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Biomedical subjects

L Ganz

Publications and source records attributed to L Ganz.

At least 19 recordsLinked to original sources
PubMed1990

Transfer of immortality by transfection of genomic DNA from SV40 established cell lines into rat embryo fibroblasts.

The cellular immortalization activity of cloned genes can be identified either in a colony-forming assa of transfected primary rat embryo fibroblasts or in a co-operation assay together with ras. However the demonstration of immortalization activities carried by cellular genes has not been reported. Here we establish that SV40 early genes integrated in genomic DNAs can be stably transferred into rat embryo fibroblasts and selected via their immortalization activity. Attempts to extend this assay to the identification of dominant genes putatively involved in the immortality of several other immortal post-crisis or tumor cells have been unsuccessful suggesting that the immortal phenotype can be brought about through different pathways.

Animals↗
PubMed1984

Visual cortical mechanisms responsible for direction selectivity.

We measured the response of some 171 directionally selective (DS) neurons in visual area 17 of the cat. Sequences of long duration (400 msec) stimulus onsets and offsets were employed to analyze the underlying mechanisms. We corroborate the existence of sub-regions of localized, anisotropic inhibition as the basic mechanism of directional tuning. At extremely small and at rather large asynchronies, DS neurons inhibit virtually non-selectively. Optimal directional selectivity occurs when the second response peak of S1 coincides with the first response peak of S2 (usually at an asynchrony of approximately 75 msec). The mechanism appears to involve the linear temporal convolution of impulse response functions.

Animals↗
PubMed1984

Mechanism of directional selectivity in simple neurons of the cat's visual cortex analyzed with stationary flash sequences.

The properties of simple neurons showing selectivity to direction of motion in area 17 of the cat cortex were examined. We analyzed in particular a sample of cells receiving a projection from 0 to 10 degrees in visual angle from the area centralis of the cat retina. Three categories of simple neurons were examined: directionally asymmetric (DA) neurons, directionally selective neurons of the unimodal type (DS1), and bimodal types (DS2). Poststimulus time histograms (PSTH) were obtained to moving white and black bars as well as to static onset sequences and static offset sequences. Our analysis involves a comparison of responses to single static flashes at various receptive-field locations with responses to sequence pairs of static flashes at those same locations. We find that DA neurons are not sensitive to the direction in which a pair of stimuli are presented. Inhibitory and excitatory responses show properties of linear summation whatever the direction of the stimulus sequence. Their behavior is reminiscent of retinal and LGN neurons. The synergy model accounts well for a DA neurons's directional asymmetry. If pairs of stimuli are close enough (usually an interstimulus distance of 20' or less for the central 10 degrees of the cat's visual field), then DS neurons show striking departures from linear summation. Specifically, this departure entails an anisotropic distribution of inhibition. The directional selectivity of DS neurons cannot be explained on the basis of a simple linear combination of their on and off region's responses. Directional selectivity is produced entirely within an on-excitatory discharge region or entirely within an off-excitatory discharge region. The excitatory discharge center of even the simplest unimodal DS neuron can be shown to be decomposable into subunits smaller than that discharge center. The fact that the spread of this anisotropy of inhibition is often much more restricted than the entire extent of the DS neuron's excitatory discharge center argues strongly that underlying subregions or modules are contributing their inputs to DS neurons. A DS neuron does not analyze motion as an isolated unit; to the contrary, it is probably embedded in a pool of mutually "cooperative" DS neurons. The basic module of directional analysis is responsive either to an on-on sequence or an off-off sequence but not to both. It is not selective to an on-off sequence. Therefore, unimodal DS neurons (DS1) are performing an analysis of single moving edges.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Event-related brain potentials to human faces in infants.

Event-related brain potentials (ERPs) in response to tachistoscopically presented photographs of 2 human faces were recorded for 4--7-month-old infants. For each infant 1 face was chosen to be presented frequently (p = .88, a low-information event) and the other infrequently (p = .12, a high-information event). Both types of events elicited in our infants a long-latency negative ERP wave (ca. 700 msec), termed Nc, and a long-latency positive wave (ca. 1,360 msec), termed Pc. We found that the discrepant, infrequently presented face elicited Nc waves which were higher in amplitude and longer in latency than those elicited by the frequent face. These differences suggest that our infants were able to remember the frequently presented face from trial to trial and to discriminate it from the discrepant face. The discrepant event elicited Pc waves which were insignificantly higher in amplitude than those elicited by frequent events. In adults and children, discrepant events have been found by numerous researchers to elicit positive P3 waves (latency ca. 300--800 msec). In our study, however, such waves could not be discerned. So, of all of the ERP waves which have been related to cognitive processes, the wave which is maturationally the earliest to appear is the Nc wave, which has been related to the perception of attention-getting events or events of interest to the subject. Our findings suggest that ERP responses could provide a sensitive means for investigating infant cognitive development since they do not depend upon an integrated motor-response system.

Discrimination Learning↗
PubMed1977

Size constancy in rhesus monkeys: effects of pulvinar, prestriate, and inferotemporal lesions.

The present study tested the theory that inferotemporal cortex integrates 1) distance information transmitted via superior colliculus-pulvinar afferents, with 2) form information transmitted via striate-prestriate cortex afferents (Gross, 1973a, 1973b). Monkeys were trained to choose the larger of two objects, independent of distance, to obtain a reward. Based on the integration theory, the following predictions concerning this size constancy discrimination were made: 1) monkeys with pulvinar lesions, unable to code distance, should be impaired and adopt strategies based on retinal image size; and 2) monkeys with prestriate lesions, unable to code retinal image size, should be impaired and adopt strategies based on distance. Contrary to these predictions, pulvinar lesions produced no deficit; and although prestriate lesions did produce an impairment, it was due to a failure to code distance in assessing the true size of the object. Thus, monkeys with prestriate lesions consistently responded to retinal image size instead of object size. Replicating an earlier report (Humphrey and Weiskrantz, 1969), inferotemporal lesions also produced an impairment; however, errors made by monkeys with inferotemporal lesions were random and could not be attributed to any consistent strategy. All monkeys reacquired the discrimmination postoperatively, indicating that there are multiple mechanisms available to the brain-damaged animal for the perception of size constancy.

Animals↗
PubMed1975

Effects of visual cortex lesions following recovery from monocular deprivation in the cat.

Six monocularly deprived (MD) and four normal cats were trained monocularly on two-choice form and pattern discriminations. MD cats trained through the initially deprived eye were able to learn the discriminations; however, they required many more trials than normals. Retention tests showed that MD cats have nearly perfect retention of the discriminations over periods of up to 4 months. With retention intervals of 6 months or longer, there is a tendency for the MD cats to show an initial drop in performance, particularly on more difficult discriminations. However, criterion performance typically was attained with considerable savings, indicating good retention even over these extended intervals. Following the preoperative training and retention testing, the cats received one of the three types of visual cortex lesions. Two MD cats received total visual cortex removal (areas 17, 18, and 19). This produced a complete postoperative loss of the discriminations with continued chance performance over 800--1000 trials. Two MD cats and two normal cats received removal of the monocular segment of area 17, with the central visual field projection region of area 17 and all of areas 18 and 19 remaining intact. This produced no loss of the discriminations in either normal or MD cats beyond what is expected on the basis of normal forgetting. Two MD cats and two normal cats received removal of areas 18, 19, and the central 5--10 deg. of the visual field projection in area 17. Postoperative retention was somewhat variable for both normal and MD cats. However, subsequent acquisition of the discriminations by both normal and MD cats was in sharp contrast to the prolonged deficits produced by total visual cortex lesions. These results indicate that one or more of visual cortical areas 17, 18, and 19 are involved in the recovery of visual discrimination capacities in MD cats. However, the monocular segment of striate cortex does not appear to be specially involved in this ability, as has been suggested by previous investigations. Possible mechanisms for the recovered visual capacities in MD cats are considered.

Animals↗