. Brain MRI revealed T2 hyperintensities in the white matter and central pons presumably related to chronic small vessel ischemic changes, unchanged from prior imaging. CSF studies revealed normal cell count, glucose, and protein. Gram stain, culture and meningoencephalitis panel were negative. Her paraneoplastic panel revealed a positive Caspr2 antibody. A repeat CT chest for cancer surveillance revealed a new lung mass. Immunotherapy treatment included plasmapheresis, corticosteroids, and intravenous immunoglobulin therapy. She underwent a biopsy of the new pulmonary lesion and the pathology was consistent with non-small cell lung carcinoma. Her symptoms slowly improved after treatment. Unfortunately, her disease progressed on repeat PET scan despite surgical resection of the lung mass. She ultimately elected for hospice. CONCLUSION We report a novel antibody, Caspr2, occurring in association with paraneoplastic OMS. While SCLC is the most common neoplasm associated with OMS among adults, non-small cell lung carcinoma should be considered. Prompt immunotherapy and neoplasm treatment may result in improvement.

Visual Experience Is Required for the Development of Eye Movement Maps in the Mouse Superior Colliculus.

The superior colliculus (SC) is a midbrain structure important for multisensory integration and sensorimotor transformation. Here we have studied eye movement representations in the SC of mice, a species that has become a popular model in vision research because of available genetic tools. Our studies show mice make saccadic eye movements spontaneously and in response to SC stimulation. The mouse SC contains an eye movement map that has the same global polarity as the overlaying visual map, just like in cats and primates. Furthermore, we show that visual experience is required for establishing the normal eye movement map. Our study provides a necessary basis for future mechanistic studies of how SC motor maps develop and become aligned with sensory maps.

Spontaneous saccadic eye movements are slower than saccades to other imagined stimuli – and even slower than REMs

There is a controversial debate whether rapid eye movements in sleep (REMs) are meaningful (functional) saccades or are due to spontaneous eye muscle contractions. We therefore compared saccadic eye movements with closed eyes to previously seen visual stimuli (dots, static images, videos), auditory stimuli, during math calculations and spontaneous saccades to REMs.

Discharge patterns of neurons in the rostral superior colliculus of cat: activity related to fixation of visual and auditory targets.

Neurons in the rostral superior colliculus (SC) of alert cats exhibit quasi-sustained discharge patterns related to the fixation of visual targets. Because some SC neurons also respond to auditory stimuli, we investigated whether there is a population of neurons in the rostral SC which is active in relation to fixation of both auditory and visual targets. We identified cells which were active with visual fixation and which continued to discharge if the fixation stimulus was briefly extinguished. The population of neurons exhibited similar discharge characteristics when the fixation stimulus was auditory. Few neurons were significantly more active during fixation of visual targets than during fixation of auditory targets. Most fixation neurons showed a diminished discharge rate during spontaneous (self-generated) saccadic eye movements away from a visual fixation stimulus, regardless of the direction of the saccade. This diminished discharge rate (or pause) typically began, on average, 12.2 ms before saccade onset and the duration of the pause was longer than the duration of the saccade. These observations are consistent with the hypothesis that increased discharge of these neurons is related to active fixation and that reductions in their activity are important for the generation of saccades. However, the lack of a precise relationship between pause duration and saccade duration implies that these neurons would be unlikely to project directly to the saccadic burst generator. The mean interval from the beginning of the pauses of fixation neurons to the beginning of the saccades away from fixation targets is also shorter than has been found in brainstem omnipause neurons. By analogy with the concept of a receptive field, a gaze position error field depicts the range of gaze position error for which a cell is active. Although fixation neurons appear to encode the magnitude and direction of the error between visual targets and the visual axis, visual error fields at the end of fixating eye movements were significantly larger than those at stimulus onset. For auditory stimuli, this difference was not significant. These observations are compatible with a number of recent experiments indicating that neural signals of eye position are damped or delayed with respect to current eye position.

Neurons in the cat pretectum that project to the dorsal lateral geniculate nucleus are activated during saccades.

1. Neurons in the pretectal nuclear complex that project to the ipsilateral dorsal lateral geniculate nucleus (LGNd) were identified by antidromic activation after electrical LGNd stimulation in awake cats, and their response properties were characterized to retinal image shifts elicited either by external visual stimulus movements or during spontaneous saccadic eye movements on a stationary visual stimulus, and to saccades in darkness. Eye position was monitored with the use of a scleral search coil and care was taken to assure stability of the eyes during presentation of moving visual stimuli. 2. Of a total sample of 134 cells recorded, 27 neurons were antidromically activated by electrical LGNd stimulation. In addition, responses from neurons that were not activated from the LGNd were also analyzed, including 19 "retinal slip" cells, which selectively respond to slow horizontal stimulus movements, and 21 "jerk" cells, which are specifically activated by rapid stimulus shifts. All recorded neurons were located in the nucleus of the optic tract and in the posterior pretectal nucleus. 3. In the light, neurons identified as projecting to the LGNd responded maximally to saccadic eye movements and to externally generated sudden shifts of large visual stimuli. Slow stimulus drifts did not activate these neurons. Response latencies were shorter and peak activities were increased during saccades compared with pure visual stimulation. No systematic correlation between response latency, response duration, or the number of spikes in the response and saccade direction, saccade amplitude, or saccade duration was found. Saccades and rapid stimulus shifts in the light also activated jerk cells but not retinal slip cells. 4. All 27 antidromically activated neurons also responded to spontaneous saccadic eye movements in complete darkness. Responses to saccades in the dark, however, had longer response latencies and lower peak activities than responses to saccades in light. As in the light, response parameters in darkness seemed not to code specific saccade parameters. Cells that were not activated from LGNd were found to be unresponsive to saccades in the dark. 5. According to their specific activation by saccades in darkness, LGNd-projecting pretectal neurons are termed "saccade neurons" to distinguish them from other pretectal cell populations, in particular from jerk neurons, which show similar response properties in light. 6. The saccade-related activation of pretectal saccade neurons may be used to modulate visual responses of LGNd relay cells following saccadic eye movements. Because the pretectogeniculate projection in cat most likely is GABAergic and terminates on inhibitory LGNd interneurons, its activation may lead to a saccade-locked disinhibition of relay cells. This input could counter the strong inhibition induced in the LGNd after shifts of gaze direction and lead to a resetting of LGNd cell activity.

Response properties of relay cells in the A-laminae of the cat's dorsal lateral geniculate nucleus after saccades.

Responses of relay cells in the A-laminae of the dorsal lateral geniculate nucleus (LGNd) during spontaneous saccades and saccade-like visual stimulation were extracellularly recorded in awake cats. Ninety-six out of 137 cells recorded (42 X and 54 Y cells) were responsive during spontaneous saccadic eye movements. All Y cells and 67% of the X cells responded with burst activity, i.e. with either one or two activity peaks during and after saccades. Thirty-three percent of the X cells were inhibited during saccades. Excitatory peaks occurred at mean latencies of 33 ms and 31 ms for X and Y cells, respectively. Comparable burst responses were obtained when retinal image shifts similar to those during saccades were induced by external saccade-like stimulus movements. However, the latencies of excitatory peak activity were significantly longer to external stimuli than to the onsets of saccades. This indicates the existence of an eye movement-related input which activates LGNd relay cells in addition to the visual input. We propose that the pretectogeniculate projection may contribute to the responses of LGNd relay cells following saccadic eye movements via a disinhibitory input and that this input could be involved in intra- and postsaccadic modulations of the transfer of visual signals to visual cortex.

On the origin of eye movement desensitization

Francine Shapiro, the founder of eye movement desensitization therapy (EMD) claims to have serendipitously discovered this technique by experiencing spontaneous saccadic eye movements in response to disturbing thoughts during a walk in the woods. This explanation is difficult to accept because normal saccadic eye movements appear to be physiologically undetectable and are typically triggered by external stimuli. In the present limited study, all subjects failed to elicit any experience of eye movements, thus calling into question how best to interpret Dr. Shapiro's experience and the origin of EMD.

Eye movements modulate activity in hippocampal, parahippocampal, and inferotemporal neurons

1. Inferotemporal, hippocampal, and parahippocampal units were recorded while monkeys were alert (as judged by eye movements) but resting, in both light and dark. 2. Spontaneous saccadic eye movements produced significant changes in unit activity for 108 of 308 cells. This activity is shown to be extraretinal either because it occurred in complete darkness or because of its timing relative to the eye movement. 3. The total saccadic modulation in the ventral temporal lobe is estimated to be over ten million action potentials.

Oculomotor activities in monkeys with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced syndrome of parkinsonism

In twoMacaca rhesus monkeys that received repeated N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injections (single dose 0.2 mg/kg, i.m.; cumulative dose 11.2–13.3 mg), changes in characteristics of spontaneous saccadic eye movements and vestibulo-ocular reflex (VOR) were evaluated. With the development of severe behavioral disturbances, amplitude of spontaneous saccadic eye movements gradually decreased. Pronounced changes in duration of saccadic eye movements, frequency of spontaneous saccades, and their pattern were observed. No changes in parameters of VOR slow component were recorded, but high total MPTP doses suppressed fast phase of the reflex.

Monkey superior colliculus represents rapid eye movements in a two-dimensional motor map.

1. Although the eye has three rotational degrees of freedom, eye positions, during fixations, saccades, and smooth pursuit, with the head stationary and upright, are constrained to a plane by Listing's law. We investigated whether Listing's law for rapid eye movements is implemented at the level of the deeper layers of the superior colliculus (SC). 2. In three alert rhesus monkeys we tested whether the saccadic motor map of the SC is two dimensional, representing oculocentric target vectors (the vector or V-model), or three dimensional, representing the coordinates of the rotation of the eye from initial to final position (the quaternion or Q-model). 3. Monkeys made spontaneous saccadic eye movements both in the light and in the dark. They were also rotated about various axes to evoke quick phases of vestibular nystagmus, which have three degrees of freedom. Eye positions were measured in three dimensions with the magnetic search coil technique. 4. While the monkey made spontaneous eye movements, we electrically stimulated the deeper layers of the SC and elicited saccades from a wide range of initial positions. According to the Q-model, the torsional component of eye position after stimulation should be uniquely related to saccade onset position. However, stimulation at 110 sites induced no eye torsion, in line with the prediction of the V-model. 5. Activity of saccade-related burst neurons in the deeper layers of the SC was analyzed during rapid eye movements in three dimensions. No systematic eye-position dependence of the movement fields, as predicted by the Q-model, could be detected for these cells. Instead, the data fitted closely the predictions made by the V-model. 6. In two monkeys, both SC were reversibly inactivated by symmetrical bilateral injections of muscimol. The frequency of spontaneous saccades in the light decreased dramatically. Although the remaining spontaneous saccades were slow, Listing's law was still obeyed, both during fixations and saccadic gaze shifts. In the dark, vestibularly elicited fast phases of nystagmus could still be generated in three dimensions. Although the fastest quick phases of horizontal and vertical nystagmus were slower by about a factor of 1.5, those of torsional quick phases were unaffected. 7. On the basis of the electrical stimulation data and the properties revealed by the movement field analysis, we conclude that the collicular motor map is two dimensional. The reversible inactivation results suggest that the SC is not the site where three-dimensional fast phases of vestibular nystagmus are generated.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in optokinetic and vestibular ocular reflex performance in teleosts and their relationship to different life styles.

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10-15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and per-/postrotatory nystagmus lasted about 10-12 s in the goldfish, but only 2-3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a 'goldfish-like' response pattern as well. Ostariophysan species differed in their reflex performance as well. A 'goldfish-like' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Eye movement-related neurons in the red nucleus

Extracellular unit activity of the parvocellular red nucleus (RN) and spontaneous horizontal eye movements were recorded in adult, nitrous oxide-anesthetized and C 1 transected cats. It was found that 7.5% of the neurons of each RN were related to spontaneous horizontal saccadic eye movements. Three types of neurons were observed: (1) bidirectional neurons which increased their frequency of discharge in relation to any horizontal eye movement; (2) unidirectional neurons which altered their frequency of discharge in relation to a horizontal eye movement of a precise direction; and (3) neurons which increased their frequency of discharge in relation to the rapid phase of an horizontal nystagmus. These 3 types of neurons modified their frequency of discharge before the initiation of the eye movement. One pair of oculomotor neurons recorded simultaneously in both RN showed a significant correlation coefficient. These results suggest that the RN may contribute to the preparation or execution of horizontal eye movements.

Saccadic reaction times, eye-arm coordination and spontaneous eye movements in normal and MPTP- treated monkeys

The oculomotor performance of monkeys was investigated before and after destruction of nigrostriatal dopamine neurons by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Stimulus-triggered saccades and their relationships to arm movements were measured in a reaction time task. Spontaneous eye movements were recorded while monkeys sat in a primate chair and looked around the laboratory without performing any task. In the reaction time task, saccades and arm movements were commonly triggered by the rapid, visible and audible opening of a small food-containing box which was located at a constant position in front of the animal at eye level. Median saccadic latencies ranged from 68 to 118 ms in intact animals. Saccades were followed by onset of electromyographic (EMG) activity in the extensor digitorum communis and the biceps brachii, the prime mover muscles for the following arm reaching movement. Latencies of stimulus-triggered saccades showed an absence of linear relationship to EMG or arm movement reaction time in intact animals (correlation coefficients of 0.15-0.56). This suggests that eye and arm movements were initiated independently from each other in this experimental situation. Treatment with MPTP resulted in 98-99.5% loss of striatal dopamine in both monkeys. This induced a 29-93% increase in saccadic latency in the reaction time task. The sequential occurrence of saccade, EMG activity and arm movement in each trial was preserved, although intervals between onset of saccades and onsets of EMGs and arm movements were prolonged by 53-173% and 33-679% respectively. Onsets of individual saccades remained uncorrelated with onsets of EMG activity or arm movement. Spontaneous eye movements were strongly reduced in frequency and amplitude after MPTP. Administration of the dopamine precursor L-Dopa increased spontaneous eye movements for less than two hours. The severe deficits in stimulus-triggered and spontaneous saccadic eye movements are oculomotor components of hypokinesia arising after MPTP-induced lesions of the nigrostriatal dopamine system in primates. The data are further evidence for a role of midbrain dopamine neurons in behavioral responsiveness and spontaneous activity.

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.

Retinotopic organization of extra-retinal saccade-related input to the visual cortex in the cat.

Single unit activity of 842 cells has been recorded in cat visual cortex and analyzed with respect to vestibular induced, and spontaneous saccadic eye movements performed in the dark. This study has been done in awake, chronically implanted cats, subsequently placed in "acute" conditions to achieve the precise retinotopic mapping of the cortical areas previously investigated. In areas 17 and 18, respectively, 27% and 24% of the cells tested were influenced by horizontal saccadic eye movements in the dark (E.M. cells). In the Clare-Bishop area, the proportion of E.M. cells was 12%, while only 2% of such cells were found in areas 19 and 21. The distribution of E.M. cells in areas 17 and 18 with respect to retinotopy showed that E.M. cells were more numerous in the cortical zones devoted to the representation of the area centralis (38% in area 17, 27% in area 18) than in the zones subserving the periphery of the visual field (17% and 12%, respectively). Two of the characteristics of E.M. cell activations appear dependent on the retinotopic organization. First, larger number of E.M. cells presenting an asymmetry in their responses to horizontal saccadic eye movements in opposite directions (directional E.M. cells) were encountered in the cortical representation of the peripheral visual field. 53% of E.M. cells recorded in area 17 and 71% in area 18 were directional in the cortex corresponding to the peripheral visual field. This percentage was of 23% and 25% respectively in the cortex devoted to area centralis. Second, E.M. cells were found to have a latency from the onset of the saccade systematically larger than 100 ms (i.e., they discharged at, or after the end of the eye movement) if they were located in the cortical representation of the area centralis, while E.M. cells related to the peripheral visual field displayed a wider range of latencies (0-240 ms). Results obtained in Clare Bishop area, although limited to the representation of the peripheral visual field, were quantitatively and qualitatively similar to those observed in the homologous retinotopic zones of areas 17 and 18. It is concluded that an extra-retinal input related to oculomotor activity is sent to the cat visual cortex and is organized, at least in areas 17 and 18, with respect to the retinotopic representation of the visual field. These data support the hypothesis of a functional duality between central and peripheral vision and are discussed in the context of visual-oculomotor integration.

Simple spike activity of Purkinje cells in the posterior vermis of awake cats during spontaneous saccadic eye movements

Extracellular recordings were made from 151 cerebellar cortical cells in the posterior vermis of 12 awake cats. Thirty-two percent ( n=48) of these cells modulated their activity with respect to the onset of spontaneous saccadic eye movements. Thirty-five cells in this group were positively identified as Purkinje cells and manifested changes in simple spike activity that were related to saccade onset. These included short excitatory, inhibitory, or biphasic changes that were superimposed on background tonic firing rates ( avg.=54 spikes/sec). Such changes were recorded before as well as after the onset of a saccade. Sixty-five percent ( n=22) of these cells were related to horizontal and vertical saccades in more than one direction of motion. These cells were randomly distributed throughout the posterior vermis and manifested no anatomical topographic organization with respect to the direction of saccadic eye movement. The results of this study suggest that lobules VI and VII of the cerebellar vermis participate in both the initiation and execution of spontaneous saccades in preferred directions.