The effect of warning stimulus modality on blink startle modification in reaction time tasks

The present study investigated the effects of lead stimulus modality on modification of the acoustic startle reflex during three reaction time tasks. In Experiment 1, participants (N = 48) were required to press a button at the offset of one stimulus (task relevant) and to ignore presentations of a second (task irrelevant). Two tones that differed in pitch or two lights served as signal stimuli. Blink startle was elicited during some of the stimuli and during interstimulus intervals. Skin conductance responses were larger during task-relevant stimuli in both groups. Larger blink facilitation during task-relevant stimuli was found only in the group presented with auditory stimuli, whereas larger blink latency shortening during task-relevant stimuli was found in both groups. Experiment 2 (N = 32) used only a task-relevant stimulus. Blink magnitude facilitation was significant only in the group presented with tones, whereas blink latency shortening was significant in both groups. Experiment 3 (N = 80) used a go/nogo task that required participants to press a button if one element of a compound stimulus ended before the second, but not if the asynchrony was reversed. The offset asynchrony was varied between groups as a manipulation of task difficulty. Startle magnitude facilitation was larger during acoustic than during visual stimuli and larger in the easy condition. The present data indicate that startle facilitation in a reaction time task is affected by stimulus modality and by task demands. The effects of the task demands seem to be independent of lead stimulus modality.     

Molecular monitoring of resistant dhfr and dhps allelic haplotypes in Morogoro and Mvomero districts in south eastern Tanzania

Background

Resistance to the antimalarial drug sulfadoxine-pyrimethamine (SP) emerged in Plasmodium falciparum from Asia in the 1960s and subsequently spread to Africa. In Tanzania, SP use as a national policy began in 1983 as a second line to chloroquine (CQ) for the treatment of uncomplicated malaria, until August 2001 when it was approved to replace CQ as a national first line.

Objective

The present study assesses the frequency of resistant dhfr and dhps alleles in Morogoro-Mvomero district in south eastern Tanzania and contrast their rate of change during 17 years of SP second line use against five years of SP first line use.

Methodology

Cross sectional surveys of asymptomatic infections were carried out at the end of rainy season during July–September of 2000, when SP was the national second line (CQ was the first line) and 2006 when SP was the national first line antimalarial treatment. Genetic analysis of SP resistance genes was carried out on 1,044 asymptomatic infections and the effect of the two policies on SP evolution compared.

Results

The frequency of the most resistant allele, the double dhps-triple dhfr mutant genotype, increased by only 1% during 17 years of SP second line use, but there was a dramatic increase by 45% during five years of SP first line use.

Conclusion

We conclude that National policy change from second line to first line SP, brought about an immediate shift in treatment practice and this in turn had a highly significant impact on drug pressure. The use of SP in specific programs only such as intermittent preventive treatment of infants (IPTi) and intermittent preventive treatment of pregnant women (IPTp) will most likely reduce substantially SP selection pressure and the SP resistance alleles alike.     

A startling absence of emotion effects: Active attention to the startle probe as a motor task cue appears to eliminate modulation of the startle reflex by valence and arousal

Research has shown that during emotional imagery, valence and arousal each modulate the startle reflex. Here, two imagery-startle experiments required participants to attend to the startle probe as a simple reaction time cue. In Experiment 1, four emotional conditions differing in valence and arousal were examined. Experiment 2, to accentuate potential valence effects, included two negative high arousal, a positive high arousal and a negative low arousal condition. Imagery effectively manipulated emotional valence and arousal, as indicated by heart rate and subjective ratings. Compared to baseline, imagery facilitated startle responses. However, valence and arousal failed to significantly affect startle magnitude in both experiments and startle latency in Experiment 1. Results suggest that emotional startle modulation is eclipsed when the probe is significant for task completion and/or cues a motor response. Findings suggest that an active, rather than defensive, response set may interfere with affective startle modulation, warranting further investigation.     

Behavioral and electrocortical evidence of an interaction between probability and task metrics in movement preparation

Recent neurophysiological evidence suggests that cognitive factors shape neural activity in cortical areas such as parietal (area 5), premotor, and primary motor cortex. The implication of these findings is that behavioral signatures of cognitive factors and movement-specific factors should likewise be interdependent. The present study provides evidence of this interdependence in both behavioral (reaction time) and electrophysiological (P300) measures. Subjects performed a two-choice pointing task, in which the angular distance between the two required movement directions (task metrics) and the probability of the two responses was varied. In a control condition, a single reaction was required in response to both stimuli to test for the influence of stimulus metrics. Results from the pointing task showed a clear interaction between the metrics and effects of probability. When the potential targets were widely separated (120 degrees), stimulus probability influences reaction time and P300 amplitude in the classic fashion (longer reaction times and larger P300 amplitudes to less probable responses). When pointing to targets that were narrowly separated (20 degrees), probability had no effect: both rare and frequent targets were "functionally frequent." The same interaction was not observed in the control condition, indicating that metrics were primarily influencing movement preparation rather than stimulus processing. The results are consistent with the theoretical framework of dynamic field theory and demonstrate that metrics are an important factor that must be taken into account when assessing the processes associated with movement preparation.     

Movement preparation and working memory: a behavioural dissociation

We can cross temporal sensorimotor contingencies by remembering sensory events or by anticipating motor responses. Here we tested the hypothesis that sensory and motor representations can be accessed according to different temporal dynamics. We predicted that the manipulation of movement representations would lead to a performance independent from the length of a delay interposed between sensory instructions and behavioural responses. Conversely, we expected a delay-dependent performance whenever temporary storage of sensory information was necessary to solve the task. We have measured reaction times and error rate in subjects performing a delayed non-matching to sample task. Task contingencies rather than explicit instructions ensured that either sensory or motor representations were used to cross the delay period on each trial. We tested our hypothesis by manipulating the length of the delays between stimulus presentation and behavioural response. We found that carrying sensory material over temporal gaps affects performance as a non-linear function of time, whereas movement representations remain robust over a wide range of delays. This novel behavioural paradigm might prove effective in dissociating the neural bases of preparatory and mnestic processes in normal human subjects, as well as their disorders in neurological patients.     

Functional brain connectivity and cognition: effects of adult age and task demands

Previous neuroimaging research has documented that patterns of intrinsic (resting state) functional connectivity (FC) among brain regions covary with individual measures of cognitive performance. Here, we examined the relation between intrinsic FC and a reaction time (RT) measure of performance, as a function of age group and task demands. We obtained filtered, event-related functional magnetic resonance imaging data, and RT measures of visual search performance, from 21 younger adults (19–29 years old) and 21 healthy, older adults (60–87 years old). Age-related decline occurred in the connectivity strength in multiple brain regions, consistent with previous findings. Among 8 pairs of regions, across somatomotor, orbitofrontal, and subcortical networks, increasing FC was associated with faster responding (lower RT). Relative to younger adults, older adults exhibited a lower strength of this RT-connectivity relation and greater disruption of this relation by a salient but irrelevant display item (color singleton distractor). Age-related differences in the covariation of intrinsic FC and cognitive performance vary as a function of task demands.     

The effect of attentional cueing on conscious awareness of stimulus and response

Attending to a cued location in space leads to faster reaction times when a stimulus is presented there. The reasons for this attentional effect, and its specific locus in the information-processing chain between stimulus and response, remain unclear. One suggestion is that attention speeds the conscious detection of stimuli. Surprisingly, this possibility appears not to have been tested directly. To resolve this question, we asked subjects to make simple responses to lateralised targets that followed either a valid, invalid or neutral cue, and to judge the perceived time of the target onset, or of their response, by delayed report of the position of a clock hand. Our results showed that only a small and non-significant part of the attentional effect is due to delayed conscious awareness of the stimulus. The greater part of the attentional effect is localised either subsequent to conscious detection of stimuli or occurs in a separate, parallel processing stream from that which generates the motor response. Electronic Publication     

Changes in the somatosensory N250 and P300 by the variation of reaction time

We investigated the relationship between somatosensory event-related potentials (ERP) and the variation of reaction time (RT). For this purpose, we recorded the ERPs (N250 and P300) in fast- and slow-reaction trials during a somatosensory discrimination task. Strong, standard, and weak target electrical stimuli were randomly delivered to the left median nerve at the wrist with a random interstimulus interval (900–1,100 ms). All the subjects were instructed to respond by pressing a button with their right thumb as fast as possible whenever a target stimulus was presented. We divided all the trials into fast- and slow-RT trials and averaged the data. N250 latency tended to be delayed when the RT was slow, but not significantly. P300 latency was delayed significantly when the RT was slow, but to a much lesser extent than the RT delay, so we concluded that the change of RT was not fully determined by the processes reflected by the somatosensory N250 or P300. Furthermore, the larger and earlier P300 in the fast-RT trials implied that when larger amounts of attentional resources were allocated to a given task, the speed of stimulus evaluation somewhat increased and RT was shortened to a great extent. N250 amplitude did not significantly vary in the two RT clusters. In conclusion, the somatosensory N250 reflects active target detection, which is relatively independent of the modulation of the response speed, whereas the somatosensory P300 could change without manipulation of either the stimulus or the response processing demand. Electronic Publication     

多重PCR归化法平行检测HBV和HCV的研究

目的：建立一种多重PCR归化法并应用于对HBV、HCV平行检测。方法：利用PCR反应5′端允许添加非互补序列的原理，运用内外两对引物，经过2轮扩增，使目的产物均带上共有序列，再以共有序列为引物进行扩增，实现多重扩增。比较和筛选四种核酸提取方法。运用正交优化法，优化并确定最佳扩增条件。对28份血标本进行对比试验，并进行质量评价。结果：归化多重PCR方法对于HBV、HCV病毒合并感染患者的诊断敏感性为83.5%，诊断特异性为70.0%，诊断指数为153．3％，诊断效率为72．2％；对HBsAg阳性患者的HBV DNA的诊断敏感性为78．6％，诊断特异性为80．0％，诊断指数为158．6％，诊断效率为79．2％。对抗－HCV阳性患者的HCV RNA的诊断敏感性为75．0％，诊断特异性为90．0％，诊断指数为165．0％，诊断效率为83．3％。结论：多重PCR归化法在多基因扩增或多种病原体的同时平行检测领域具有较大应用潜力。该方法实用、准确、可靠，对HBV HCV的防治具有实际意义。