Alterations in visual receptive fields in the superior colliculus induced by amphetamine

Visual response properties were examined in the superficial layers of the superior colliculus (SC) of anesthetized, paralyzed cats before and after i.v. administration of d-amphetamine. Receptive fields (RFs) of single SC units were plotted using small spots of light presented to the contralateral eye. Within the first hour following d-amphetamine injections, RF size gradually increased, reaching a maximum 86 min post-injection. On average, the area of the RF increased by 5.6 times and RF expansion was observed in all single units examined in the superficial layers. Over the subsequent 4-8 h following the injection, RF area gradually decreased and returned to control dimensions. Most RFs displayed asymmetrical patterns of expansion, showing relatively more horizontal than vertical growth. As RF expansion developed, responses to stimuli flashed "on" and "off" at various locations both inside and outside the borders of the control RF became progressively more vigorous. In contrast, no significant changes were noted in direction-selective responses at any time after d-amphetamine injections. Using an array of light bar stimuli of different lengths, the strength of surround suppression was found to be significantly diminished by d-amphetamine. The reduction in surround suppression was especially clear for bar lengths which exceeded the diameter of the control RF. No RF expansion was observed in the superficial layers of the SC when d-amphetamine was injected intravitreally. Furthermore, d-amphetamine had no discernable effect on the RF sizes of cells in the visual cortex. These results suggest that the RF changes in the SC were not of either retinal or cortical origin. We conclude that the mean retinal area which can potentially influence the activity of RFs in the superficial layers of the SC may be on average over 5 times greater than the RF area determined using conventional methods and criteria. These findings raise the interesting possibility that the relatively small size and sharp borders characteristic of RFs in the superficial layers arise from local inhibitory networks which delimit a broader field of excitatory activity supplied by retinal and cortical afferent terminals. Thus, in order to generate the RF changes observed here, either these local inhibitory circuits are amphetamine sensitive, or more likely, these inhibitory networks are dynamically modulated by an, as yet unidentified, amphetamine-sensitive input affecting visual RFs in the superficial layers.     

Serotonin, the superior colliculus, and grooming behavior in cats with neocortical lesions.

Previous studies of cats with pontile lesions indicate that a serotonergic deficit exists in the superior colliculi and that this deficit is involved in an abnormal grooming behavior. Cats with frontal neocortical lesions exhibit the same serotonergic deficit and abnormal grooming behavior. The present study with 20 male cats established that the serotonergic deficit is involved in mediation of the abnormal grooming behavior in cats with frontal neocortical lesions. Microinjections of 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT) into the superior colliculi abolished or significantly reduced the abnormal behavior in Ss with frontal neocortical lesions, whereas no effects of 5-HTP were observed after injections into the superior colliculi, into the tegmentum beneath the superior colliculi, or into the medial dorsal nucleus rostral to the superior colliculi. Tryptophan, noradrenaline, and gamma-aminobutyric acid had no effect on abnormal behavior when injected into the superior colliculi. Evidence implicating a serotonergic deficit in the mediation of abnormal behavior was obtained by systemic injections: The behavior was abolished with 5-HTP in Ss with frontal neocortical lesions and in adrenalectomized Ss previously treated with para-chlorophenylalanine. Findings also demonstrate that the abnormal behavior is induced by frontal neocortical lesions and not by more caudal lesions of the cortex. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A deficit in ambient visual guidance following superior colliculus lesions in rats.

21 male black-hooded rats were tested for their ability to locate a hidden platform in the Morris swimming pool, in which extrapool cues are required to guide locomotion. At the end of each trial, Ss were either removed immediately or allowed to remain on the platform for 60 sec. As in a previous experiment by the present authors (see record 1984-06177-001), bilateral lesions of the superior colliculus (SC) produced a severe deficit. Permitting the Ss to stay on the platform did not significantly affect performance in either Ss with SC lesions or sham-operated controls. Results indicate that the reduced orienting behavior on the platform observed in the rats with lesions in the previous experiment was not the cause of their navigational impairment. It is concluded that the impairment following SC lesions came about during the swimming itself; therefore, it may be attributed to a disturbance of, or a failure to utilize, ambient vision. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Marginal and extramarginal cortical lesions and visual discrimination by cats.

75 mongrel cats learned a shape discrimination with 0, 1, or 2 irrelevant cues. They were then subjected to either sham operations, ablation of the marginal and splenial gyri, or lesions in the extramarginal (EM) cortex. The 32 EM cats comprised 4 groups, 3 with small (EM1), intermediate (EM2), large (EM3) decortications, and a 4th group with both EM lesions and heavy degeneration in the lateral geniculate nucleus (LGN). Ss with marginal or extensive extramarginal lesions were severely impaired in shape and size discrimination. Results show the following: (a) The errors made by marginal gyrus cases increased sharply as a function of the number of irrelevant cues present in shape discrimination training; no other group, including Group EM3, was affected by this variable. (b) Ss with extramarginal ablations and strong LGN degeneration were no more severely impaired than were Ss with comparable extramarginal damage and little or no LGN degeneration. While the nature of the 2 kinds of deficits remains unclear, they seem parallel to those following posterior cortical lesions in monkeys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of superior colliculus lesions on rats' orienting and detection of neglected visual cues.

Superior colliculus lesions generally result in deficit in visual orienting described as sensory neglect. This observation was confirmed in this study: Rats with lesions did not orient to some stimuli that intact rats readily oriented to. However, rats with lesions did orient to stimuli that the intact rats treated as more salient. Also, when the less salient stimuli signaled aversive stimulation, the rats with lesions detected these stimuli. These findings suggest that superior colliculus lesions do not affect the detection of visual stimuli that have been neglected. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of dark-rearing, strobe-rearing and acute visual cortex removal on the visual responses in the superficial superior colliculus of the guinea-pig

The interaction of zinc and vitamin A in rats receiving a regional diet of Manaus, supplemented with vitamin A, zinc and zinc and vitamin A was studied. The regional diet was elaborated according to data of Shrimpton and Giugliano (6), for families receiving less than two minimum salaries. The biological test to study the interaction was based on the depletion of zinc and vitamin A in rats in the period of lactation, and a period of repletion where supplements of zinc (0.82 mg%) and vitamin A (94.2 micrograms %) were given, either separately or together, according to the recommendations of the Committee on Laboratory Animal Diets (7). From the results, it was concluded that there was an interaction of these nutrients in terms of mobilization of hepatic vitamin A. Although the regional diet of Manaus did not meet the zinc RDA, the amount present was enough to utilize the available vitamin A. Although the amount of zinc present in the diet, as determined by parameters of bioavilability, such as growth, concentration in organs and zinc-dependent enzymes, was adequately used by the animals, probably due to promoting factors in the diet. The Manaus regional diet needs to be supplemented with vitamin A in order to maintain the hepatic reserves, and with zinc, to maintain the normal levels of vitamin A in plasma.     

Effect of superior colliculus, striate, and prestriate lesions on visual sampling in rhesus monkeys.

27 male rhesus monkeys were tested for pattern discrimination retention and for color discrimination learning, with and without stimulus-response (S-R) separation, following superior colliculus lesions, partial striate cortex lesions, foveal prestriate lesions, or control lesions involving cortical or subcortical structures. Only the prestriate Ss were reliably impaired in pattern retention and in color discrimination tasks without S-R separation. In color discriminations involving S-R separation, collicular Ss were deficient compared either with the controls or with those with striate lesions. These findings suggest that the primate superior colliculus, like prestriate cortex, is involved in visual sampling behavior required by S-R separation, and thus participates in orientation to visual stimuli. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual sampling after lesions of the superior colliculus in rats.

In 2 experiments with 20 male black-hooded rats, Ss with bilateral lesions of the superior colliculus showed significantly poorer relearning of a horizontal/vertical stripe discrimination than control Ss. In Exp I, all Ss showed disruption of performance when a stimulus–response (S–R) separation was introduced by raising the stimuli above the site of responding. However, colliculectomized Ss were much more disturbed by the S–R separation than were control Ss. In Exp II, all Ss showed lower performance levels when conflicting patterns were introduced into the upper portion of the stimulus doors, but this time Ss with collicular lesions were less disturbed than controls. It is suggested (a) that when the stimulus and response sites are discontinuous, rats must make an appropriate orienting response to effectively sample the visual stimuli and (b) that lesions of the superior colliculus alter performance by interfering with this orienting behavior. The impairment in relearning is attributed to the absence of preoperative overtraining on the discrimination task. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting effects of lateral striate and superior colliculus lesions on visual discrimination performance in rhesus monkeys.

Tested 3 rhesus monkeys with lesions of lateral striate cortex (LSC), 4 monkeys with superior colliculus (SC) lesions, and 3 unoperated monkeys for retention of a preoperatively acquired pattern discrimination. The 3 groups of monkeys were then tested in 2-choice, color discrimination tests, 1 involving varying degrees of stimulus–response (S–R) separation and the other, administered several months later, involving various directions of S–R separation. Ss were also tested in a series of 2-choice pattern discriminations, following each of which they were tested for relearning when the patterns were masked with bars or circles. LSC lesioned Ss were moderately retarded in retention of the pattern discrimination, whereas those with SC lesions were not. SC lesioned Ss, but not those with LSC lesions, were impaired in both S–R separation tests, which demonstrates that their deficit was not transient or solely due to a difficulty in shifting the gaze in 1 direction. The LSC Ss, unlike those with SC lesions, were deficient in relearning discriminations between masked patterns. Findings suggest that SC and LSC may be involved in 2 different aspects of attention, respectively: shifting attention (and orientation) from 1 spatial locus to another and maintaining attention on fixated stimuli. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cellular morphology in the visual layer of the developing rat superior colliculus

Foldback sequences in nuclear DNA from cultured Hamster fibroblasts (BHK-21/C13 cells) have been characterized by electron microscopy. One half of the structures observed when denatured hamster DNA is allowed to anneal in the range O less than Cot1 less than 1 x 10(-4) M sec result from the annealing of inverted sequences forming foldback DNA. The remainder have a probable bimolecular origin. arising from rapidly-annealing sequences of satellite-like complexity. The average length of the inverted sequences in the foldback molecules is about 0.9 kilobases. There is estimated to be about 42,000 such sequences (21,000 pairs) in the hamster genome, approximately 45% of which form looped structures with a mean loop length of 1.74 kilobases. Contrary to previous reports, binding of the renatured duplex molecules to hydroxyapatite results in a poor recovery of structures containing identifiable foldback sequences, due to preferential enrichment of the bound fraction with duplexes formed by intermolecular annealing.     

Alterations in receptive field properties of superior colliculus cells produced by visual cortex ablation in infant and adult cats

To determine if functional alterations in the superior colliculus might account for recovery of visual behaviors following visual cortex removal in infant cats, the receptive field characteristics of single units in the superior colliculus of cats whose visual cortex was removed within the first week of life were compared with those of cats which sustained visual cortex lesions in adulthood and with those of normal cats. In the normal superior colliculus, 90% of all cells responded to moving stimuli irrespective of shape or orientation. Sixty-four percent of these units were directionally selective, responding well to movement in one direction but poorly or not at all to movement in the opposite direction. Ninety percent of units were binocular, the vast majority of these responding equally to stimulation of either eye or showing only slight preference for stimulation of the contralateral eye. Responses to stationary flashes of light were observed in only 33% of all visually activated cells in the normal superior colliculus. After visual cortex ablation in adult cats, only six percent of movement sensitive cells were directionally selective. Binocular preference was shifted following adult visual cortex lesions such that sixty percent of all cells responded exclusively or predominantly to stimulation of the contralateral eye. Seventy-one percent of all visually responsive units responded to stationary lights flashed on or off within their receptive field boundaries. Lesions limited primarily to area 17 had the same effect as larger lesions of visual cortex. Infant visual cortex lesions resulted in receptive field alterations similar to those observed after adult ablation. Only fifteen percent of motion sensitive units were directionally selective. Seventy-one percent responded exclusively or predominantly to stimulation of the contralateral eye. Seventy-six percent of visually responsive cells were activated by stationary light. Lesions largely confined to area 17 produced the same alterations as more extensive lesions of visual cortex. Thus, no evidence was found that the superior colliculus is involved in the functional reorganization presumed to occur following visual cortex ablation in infant cats. Recovery of visual behaviors following neonatal injury may therefore not involve alterations in the receptive fields of single cells.     

Performance on the visual cliff by cats with marginal gyrus lesions

Lesions in 12 cats that destroyed almost all of area 17 (Group MS) abolished differential responding on the visual cliff. Performance was not impaired in 9 cats in which regions of the striate cortex were spared in the depths of the splenial sulcus or in 23 cats with damage to extramarginal areas. There were 37 controls. Additional experiments indicated that the deficit in performance by MS cats was not reduced either by the administration of amphetamine or by increases in cues for motion parallax. Monocularly occluded normal cats preferred the shallow surface of the visual cliff, demonstrating that the deficit was not due solely to removal of neurons sensitive to binocular disparity. The findings were discussed in light of electrophysiological evidence that lesions of the visual cortex disrupt functions of the superior colliculus.     

Further analysis of S-R separation effects on visual discrimination performance on normal rhesus monkeys and monkeys with superior colliculus lesions.

Tested the orientation and attention hypotheses by requiring 4 monkeys with superior colliculus lesions and 2 controls to discriminate between stimuli presented in different parts of the visual field, at durations either too brief or sufficiently long to permit fixation. Findings indicate that before the lesions, Ss discriminated between 2 color-differentiated stimuli presented on a screen only when they fixated the center of the screen. The stimuli were presented 8, 20, or 32° from the screen's center, for 2 sec or 100 msec, a duration too brief to permit their fixation. Performance declined when the response sites, located either centrally or peripherally, were separated from the stimuli, whether they were presented for 2 sec or 100 msec. Findings suggest that the stimulus-response separation effect is due to selective attention to the response sites and not to fixating them during stimulus presentation. Following superior colliculus lesions, Ss were impaired in discriminating between peripheral stimuli, but only when they responded centrally. This deficit was not due to a failure to fixate the stimuli, for it occurred when the stimuli were 100 msec or 2 sec, or to reduced sensory capacities, since it disappeared when Ss responded peripherally. It is concluded that this deficit may reflect deficient attentional shifts from the response sites to the stimuli. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional behavior in feral cats with ablations of prefrontal cortex and subsequent lesions in amygdala.

Bilateral ablations of gyrus proreus in 6 cats did not significantly alter either the intensity or the pattern of flight behavior during confrontation with a human. The scores for defense behavior were reduced in only 2 Ss. Subsequent lesions in the rostral part of the basolateral nuclei of amygdala reduced flight and transiently decreased defense scores in all Ss. It is concluded that the prefrontal cortex does not seem necessary for the flight and defense responding observed in feral cats. The role of amygdala in the regulation of these behaviors is confirmed. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microsaccadic response to visual events that are invisible to the superior colliculus.

Even when people think their eyes are still, tiny fixational eye movements, called microsaccades, occur at a rate of –1 Hz. Whenever a new (and potentially dangerous) event takes place in the visual field, the microsaccadic frequency is at first inhibited and then is followed by a rebound before the frequency returns to baseline. It has been suggested that this inhibition-rebound response is a type of oculomotor reflex mediated by the superior colliculus (SC), a midbrain structure involved in saccade programming. The present study investigated microsaccadic responses to visual events that were invisible to the SC; the authors recorded microsaccadic responses to visual oddballs when the latter were equiluminant with respect to the standard stimuli and when both oddballs and standards were equiluminant with respect to the background. Results showed that microsaccadic responses to oddballs and to standards were virtually identical both when the stimuli were visible to the SC and when they were invisible to it. Although the SC may be the generator of microsaccades, this research suggests that the specific fixational oculomotor activity in response to visual events can be controlled by other brain centers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reinstatement of orienting behavior by d-amphetamine in rats with superior colliculus lesions.

Assessed the involvement of the nigrotectal pathway in the expression of visual orienting behavior by a combination of superior colliculus (SC) lesions and increased dopamine transmission produced by administration of dextroamphetamine (1 mg/kg, intraperitoneally [ip]), using 60 naive male Long-Evans rats. Orienting behavior elicited by apparently moving or stationary light displays, its habituation, and recovery were observed. In intact Ss, amphetamine injections had a small but reliable effect on the habituation of orienting behaviors. Ss with SC lesions did not orient to the lights. Amphetamine-injected Ss with SC lesions did orient, and the topography of their orienting behavior, rate of habituation, and recovery of orienting with changes in the light display were comparable to those of the intact S. Results suggest a view of SC-lesion-impaired orienting behavior as a disturbance of sensory attention and emphasize the interaction of the SC and other neural systems in processes mediating the direction of attention. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination impairments in rhesus monkeys with combined lesions of superior colliculus and striate cortex.

To test the hypothesis that posterior inferotemporal cortex and the adjoining foveal prestriate cortex contribute to vision by combining inputs from striate cortex and superior colliculus, a total of 18 rhesus monkeys with combined collicular and partial striate lesions, foveal prestriate-posterior inferotemporal lesions, or subcortical lesions (controls) were tested in a series of visual discrimination tasks. Prestriate-inferotemporal lesions, unlike striate-collicular lesions, consistently impaired retention of a pattern discrimination and produced partial impairments in a size discrimination test. However, prestriate-inferotemporal and striate-collicular lesions produced similar deficits in pattern discrimination learning and no deficits in brightness discrimination learning. The deficits of the striate-collicular monkeys are discussed with regard to the "input-combining" hypothesis and alternative views. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus

1. The response characteristics of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus were investigated.2. As has been noted for other mammalian species, a distinct difference between the functional organizations of the superficial and deeper layers of the superior colliculus was observed.3. Neurones in the superficial layers were exclusively visual, with small receptive-fields, and generally did not show response decrements with repeated stimulation. The sizes of the receptive-fields did not vary appreciably as a function of retinal eccentricity.4. In the deeper layers, visual receptive-fields were large, or could not be accurately delimited, and response habituation was often evident. In addition, many cells in the deeper layers of the colliculus responded only to somatosensory stimuli. Far fewer cells, which appeared to be confined to the caudal portions of the colliculus, responded to auditory stimuli. Polymodal cells were also encountered.5. Selectivity to opposing directions of movement was tested for ninety-four visual cells. Using a ;null' criterion, 27.7% of these cells were judged to be directionally selective. A distribution of the preferred directions of these cells showed a significant preference for movement with an upper-nasal component. With a statistical criterion, 60.6% of these cells were considered to show a significant asymmetry in responding to movement in opposing directions.6. Directional selectivity was also tested for ninety-two cells following acute, unilateral, lesions of the visual cortex. For the eighty cells recorded, homolateral to the ablated cortex, 27.5% were judged as directionally selective using the statistical criterion, while 12.5% were selective with the ;null' criterion. Of the twelve cells isolated in the colliculus, contralateral to the lesions, seven were judged as directionally selective with the statistical, and three with the ;null' criterion.7. The effects of visual cortical lesions upon directional selectivity appeared to be confined to cells in the superficial layers of the colliculus. It was suggested that directional selectivity of many cells in the superficial layers of the tectum of the hamster is organized cortically.8. A clear spatial correspondence was observed for the receptive-fields of visual, somatosensory, and auditory neurones.9. As has been suggested for other species, the hamster's superior colliculus appears to play an important role in orienting the animal toward visual, somatosensory, and auditory stimuli.