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PubMed2001

Determinants of chlorpyrifos exposures and urinary 3,5,6-trichloro-2-pyridinol levels among termiticide applicators.

The exposures and work activities of 41 applicators in North Carolina using chlorpyrifos-containing termiticides were characterized. Personal air and urine samples were collected on multiple days within one week. Detailed information about chemical use, tasks, personal protective equipment and hygiene was recorded. During the 202 applicator-days monitored, 415 treatment jobs were performed. Full-shift chlorpyrifos exposures ranged from <0.048 to 110 microg/m(3) (N=184), with a geometric mean (GM) of 10 microg/m(3). Urinary 3,5,6-trichloro-2-pyridinol (TCP) levels ranged from 9.42 to 1960 microg/g creatinine (N=271) and varied significantly by day of the week (GM range: 169-262 microg/g creatinine). Predictive models for chlorpyrifos air exposure and urinary TCP levels were developed using mixed-effects stepwise linear regression. Determinants of airborne chlorpyrifos exposure included minutes chlorpyrifos applied and enclosed crawl space treated (yes/no). Determinants of TCP levels (depending on the model) included day-of-the-week, the chlorpyrifos air concentration one and two days before urine collection, minutes of chlorpyrifos applied one and two days before urine collection, enclosed crawl space treated (yes/no), and commercial structure treated (time-weighted). Within- and between-worker variability was similar for airborne chlorpyrifos; however, for TCP, between-worker variability exceeded within-worker variability by six times. The elimination half-life of TCP (26.9 h) and possibly the short sampling interval (one week) may explain the low TCP within-worker variability. Applicators' weekly mean ln(TCP levels) and weekly mean ln(chlorpyrifos air concentrations) were highly and positively linearly correlated (r(2)=0.73, P<0.0001). In summary, mixed-effects models were successfully constructed to predict airborne chlorpyrifos exposure and urinary TCP levels.

Adolescent↗
PubMedDate not supplied

Practicing medicine in a new environment: what can we learn from the business managers?

Physicians, once only responsible for patient care, now are responsible for their organization's management. Although this paradigm shift occasioned much opposition, most aspects of this change are improving as the rules are reevaluated and reconsidered. Physician managers have difficult tasks for which medical school provides no preparation. Employees must be individually evaluated, so their unique talents can be properly exploited and appropriately compensated. Each person's weaknesses must be improved upon with delicacy, while his or her strengths are given greater and greater focus. This is especially true with regards to billing and coding because the financial health of all healthcare businesses requires organizational competence in this arena. It is vital to have an understanding of each staff member's skills, talents, and knowledge, and a proper deployment of each person into the appropriate job. The goal of any manager is a group of satisfied employees who enjoy their work and make appropriately recognized contributions.

Benchmarking↗
PubMedDate not supplied

When push comes to shove: compensation for passive perturbation of the head during natural gaze shifts.

The effects of passive displacements to the head delivered by an abrupt push to the upper body were studied in human subjects during gaze shifts to nearby targets while the head was completely unrestrained. Accurate measurements of gaze were obtained via the Maryland Revolving Field Monitor, used to measure head and eye rotations unconfounded with translations, and by an acoustic ranging system, used to measure head translations. Compensation for head perturbations was quite good, with gaze errors much the same as gaze errors in the absence of the push. Compensation along one or both meridians was achieved by means of the vestibulo-ocular response in many of the gaze shifts. The results suggest an impressive ability to coordinate head and eye movements during natural gaze shifts, carried out by one or more different kinds of compensatory systems that the subject can access at will or according to task demands.

Eye Movements↗
PubMed1999

Long-term reversal of hemispheric specialization for visual memory in a split-brain macaque.

Accuracy of response and pattern of ocular fixations in three split-brain macaques were used to evaluate performance of each hemisphere in a continuous visual recognition task. The animal indicated by ocular fixation upon response points whether a displayed image or face was 'NEW' or 'OLD'. An inadvertent lesion of cingulate gyrus severely reduced contralateral fixations and impaired performance of the affected hemisphere in one animal, confirming the inferred relation between hemisphere and laterality of fixations. The hemispheres in the other two animals were initially remarkably similar in accuracy with human faces and with images; but the right hemisphere was significantly superior to the left for macaque faces. Parallel to this, in the one animal tested while simultaneously using both eyes/hemispheres, fixations were made primarily on the left half of human and macaque faces (right hemispheric control), whereas for images the ocular fixations were predominantly focused on the right half. However, after further, extensive training the left hemisphere performed with significantly greater accuracy than the right on all material and this shift was accompanied and further corroborated by a reversal of the fixational pattern to favor the right half of faces, as continued to be the case with images. Thus, over the long term both the pattern of ocular fixations and the accuracy of performance demonstrate a migration from right to left hemispheric dominance as familiarity with the task increased. Performance of the initially superior hemisphere actually diminished with this shift, presenting a uniquely puzzling question of hemispheric balance in the absence of the forebrain commissures.

Animals↗
PubMedDate not supplied

Comparison of horizontal head movements evoked by auditory and visual targets.

Head movement propensity-the pattern of head saccades dependent on methods of target presentation-varies among individuals. The present group of 9 young adults was previously ranked in a visual saccadic task according to this propensity. The present report examines how and why this propensity changes if the saccades are made to auditory targets. 1) Spatially identical, interleaved, auditorily and visually elicited horizontal saccadic gaze shifts (jumps) differed in amplitude and in starting and/or ending position. The jumps were executed in two head movement modes: first, the non-aligned mode was a standard reaction-time single gaze step between two points. Second, the head-aligned mode required alignment of the head with the fixation (starting) point; thereafter both modes were identical. All results in the auditory task are expressed relative to the visual results. 2) In the non-aligned mode, head movement amplitudes were increased on average by 15% (for example, an 80 degrees jump elicited a 12 degrees larger head movement), and velocity decreased by 12%, reflecting the increased demands of the auditory task. More importantly, the differences between subjects was narrowed; that is, head movement propensity was homogenized in the auditory task. In the visual task, head-movers willingly move their heads off and across the midline, whereas non-movers are unwilling to leave the midline from eccentric starting points or to eccentric ending points. This is called the midline attraction effect and was previously linked to spatial reference frames. The homogenization in the auditory task was characterized by head-movers increasing, and non-movers decreasing, their midline attraction, suggesting altered spatial reference frames. 3) For heuristic purposes, the ideal head-mover is defined by a gain of 1.0 in the visual task, and by external earth-fixed reference frames. Similarly, the ideal non-mover has a gain of 0.0 and has a bias toward body (or some par of the body)-fixed reference frames. In the auditory task these gains (and reference frames) in head movers and non-movers are homogenized (close to 0.5), either by the participation of the head (movement of the ears in space) in sensory acquisition or by differences in central nervous processing of the two modalities, or both.

Acoustic Stimulation↗
PubMed2001

Long-lasting rebound cue effects following single doses of nicotine and amphetamine: implications for understanding tolerance.

RATIONALE: Previous drug-discrimination studies have, with the exception of nicotine (NIC), demonstrated tolerance to the cue effects of a broad range of drugs of abuse. Barrett et al. have shown that tolerance to a drug's cue properties reflects drug-induced rebound shifts in the discrimination baseline and not a weakened or less salient cue. OBJECTIVES: The objective of the present study was to use a discrimination task sensitive to bidirectional cue changes to characterize the interoceptive cues associated with both the primary and rebound cues produced by nicotine in an attempt to understand why a recent study by Shoaib et al. failed to observe tolerance to the nicotine cue. METHODS: Since dopamine (DA) has been implicated in mediating the NIC cue, rats were trained to discriminate between 0.25 mg/kg amphetamine (AMPH), an indirect DA agonist, and 0.033 mg/kg haloperidol (HAL), a DA antagonist at the D2 receptor site. Training doses were chosen so that rats responded about equally on both levers when tested on saline (SAL) following acquisition. This procedure provided a behavioral baseline to assess NIC-related changes along a presumed continuum of DA-mediated cues. Following acquisition of the discrimination: (i) NIC substitution tests were conducted, (ii) rats were tested for lever choice at intervals from 2 h to 48 h following treatment with single doses of 0.25 mg/kg and 0.50 mg/kg NIC, and (iii) rats were challenged with test doses of NIC during a period of NIC rebound. RESULTS: (i) NIC substituted for AMPH in a dose- dependent manner. (ii) At short intervals after treatment with 0.25 mg/kg and 0.50 mg/kg NIC, rats responded primarily on the AMPH lever followed by a shift to predominant responding on the HAL lever 16-24 h post-treatment, before returning to predrug levels. (iii) No evidence was observed for acute tolerance to NIC. CONCLUSIONS: The robust and long-lasting rebound cues associated with training level doses of NIC suggest that maximal tolerance would likely develop to the NIC cue during the acquisition phase of the conventional NIC-saline discrimination study.

Amphetamine↗
PubMed2000

Exposure and acute exposure-effects before and after modification of a contaminated humidification system in a synthetic-fibre plant.

OBJECTIVE: Follow-up study of exposure and acute exposure-effects after modification to steam humidification of a contaminated cold water system which had caused an outbreak of humidifier fever in a synthetic-fibre plant. METHODS: Before and after modification of the system aerobiological measurements were performed. Concentrations of fungi and bacteria, in colony forming units (cfu) per m3, were measured by stationary air sampling with an Andersen sampler. Endotoxin levels (pg/m3) were determined by Limulus Amoebocyte Lysate (LAL) assay in pooled dust from personal air sampling. An indication of exposure levels of oil-mist was obtained by monitoring with a direct reading optical photometer. Changes as acute exposure-effects in spirometry and white blood cell count, during an afternoon shift were compared in exposed and non-exposed workers before and after modification. RESULTS: Measured levels of fungi, total bacteria, Gram-negative bacteria and endotoxins both before and after modification were below levels which would be expected to be associated with the exposure-effects. However, after modification, we found that the statistically significant differences in levels of bacteria and endotoxins with a department without humidification no longer existed. Mean oil-mist concentrations were below 1 mg/m3, with short-time peak exposure during certain tasks of up to 5 mg/m3. Before modification, in exposed workers there was significantly more decline of spirometry, and more increase of white blood cell count during the first afternoon shift, compared with non-exposed workers. In exposed workers, the white blood cell count increase was positively associated with decline of spirometry. After modification, differences between exposed and non-exposed workers no longer existed. CONCLUSION: Follow-up investigation of acute exposure-effects demonstrated the effectiveness of remedial actions taken against a contaminated humidification system. Follow-up of exposure-effects in particular is recommended when there is doubt about the interpretation of exposure measurements.

Bacteria↗
PubMed2001

A medial to lateral shift in pre-movement cortical activity in hemi-Parkinson's disease.

OBJECTIVE: Recent evidence suggests that cortical activity associated with voluntary movement is relatively shifted from medial to lateral premotor areas in Parkinson's disease. This shift occurs bilaterally even for unilateral responses. It is not clear whether the shift in processing reflects an overall change in movement strategy, thereby involving alternate cortical areas, or reflects a compensatory change whereby, given the appropriate conditions, less impaired cortical areas are able to provide a similar function in compensation for those areas which are more impaired. This issue was examined in patients with hemi-Parkinson's disease, in whom basal ganglia impairment is most pronounced in one hemisphere. METHODS: Fourteen patients with hemi-Parkinson's disease and 15 age-matched control subjects performed a Go/NoGo finger movement task and the contingent negative variation (CNV) was recorded from 21 scalp positions. RESULTS AND CONCLUSIONS: Maximal CNV amplitudes were found over central medial regions for control subjects, but were shifted more frontally for Parkinson's disease patients, reduced in amplitude over the midline and lateralized towards the side ipsilateral to the greatest basal ganglia impairment. This shift in cortical activity from medial to lateral areas in Parkinson's disease patients appears to reflect a compensatory mechanism operating predominantly on the side of greatest basal ganglia impairment.

Action Potentials↗
PubMed1995

Discrimination training, partial reinforcement, and increases in intertrial interval all reduce response speed in a continuously reinforced key-pecking task.

Pigeons were trained in a discrete-trial task in which a response to the center key obtained illumination of a side key and a single response to the side key terminated a trial with either reinforcement or nonreinforcement. Center-key speeds (i.e., reciprocals of latencies) declined with increases in intertrial interval, and it is argued that this effect is related to a decreased likelihood as intertrial interval increases that birds will be near the key at trial onset. Side-key speeds on trials with reinforcement decreased both with increases in intertrial interval and with shifts from continuous reinforcement to either a discrimination or a partial-reinforcement condition. The effects on side-key speeds are compared with effects observed in alley-running tasks using rats, and an interpretation in terms of frustration theory is offered for the results obtained in both types of task.

Journal Article↗
PubMed1998

Event-related potentials associated with correct and incorrect responses in a cued antisaccade task.

In an antisaccade task, subjects are instructed to inhibit a reflexive saccade towards a peripheral stimulus flash and to generate a saccade in the opposite direction. It has been shown recently that normal subjects will generate a high number of incorrect prosaccades in an antisaccade task if the fixation point is extinguished 200 ms before the stimulus appears and if a valid cue for the subsequent antisaccade is given during this gap period. In the present study we recorded cerebral event-related potentials from 19 scalp electrodes from normal subjects prior to correct and incorrect responses in a cued antisaccade task to investigate the neural processes associated with correct antisaccades and incorrect prosaccades in this task. Correct antisaccades and incorrect prosaccades were associated with a negative potential with a maximal amplitude around stimulus onset over the dorsomedial frontal cortex. This potential was higher prior to correct antisaccades than prior to incorrect prosaccades. The execution of a correct antisaccade was preceded by a shift of a negative potential from the parietal hemisphere contralateral to the visual stimulus towards the parietal hemisphere ipsilateral to the stimulus. These results support the view that the supplementary eye fields participate in the inhibition of incorrect saccades in a cued antisaccade task and show that the parietal cortex participates in generating a neural representation of the visual stimulus in the hemifield ipsilateral to the stimulus before generating a motor response.

Adult↗
PubMed1982

Readiness-potentials preceding unrestricted 'spontaneous' vs. pre-planned voluntary acts.

The nature of readiness-potentials (RPs) that may be associated with fully endogenous, 'freely' voluntary acts was investigated. Restriction on when to act were eliminated and instructions fostered 'spontaneity.' The 'self-initiated' RPs exhibited in these conditions were categorizable into two (possibly three) types, all of which could be exhibited by the same subject. Type I had an early onset at about -1050 +/- 175 msec and a long ramp-like form, resembling self-paced RPs. In type II the main negative shift began at about -575 +/- 150 msec, and at about -240 +/- 50 msec in type III. Type II partially resembled the similarly timed NS' component in self-paced RPs. For acts produced at known, preset times, in which freedom of choice was eliminated but planning to act was required, RPs resembled self-initiated type I RPs and self-paced RPs. All RPs were maximal at the vertex, especially type II even though it was also bilaterally asymmetrical. These distributions suggest that cortical areas other than area 4 and 6 contribute importantly, especially to type II. All RPs, whether in self-initiated or pre-planned acts, appear related specifically to preparation for a motor action. When task-related skin stimuli replaced self-initiated movements, under similar conditions of attentiveness (and expectancy), there were either no or relatively small event-preceding-slow potential shifts. All post-stimulus P300 waves were very large. Two volitional processes are postulated: process I is associated with development of pre-planning or preparation to act in the near future (seconds), whether voluntary choice is present (type I RPs) or absent (pre-set RPs); process II, with an onset at roughly 0.5 sec before the act, is associated more uniquely with voluntary choice and with the more specific as well as endogenous urge or intention to act; it can be present in the comparative absence of or in sequence and overlapping with process I.

Brain↗
PubMed2000

A silent event-related functional MRI technique for brain activation studies without interference of scanner acoustic noise.

A new data acquisition method for silent, event-related functional MRI in which scanner acoustic noise does not interfere with brain activation is introduced and evaluated in an auditory tonotopic mapping experiment. This method takes into account the hemodynamic-response characteristics of the brain during activation, associated with both task performance and scanner noise. A data acquisition scheme was designed to collect task-induced brain activation signals without interference of scanner noise on stimulus delivery or on the measured response. The advantages of the technique were demonstrated in a tonotopic mapping experiment of human auditory cortex. Tonotopic maps obtained by the technique in normal subjects showed distinct spatial shifts of the activation foci in the lateral part of Heschl's gyrus with changing stimulus frequency, whereas no systematic shift was shown in a conventional event-related experiment using the same stimulation paradigm. Signal change in the activation foci with the new technique was 54% larger than with the conventional technique, suggesting an increased dynamic range of the signal change associated with task-induced brain activation under silent conditions.

Acoustic Stimulation↗
PubMed2001

Evidence for impairment of behavioural inhibition in performance of operant tasks in tPA-/- mice.

We have previously shown that mice that lack the serine protease, tissue plasminogen activator (tPA), show over-responding on the active lever during time-out periods in an I.V. cocaine self-administration task. To investigate this effect further, tPA knockout mice (tPA-/-) were tested in a number of operant paradigms for a liquid food reinforcer. tPA-/- and wild-type (WT) control mice acquired a fixed ratio (FR) and a fixed interval (FI) task equally. However, extinction from the FR schedule resulted in a significant decrease in responses on the active and inactive levers in the WT mice whilst responding on the inactive lever remained high in the tPA-/- animals. In a differential reinforcement of low rate (DRL) task, tPA-/- mice acquired the task at a slower rate than WT animals. This was characterised by high levels of responding on the active lever during the first 15 sessions in the tPA-/- mice. Burst responding on the active lever (lever press rate with an inter-response time of less than 3 s) was especially high in these animals. This behaviour pattern resulted in the animals obtaining less reinforcers than the WT controls. Acute cocaine dose-dependently shifted the pattern of behaviour on the active lever towards shorter inter-response times. However, there was no difference between the tPA-/- and WT mice in their sensitivity to cocaine on this task. Repeated administration of a low dose of cocaine did not alter performance on this task in either set of animals. When the DRL task was modified to allow the tPA-/- and WT mice an equal number of reinforced trials per session there was no difference in the ability of the animals to perform the task. This would suggest that the tPA-/- mice have a tendency to over-respond but that this can be overcome when the task is modified to allow equal opportunity to learn.

Animals↗
PubMed1988

Management, productivity and admitting departments.

It is the task of the manager of an admitting department to complete the tasks of the department with the minimum amount of manpower consistent with high quality. High productivity is a combination of an effective workplace and manipulation of the work flow and the staffing to minimize the amount of avoidable idle time within the department. This can take the form of load shifting and creative staffing. The monitoring of the productivity level in the department can be accomplished by comparison of the actual time spent by the employees and the standard time (the time determined that is should take to complete all of the tasks). Quality can be determined by random review of the output to determine the error rate. Both the measurement of productivity and quality provide the manager with indications of whether the department is operating at the optimal level, or if further investigation is needed.

Admitting Department, Hospital↗
PubMedDate not supplied

Impaired visual attention in children with dyslexia.

Reading involves the correct and rapid identification of visual stimuli with letters and words. The processing of visual stimuli depends not only on the integrity of the peripheral and central visual system but also on the attentional systems involved. In the present study, a cue-target visual attention task was administered to a population-based sample of 25 children with dyslexia from 10 to 12 years of age. A control group matched for group size, age, and gender was obtained from the same general population. A two-stage screening process involved a spelling task of regular words followed by a battery of five single-word reading tasks. The cue-target task involved both a computer-controlled stimulus presentation and a computer-controlled measurement of reaction time. The data were analyzed by visual field, cue condition (valid, invalid, and no cue), and cue-target interval (CTI). The results showed a general pattern of slower responses in the dyslexia group compared to the control group. The dyslexia group also had longer reaction times in the short CTI condition (covert shift of attention) and in the long CTI condition (overt shift of attention). The findings may reflect a general attentional deficit to visual stimuli in dyslexia, possibly related to problems with the recruitment of necessary cognitive resources for the performance of complex reaction time tasks and for fluent reading.

Attention↗
PubMed1993

Cognitive brain potentials in a three-stimulus auditory "oddball" task after closed head injury.

Event-related potentials (ERPs) were recorded in a three stimulus oddball task from 16 patients who had sustained a severe closed head injury at least 6 months before testing, and from 16 control subjects. The stimuli comprised a random sequence of frequent non-target tones (P = 0.70), rare target tones (P = 0.15), and rare novel sounds (P = 0.15). The task requirement was to respond promptly to each target tone. From a latency of 200 msec onwards, the ERPs evoked by frequent non-targets were substantially more negative-going in the head-injured than in the control group. When this difference in the ERPs to the frequent tones was taken into account, there was no evidence to suggest that either the latency or the amplitude of the target-evoked N2 and P3b components differed between the groups. The novel stimuli evoked a prominent P3a component. The amplitude and scalp distribution of this component differed little between the groups, but its peak latency was reliably longer in the head-injured subjects. The findings in respect of the N2 and P3b components suggest that impairments in early processing of task-relevant stimuli are not an invariant feature of closed head injury. The findings regarding P3a suggest that, in the majority of patients, head injury has only a limited effect on the neural systems underlying involuntary shifts of attention.

Acoustic Stimulation↗