Biomedical subjects

J Overduin

Publications and source records attributed to J Overduin.

6 recordsLinked to original sources

PubMed2001

Problems of modern cosmology: how dominant is the vacuum?

It would be hard to find a cosmologist today who does not believe that the vast bulk of the Universe (95% or more) is hidden from our eyes. We review the evidence for this remarkable consensus, and for the latest proposal, that the mysterious dark matter consists of as many as four separate ingredients: baryons, massive neutrinos, new "exotic" dark matter particles, and vacuum energy, also known as the cosmological constant (lambda). Of these, only baryons fit within standard theoretical physics; the others, if their existence is confirmed, will mean rewriting textbooks. Fresh experimental evidence has recently appeared for and against all four components, so that the subject is in a state of turmoil and excitement. The past 3 years in particular have seen the fourth (vacuum) component come into new prominence, largely at the expense of the third (exotic dark matter). We conclude our review by exploring the possibility that the energy density of the vacuum is in fact so dominant as to leave little room for significant amounts of exotic dark matter.

Astronomy↗

PubMed2001

Matter, spacetime and the vacuum.

We distinguish three historical and scientific views of matter, spacetime, and the relationship between them: the absolute approach of Newton, the relational approach most often associated with Mach, and a third, geometrical approach which inspired Einstein and continues to drive efforts toward a unified theory of fundamental interactions today. Which is correct? We suggest that this is, to a large extent, an "ill-posed question," reminiscent of the wave/particle debate in earlier times. The boundary between matter and spacetime is no longer easy to draw, and it is likely that they are complementary aspects of the same reality. There is no clearer illustration of this than the modern view of the vacuum. We review the importance of this concept in cosmology, and explore the extent to which the old idea of an "empty" vacuum might still be maintained. If the real cosmological vacuum is far from empty, as observations now suggest, then it may be possible to achieve an even simpler goal: a Universe with a net energy of zero.

Extraterrestrial Environment↗

PubMed1997

Conditioned insulin and blood sugar responses in humans in relation to binge eating.

This study proposed to demonstrate a classically conditioned blood sugar decrease in humans and to clarify its relevance for binge eating. Six conditioning trials were run in healthy females. The conditioned stimulus (CS) was a compound peppermint flavor/fragrance, whereas the unconditioned stimulus (UCS) consisted of 50 g of oral glucose. Control subjects received an aspartame drink as the UCS. Ad lib glucose intake, blood parameters, and subjective craving were monitored before and after conditioning. Results showed that the experimental group failed to show conditioned blood sugar and glucagon decreases or C-Peptide increases. Although an increased insulin response was found in the experimental group, the effect size did not exceed that of spontaneous fluctuations. No increases in craving for sweet substances were found. An impressive increase (mean: 78%) in glucose intake after conditioning was found in both conditions, as well as in a subsequently run third condition with plain water as the UCS. The increased glucose intake probably resulted from an initial neophobia to the laboratory setting that subsided as subjects had experienced more lab sessions. Importantly, because no conditioned hypoglycemia occurred in the present study, its relationship with subjectively experienced craving for sweet substance could not be determined.

Adolescent↗

PubMed1995

Stroop interference and food intake.

OBJECTIVE: The Stroop task is aimed at assessing attentional bias. Words are displayed one by one on a computer screen and subjects are instructed to name the color in which every word is printed. The attentional bias is supposed to be reflected in the extent to which the word meanings interfere with the speed of color naming: The longer the color naming latency, the larger the attentional bias. Experiments using this task have demonstrated attentional bias for eating and body shape-related words in bulimic, anorexic, and restrained subjects. Explanations of these results have generally been formulated in terms of restricted food intake or emotional concerns about food and body shape-related themes. In contrast, in the present article it was proposed that Stroop interference might reflect a tendency either to withdraw or approach food or body shape-related stimuli. METHOD: Fifty-one subjects (25 unrestrained, 26 restrained) were administered a Stroop task containing neutral, food, and body shape-related words. There were two conditions to which subjects were randomly allocated: the "appetizer" and "no-appetizer" condition. The appetizer was a bit of pudding to be ingested by the subject just before the Stroop task. Following the Stroop task an ice cream taste test was presented in which the subjects were allowed to eat as much as they liked. The amount of ice cream eaten was registered secretly. RESULTS: The results show that in unrestrained subjects Stroop interference for food words was found only in the appetizer condition. Restrained subjects, however, showed a permanent interference for food words. A significant correlation of .58 between Stroop food-word interference and ice cream intake was found only in unrestrained subjects. In restrained eaters the correlation was near 0. No effect of condition or restraint was found on Stroop body shape-word interference. DISCUSSION: The findings indicate that (1) ingestion of an appetizer seems to have evoked an attentional bias for food words in nonrestraints that correlated with food intake; (2) restrained eaters showed continuous attentional bias. This appears to support the urge-to-act explanation of Stroop interference. The lack of correlation between restraints' attentional bias and ad lib food intake could have been caused by inhibition of approach which is one of the characteristics of restrained eating: The present procedure seems not to have triggered disinhibited eating in these subjects. Among other things it is concluded that Stroop interference, as a measure of "craving" triggered by food cue, might be a useful aid in assessing the risk of relapse in treated binge eating patients.

Anorexia Nervosa↗

PubMedDate not supplied

Introduction and commentary to: M.I. Mityushov (1954) "Conditioned reflex secretion of insulin".

Recent research on the role of classical conditioning in homeostatic regulation (Dworkin, 1993; Siegel, Krank & Hinson, 1987) has underscored the potential importance of the work of earlier Eastern-European work on physiological conditioning. The present article is a translation and discussion of a paper on blood glucose conditioning, first published in 1954 by the Russian physiologist M.I. Mityushov. Mityushov was able to demonstrate conditioned hypoglycemia in humans and dogs after using an injection procedure as the CS and intravenous glucose as the UCS. The translation is preceded by a general introduction and followed by a reanalysis and discussion of Mityushov's results.

Animals↗

PubMedDate not supplied

Cue reactivity to food- and body-related stimuli in restrained and unrestrained eaters.

In the present study, psychophysiological cue reactivity was monitored in 11 restrained (nonclinical but disinhibitive) and 13 unrestrained (control) subjects. The cues consisted of slides depicting either personally "favourite" binge food items or the subject's own body. The parameters monitored included skin conductance, heart rate, startle eyeblink EMG, and facial (corrugator and zygomatic) EMG. Although for several parameters the expected main effect of slide type was found, no between-group differences in cue reactivity could be demonstrated. Several explanations of the present finding, as well as possible future directions for cue reactivity research, are discussed, with emphasis placed upon the role of classical conditioning in eating disorders.

Adult↗