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Biomedical subjects

R Epstein

Publications and source records attributed to R Epstein.

At least 19 recordsLinked to original sources
PubMed2002

Shell mix in the compressed core of spherical implosions.

The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be 3.4(+/-1.2) g/cm(3) from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, 3.6(+/-1) g/cm(3), accounts for only approximately 50% of the neutron-burn-averaged electron density, n(e)=2.2(+/-0.4)x10(24) cm(-3).

Journal Article↗
PubMed2001

Long-term sleep disturbances in adolescents after minor head injury.

It has been demonstrated that patients in the acute phase after minor head injury (MHI) complain of sleep disturbances. The purpose of the present study was to characterize the long-term effects of MHI on sleep in adolescents. Nineteen adolescents who had suffered MHI 3 years before the study and had complained of sleep disturbances completed a sleep questionnaire and were investigated in the sleep laboratory by whole-night polysomnographic recordings and were actigraphically monitored for 5 days at home. Questionnaire results revealed severe complaints regarding sleep behavior. Polysomnographic recordings revealed that in comparison with controls, MHI was associated with lower sleep efficiency (79.8 +/- [9.8]% vs 87.7 +/- [6.8]%; P < 0.005), with more wake time (10.6 +/- [9.0]% vs 3.4 +/- [4.4]%; P < 0.005), and with more awakenings lasting more than 3 minutes (2.1 +/- [1.5] vs 0.6 +/- [0.8]; P < 0.005). These findings were confirmed by actigraphic monitoring that revealed lower sleep efficiency (90 +/- [5]% vs 94 +/- [3]%; P < 0.05), more minutes of wake time (49 +/- [21] min vs 28 +/- [15] min; P < 0.05), and a trend toward more awakenings longer than 5 minutes (1.8 +/- [0.8] vs 1.2 +/- [0.8]; P = 0.063). Our data demonstrated that 3 years after MHI without any discernible clinical sequel, adolescents still complain of sleep disturbances that could be confirmed by both polysomnographic and actigraphic monitoring.

Adolescent↗
PubMed2000

Sleep-wake cycles in women with binge eating disorder.

OBJECTIVE: Binge eating disorder (BED) is a new diagnostic category in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). The majority of studies on sleep characteristics in overweight women have used nonbinging obese women. The aim of this study was to evaluate sleep characteristics in obese BED patients in comparison to non-BED obese (OB) and nonbinging normal weight (NW) women. METHOD: Eighteen females with BED, 13 OB, and 16 NW women were recruited. Sleep-wake patterns were monitored for 1 week using mini-actigraphs and self-report questionnaires. RESULTS: Their ambulatory sleep data revealed that BED and OB subjects had significantly lower sleep efficiency, had more wake during sleep, and had less zero activity than the NW group. The self-report questionnaires presented significantly more sleep disturbances in the BED and OB groups than in the NW group. DISCUSSION: The objective results support the subjective sleep disturbances reported by the two obese groups, the BED and the OB. A possible explanation for these findings could be weight-related physical discomfort or the existence of breathing disorders in sleep. Further research, for example, overnight polysomnography recordings and follow-up treatment, is required.

Adult↗
PubMed2000

The neural-cognitive basis of the Jamesian stream of thought.

William James described the stream of thought as having two components: (1) a nucleus of highly conscious, often perceptual material; and (2) a fringe of dimly felt contextual information that controls the entry of information into the nucleus and guides the progression of internally directed thought. Here I examine the neural and cognitive correlates of this phenomenology. A survey of the cognitive neuroscience literature suggests that the nucleus corresponds to a dynamic global buffer formed by interactions between different regions of the brain, while the fringe corresponds to a set of mechanisms in the frontal and medial temporal lobes that control the contents of this global buffer. A consequence of this account is that there might be conscious imagistic representations that are not part of the nucleus. I argue that phenomenology can be linked to psychology and neuroscience and a meaningful way that illuminates both.

Cognition↗
PubMed2000

Substantive thoughts about substantive thoughts: a reply to Galin.

In his commentary, David Galin raises several important issues that deserve to be addressed. In this response, I do three things. First, I briefly discuss the relation between the present work and the metaphoric theories of thought developed by cognitive lin- guists such as Lakoff and Johnson (1998). Second, I address some of the confusions that seem to have arisen about my use of the terms "substantive thought" and "nucleus." Third, I briefly discuss some of the directions that Galin suggests for further research.

Cognition↗
PubMed2000

Actigraphic monitoring (actigraphy) of circadian locomotor activity in schizophrenic patients with acute neuroleptic-induced akathisia.

BACKGROUND: Actigraphy is a quantitative method for measurement of motor activity. In the present study we used actigraphy to examine diurnal variations in locomotor activity of schizophrenic patients with neuroleptic-induced akathisia (NIA). METHOD: Thirty-two schizophrenic patients, 16 with NIA and 16 without (DSM-IV criteria) underwent 24-h actigraphic monitoring. Clinical assessments of NIA were conducted with Barnes Akathisia Scale (BAS) at 08:00, 12:00, 16:00 and 20:00. Sleep parameters (duration, latency, continuity and efficacy) were assessed by actigraphy. Sleep quality was evaluated by a self-rated sleep questionnaire. RESULTS: NIA patients demonstrated persistent higher daytime motor activity from 11:30 to 14:15 and from 18:00 to 21:00 than controls. There were no differences between the groups in nighttime motor activity, confirming clinical observations that NIA tends to disappear during sleep. Subject's sleep assessments were similar in the two groups. CONCLUSIONS: Actigraphy seems to be a reliable, non-invasive, method of measuring motor activity in patients with NIA. Its sensitivity and specificity as an objective quantitative diagnostic instrument in patients with NIA merits further investigation.

Adult↗
PubMed2000

Formal perceptual evaluation of voice quality in the United Kingdom.

This document is a position statement on the formal perceptual evaluation of voice quality in the United Kingdom (UK). It addresses a number of clinical issues pertaining to the complexity of voice quality analysis. There is also a brief description of the three formal perceptual protocols most commonly used in the UK: The Vocal Profile Analysis (VPA), GRBAS and The Buffalo III Voice Profile. Potential clinical problems with perceptual voice quality evaluation are highlighted. Problems associated with the lack of defined terminology, limitless variety of voice quality, general lack of reliability data and difficulties in determining specificity and sensitivity are discussed. A practical guide for selecting an evaluation scheme is described. The conclusion is that the GRBAS scheme should be recommended as the absolute minimum standard for practising UK voice clinicians. However, there is a clear need to develop a more satisfactory perceptual rating scheme that is clinically realistic, theoretically sound, internationally acceptable and has proven reliability.

Female↗
PubMed1999

Naturalistic sleep monitoring in women suffering from bulimia nervosa.

OBJECTIVE: Eating disorders may be associated with alterations in sleep. There is evidence that some bulimia nervosa (BN) patients have sleep abnormalities. No studies of their sleep-wake cycles in a natural environment have as yet been reported. The purpose of this study was to evaluate an objective and subjective sleep-wake cycle of BN compared to a healthy age-equated control group (CON). METHOD: Twenty-nine BN female and eighteen CON subjects were recruited. Sleep-wake patterns were monitored using ambulatory monitoring, mini-actigraphs (Min-Act), for 1 week. Each subject completed self-report questionnaires. RESULTS: The self-reporting questionnaires revealed that BN complained of significantly more sleep disturbances than CON. The ambulatory sleep data revealed significant differences between BN and CON in sleep onset and offset time. DISCUSSION: BN had sleep onset and sleep offset of 1 hr later, which may be connected to binge-purge patterns during the day. It is suggested that future research should focus on BN after remission.

Adolescent↗
PubMed1999

Left-handedness and achievements in foreign language studies.

Studies of brain lateralization lend support to the hypothesis that language-motor functions in left-handers are differently organized from those in right-handers. However, the implications of these differences regarding cognitive functioning are as yet subject to controversy. This concerns all hypotheses raised and empirical data collected over the years. Although it was suggested that left-handers are at higher risk of having language and reading deficits, empirical data from clinical and nonclinical populations are inconclusive at the present time. No effort, however, has been invested in examining possible differences in academic studies of foreign languages according to handedness. Here we report data indicating inferior achievements of left-handed native Hebrew speakers in studies of English as a foreign language. Left-handed pupils significantly more than right-handers were placed in lower level English classes and had more difficulties in applying orthographic-phonological mapping rules in reading English words and pseudowords. However, left-handers' difficulties in this task were not correlated with their performance in a word recognition task. It is thus suggested that the "common symptom" of poor word reading in left-handers indicates different processing failures in different left-handers, some of which impede the buildup of an internal representational system of mapping orthography to phonology and some of which concern mainly the precision of word production.

Achievement↗
PubMed1999

The parahippocampal place area: recognition, navigation, or encoding?

The parahippocampal place area (PPA) has been demonstrated to respond more strongly in fMRI to scenes depicting places than to other kinds of visual stimuli. Here, we test several hypotheses about the function of the PPA. We find that PPA activity (1) is not affected by the subjects' familiarity with the place depicted, (2) does not increase when subjects experience a sense of motion through the scene, and (3) is greater when viewing novel versus repeated scenes but not novel versus repeated faces. Thus, we find no evidence that the PPA is involved in matching perceptual information to stored representations in memory, in planning routes, or in monitoring locomotion through the local or distal environment but some evidence that it is involved in encoding new perceptual information about the appearance and layout of scenes.

Adolescent↗
PubMed1999

Sleep patterns in autistic children.

Sleep disturbances are regarded as a common clinical feature in autistic children. This concept is based primarily on informal observations or studies conducted with questionnaires. In this study we compared data obtained by questionnaires to that obtained with actigraphy. Among 22 autistic children, 12 were reported as having sleep problems and 8 patients completed 72 hours actigraphy. While the employment of questionnaires disclosed that autistic children had an earlier morning awakening time and multiple and early night arousals, actigraphic monitoring showed that with the exception of an earlier morning arousal time (p = .045), sleep patterns of autistic children were similar to that of normal children. Parental oversensitivity to sleep disturbances of the autistic children may explain this phenomenon.

Autistic Disorder↗
PubMed1999

Repetition blindness for locations: evidence for automatic spatial coding in an RSVP task.

The authors report a new phenomenon called repetition blindness (RB) for locations: When 3 or 4 letters are presented rapidly and sequentially at random locations within a spatial array, experimental participants have difficulty reporting pairs of letters appearing in the same location within 250 ms of each other. This deficit occurs both during report of letter identities and during report of the locations in which the letters appear; it can also be found using a partial report task. During letter report, the deficit is found for 4-location arrays but not for 8-location arrays. In contrast, letter RB is not found during location report even when the letters are always chosen from a set of 4. These results indicate that a small number of locations--but not letters--can be encoded automatically even when they are not explicitly reported. The authors argue that RB for locations results from a difficulty individuating 2 tokens at the same spatial location.

Adult↗
PubMed1998

Starting times of school: effects on daytime functioning of fifth-grade children in Israel.

In the present study we investigated the effects of school starting time on daytime behavior and sleep. Eight-hundred and eleven 5th grade pupils (10-12 years old) from 28 classes in 18 schools throughout Israel were divided into "early risers" (N = 232) who started school at 07:10 (42%) at least 2 times a week, and "regular risers" (N = 340) who always started school at 08:00 (58%). The remaining 239 pupils started school between 7:20 and 07:55 (and also after 08:00), and were not included in the study. Self-administered questionnaires concerning sleep habits during school days, weekends, and holidays, daytime fatigue, sleepiness, and difficulties concentrating and paying attention in school were completed by all children. Mean sleep time of the "early risers" was significantly shorter than that of the "regular risers." Early risers complained significantly more about daytime fatigue and sleepiness, and about attention and concentration difficulties in school. Their complaints were independent of the reported hours of sleep. We conclude that early starting of school negatively affects total sleep time and, as a consequence, has a negative effect on daytime behavior. The implications of these findings to the ongoing controversy concerning sleep need in contemporary society are discussed.

Adolescent↗
PubMed1998

A cortical representation of the local visual environment.

Medial temporal brain regions such as the hippocampal formation and parahippocampal cortex have been generally implicated in navigation and visual memory. However, the specific function of each of these regions is not yet clear. Here we present evidence that a particular area within human parahippocampal cortex is involved in a critical component of navigation: perceiving the local visual environment. This region, which we name the 'parahippocampal place area' (PPA), responds selectively and automatically in functional magnetic resonance imaging (fMRI) to passively viewed scenes, but only weakly to single objects and not at all to faces. The critical factor for this activation appears to be the presence in the stimulus of information about the layout of local space. The response in the PPA to scenes with spatial layout but no discrete objects (empty rooms) is as strong as the response to complex meaningful scenes containing multiple objects (the same rooms furnished) and over twice as strong as the response to arrays of multiple objects without three-dimensional spatial context (the furniture from these rooms on a blank background). This response is reduced if the surfaces in the scene are rearranged so that they no longer define a coherent space. We propose that the PPA represents places by encoding the geometry of the local environment.

Brain Mapping↗