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Biomedical subjects

A Pipingas

Publications and source records attributed to A Pipingas.

12 recordsLinked to original sources
PubMed2001

Steady state visually evoked potential (SSVEP) topography in a graded working memory task.

The steady state visually evoked potential (SSVEP) elicited by a diffuse 13-Hz visual flicker was recorded from 64 scalp sites in 30 subjects performing a low and high demand version of an object working memory task. During the perceptual component of the task, the SSVEP amplitude was reduced at left and right parieto-occipital sites. During the hold or memory component of the task, the SSVEP amplitude exhibited a load-dependent increase at frontal and occipito-parietal sites, while the SSVEP latency exhibited a load-dependent reduction at central and left frontal sites. We suggest that SSVEP amplitude changes index cortical information processing modes in that perceptual processes are associated with an SSVEP amplitude reduction, while holding information in active short-term or working memory is associated with an SSVEP amplitude increase. We also discuss changes in SSVEP amplitude and latency in terms of changes in the behavior of cortico-cortico and thalamo-cortico loops that utilize cortical layer I. Such cortico-cortico and thalamo-cortical loops are also proposed to constitute a neurophysiological mechanism for holding information in working memory.

Adult↗
PubMed2000

Pemphigus vulgaris of the uterine cervix revisited: case report and review of the literature.

Pemphigus vulgaris is an autoimmune disease characterized by acantholytic blisters and erosions involving the oral mucosa, skin, and less frequently other mucosal surfaces. Although the cytology of scrapings from the cutaneous and oral lesions has been well-documented, there are relatively few reports in the literature of the cytologic appearance of pemphigus on cervicovaginal smears. This report documents a case of pemphigus involving the cervix, in which the diagnosis was not known at the time of the cervical smear and biopsy. The cytologic features of this case and those in the literature are described in detail, highlighting the necessity of awareness of the disease and its presentation on cervicovaginal smears, in preventing an overdiagnosis of neoplasia.

Adult↗
PubMed2000

Frontal steady-state potential changes predict long-term recognition memory performance.

Converging evidence from event-related potential and functional brain imaging studies suggests that the brain activity at posterior regions of the frontal cortex can predict the strength of long-term memory traces. This study examined the relationship between posterior frontal steady-state visually evoked potential (SSVEP) latency changes and recognition memory after a delay of 7 days. Thirty-five female subjects viewed an 18-min television documentary program interspersed with 12 unfamiliar television advertisements while brain electrical activity was recorded from four pre-frontal, two posterior frontal and two occipital scalp sites. After 7 days, the recognition memory was tested for images coinciding with the 20 most prominent frontal SSVEP latency minima and maxima during the viewing of ten contiguous advertisements (advertisements 2-11). We found that images coinciding with posterior frontal latency minima were more likely to be recognized (58.7% recognition) than images coinciding with SSVEP latency maxima (45.3% recognition). Furthermore, the relationship between posterior frontal SSVEP latency and recognition performance after 7 days was only apparent at the left posterior frontal site. The correlation between the recognition performance and SSVEP latency evaluated at all eight sites reached significance only at the left posterior frontal site. These findings suggest that frontal SSVEP latency variations can be used to assess the strength of long-term memory encoding for naturalistic stimuli.

Adult↗
PubMed2000

Steady-state visually evoked potential topography during the continuous performance task in normal controls and schizophrenia.

OBJECTIVES: To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patients diagnosed with schizophrenia and normal controls while undertaking a visual vigilance task. METHODS: Twenty patients diagnosed with schizophrenia and 18 normal controls performed the A-X version of the continuous performance task (CPT A-X) where subjects are required to press a micro-switch on the unpredictable appearance of an 'X' that had been preceded by an 'A.' Brain electrical activity was recorded from 64 scalp sites and a 13 Hz spatially uniform visual flicker presented with the task was used to elicit a steady-state visually evoked potential (SSVEP). RESULTS: Following the appearance of the 'A' and 'X,' the control group demonstrated a transient SSVEP latency reduction at parietal and prefrontal sites. By contrast, the patients group showed no such SSVEP latency reduction. The prefrontal SSVEP latency changes in the 500 ms interval following the appearance of the 'X' were correlated with mean individual reaction time in both populations. CONCLUSIONS: We suggest that the SSVEP latency reduction may index excitatory processes and that the absence of prefrontal SSVEP latency reduction in schizophrenic patients may be a manifestation of reduced prefrontal activity or 'hypofrontality' observed with other neuroimaging modalities.

Adult↗
PubMed1998

Steady state visual evoked potential (SSVEP) changes in response to olfactory stimulation.

The location, nature and characteristics of brain activity during detection and identification of odors are of importance if brain function techniques are to be of value to sensory systems. Steady state probe topography (SSPT) has been used in our laboratory to record steady state visual evoked potentials (SSVEP), which have demonstrated cognitive task-related changes in a variety of testing paradigms. The enhanced spatial (when using 64 channels) and temporal resolution (380 ms) of the system enable the brain electrical activity changes occurring before, during and after delivery of an odor to be examined. We have developed a system which can deliver odors during normal respiration and the accurate timing needed for SSVEP recordings. The system is based on the premise that a subject breathing butanol compared with filtered medical air will demonstrate SSVEP topographic changes associated with detection and identification of butanol. During our experiments the subject has either an air sample or an equal volume of butanol injected into the inspiratory airflow. These are randomized, and every breath has the same stimulus system with no known clues as to the differences apart from detection. The results from a panel of 10 female subjects--who all identified the butanol correctly--showed that butanol delivery resulted in sequences of changes in SSVEP topography (amplitude and latencies) which involved parietal, frontal and temporal regions. While consistent with other studies (parietal changes), our results revealed more dynamic temporal changes involving prefrontal and parietal regions at different periods around odor delivery.

Brain↗
PubMed1998

Functional brain electrical activity mapping in boys with attention-deficit/hyperactivity disorder.

BACKGROUND: Symptoms of attention-deficit/hyperactivity disorder (ADHD) have been associated with frontal lobe deficits. We used a novel brain electrical imaging method to investigate rapid and continuous changes in brain activity during the continuous performance task (CPT) in normal boys and in boys with ADHD. The amplitude and latency topography of the steady-state visually evoked potential (SSVEP) were examined while subjects performed the "X" version of the CPT (CPT-X; the reference task) and the "A-X" version of the CPT (CPT-AX). METHODS: Seventeen boys meeting DSM-III-R criteria for ADHD and 17 age-matched controls participated in the study. Brain electrical activity was recorded from 64 scalp sites. During the reference task, subjects pressed a microswitch on the unpredictable appearance of the letter X. During the CPT-AX, subjects were required to press the microswitch on the appearance of the letter X only if an A had preceded it. RESULTS: In the interval between the appearances of the A and the X of the correct trials of the CPT-AX, control boys showed transient reductions in SSVEP latency at right prefrontal sites. By contrast, boys with ADHD showed no change or an increase in prefrontal SSVEP latency at right prefrontal sites. CONCLUSION: Our results suggest increased speed of prefrontal neural processing in children without ADHD following a priming stimulus, and a deficit in such processes in children with ADHD.

Adolescent↗
PubMed1995

Steady-state visually evoked potential topography during the Wisconsin card sorting test.

This paper describes, for the first time, changes in steady-state visually evoked potential (SSVEP) topography associated with the performance of a computerised version of the Wisconsin card sort test (WCS). The SSVEP was recorded from 64 scalp sites and was elicited by a 13 Hz spatially uniform visual flicker presented continuously while 16 subjects performed the WCS. in the WCS, the sort criterion was automatically changed after subjects had sorted 10 cards correctly. Feedback on the 11th card always constituted a cue for a change in the sort criterion. It was found that in the 1-2 sec interval after the occurrence of the cue to change sort criterion, the prefrontal, central and right parieto-temporal regions showed a pronounced attenuation in SSVEP amplitude and an increase in phase lag. These changes, interpreted as an increase in regional cortical activity, are not apparent in the equivalent portions of the WCS when the sort criterion does not need to be changed. These results indicate that the levels of prefrontal and right parieto-temporal activity varied during the performance of the WCS, peaking at the times a change in sort criterion was required.

Adult↗
PubMed1994

Umbilical vein injection for retained placenta: clinical feasibility study of a new technique.

Intraumbilical oxytocin infusion for retained placenta is a relatively new and promising technique. We have tested the clinical feasibility of different infusion techniques in this study. Nine patients had intraumbilical infusions through a mucus aspiration catheter and 12 by an 18 gauge needle. Infusion was successful in 7(77.7%) of 9 cases following catheterisation and in 7(58.3%) of 12 cases following direct injection. Both techniques were clinically feasible, but direct injection was somewhat easier than catheterisation. The importance of non-operative management of retained placenta, particularly in areas with limited medical facilities, is discussed and an approach to the management of retained placenta proposed.

Adult↗
PubMed1993

Umbilical vessel oxytocin administration for retained placenta: in vitro study of various infusion techniques.

OBJECTIVE: The aim of our study was to investigate whether the discrepancies in results between various studies of umbilical vein administration of oxytocin for retained placenta may be related to differences in the infusion techniques used. STUDY DESIGN: An in vitro, descriptive study was performed. Contrast medium was injected into the umbilical vessels of 25 freshly delivered placentas and sequential x-ray films were taken. RESULTS: Capillary filling was inconsistent after injection of 20 ml of solution into the umbilical vein without or with "milking" of the cord (1/5 and 2/5, respectively). These are the techniques most commonly used in reported controlled clinical studies. Injection via an infant mucus aspiration catheter introduced along the umbilical vein to 5 cm from the placental insertion demonstrated a cotyledonary pattern in three of five cases after 20 ml and in all 5 after 30 ml. CONCLUSION: The latter method (use of increased infusion volumes) is recommended in future studies to determine the effectiveness of umbilical vein administration of oxytocin for retained placenta.

Female↗
PubMed1990

Steady-state visually evoked potential topography associated with a visual vigilance task.

This paper describes data which demonstrate a correlation between the magnitude of the Steady-State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13Hz uniform visual flicker presented continuously while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a series of 180 geometrical shapes comprising a sequence of 60 squares, 60 circles and a further 60 squares. Each viewing of the 180 shapes constituted a trial. Trials 1 and 2 were identical while trial 3 differed from the first two in that one of the circles was modified. Subjects were ignorant as to the location of the modified circle and prior to the third trial, were challenged to identify the modified circle. A comparison of trials 2 and 3 indicated that the appearance of the modified circle was associated with an attenuation of the SSVEP in the occipito/parietal region. The same comparison indicated a pronounced SSVEP attenuation in the centro/parietal region during the interval that subjects were anticipating the appearance of the modified circle. These results suggest a distinction between the cortical activation patterns occurring during different phases of a visual vigilance task.

Adolescent↗
PubMedDate not supplied

Human neural responses elicited to observing the actions of others.

Monkey electrophysiological and human neuroimaging studies indicate the existence of specialized neural systems for the perception and execution of actions. To date, the dynamics of these neural systems in humans have not been well studied. Here, we investigated the spatial and temporal behavior of human neural responses elicited to viewing motion of the face, hand, and body. Scalp event-related potentials (ERPs) were recorded in 20 participants viewing videotaped mouth (opening, closing), hand (closing, opening), and body stepping (forward, backward) movements. ERP peak differences within the movements of each body part were compared using topographical maps of voltage, voltage difference, and Student's t-test at ERP peak latencies. Predominantly temporoparietal negative ERPs occurred to motion of all body parts within 200 ms postmovement onset. Hand closure elicited a significantly greater negativity than opening, particularly in the left hemisphere. Vertex positive ERPs within 300 ms postmovement onset were elicited to hand and body motion. A significantly greater positivity occurred for the body stepping forward relative to stepping backward. The ERP topography was consistent with observed activation foci in human neuroimaging studies. Our data indicate that the neural activity of a system dedicated to the perception of high-level motion stimuli can rapidly differentiate between movements across and within body parts.

Adult↗