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Biomedical subjects

L J Mulder

Publications and source records attributed to L J Mulder.

At least 19 recordsLinked to original sources
PubMed1998

Color selection and location selection in ERPs: differences, similarities and 'neural specificity'.

It was hypothesized that color selection consists of two stages. The first stage represents a feature specific selection in neural populations specialized in processing color. The second stage constitutes feature non-specific selections, related to executive attentional processes and/or motor processes. This hypothesis was tested by investigating the effects of selectively attending to a specific color, location, or conjunction of location and color on the ERPs elicited by briefly flashed gratings. The gratings differed on three dimensions: color (red or blue), location in the visual field (4.4 degrees to the left or right of fixation) and form (target or non-target). Subjects had to respond to the presentation of target gratings in the attended category. Color selection was reflected in an enhanced parietal positivity in the 150-190 ms interval. Source analyses suggested that this color selection positivity might be generated in the basal occipital cortex, possibly human V4, an area of the brain specialized in color processing. The effect was separated from the P1 spatial attention effect both in topography and sources. Color selection was also reflected in a contralateral occipitotemporal negativity, which resembled the N1 spatial attention effect both in timing and topography. And finally, color selection was reflected in an N2b component. This N2b was similar in timing, topography and sources to the N2b's elicited by location selection and conjunction selection. We suggested that the N2b reflects feature non-specific selection processes, elicited by a range of attended stimuli, and possibly reflects activity in the anterior cingulate cortex. The NP80 was unaffected by attention to color and/or location and localized in striate cortex.

Adult↗
PubMed1998

Influence of respiratory activity on the cardiac response pattern to mental effort.

A group of 32 healthy adult volunteers completed three blocks of a reaction time task that varied in the degree of controlled processing load. A rest period preceded each of the task blocks. The task blocks were presented in the order of either increasing or decreasing cognitive load. For each of the six periods, mean values and spectral measures of heart rate and respiration variability were calculated. The spectral measures were obtained for three different frequency bands. Differences between the cardiac measures of the task and preceding rest periods were compared with respect to differences in task load and the order of task presentation. All comparisons were carried out while adjusting for respiratory variability in the corresponding frequency band. The frequency band in which task load-related changes in heart rate variability became manifest appeared to be dependent on the individual's breathing pattern.

Adult↗
PubMed1997

An ERP study of visual spatial attention and letter target detection for isoluminant and nonisoluminant stimuli.

The event-related potential (ERP) effects of visual spatial attention and letter target detection for stimuli presented against a (nonisoluminant) dark background or against an isoluminant grey background were investigated. The goal was to study how the perceptual variable of luminance would influence early ERP reflections of selective attention. Such effects could further substantiate the claim that selective attention operates at the level of early perceptual processing and could provide evidence regarding the role of different visual routes in selective attention. Isoluminance increased the peak latency of the early ERP deflections (NP80, P1, and N1) by 40-50 ms. The ERP effects of spatial attention, consisting of P1 and N1 amplitude enhancements, were similarly delayed by isoluminance, supporting the idea that early selective processing is strongly dependent on bottom-up perceptual processing. P300 latency and reaction time were delayed by 70-75 ms, the additional delay probably reflecting that isoluminance affected decision processes in addition to perceptual processes. Isoluminance left the scalp topographies of the early ERP deflections largely unaffected, although a slight shift of the N1 topography in the isoluminant condition toward more inferior lateral posterior regions of the scalp could have reflected an increased contribution from ventral (occipitotemporal) brain areas. Relative to nontarget letters, targets presented at both attended and unattended spatial positions elicited an early contralaterally dominant lateral occipitotemporal negativity (N2pc). This ERP component is proposed to reflect an early, partly automatic process of template matching, consistent with indications from spatiotemporal dipole modelling that the N2pc was generated in inferior occipitotemporal brain regions.

Adult↗
PubMed1996

[The combination of oral lysine-acetylsalicylate and metoclopramide compared with oral sumatriptan in the treatment of migraine attacks. A randomized, double-blind, placebo-controlled clinical trial].

A combination of lysine acetylsalicylate (equivalent to 900 mg aspirin) and 10 mg metoclopramide (LAS + MTC) was compared with oral sumatriptan (100 mg) and placebo in 421 patients with migraine in a randomized, double-blind, clinical trial. LAS + MTC was as effective as sumatriptan with a decrease in headache from severe or moderate to mild or none in 57% and 53%, respectively, for the first migraine attack treated, the primary efficacy parameter. Both treatments were better than placebo (success rate 24%, p < 0.001). LAS + MTC was better tolerated than sumatriptan (adverse events in 18% and 28%, respectively, p < 0.05).

Administration, Oral↗
PubMed1996

Covariation of phasic cortical and cardiovascular responses in a detection task.

The relationship between cardiovascular and cortical responses was examined in an experiment in which subjects performed a detection task and a simple reference task. The detection task was developed according to Skinner et al., (1987). Cortical activity was examined with event related brain potentials (ERPs). ERPs revealed more cortical activation during detection task blocks. Both tonic and phasic measures of cardiovascular activity were derived. Tonic measures were heart rate (HR), systolic blood pressure (SBP). T-wave amplitude (TWA), respiration linked HR-variability and a measure for baroreflex sensitivity. These measures revealed no important differences between the reference task and detection task blocks. Phasic cardiovascular measures were evoked HR, SBP and TWA. Evoked HR showed a larger deceleration and evoked SBP showed a smaller decrease on detection task blocks. Evoked TWA did not differentiate between both types of task. It is concluded that an adjusted version of the fronto-cortical control hypothesis of Skinner could best account for the data.

Adult↗
PubMed1996

Analysis of Centers for Disease Control and Prevention criteria for the eosinophilia-myalgia syndrome in a geographically defined population.

OBJECTIVE: To test whether individuals can be identified in a geographically defined population who would meet criteria for the eosinophilia-myalgia syndrome (EMS) established by the US Centers for Disease Control and Prevention (CDC), i.e, (1) eosinophil count > 1 x 10(9)/l, (2) myalgia severe enough to limit usual activities of daily living, and (3) no evidence of infection or neoplasm that could explain the first 2 findings. METHODS: To discover the number of individuals who would meet CDC criteria, the population was exhaustively searched using methods adapted from active pharmacoepidemiologic surveillance. Medical consultants and primary care practitioners were questioned as many as 5 times in a search for patients with severe myalgia. A predetermined protocol was used to screen those patients who appeared to meet CDC criteria for EMS using active surveillance methods. The study population was limited to Québec and Ontario (combined population 18,980,000) with special attention to the period July 1, 1992, to June 30, 1993. RESULTS: The prevalence of severe incapacitating myalgia was 43 per 100,000 persons, including 19 individuals with eosinophilia > 1 x 10(9)/l, who met CDC criteria for EMS. None of these individuals were reported to have taken L-tryptophan (LT). CONCLUSION: The CDC criteria for EMS are met by individuals in the general population who have never been exposed to LT.

Adult↗
PubMed1995

The effectiveness of combined oral lysine acetylsalicylate and metoclopramide compared with oral sumatriptan for migraine.

Aspirin is commonly used to treat migraine attacks, although sumatriptan, a much more expensive treatment, is also effective. We compared a combination of lysine acetylsalicylate (equivalent to 900 mg aspirin) and 10 mg metoclopramide (LAS+MTC) with oral sumatriptan (100 mg) and placebo in 421 patients with migraine. LAS+MTC was as effective as sumatriptan with a decrease of headache from severe or moderate to mild or none of 57% and 53%, respectively, for the first migraine attack treated. Both treatments were better than placebo (success rate 24%, p < 0.0001). LAS+MTC was significantly more effective in the treatment of nausea than sumatriptan (p < 0.0001) and was better tolerated (adverse events in 18% and 28%, respectively, p < 0.05). LAS+MTC is as effective as sumatriptan in the treatment of migraine attacks. It is also much cheaper.

Administration, Oral↗
PubMed1995

The role of neuroimaging in the discovery of processing stages. A review.

In this contribution we show how neuroimaging methods can augment behavioural methods to discover processing stages. Event Related Brain Potentials (ERPs), Brain Electrical Source Analysis (BESA) and regional changes in cerebral blood flow (rCBF) do not necessarily require behavioural responses. With the aid of rCBF we are able to discover several cortical and subcortical brain systems (processors) active in selective attention and memory search tasks. BESA describes cortical activity with high temporal resolution in terms of a limited number of neural generators within these brain systems. The combination of behavioural methods and neuroimaging provides a picture of the functional architecture of the brain. The review is organized around three processors: the Visual, Cognitive and Manual Motor Processors.

Arousal↗
PubMed1995

Rhabdomyolysis associated with influenza A virus infection.

Rhabdomyolysis is characterized by local or generalized skeletal muscle necrosis. It is caused by many clinical conditions and drug or alcohol abuse. Clinical symptoms are muscle pain and muscle weakness. Laboratory investigations show a rise in serum creatine phosphokinase and electrolyte disturbances. The most serious complication is acute renal failure. We present a patient with rhabdomyolysis and renal failure associated with a recent Influenza A virus infection.

Acute Kidney Injury↗
PubMed1994

Heart rate variability spectra based on non-equidistant sampling: the spectrum of counts and the instantaneous heart rate spectrum.

This paper compares two methods to estimate heart rate variability spectra, i.e., the spectrum of counts and the instantaneous heart rate spectrum. Contrary to Fourier techniques based on equidistant sampling of the interbeat intervals, the spectrum of counts and the instantaneous heart rate spectrum are based on non-equidistant sampling: the values are determined at R-wave moments. A consequence of the non-equidistant occurrence of the R-peaks in a heart rate signal is the appearance of the sidebands of the harmonic components of the mean heart rate in the spectra. These sidebands contaminate the signal components in the spectrum. The sideband distortion in the instantaneous heart rate spectrum was found to be smaller than in the spectrum of counts. Simulations using the IPFM-model were made to quantify this difference. On the basis of these simulations, sideband distortion appeared to be dependent on the mean heart rate, the modulation depth and the modulation frequency.

Computer Simulation↗
PubMed1992

Measurement and analysis methods of heart rate and respiration for use in applied environments.

Cardiovascular measures are used in applied settings to assess mental load. It is neither desirable nor possible to adapt the working situation to the needs of the experimenter, as can be done in the laboratory; the purpose of this paper is to discuss how invested effort, mental efficiency, and changes in cardiovascular state can be measured in applied settings, including non-stationary ones. This paper discusses the theoretical background of fluctuations in heart rate and respiration and the application of existing methods in laboratory and normal working situations. Data acquisition and analysis methods are then presented, particularly the problems of artifact detection and correction and variability indices in spectral bands in relation to the reliability of these measures. In the last section the interpretation of data acquired in environments and the specific problems inherent in such situations are discussed.

Arousal↗
PubMed1992

A psychophysiological study of the use of partial information in stimulus-response translation.

Ss performed a hybrid go/no-go reaction task in which colored letters were assigned in various ways to 4 finger responses, 2 on each hand. In addition to reaction time, psychophysiological measures were used to assess the duration of stimulus identification and the onset of central and peripheral motor activity. The results suggest that response selection can begin on the basis of 1 stimulus dimension (e.g., color), while the other dimension (e.g., letter form) has not yet been identified. Other results are discussed with regard to "selection for action" (Allport, 1987) and the importance of stimulus-response translation strategies in the use of partial information.

Adult↗
PubMed1991

Psychophysiological evidence for continuous information transmission between visual search and response processes.

This study was designed to test whether information transmission between the perceptual and motor levels occurs continuously or in discrete steps. Ss performed visual search across nontargets that shared visual features with one of two possible targets, each assigned to a different response. In addition to reaction time, psychophysiological measures were used to assess the duration of target search and the onset of central and peripheral motor activity. Nontargets sharing features with a target selectively activated the response associated with that target, even when it was not present in the display. This suggests that information transmission to the motor level can consist of fine-grained visual information and that visual search and response selection occur in parallel.

Adult↗
PubMed1991

Changes in sympathetic and parasympathetic cardiac activation during mental load: an assessment by spectral analysis of heart rate variability.

Spectral analyses of heart rate (HR) and blood pressure (BP) fluctuations yield three typical peaks at a low (0.02-0.06 Hz), a mid (0.07-0.14 Hz) and a high (around the respiratory frequency) frequency area. These so-called bands attract the interest of researchers because they seem to offer the facility of non-invasively studying autonomic cardiovascular control mechanisms. The high frequency component is solely under vagal control, the influence of sympathetic/vagal efferents on the low and mid frequency band is unclear. We therefore investigated in a single case study (23 year old male) the effects of propanol (0.06 mg/kg, 30 min. interruption, 0.12 mg/kg i.v.), dobutamine (1.14 micrograms/kg/min for 30 minutes, then 2.21 micrograms/kg/min i.v., then 4.42 micrograms/kg/min), atropine (0.01 mg/kg within 5 minutes, 30 minutes later 0.02 mg/kg within 5 minutes), and carbachol (0.125 mg, 30 min. interruption, 0.25 mg s.c.) upon HR, HR-variability spectra, BP and respiratory parameters at rest and during 5 minutes of a mental task. Under all four drug conditions BP is elevated at rest and mental stress, the latter always giving higher results than the former. Atropine shortens interbeat intervals (IBI) by almost 50 percent (from 939 msec to 514 msec), the high dose of dobutamine reduces IBI from 725 to 580 msec, propranolol increases interval length by 10 percent. Drug effects on spectral bands give clear results with atropine: It reduces spectral energy in all three frequency bands at rest and during mental stress. The other drugs show no clear-cut effects on HR-variability spectra. Even though results of a single case study should be interpreted with great caution we believe that the following conclusion can be made: At rest and during short-lasting mental stress all frequency bands in HR-variability spectra are to a large extent under parasympathetic control.

Adult↗
PubMed1991

On the usefulness of finger blood-pressure measurements for studies on mental workload.

Two experiments were conducted to explore the usefulness of the Penaz method for non-invasive, continuous finger blood pressure measurements during mental stress testing. In the first study, blood pressure was measured with the Penaz method, in the second it was measured intra-arterially. Two different subject groups were used. In both experiments the same mental task, a memory search and counting task, was used. Experimental effects, consisting of rest-task differences in heart rate and blood pressure, its (spectral) variability and the coherence between fluctuations in the two signals (e.g. baroreflex sensitivity) are compared for the two measuring methods. Experimental effects on mean pressure values, spectral variability measures and baroreflex sensitivity are similar for the two types of measurement. Effects on mean pressure are smaller in the finger pressure indices. It is concluded that the Penaz instrument can provide us with a useful method for studying cardiovascular reactivity in mental stress research.

Adolescent↗