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Biomedical subjects

R J Barry

Publications and source records attributed to R J Barry.

At least 55 records · Page 3Linked to original sources
PubMed1995

Maximum variance of late component event related potentials (190-240 ms) in unmedicated schizophrenic patients.

The averaging of individual late component event related potential (ERP) responses, particularly P300, has revealed significant differences between schizophrenic patients and normal subjects. However, the averaging process removes the variability of the individual epochs that constitute that average. The response-variance-curve (RVC) method quantifies the variability of the individual epochs and allows examinations of windows of maximum variance. In this study, we examine the complementary nature of the RVC method to the traditional averaging approach. The averaged N200 and P300 ERP components differed significantly between the schizophrenic and normal groups, but not between the unmedicated and medicated schizophrenic patients. The RVC measure, on the other hand, revealed systematic differences in variability, maximal between 190 and 240 ms, between the unmedicated and medicated schizophrenic patients. The RVC measure therefore provides a focused time frame in which to examine dysfunctions in information processing and macroscopic scale changes in brain function due to medication.

Acoustic Stimulation↗
PubMed1995

Event related response variability in schizophrenia: effect of intratrial target subsets.

The response-variance-curve (RVC) method quantifies the variability of the individual epochs that constitute the average event related potential (ERP), providing complementary information to that offered by ERPs. Numerous studies have found that average ERP late components of an auditory "oddball" paradigm can differentiate schizophrenic patients from normal subjects. Our previous study of the RVC measure revealed significant differences between medicated and unmedicated schizophrenic patients in the maximum ERP variability from 190 to 240 ms. In the present study of unmedicated schizophrenic patients and normal control subjects, we examined the influence of intertarget intervals (generated by pseudorandom stimulus sequences in an auditory oddball paradigm) on the intratrial effects of ERP variability measured by the RVC. The ERPs of unmedicated schizophrenic patients were characterized by an instability in a latency window corresponding to the N200 component. The effect was particularly large at an intertarget interval of 7.8 s and was significantly reduced on either side of this intertarget interval.

Acoustic Stimulation↗
PubMed1995

Decelerative changes in heart rate during recognition of visual stimuli: effects of psychological stress.

The present study investigated whether the anticipatory heart rate (HR) deceleration response may reflect a pre-attentive process of stimulus registration and how reaction time (RT) and HR responses are influenced by the introduction of a psychological stressor. 60 subjects participated in a signalled RT task with a feedback stimulus containing information on their reaction time and accuracy. Changes in HR, skin conductance (SC) and respiration activity were monitored during performance in two conditions of a visual stimulus recognition task with a fixed foreperiod. In one condition subjects were informed that some electric shocks would be delivered to their right wrist (stress condition); in the other, subjects were simply engaged in the stimulus recognition without the stressor (no-stress condition). Stimuli consisted of geometrical figures and for each trial subjects were required to determine whether a probe stimulus was the same as or different from one of two memory items. Two reliable anticipatory HR decelerations, one preceding the imperative stimulus and the other preceding the feedback signal, were observed. Because the HR deceleration preceding the feedback signal (that did not require the inhibition of any specific motor response) was more pronounced than that obtained for the probe stimulus, it was concluded that HR deceleration response is an expression of stimulus processing rather than response preparation. Reaction times for 'same' stimuli were shorter than for 'different' stimuli. Averaged respiratory activity showed that with the onset of a warning signal subjects inspired and held their breath until they received the feedback signal. The averaged skin conductance data showed two main phasic increases, one after the probe stimulus onset and the other after the delivery of the feedback signal. This was taken to reflect the orienting response to the most significant stimuli.

Adult↗
PubMed1995

Eye movement and electrodermal responses to threat stimuli in post-traumatic stress disorder.

A core feature of post-traumatic stress disorder (PTSD) is hypervigilence to threatening material. This study measured processing of threat material in PTSD with simultaneously acquired initial eye movements and electrodermal activity, following presentation of threatening and neutral words. Ten PTSD subjects and 10 controls were presented with 4 words in parafoveal range. On trials in which a threat word was present, PTSD subjects demonstrated initial eye fixations on the threat word more than controls. PTSD subjects also demonstrated more orienting responses on all trials than controls. These results suggest that processing of threat information in PTSD can be usefully investigated with convergent psychophysiological methodologies.

Adult↗
PubMed1994

Single photon emission computed tomography (SPECT) measures of brain function in schizophrenia.

This study explores SPECT measured in schizophrenic patients at rest. Left temporal lobe activity was found to be decreased with increasing positive symptoms' scores scores. Medicated patients showed a reversal of this pattern underlying this positive symptom effect. Patients with a recent history of auditory hallucinations showed an atypical right temporal lobe dominance, which occurred independently of medication status. These preliminary data are suggestive of the potential utility of SPECT to elucidate symptom/medication/brain activity interrelationships in schizophrenia.

Antipsychotic Agents↗
PubMed1993

Elicitation and habituation of the electrodermal orienting response in a short interstimulus interval paradigm.

The present experiment was carried out to investigate elicitation and habituation of the electrodermal Orienting Response with stimulus trains utilising a short interstimulus interval (ISI) of 1.1 s. We sought evidence for within-train response decrement to repeated stimulus presentation, response recovery to a change stimulus and dishabituation following the change stimulus--the three properties necessary to unequivocally identify a decremental process as habituation. No autonomic study could be found using such a short ISI. Autonomic studies on this time scale are necessary if these measures are to be integrated with central event-related potential (ERP) measures of electrical brain function. Overcoming this paradigm gap required the development of novel measurement procedures to estimate the small electrodermal responses obtained, usually occurring on the recovery slope of the response to the previous stimulus in the train. With our novel measurement procedures, evidence was found indicating that electrodermal activity in such a paradigm exhibited the three classic criteria of habituation.

Acoustic Stimulation↗
PubMed1993

Stimulus intensity and novelty interact in elicitation of the phasic electrodermal orienting response.

For many years, it has been well-accepted that the amplitude of the phasic orienting response is directly dependent on both stimulus intensity and novelty, at least within innocuous intensity ranges. Surprisingly, the joint contribution of these stimulus parameters has not been convincingly specified in the literature. A two-step analytical procedure, which is logically necessary to provide a valid solution to the problem, is outlined. Data are then presented which demonstrate that there is a multiplicative relationship between the two parameters in their joint determination of response amplitude. That is, stimulus intensity and novelty interact in the production of the phasic electrodermal orienting response to innocuous stimuli.

Acoustic Stimulation↗
PubMed1993

Positive and negative shifts of the readiness potential: preparatory effects.

Freude and Ullsperger (1989) reported that positive potentials occurred on some trials in a single trial analysis of the Readiness Potential (RP). The present study investigated the effect of split attention on the occurrence of RPs of different polarities as well as comparing the post-movement potential and auditory-evoked potential after RPs of different polarities. In part 1 of the study, subjects (n = 16) pressed a key in a self-paced manner, concentrating on the movement. In part 2 they were asked to discriminate between two randomly-ordered tones, triggered by the key press (with a delay of 560 ms), and to announce the result to the experimenter verbally. The results of part 1 matched previous findings, in that in 41% of all trials RP was positive. In part 2 there was a significant increase in the relative frequency of positive RPs to 54%. This resulted in the magnitude of the averaged RP decreasing from part 1 to part 2. The early component of the averaged RP, which had begun about 1300 ms before the movement in part 1 of the study, disappeared in part 2, where the averaged RP began only 350 ms before the movement. The post-movement potential was significantly larger when the preceding RP was negative. In part 2 of the study we found an N100 in response to the tone; this was larger after positive RPs, but the difference was not significant. The implications of these novel findings for interpretation of the averaged RP are discussed.

Adult↗
PubMed1993

Habituation of phasic and tonic components of the orienting reflex.

This study examined phasic and tonic measures of electrodermal activity in a simple habituation paradigm with innocuous visual stimuli. Prestimulus skin conductance levels were taken as measures of the arousal level existing at each stimulus presentation, and the subsequent electrodermal responses were taken as indices of the phasic orienting reflex (OR) elicited by each stimulus. The arousal level was considered as a tonic OR measure. Both the tonic and phasic ORs showed effects of trials. Arousal levels also showed an initial sensitization, as suggested by dual-process theory. After within-subject effects of arousal changes over trials were removed by simple regression analyses, novelty still remained as the major determinant of phasic OR magnitude. This finding is discussed in relation to the OR mechanism.

Adult↗
PubMed1993

Graphical and statistical techniques for cardiac cycle time (phase) dependent changes in interbeat interval: problems with the Jennings et al. (1991) proposals.

Two apparently new effects in human cardiac responding, "primary bradycardia" and "vagal inhibition", were first described by the Laceys. These effects have been considered by some researchers to reflect differential cardiac innervation, analogous to similar effects observed in animal preparations with direct vagal stimulation. However, it has been argued that such effects arise merely from the data-analytic techniques introduced by the Laceys, and hence are not genuine cardiac cycle effects. Jennings, van der Molen, Somsen and Ridderinkhoff (Psychophysiology, 28 (1991) 596-606) recently proposed a plotting technique and statistical procedure in an attempt to resolve this issue. The present paper demonstrates that the plotting technique fails to achieve their stated aim, since it identifies data from identical cardiac responses as showing cardiac-cycle effects. In addition, the statistical procedure is shown to be reducible to a trivial test of response occurrence. The implication of these demonstrations, in the context of other work, is that this area of investigation has reached a dead end.

Arousal↗
PubMed1992

Does the N100 evoked potential really habituate? Evidence from a paradigm appropriate to a clinical setting.

This study examined the N100 component of the event related potential in a habituation paradigm with short interstimulus intervals. The paradigm was designed to be relatively brief in duration (approx. 4 min for each of two conditions), so that it could be used for clinical populations with cognitive dysfunction, in which compliance may be a problem with long paradigms. Two conditions - Ignore and Attend - were employed with normal subjects. In each condition, 15 stimulus trains, each consisting of 10 innocuous tones, were presented. The eighth tone was a change stimulus. There was a fixed interstimulus interval of 1.1 s and an inter-train interval of 5 s. From the perspective of traditional Orienting Response theory, evidence was sought for within-train habituation in terms of diminished N100 amplitude to repeated stimuli, response recovery to the change stimulus, and dishabituation of the response to the following standard stimuli. Habituation was suggested by significant decreases of approx. 50% with stimulus repetition, and response recovery to the change stimulus in both conditions. However, there was no evidence of dishabituation following the change stimulus. These results confirm that N100 fails to meet the formal requirements of response habituation, suggesting instead that it may index an earlier process than the Orienting Response.

Acoustic Stimulation↗
PubMed1991

HGM1: a research-oriented portable heart rate and galvanic skin response monitor.

A convenient portable recording device, HGM1, which allows digital field recording of skin conductance and heart rate data with laboratory levels of precision, is described. Examples of individual data are provided from a study of orienting response habituation, and from students participating in a study of examination anxiety, recorded while they sat scheduled class examinations. These illustrate the potential value of the device in field studies.

Adolescent↗
PubMed1990

Scoring criteria for response latency and habituation in electrodermal research: a study in the context of the orienting response.

Levinson and Edelberg's (1985) recent critique of scoring criteria for electrodermal studies pointed to the need to reduce the latency range used to define the electrodermal response. The present study examined the impact of such a narrowing of the latency window upon habituation and instructional effects in studies of the orienting response to low intensity innocuous stimuli. The first experiment found only a small effect of halving the latency window upon habituation to neutral stimuli, apparent as a strengthening of trends over trials. A second experiment showed somewhat larger effects with significant stimuli, apparent as slightly modified trial and group effects. These data support the view that nothing is to be lost by moving to a narrower latency range to define the electrodermal orienting response to stimulus presentation, and suggest that the advantages of such a change will become increasingly important as nonspecific electrodermal fluctuations increase with increasing electrodermal arousal. An analysis of habituation criteria within this context suggested that the choice of two rather than three no-response trials to define habituation adds to the benefits obtained by the selection of a narrow latency window to define the response.

Adult↗
PubMed1989

Solubilization and partial purification of retinyl ester synthetase and retinoid isomerase from bovine ocular pigment epithelium.

Studies reported previously from this laboratory have demonstrated that membranes from the pigment epithelium of the vertebrate eye can transform free all-trans-retinol to 11-cis-retinol as well as 11-cis- and all trans-retinyl esters (Bernstein, P. S., Law, W. C., and Rando, R. R. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1849-1853; Bernstein, P. S., Law, W. C., and Rando, R. R. (1987) J. Biol. Chem. 262, 16848-16857; Fulton, B. S., and Rando, R. R. (1987) Biochemistry 26, 7938-7945). The congeneric retinals are also formed under conditions where retinol redox activity is present. Here we report the successful solubilization of both the retinyl ester synthetase and isomerase activities from the pigment epithelium membranes of the bovine eye. The zwitterionic detergent Zwittergent 3-14(N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate; cmc 0.012%) gave optimal solubilization of both activities. Three initial criteria for successful solubilization were used. First, high speed centrifugation (greater than 150,000 x g) left the activities in the supernatant. Second, the solubilized enzymatic activities were found in the included volume upon gel filtration. Finally, the solubilized activities were quantitatively passed through a 0.22-microns filter. Employing anion exchange and gel filtration chromatography results in a partial purification of the retinyl ester synthetase (approximately 189-fold). The solubilized retinoid isomerase is also partially purified (approximately 10-14-fold) following anion exchange chromatography. It is also shown that the membrane-bound and solubilized ester synthetase catalyzes the esterification of retinol using added lecithins as exogenous acyl donors. In addition, evidence is provided indicating that there is a positional selectivity for the acyl group transfer from the lecithin to retinol. The transfer occurs largely, if not entirely, from the 1-position of the lecithin.

Acyltransferases↗
PubMed1989

Methods and mechanisms in electrodermal studies of omission responding.

Barry and O'Gorman (1987) employed a response-averaging technique to investigate the electrodermal orienting response (OR) to stimulus omission. We obtained reliable evidence of increased response latency to stimulus omission, supporting an explanation of the missing-stimulus effect in terms of Maltzman's voluntary OR. Wilson's (1989) commentary on our article addresses both methodological and theoretical aspects. This response first examines his methodological difficulties, and provides simulation exercises which serve as a validation of our procedure. We then examine Wilson's theoretical points. His alternative theoretical explanation of the missing-stimulus effect, in terms of a systematic bias in the time-keeper of the stimulus-comparator process, is shown to be untenable. His remaining problem, concerning what he terms "assessment of stimulus significance", appears to have arisen through misinterpretation of our theory. A clarification of our theoretical position indicates the internal consistency of our use of "significance" and "voluntary OR".

Arousal↗
PubMed1988

Elucidation of the 2-aminoethylphosphonate biosynthetic pathway in Tetrahymena pyriformis.

The biosynthetic reaction pathway leading to the natural product, 2-aminoethylphosphonate in Tetrahymena pyriformis has been elucidated. Incubation of [32P]PEP and [14C]PEP with T.pyriformis cellular homogenate fortified with Mg2+ and alanine/pyridoxal phosphate, yielded 2-aminoethylphosphonate as the minor reaction product (2-5% yield) and phosphoglycerate and pyruvate plus orthophosphate as the major products. Inclusion of thiamine pyrophosphate in the reaction mixture increased the yield of 2-aminoethylphosphonate by a factor of 10. Incubation of phosphonoacetaldehyde or phosphonopyruvate in the cellular homogenate also provided 2-aminoethylphosphonate. The cellular homogenate catalyzed the transformation of phosphonoacetaldehyde to 2-aminoethylphosphonate in an ca. 80% yield. However, the maximum yield of 2-aminoethylphosphonic acid obtained by use of phosphonopyruvate was only 15%. The major reaction pathways induced by treatment of phosphonopyruvate with the cellular extract involved its competitive conversion to PEP and pyruvate plus orthophosphate.

Acetaldehyde↗