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L M Chalupa

Publications and source records attributed to L M Chalupa.

At least 91 records · Page 5Linked to original sources
PubMed1978

Functional properties of the corticotectal projection in the golden hamster.

Approximately 31% of the cells recorded in the hamster's superior colliculus could be activated by stimulation of the ipsilateral primary visual cortex. While cortically activated cells were encountered in all laminae of the colliculus where visual cells were isolated, the highest probability of driving visual cells was observed in the deeper laminae, that is, those ventral to the stratum opticum. Response latency, jitter (latency variability), latency shifts as a function of shock intensity, thresholds, and spike numbers did not vary as a function of depth in the colliculus. There was a clear correspondence between the visual fields of the best cortical stimulus points and the receptive fields of cortically activated cells recorded in the superficial laminae of the colliculus. However, there was considerably less retinotopic fidelity for the cortical areas from which cells isolated in the deeper laminae could be driven. This suggests a greater degree of convergence from relatively widespread cortical regions upon visual cells of the deeper laminae. The visal organization) of the cortically activated cells did not differ appreciably from the overall sample of visual cells recorded in the colliculus. Only 3 of the 159 cells tested were driven by stimulation of the contralateral visual cortex and two of these were responsive only at very long latencies.

Animals↗
PubMed1978

Directional selectivity in hamster superior colliculus is modified by strobe-rearing but not by dark-rearing.

Visual response properties of superior collicular neurons of normal hamsters were compared with those of animals reared from birth to adulthood in either total darkness or with stroboscopic illumination. Directional selectivity was markedly reduced only in the strobe-reared animals, thus demonstrating visual plasticity in a system that develops apparently normally without visual experience.

Action Potentials↗
PubMed1978

Receptive field characteristics of superior colliculus neurons and visually guided behavior in dark-reared hamsters.

Visual response properties of single neurons in the superior colliculus of golden hamsters reared from birth to adulthood in total darkness were compared to those of normal hamsters. Directional selectivity, speed preferences, and receptive field organization in dark-reared hamsters were essentially the same as those found in normally reared animals. Subtle neurophysiological effects of visual deprivation were indicated by the longer latencies of "on" responses to flashed spots of light in the dark-reared animals. Also, in the visually deprived animals three cells were encountered which changed their responses from phasic to tonic as the size of the visual stimulus was increased. In normally reared animals all cells responding to stationary stimuli showed only phasic responses regardless of spot size. Behaviorally, dark-reared animals could not be distinguished from normal animals on the basis of visual orienting and following tests. It was concluded that in the golden hamster visual experience during development has a minimal role in the induction or maintenance of the normal functional development of the superior colliculus.

Animals↗
PubMed1978

Modification of visual response properties in the superior colliculus of the golden hamster following stroboscopic rearing.

1. Visual response properties of superior collicular neurones were investigated in golden hamsters reared from birth to adulthood in a stroboscopic environment.2. In comparison to normally reared animals, there was a marked decrease in the incidence of directionally selective cells in the colliculus of the strobe-reared hamsters. This effect was apparent when directional selectivity was determined by either the null criterion or a statistical measure. The reduction in directionally selective cells was found in both superficial and the deep layers of the colliculus.3. Neurones in strobe-reared hamsters also exhibited a different speed preference distribution from that obtained for normal animals, in that more cells in the restricted hamsters responded only to slow velocities, and less were broadly tuned with regard to the speed of moving stimuli.4. In addition to the effects obtained in dynamic response properties, there were also changes in the static response properties of superior collicular neurones. These were an increase in the proportion of cells whose responses were not affected by changing the size of a stationary flashed stimulus, and a concomitant decrease in the number of cells demonstrating either partial or complete suppression when the size of a flashed stimulus exceeded the boundaries of the receptive field activating region. Furthermore, while all cells which responded to stationary stimuli in normal animals yielded only phasic responses to stimulus onset and/or offset, in the strobe-reared hamsters eight cells were encountered which responded in a sustained fashion to stationary spots.5. There was no indication of an increased responsivity in the restricted animals to strobe stimulation, even when a strobe rate identical to that employed in the rearing environment was employed.6. The results were interpreted as indicating a disruption of normal visual functional organization in the hamster's superior colliculus by an aberrant visual input during development.

Action Potentials↗
PubMed1978

Functional and anatomical consequences of neonatal visual cortical damage in superior colliculus of the golden hamster.

1. In normal hamsters the visual cortex sends a retinotopically organized projection to the ipsilateral superior colliculus. 2. Acute or chronic unilateral ablations of visual cortex in adult animals decrease the incidence of directionally selective cells encountered in the superficial laminae of the ipsilateral colliculus, but not in the deeper layers (those ventral to the stratum opticum). 3. Unilateral ablations of visual cortex in infant hamsters induce an aberrant crossed projection to the contralateral superior colliculus, confirming the finding of Mustari and Lund (58) in the rat. Horseradish peroxidase (HRP) experiments demonstrated that the cells whose axons comprise the normal as well as the anomalous projection are pyramidal neurons in layer V of cortex. 4. In adult hamsters that underwent early brain damage, about 13% of the cells in the colliculus could be activated by stimulation of the contralateral visual cortex. Only 1 unit (of the 159 cells tested) could be driven by similar stimulation in normal adult hamsters. This indicates that the anomalous crossed projection forms functional synapses in the contralateral tectum. 5. No cells (of the 113 tested) could be activated from the contralateral cortex in hamsters that sustained chronic ablations of visual cortex in adulthood; thus indicating that there is some limited time period during development when unilateral ablations of visual cortex induce an anomalous corticotectal pathway. 6. The visual response properties of superior collicular neurons in the neonatally brain-damaged animals were compared to those of normal hamsters, as well as to those with acute or chronic ablations of visual cortex sustained in adulthood. 7. There was no indication that the anomalous projection contributes to the organization of normal visual response properties in the superior colliculus of the neonatally brain-damaged animals. In fact, the incidence of directionally selective cells in these hamsters was found to be significantly lower than that of normals in both the superficial and deep laminae of the colliculus. 8. We conclude that while unilateral damage of visual cortex in the hamster induces an anomalous corticotectal projection that makes functional synapses, this aberrant input does not compensate for missing, normal corticotectal pathway in the organization of superior collicular response properties.

Animals↗
PubMed1977

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.

Action Potentials↗
PubMed1976

Cortical and subcortical visual evoked potential correlates of reaction time in monkeys.

The relationships between reaction time (RT) and evoked potentials were investigated in three monkeys (Macaca nemestrina) during the performance of a simultaneous brightness discrimination task. Evoked potentials from the lateral geniculate, medial and inferior pulvinar, midbrain reticular formation, hippocampus, and striate and prestriate cortex were recorded concurrently with RT in response to the discriminative stimuli. An early component of the geniculate response and a late positive wave in striate cortex were found to be related systematically to RT. These components were largest for short RTs and diminished progressively in amplitude as RT lengthened. The statistical significance of these relationships was supported by a detailed analysis of single trials. The increases in amplitude of evoked potentials associated with short RTs were attributed to increased arousal level and were discussed in terms of reticular formation modulation of central excitability levels.

Animals↗
PubMed1976

Effect of pulvinar lesions on visual pattern discrimination in monkeys.

This study compares the performance (percent correct responses and reaction times) of three unoperated control monkeys with the postoperative performance of eight monkeys with pulvinar lesions, either inferior pulvinar or medial and lateral pulvinar, on a tachistoscopically presented visual pattern-discrimination task highly demanding of attention. To further emphasize and assess the attentional factor in visual pattern discrimination, all monkeys who attained criterion performance (90% correct response on three consecutive sessions of 100 trials each) were tested for the effects of visually distracting interference stimuli added to the original discriminative stimuli. In addition, retention of postoperatively learned discriminations was tested after a 6-wk interval withou training and compared with the performance of control monkeys. Four monkeys with only inferior pulvinar lesions and one monkey with inferior pulvinar plus medial and lateral pulvinar lesions were markedly impaired in the postoperative learning of a visual pattern discrimination. Three of these monkeys failed to acquire criterion perfromance in 9,000 or more training trials, while two learned to ceiterion level only after prolonged training (7,400 and 6,900 trials). In contrast, monkeys with medial and lateral pulvinar lesions showed no deficit in learning ability compared to unoperated control monkeys. Furthermore, the performance of the two monkeys with inferior pulvinar lesions, who attained the criterion level of learning only with difficulty, was further impaired by the addition of distracting interference stimuli, where the performance of monkeys with medial and lateral pulvinar lesions as well as the control monkeys was only temporarily disrupted by this procedure. None of the monkeys with pulvinar lesions, who were tested for retention of the postoperatively learned discrimination, showed appreciable deficits in comparison to control monkeys. All monkeys, including controls and those uith pulvinar lesions who were able to learn the visual pattern discrimination, showed a common pattern of reaction time (RT) change during the course of the learning; that is, RT was low during change-level performance, increased during learning, and decreased once criterion performance was achieved. Reaction times of monkeys with inferior pulvinar lesions tended to be longer than for controls or for those with medial and lateral pulvinar lesions. These results provide the first behavior evidence that the inferior pulvinar of monkeys is involved in visual pattern discrimination and add further support to the concept of a second visual system in which the inferior pulvinar plays a role. The attentional aspects of the visual pattern-discrimination task employed in this study and the additional effects obtained with distracting stimuli suggest that the impairments arising from inferior pulvinar lesions may be dependent in part on visual attentional factors.

Acoustic Stimulation↗
PubMed1975

Response plasticity of lateral geniculate neurons during and after pairing of auditory and visual stimuli.

Neurons of the lateral geniculate nucleus, responsive only to visual stimulation, show response plasticity during and after pairing of auditory and visual stimuli. Modal response histograms reveal a gradual decrement in the number of spikes at interstimulus pairing intervals of 0 and 100 milliseconds but not 500 milliseconds. This plasticity effect, limited to tonic units, may persist for 2 to 3 minutes after termination of click-flash pairing.

Action Potentials↗