Paired Trials Research Articles

Effects of female feeding regime in a sexually cannibalistic mantid: fecundity, cannibalism, and male response inStagmomantis limbata(Mantodea)

1. Female feeding regime exhibited a cascade of effects on reproductive biology and behaviour in the mantidStagmomantis limbata(Hahn).2. Well‐fed females (High diet) consistently attained greater body mass, thicker abdomens, and higher fecundity than food‐limited females (Low diet) in four annual generations. Dorso‐ventral abdominal thickness strongly correlated with fecundity.3. In an experiment in captivity, Low diet females were more likely to cannibalize males than High diet females.4. High diet females attracted more males than Low diet females in several contexts. In terms of long‐range attraction, caged High diet females attracted more males in the field. In terms of short‐range attraction, males preferentially mounted and copulated with High diet females in captive paired choice trials. In naturally‐occurring pairs in the field, a preference for females with thick abdomens was evident. These results point to two possible explanations: male choice for well‐fed females and state‐dependent female pheromone emission.5. Two years of field data indicate considerable variation in female feeding success, as measured by abdominal thickness. Average feeding success in nature appears to be relatively high, when comparing the rate of abdominal expansion in the field to captive females maintained on High diets.6. In the field, nearly all mounts and copulations occurred in September in both years, when female feeding success is expected to be high. If mating activity occurs during a window of high female feeding success, so as to reduce the risk of cannibalism for males, then the female feeding regime may be implicated in the phenology of mating activity in cannibalistic species.

Amygdala conditioning modulates sensory input to the cerebellum

Localization of emotional learning in the amygdala and discrete motor learning in the cerebellum provides empirical means to study the mechanisms mediating the interaction between fast emotional and slow motor learning. Behavioral studies have demonstrated that fear conditioning facilitates the motor conditioning. The present study tests the hypothesis that the amygdala output induces this facilitation by increasing the salience of the conditioned stimulus (CS) representation in the pontine nucleus (PN) input to the cerebellum. Paired trials of CS–US (unconditioned stimulus) were applied to anesthetized rats, a condition that allows for amygdala-based fear conditioning but not cerebellar-based motor conditioning. Multiple unit recordings in the PN served to assess the salience of the CS. Results showed that CS–US conditioning increased the PN-reactivity to the CS. Lidocaine-induced reversible inactivation of the amygdala prevented the facilitatory effect of conditioning on the PN-reactivity to the CS. These findings suggest that the amygdala-based conditioned responses reach the PN and increase the salience of the CS signal there, perhaps facilitating cerebellar conditioning. This facilitatory effect of the amygdala may be conceptualized under the ‘two-stage theory of learning’, which predicts that emotional learning in the first stage accelerates the motor learning in the second stage. We hereby demonstrate the physiological mechanism through which fast emotional learning in the first stage facilitates slow cerebellar learning in the second stage.

Interaction between Mutualisms: Ant‐Tended Butterflies Exploit Enemy‐Free Space Provided by Ant‐Treehopper Associations

Although mutualisms have been intensively investigated, demonstration of indirect effects between co-occurring mutualistic systems is rare. For instance, the ecological consequences of co-occurrence of ant-tended insects on a plant have never been examined for survival effects on either trophobiont species. Here, we assess the selective pressures mediating co-occurrence of a facultative ant-tended butterfly (Parrhasius polibetes) with ant-tended treehoppers (Guayaquila xiphias) on Schefflera vinosa shrubs. We evaluated host plant selection and caterpillar survival in P. polibetes in the presence and absence of ant-treehopper associations. Paired trials revealed that butterflies preferably oviposit on branches hosting ant-tended treehoppers when they had a choice between those and branches without this interaction. Presence of ant-tended treehoppers on a branch reduced the abundance of P. polibetes' natural enemies and improved caterpillar survival in both premyrmecophylic and ant-tended phases. Thus ant-tended treehoppers create an enemy-free space on foliage that butterflies exploit to protect larval offspring. These findings connect two widely documented ant-trophobiont mutualisms and highlight the importance of considering multiple interactions for a proper understanding of ant-plant-herbivore systems. Detection of other ant-based mutualisms on oviposition to improve offspring survival may have represented an important evolutionary step in the process of host plant selection in facultative myrmecophilous butterflies.

Human brain connectivity during single and paired pulse transcranial magnetic stimulation

ObjectiveIntracortical inhibition (SICI) and facilitation (ICF) in the human motor cortex can be measured using a paired pulse transcranial magnetic stimulation (ppTMS) protocol. Recently, a technical device has been introduced, which allows recording electroencephalographic (EEG) responses to TMS of a given scalp site. The latency, amplitude and scalp topography of such responses are considered a reflection of cortico-cortical connectivity and functional state. The aim of the present study is to better characterize the neuronal circuits underlying motor cortex connectivity as well as the mechanisms regulating its balance between inhibition and facilitation by means of EEG navigated-ppTMS coregistration. MethodsSub-threshold and supra-threshold single and ppTMS of the left primary motor cortex were carried out during a multi-channel EEG recording on 8 healthy volunteers; the between-pulse intervals used in the paired pulse trials were 3 (for SICI) and 11ms (for ICF). Motor evoked potentials (MEPs) from the opposite hand were simultaneously recorded. ResultsSingle and ppTMS induced EEG responses characterized by a sequence of negative deflections peaking at approximately 7, 18, 44, 100 and 280ms alternated with positive peaks at approximately 13, 30, 60 and 190ms post-TMS. Moreover, ppTMS modulated both EEG evoked activity and MEPs. Amplitude variability of EEG responses was correlated with – and therefore might partially explain – amplitude variability of MEPs. InterpretationEEG-ppTMS is a promising tool to better characterize the neuronal circuits underlying cortical effective connectivity as well as the mechanisms regulating the balance between inhibition and facilitation within the human cortices and the corticospinal pathway.

Stimulus Novelty, and Not Neural Refractoriness, Explains the Repetition Suppression of Laser-Evoked Potentials

Brief radiant laser pulses selectively activate skin nociceptors and elicit transient brain responses (laser-evoked potentials [LEPs]). When LEPs are elicited by pairs of stimuli (S1-S2) delivered at different interstimulus intervals (ISIs), the S2-LEP is strongly reduced at short ISIs (250 ms) and progressively recovers at longer ISIs (2,000 ms). This finding has been interpreted in terms of order of arrival of nociceptive volleys and refractoriness of neural generators of LEPs. However, an alternative explanation is the modulation of another experimental factor: the novelty of the eliciting stimulus. To test this alternative hypothesis, we recorded LEPs elicited by pairs of nociceptive stimuli delivered at four ISIs (250, 500, 1,000, 2,000 ms), using two different conditions. In the constant condition, the ISI was identical across the trials of each block, whereas in the variable condition, the ISI was varied randomly across trials and single-stimulus trials were intermixed with paired trials. Therefore the time of occurrence of S2 was both less novel and more predictable in the constant than in the variable condition. In the constant condition, we observed a significant ISI-dependent suppression of the biphasic negative-positive wave (N2-P2) complex of the S2-LEP. In contrast, in the variable condition, the S2-LEP was completely unaffected by stimulus repetition. The pain ratings elicited by S2 were not different in the two conditions. These results indicate that the repetition-suppression of the S2-LEP is not due to refractoriness in nociceptive afferent pathways, but to a modulation of novelty and/or temporal predictability of the eliciting stimulus. This provides further support to the notion that stimulus saliency constitutes a crucial determinant of LEP magnitude and that a significant fraction of the brain activity time-locked to a brief and transient sensory stimulus is not directly related to the quality and the intensity of the corresponding sensation, but to bottom-up attentional processes.

Apomorphine conditioning and sensitization: The paired/unpaired treatment order as a new major determinant of drug conditioned and sensitization effects

Repeated treatments with psychostimulant drugs generate behavioral sensitization. In the present study we employed a paired/unpaired protocol to assess the effects of repeated apomorphine (2.0 mg/kg) treatments upon locomotion behavior. In the first experiment we assessed the effects of conditioning upon apomorphine sensitization. Neither the extinction of the conditioned response nor a counter-conditioning procedure in which we paired an inhibitory treatment (apomorphine 0.05 mg/kg) with the previously established conditioned stimulus modified the sensitization response. In the second experiment, we administered the paired/unpaired protocol in two phases. In the second phase, we reversed the paired/unpaired protocol. Following the first phase, the paired group alone exhibited conditioned locomotion in the vehicle test and a sensitization response. In the second phase, the initial unpaired group which received 5 paired apomorphine trials during the reversal phase did not develop a conditioned response but developed a potentiated sensitization response. This disassociation of the conditioned response from the sensitization response is attributed to an apomorphine anti-habituation effect that can generate a false positive Pavlovian conditioned response effect. The potentiated sensitization response induced by the treatment reversal protocol points to an important role for the sequential experience of the paired/unpaired protocol in behavioral sensitization.

Infant attention and visual preferences: converging evidence from behavior, event-related potentials, and cortical source localization.

In this study, we had 3 major goals. The 1st goal was to establish a link between behavioral and event-related potential (ERP) measures of infant attention and recognition memory. To assess the distribution of infant visual preferences throughout ERP testing, we designed a new experimental procedure that embeds a behavioral measure (paired comparison trials) in the modified-oddball ERP procedure. The 2nd goal was to measure infant ERPs during the paired comparison trials. Independent component analysis (ICA) was used to identify and to remove eye-movement components from the electroencephalographic data, thus allowing for the analysis of ERP components during paired comparison trials. The 3rd goal was to localize the cortical sources of infant visual preferences. Equivalent current dipole analysis was performed on the ICA components related to experimental events. Infants who demonstrated novelty preferences in paired comparison trials demonstrated greater amplitude Negative central ERP components across tasks than infants who did not demonstrate novelty preferences. Visual preference also interacted with attention and stimulus type. The cortical sources of infant visual preferences were localized to inferior and superior prefrontal cortex and to the anterior cingulate cortex.

Effect size and duration of recommended management practices on carbon sequestration in paddy field in Yangtze Delta Plain of China: A meta-analysis

Increasing evidence has shown that recommended management practices (RMPs) benefit carbon sequestration in cropland soils, but the differences in the effect size and duration between RMPs are not well documented, especially in paddy fields where multiple cropping systems are in use. In order to select feasible techniques and develop effective strategies for soil organic carbon (SOC) management for long-term sustainable rice production that promote environmental health, we conducted a meta-analysis to compare the carbon sequestration effects based on size and duration of several common RMPs using in the Yangtze Delta Plain of eastern China. The meta-analysis data base included 26 long-term field experiments with 86 paired trials. The mean depth of soil sampling in all trials was 16.5 cm. Results showed that there were significant effects from applications of crop residue and animal manure applications on levels of carbon sequestration. Crop residue additions and animal manure applications increased SOC by 0.41 Mg ha −1 yr −1 and 0.34 Mg ha −1 yr −1 on average during the experiment period, respectively. In contrast, reduced/no tillage practices had no effect on levels of carbon sequestration in the study area. Crop residue additions and animal manure applications will enhance SOC, but only over periods of about 20 and 40 years, respectively. Significantly greater effect of RMPs on carbon sequestration occurred in a triple cropping system incorporating with double rice than that in double cropping system with only a single rice season. The above results suggest that increases in organic matter, such as additions of crop residues and animal manure to soils may have great effects on carbon sequestration in paddy fields in the research area.

The anatomy of a slip: Kinetic and kinematic characteristics of slip and non-slip matched trials

To improve understanding of slip propagation mechanisms, one could compare features of early stance phase during slips and non-slips. This study investigated the similarities and differences in kinematics and utilized COF of paired trials, defined as a matched pair of slip and non-slip trials produced by the same participant walking on the same floor condition at the same walking speed condition. Twenty-two participants produced 47 matched trial pairs while walking at 1.5, 1.8 and 2.1 m/s, over a forceplate with an available COF ranging from 0.12 to 0.21. Heel displacement was captured with an infrared motion tracking system and utilized COF was derived from ground reaction forces. ANOVA revealed no significant differences between the slip and non-slip groups in horizontal heel velocity just prior to heel strike or for heel velocity or slip distance during the 20 ms period following heel strike. Significant differences were found between the groups in utilized COF and horizontal heel velocity at 25 and 30 ms following heel strike. Differences in heel kinematics and kinetics during early stance phase between the slip and non-slip trials are discussed. The results differ from several previous studies, likely due to methodological differences, as the present study was conducted on marginally slippery surfaces, as opposed to very low COF conditions with thick contaminant layers.

Bias in trials comparing paired continuous tests can cause researchers to choose the wrong screening modality

BackgroundTo compare the diagnostic accuracy of two continuous screening tests, a common approach is to test the difference between the areas under the receiver operating characteristic (ROC) curves. After study participants are screened with both screening tests, the disease status is determined as accurately as possible, either by an invasive, sensitive and specific secondary test, or by a less invasive, but less sensitive approach. For most participants, disease status is approximated through the less sensitive approach. The invasive test must be limited to the fraction of the participants whose results on either or both screening tests exceed a threshold of suspicion, or who develop signs and symptoms of the disease after the initial screening tests.The limitations of this study design lead to a bias in the ROC curves we call paired screening trial bias. This bias reflects the synergistic effects of inappropriate reference standard bias, differential verification bias, and partial verification bias. The absence of a gold reference standard leads to inappropriate reference standard bias. When different reference standards are used to ascertain disease status, it creates differential verification bias. When only suspicious screening test scores trigger a sensitive and specific secondary test, the result is a form of partial verification bias.MethodsFor paired screening tests with bivariate normally distributed scores, we give formulae and programs to quantify the effect of paired screening trial bias on a paired comparison of area under the curves. We fix the prevalence of disease, and the chance a diseased subject manifests signs and symptoms. We derive the formulas for true sensitivity and specificity, and those for the sensitivity and specificity observed by the study investigator.ResultsThe observed area under the ROC curves is quite different from the true area under the ROC curves. The typical direction of the bias is a strong inflation in sensitivity, paired with a concomitant slight deflation of specificity.ConclusionIn paired trials of screening tests, when area under the ROC curve is used as the metric, bias may lead researchers to make the wrong decision as to which screening test is better.

Cooling via one hand improves physical performance in heat-sensitive individuals with Multiple Sclerosis: A preliminary study

BackgroundMany individuals afflicted with multiple sclerosis (MS) experience a transient worsening of symptoms when body temperature increases due to ambient conditions or physical activity. Resulting symptom exacerbations can limit performance. We hypothesized that extraction of heat from the body through the subcutaneous retia venosa that underlie the palmar surfaces of the hands would reduce exercise-related heat stress and thereby increase the physical performance capacity of heat-sensitive individuals with MS.MethodsTen ambulatory MS patients completed one or more randomized paired trials of walking on a treadmill in a temperate environment with and without cooling. Stop criteria were symptom exacerbation and subjective fatigue. The cooling treatment entailed inserting one hand into a rigid chamber through an elastic sleeve that formed an airtight seal around the wrist. A small vacuum pump created a -40 mm Hg subatmospheric pressure enviinside the chamber where the palmar surface of the hand rested on a metal surface maintained at 18–22°C. During the treatment trials, the device was suspended from above the treadmill on a bungee cord so the subjects could comfortably keep a hand in the device without having to bear its weight while walking on the treadmill.ResultsWhen the trials were grouped by treatment only, cooling treatment increased exercise durations by 33% (43.6 ± 17.1 min with treatment vs. 32.8 ± 10.9 min. without treatment, mean ± SD, p < 5.0·10-6, paired t-test, n = 26). When the average values were calculated for the subjects who performed multiple trials before the treatment group results were compared, cooling treatment increased exercise duration by 35% (42.8 ± 16.4 min with treatment vs. 31.7 ± 9.8 min. without treatment, mean ± SD, p < 0.003, paired t-test, n = 10).ConclusionThese preliminary results suggest that utilization of the heat transfer capacity of the non-hairy skin surfaces can enable temperature-sensitive individuals with MS to extend participation in day-to-day physical activities despite thermally stressful conditions. However, systematic longitudinal studies in larger cohorts of MS patients with specific deficits and levels of disability conducted under a variety of test conditions are needed to confirm these preliminary findings.

Forward conditioning with wheel running causes place aversion in rats

Backward pairings of a distinctive chamber as a conditioned stimulus and wheel running as an unconditioned stimulus (i.e., running-then-chamber) can produce a conditioned place preference in rats. The present study explored whether a forward conditioning procedure with these stimuli (i.e., chamber-then-running) would yield place preference or aversion. Confinement of a rat in one of two distinctive chambers was followed by a 20- or 60-min running opportunity, but confinement in the other was not. After four repetitions of this treatment (i.e., differential conditioning), a choice preference test was given in which the rat had free access to both chambers. This choice test showed that the rats given 60-min running opportunities spent less time in the running-paired chamber than in the unpaired chamber. Namely, a 60-min running opportunity after confinement in a distinctive chamber caused conditioned aversion to that chamber after four paired trials. This result was discussed with regard to the opponent-process theory of motivation.

How do biological control and hybridization affect enemy escape?

Two mechanisms often linked with plant invasions are escape from enemies and hybridization. Classical biological control aims to reverse enemy escape and impose top-down population control. However, hybridization has the potential to alter interactions with enemies and thus affect biological control. We examined how introductions of biological control agents affect enemy escape by comparing specialist enemy loads between the native and introduced ranges of two noxious weeds (spotted and diffuse knapweed; Centaurea stoebe L. and C. diffusa Lam.) that have been the targets of an extensive biological control program. Hybrids between spotted and diffuse knapweed are often found within diffuse knapweed sites in North America, so we also compared enemy loads on plants that appeared morphologically like diffuse knapweed and hybrids. Finally, we tested the preference for diffuse knapweed, hybrids, and spotted knapweed of one of the agents thought to be instrumental in control of diffuse knapweed ( Larinus minutus; Curculionidae). In North America spotted knapweed has largely escaped its root herbivores, while seedhead herbivore loads are comparable in the introduced and native ranges. Diffuse knapweed exhibited seedhead herbivore loads five times higher in the introduced compared to native range. While this pattern of seedhead herbivory is expected with successful biological control, increased loads of specialist insect herbivores in the introduced range have rarely been reported in the literature. This finding may partially explain the better population control of diffuse vs. spotted knapweed. Within North American diffuse knapweed sites, typical diffuse knapweed and hybrid plants carried similar herbivore loads. However, in paired feedings trials, the specialist L. minutus demonstrated a preference for newly created artificial hybrids over North American diffuse knapweed and for European diploid spotted knapweed over North American tetraploid spotted knapweed. Overall though, hybridization does not appear to disrupt biological control in this system.

Cerebellum volume and eyeblink conditioning in schizophrenia

Although accumulating evidence suggests that cerebellar abnormalities may be linked to the symptoms and course of schizophrenia, few studies have related structural and functional indices of cerebellar integrity. The present study examined the relationship between the volume of specific subregions of the cerebellum and cerebellar function, as measured by eyeblink conditioning (EBC). Nine individuals with schizophrenia and six healthy comparison participants completed structural magnetic resonance imaging of the brain and a delay EBC procedure. Volumetric measurements were taken for the whole brain, whole cerebellum, cerebellar anterior lobules I–V and posterior lobules VI–VII. The schizophrenia group had smaller cerebellar anterior lobes and exhibited impaired EBC relative to the comparison group. In the comparison group, larger anterior volume correlated with earlier conditioned response onset latencies and increased amplitudes of the unconditioned blink response during paired trials (i.e., when the conditioned and unconditioned stimuli co-occurred). The findings that smaller anterior cerebellar volumes and EBC impairments were associated with schizophrenia are consistent with non-human studies showing that anterior cerebellar abnormalities are associated with deficits in delay EBC. The lack of a significant correlation between indices of EBC and cerebellar volume within the schizophrenia group suggests an aberrant relationship between cerebellar structure and function.

Efficacy and safety of a paired sedation and ventilator weaning protocol for mechanically ventilated patients in intensive care (Awakening and Breathing Controlled trial): a randomised controlled trial

Approaches to removal of sedation and mechanical ventilation for critically ill patients vary widely. Our aim was to assess a protocol that paired spontaneous awakening trials (SATs)-ie, daily interruption of sedatives-with spontaneous breathing trials (SBTs). In four tertiary-care hospitals, we randomly assigned 336 mechanically ventilated patients in intensive care to management with a daily SAT followed by an SBT (intervention group; n=168) or with sedation per usual care plus a daily SBT (control group; n=168). The primary endpoint was time breathing without assistance. Data were analysed by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00097630. One patient in the intervention group did not begin their assigned treatment protocol because of withdrawal of consent and thus was excluded from analyses and lost to follow-up. Seven patients in the control group discontinued their assigned protocol, and two of these patients were lost to follow-up. Patients in the intervention group spent more days breathing without assistance during the 28-day study period than did those in the control group (14.7 days vs 11.6 days; mean difference 3.1 days, 95% CI 0.7 to 5.6; p=0.02) and were discharged from intensive care (median time in intensive care 9.1 days vs 12.9 days; p=0.01) and the hospital earlier (median time in the hospital 14.9 days vs 19.2 days; p=0.04). More patients in the intervention group self-extubated than in the control group (16 patients vs six patients; 6.0% difference, 95% CI 0.6% to 11.8%; p=0.03), but the number of patients who required reintubation after self-extubation was similar (five patients vs three patients; 1.2% difference, 95% CI -5.2% to 2.5%; p=0.47), as were total reintubation rates (13.8%vs 12.5%; 1.3% difference, 95% CI -8.6% to 6.1%; p=0.73). At any instant during the year after enrolment, patients in the intervention group were less likely to die than were patients in the control group (HR 0.68, 95% CI 0.50 to 0.92; p=0.01). For every seven patients treated with the intervention, one life was saved (number needed to treat was 7.4, 95% CI 4.2 to 35.5). Our results suggest that a wake up and breathe protocol that pairs daily spontaneous awakening trials (ie, interruption of sedatives) with daily spontaneous breathing trials results in better outcomes for mechanically ventilated patients in intensive care than current standard approaches and should become routine practice.

Effectiveness of repellents for reducing damage to eucalypt seedlings by browsing mammals

Summary Marsupial herbivores cause significant damage to seedlings in forestry operations. Damage can lead to changes in tree form, reduced growth rates and seedling death. Non-lethal tactics, as a component of an integrated browsing management strategy, are currently sought to assist in reducing this damage. One such tactic involves making seedlings deterrent or unpalatable through the application of chemical repellents. We investigated the effect of three chemical repellents, Plant Plus, Sentree and Hot Shot, upon browsing of Eucalyptus nitens seedlings by two marsupial herbivores known to browse newly established plantations in Tasmania: the common brushtail possum and the red-bellied pademelon. One repellent was designed to deter herbivores through an unpleasant odour (Plant Plus), one to be unpalatable (Hot Shot), and the third to be both deterrent and unpalatable (Sentree). We ran a combination of paired feeding trials (one repellent + control) and cafeteria trials (all three repellents at once with no control) with captive possums and pademelons, for three nights per trial. Both species consumed significantly more foliage from control seedlings than those treated with Plant Plus or Sentree repellents. Pademelons also preferred controls to Hot Shot treated seedlings but, interestingly, possums consumed significantly more foliage from seedlings treated with Hot Shot than from control seedlings. The most effective repellent against both herbivores was Sentree, and the marked reduction in browsing indicates that further testing in the field is warranted.

Effect of external stents on prevention of intimal hyperplasia in a canine vein graft model

External stents have been used to reduce intimal hyperplasia of vein grafts. The aim of the present study was to define the size of an external stent appropriate for a particular graft by comparing vein grafts with different sizes of external stents. A series of paired trials was performed to compare femoral vein grafts with different sizes of external stents, where 30 modeled canines were equally divided into three groups: 6-mm external stent vs non-stent control, 4-mm vs 6-mm external stent, and 4-mm vs 8-mm external stent. At day 3 after operation, color Doppler flow imaging (CDFI) was done to observe blood flow in the lumen. Four weeks later, CDFI was re-checked and the veins were harvested, stained and measured. All grafts were patent without formation of thrombosis. External stents significantly reduced intimal thickness of the vein grafts with a 6-mm external stent compared with the vein grafts without external stents (P < 0.05). The vein grafts with the 4-mm external stent had similar intimal, medial and adventitial thicknesses compared with those with the 6-mm external stent and the 8-mm external stent. External stents can reduce intimal hyperplasia of vein grafts. Stents of different diameters exert the similar effect on prevention of intimal hyperplasia.

Disengagement of the location negative priming effect: The influence of an intervening response

Reaction time is significantly longer when a target stimulus arises at a location that has just contained a distractor event, relative to when it appears at a new location [i.e., called, the location negative priming (NP) effect]. The NP effect is eliminated when the second of two paired trials (i.e., prime-to-probe trials) predictably lacks a distractor when the preceding trial contains both a target and a distractor event (T+D), but not when a prime distractor appears alone (D-only). We tested the possibility that the failed NP process disengagement seen with D-only prime trials resulted because they do not require the production of an overt intervening response. This possibility was supported. Results also showed that the intervening response had to meet prerequisites; namely, the response had to be prime-generated, i.e., come from the subset of experimental responses and have engaged in a conflict with the prime distractor-activated response.

Manganese and Welding Fume Exposure and Control in Construction

Overexposure to welding fume constituents, particularly manganese, is of concern in the construction industry due to the prevalence of welding and the scarcity of engineering controls. The control effectiveness of a commercially available portable local exhaust ventilation (LEV) unit was assessed. It consisted of a portable vacuum and a small bell-shaped hood connected by a flexible 2 inch (50.8 mm) diameter hose, in both experimental and field settings. The experimental testing was done in a semienclosed booth at a pipefitter training facility. Five paired trials of LEV control vs. no control, each approximately 1 hr in duration and conducted during two successive welds of 6 inch (152.4 mm) diameter carbon steel pipe were run in random order. Breathing zone samples were collected outside the welding hood during each trial. In the field scenario, full-shift breathing zone samples were collected from two pipefitters welding carbon steel pipe for a chiller installation on a commercial construction project. Eight days of full-shift sampling were conducted on both workers (n = 16), and the LEV was used by one of the two workers on an alternating basis for 7 of the days. All samples were collected with personal sample pumps calibrated at 2 L/min. Filter cassettes were analyzed for total particulate and manganese concentration by a certified laboratory. In the experimental setting, use of the portable LEV resulted in a 75% reduction in manganese exposure (mean 13 μg/m 3 vs. 51 μ g/m 3 ; p < 0.05) and a 60% reduction in total particulate (mean 0.74 mg/m 3 vs. 1.83 mg/m 3 ; p < 0.05). In the field setting, LEV use resulted in a 53% reduction in manganese exposure (geometric mean 46 μ g/m 3 vs. 97 μ g/m 3 ; p < 0.05) but only a 10% reduction in total particulate (geometric mean 4.5 mg/m 3 vs. 5.0 mg/m 3 ; p > 0.05). These results demonstrate that LEV use can reduce manganese exposure associated with welding tasks in construction.

State-Dependent Mechanisms of LTP Expression Revealed by Optical Quantal Analysis

The expression mechanism of long-term potentiation (LTP) remains controversial. Here we combine electrophysiology and Ca(2+) imaging to examine the role of silent synapses in LTP expression. Induction of LTP fails to change p(r) at these synapses but instead mediates an unmasking process that is sensitive to the inhibition of postsynaptic membrane fusion. Once unmasked, however, further potentiation of formerly silent synapses leads to an increase in p(r). The state of the synapse thus determines how LTP is expressed.