PubMed Health⌕ Search

Biomedical subjects

G I Collins

Publications and source records attributed to G I Collins.

9 recordsLinked to original sources
PubMed1984

Electrophysiological aspects of benzodiazepine antagonists, Ro 15-1788 and Ro 15-3505.

The comparative action of two specific benzodiazepine antagonists, Ro 15-1788 and Ro 15-3505 was examined in six healthy volunteers. Medication was given i.v. in a double-blind cross over pattern, and EEG was recorded throughout each experimental session. Ten minutes after the injection of one of the antagonists or placebo, midazolam was injected in incremental doses until first signs of drowsiness appeared in the EEG. The EEG was computer analyzed, using adaptive segmentation and time-dependent clustering. Continuous power profiles for various frequency bands, as well as power ratios for the physiological frequency bands (e.g. sigma/alpha power ratio) were generated. It has been found that sigma/alpha power ratio was the most sensitive parameter detecting early effects of midazolam on the EEG signal, thus enabling a semi-quantitative titration of the antagonists by midazolam. Ro 15-1788 in doses of 5 mg i.v. was counteracted on average by 7.3 mg midazolam. From the EEG analysis it has been found that Ro 15-3505 was at least 4-5 times more potent than Ro 15-1788.

Adult↗
PubMed1979

Alteration by enflurane of Electrophysiologic correlates of search in short-term memory.

Effects of controlled subanesthetic concentrations of enflurane on short-term memory functions and associated scalp evoked potentials were studied in eight male volunteers. Short-term memory processes were assessed through a search task. A series of digits (one, three, five, seven, nine, or 11 digits in each series) was presented visually, followed by a test digit, which in half of the trials was part of the series, and in half of the trials was not. The subject responded by pressing one of two switches, signalling "yes" or "no" accordingly. Averaged evoked potentials elicited by the test digit were obtained from seven sites on the scalp. End-tidal enflurane concentrations between 0.12 and 0.25 per cent increased significantly by 30-40 msec the latency of the components of the evoked potentials reflecting sensory processing, but did not affect their amplitude significantly. This increase could not explain the 287-msec increase in reaction time. Amplitude of late components of the averaged potential reflecting information processing was markedly decreased, which the authors interpret as indicating increased trial-to-trial variation in latency of the late component. The authors conclude that enflurane delays and introduces variance into the short-term memory processes and subsequent decision processes that preced overt responses.

Adult↗
PubMed1978

Late components of the visual evoked potential to search in short-term memory.

The present paper investigated the changes in the morphology of the VEP as a function of the amount of search in short-term memory. The task required that the subject responds with a "yes" or "no", depending on whether a test digit has been part of a set of digits he had just seen. Six sizes of sets were used, 1, 3, 5, 7, 9 and 11. EEG was recorded from C3, C4, T3, T4, Cz, Pz and Oz, and sampled every 4 msec to obtain VEP to the test digit. Two late components were found to increase in latency with increasing set size: (a) P270, which was masked by the P350 component for small set sizes; it preceded P350 for longer memory sets and its latency increased up to set 7 with an average slope of 20.5 msec per item and (b) P350, which increased in latency up to set size 7 with an average slope of 22 msec per item. It was suggested that P270 reflects the serial search process. When search is terminated another general processor is called into action. This process is reflected in the P300 and is believed to be independent of the memory set size. Amplitude did not correlate with the amount of search. The morphology of the VEP changed for sets above short-terms span, and latency changes in P270 and P350 no longer predicted RT changes. Since subject's strategy was not controlled for supra-span sets, no definite conclusions were offered.

Adult↗
PubMed1978

Decision-making behaviour during inhalation of subanaesthetic concentrations of enflurane.

The effect of subanaesthetic concentrations of enflurane on decision-making behaviour in risk situations was assessed using a signal detection task. The subject heard noise alone (white noise) or a signal superimposed on the noise (1000-Hz tone) and had to report what he heard in each trial. Risk situations were manipulated by changing the monetary reward and penalty associated with correct and incorrect responses. Eight male volunteers participated in this study. It was found that under anaesthetic influence they did not avoid the same risks which had been avoided under control conditions. The findings are explained in terms of influence of the gas on loss of control and lessened responsibility for the result of behaviour.

Adult↗
PubMed1978

Effects of low concentrations of enflurane on probability learning.

The effects of controlled subanaesthetic concentrations of enflurane on learning behaviour and on ability to change previously developed decision strategies were studied in 10 male volunteers, using a probability learning task. Subjects were instructed to predict on each of 200 consecutive trials, whether a left or a right light would appear. The appearance of lights was pre-determined by a set relative frequency unknown to the subject. The relative frequency was automatically changed at the end of the first 100 trials, from 8/10 lights in the left side to 4/10. It was found that enflurane at subanaesthetic concentration of 0.25% (end-tidal) slowed the rate of learning, and increased the number of trials required for readjusting the prediction strategy to the changed situation.

Adult↗
PubMed1977

Search in short-term memory during inhalation of a general anesthetic in man.

Effects of controlled subanesthetic concentrations of enflurane on short-term memory functions were studied in male volunteers. Short-term memory processes were assessed through a search task: A series of digits, words, or familiar pictures, was visually presented, followed by a test digit which in half the trials was part of the series, and in half of the trials it was not. The subject responded by a press on one of two switches signalling 'yes' or 'no' accordingly. Memory set size varied between 1 to 11 for digits and 1 to 8 for words and pictures. Enflurane in air was delivered through a non-rebreathing system. Low concentrations of enflurane did not change the slope of the search function, but increased the intercept by few hundred milliseconds. This was interpreted to indicate anesthetic effect on the cognitive processes reflected in the intercept, that is, stimulus reception and evaluation and response variables. No effect was observed on retrieval time from the short-term store.

Adult↗