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Biomedical subjects

W Isaac

Publications and source records attributed to W Isaac.

At least 19 recordsLinked to original sources
PubMed1991

The effects of occipital ablation on a conditioned visual avoidance learning task in young and old rats.

Previous data indicate that learning of a conditioned visual avoidance task following simultaneous complete bilateral occipital ablations is affected by the age of the organism as well as the postoperative recovery period. The present study investigated the performance of the avoidance task, following complete occipital ablations, in young and older rats given two different recovery intervals. Young rats given 10 days to recover performed more poorly than the young control animals; given 20 days to recover, young rats performed comparable to controls. Older rats given 10 days to recover performed significantly better than the controls; given 20 days to recover, older rats did not show a decrease in performance. The present finding is consistent with previous data which show that the occipital cortex exerted an inhibitory effect on the learning ability of the avoidance task in older rats, which, upon removal, enhanced the performance of these rats on the task.

Aging↗
PubMed1989

Extracranial and digital vascular events: an analysis of methods in BVP amplitude and biofeedback research.

The purpose of the present study was to assess and compare the effects of within and between-session exposure to environmental context on left temporal artery pulse amplitude, right temporal artery pulse amplitude, and left digital pulse amplitude. Subjects were individually tested for 20 min daily over a period of eight consecutive days. A significant interaction was found for Position X Interval. These results show that exposure to the experimental context occurs with diametrically opposite effects on temporalis and digital pulse amplitude within session. Moreover, these results would support the hypothesis that controversial findings within the headache and biofeedback literature may be partially attributable to methodological differences where, for example, different authors use different transducer locations and/or evaluate pulse amplitude at different points within or among sessions. Indeed, research on the effects or lack thereof of therapeutic manipulations may have little or nothing to do with the intervention or experimental manipulations themselves. These effects may be masked or augmented by subject and methodological confounds during baseline and testing conditions.

Adolescent↗
PubMed1988

Age changes in electrophysiological measures of the superior colliculus and occipital cortex.

Locomotor activity and electrophysiological recordings of the superior colliculus and the occipital cortex were measured for two age groups of rats (100-105 and 230-235 days old) tested in ambient light and dark sensory conditions. Age differences in response to ambient illumination were observed in both behavioral and electrophysiological data. While no age differences were found for the superior colliculus data, cortical activity of the older rats differed from that found in the younger rats. These results are interpreted in terms of potential cortical development and arousal functions.

Aging↗
PubMed1986

Effects of simultaneous vs sequential stimulus presentation on memory performance following temporal lobe resection in humans.

This study examines the differential effects of simultaneous vs sequential stimulus presentation on performance of a visuo-spatial memory task in patients following unilateral temporal lobectomy for relief of complex-partial seizures. Eleven subjects with surgical resection of the left temporal lobe, 13 subjects with surgical resection of the right temporal lobe, and 12 normal controls were examined. Results indicate that both the Right and the Left surgical groups were impaired on the visuo-spatial memory task employed. Further, the Right resection group was significantly more impaired for the recall of stimuli presented in the sequential condition as compared to the simultaneous condition.

Adult↗
PubMed1986

Effects of drugs, age and illumination on response speed of squirrel monkeys.

Four young (2 1/2 years) and four older (over 10 years) squirrel monkeys were used to study age differences in the effects of d-amphetamine, methylphenidate and illumination on response speed. Although young monkeys were faster than the old monkeys, only the older monkeys showed an illumination effect. Both d-amphetamine and methylphenidate slowed response speed but only in the older monkeys showed an illumination illumination was present. These results suggest that older, mature squirrel monkeys are more sensitive to the effects of d-amphetamine, methylphenidate and illumination than young squirrel monkeys.

Age Factors↗
PubMed1984

Disruption and habituation of stable fixed-interval behavior in younger and older monkeys.

Reactivity to novel and irrelevant stimuli has been shown to vary as a function of age. Since differential responsivity to irrelevant events may account for purported age differences on other tasks, the present experiment studied the extent to which these age differences may be reduced with repeated exposure, i.e., habituation. Young (2 to 3 years) and old (15+ years) squirrel monkeys were trained and their performance stabilized over months on a fixed-interval operant task. This behavior was then disrupted by periodic presentations of an auditory stimulus of moderate intensity. Disruption of stable behavior and habituation to the tone stimulus were evaluated across several measures including overall response rates between and within the daily sessions; recovery of baseline response rates during the tone stimulus; and the curvature of the fixed interval "scallop." Old monkeys responded for sweet fruit juice more frequently, but less efficiently, than young monkeys. Their responding was more severely disrupted by intermittent novel auditory stimuli, to which they were slower to habituate.

Acoustic Stimulation↗
PubMed1981

Behavioral and neurochemical interactions of dextroamphetamine and methylphenidate in rats.

The effects of dextroamphetamine and methylphenidate on locomotor activity and brain levels of norepinephrine and dopamine were compared in male Sprague-Dawley rats. Both drugs produced a dose-related increase in locomotor activity during the hour immediately following intraperitoneal administration. However, combined administration of drugs elicited only the effect of dextroamphetamine. Brain levels of norepinephrine and dopamine also increased 1 hr after dextroamphetamine dosing. Methylphenidate did not exhibit these effects and antagonized the neurochemical changes produced by dextroamphetamine. Although both drugs are considered to exert their effects by indirect activation of brain catecholamine systems, differences in their mechanism of action appear to result in a lack of additive or antagonistic effects when dextroamphetamine and methylphenidate are coadministered. These findings may have clinical significance with respect to the use of such agents in minimal brain dysfunction.

Aging↗
PubMed1979

Effects of d-amphetamine and methylphenidate upon auditory threshold in the squirrel monkey.

The effects of d-amphetamine sulfate and methylphenidate hydrochloride on auditory thresholds in ten squirrel monkeys were examined using a 4.2 kHz stimulus in a free field. The results indicated that d-amphetamine raised auditory thresholds but methylphenidate did not alter the thresholds. The elevation of sensory thresholds by d-amphetamine was in agreement with previous studies suggesting that the drug acts as a behavioral depressant in diurnal animals.

Animals↗
PubMed1977

Effects of amphetamine and methylphenidate on fixed-interval responding in the squirrel monkey.

The effects of oral doses of d-amphetamine and methylphenidate on a fixed-interval operant response were studied in four young male squirrel monkeys. A fixed-interval of 80 sec with a limited hold of 20 sec was used. Methylphenidate produced no observable changes in behavior, while d-amphetamine produced dose related changes in both the rate of responding and the temporal patterning of responses. Since dose levels used included, and exceeded, human clinical dosages, the present findings may have implications for future research involving the clinical use of these drugs.

Animals↗
PubMed1977

Differences in placebo effects.

Constant volume injections of water and saline were evaluated in terms of their effects upon locomotor activity in the rat. Both solutions produced an overall decrease in activity and were found to be nonequivalent in their effect.

Animals↗