The effects of 5-HT1A receptor agonists, 5-HT1A receptor antagonists and their interaction on the fear-potentiated startle response

Time-resolved small-angle X-ray scattering (TR-SAXS) was used to monitor the structural changes that occur upon the binding of the natural substrates to a mutant version of the allosteric enzyme aspartate transcarbamoylase from Escherichia coli, in which the creation of a critical link stabilizing the R state of the enzyme is hindered. Previously, SAXS experiments at equilibrium showed that the structures of the unligated mutant enzyme and the mutant enzyme saturated with a bisubstrate analog are indistinguishable from the T and R state structures, respectively, of the wild-type enzyme (Tauc et al., Protein Sci. 3:1998-2004, 1994). However, as opposed to the wild-type enzyme, the combination of one substrate, carbamoyl phosphate, and succinate, an analog of aspartate, did not convert the mutant enzyme into the R state. By using TR-SAXS we have been able to study the transient steady-state during catalysis using the natural substrates rather than the nonreactive substrate analogs. The steady-state in the presence of saturating amount of substrates is a mixture of 60% T and 40% R structures, which is further converted entirely to R in the additional presence of ATP. These results provide a structural explanation for the reduced cooperativity observed with the mutant enzyme as well as for the stimulation by ATP at saturating concentrations of substrates. They also illustrate the crucial role played by domain motions and quaternary-structure changes for both the homotropic and heterotropic aspects of allostery.     

Recollection and familiarity through the looking glass: When old does not mirror new.

The authors use the qualitative differences logic to demonstrate that 2 separate memory influences underlie performance in recognition memory tasks, familiarity and recollection. The experiments focus on the mirror effect, the finding that more memorable stimulus classes produce higher hit rates but lower false-alarm rates than less memorable stimulus classes. The authors demonstrate across a number of experiments that manipulations assumed to decrease recollection eliminate or even reverse the hit-rate portion of the mirror effect while leaving the false-alarm portion intact. This occurs whether the critical distinction between conditions is created during the test phase or manipulated during the study phase. Thus, when recollection is present, it dominates familiarity so that the hit-rate portion of the mirror effect primarily reflects recollection; when recollection is largely absent, the opposite pattern associated with the familiarity process emerges. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Predictive validity of the potentiated startle response as a behavioral model for anxiolytic drugs

The fear-potentiated startle (PSR) paradigm is a putative behavioral model for the determination of anxiolytic properties of drugs. The present study further investigated the predictive validity of the model. Predictive validity is high, when only drugs clinically used as anxiolytics attenuate PSR dose dependently. Results showed that startle potentiation decreased dose dependently after the administration of the anxiolytics CDP (2.5-10 mg/kg, IP) and alprazolam (1-3 mg/kg, IP). After administration of the clinically non-anxiolytic drugs amitriptyline (2.5-10 mg/kg, IP), carbamazepine (5-20 mg/kg, IP), fentanyl (0.0025-0.04 mg/kg, SC), naloxone (2.5-10 mg/kg, IP), nicotine (0.4-1.6 mg/kg, IP), alcohol (500-2000 mg/kg, IP), and d-amphetamine (0.6-2.4 mg/kg, IP), a dose-dependent decrease in startle potentiation was not found. The PSR correctly discriminated most of the drugs tested in clinically anxiolytic and clinically non-anxiolytic drugs. However, haloperidol behaved as a false positive, and results of nicotine and alcohol were at variance with results reported by others.     

Assessing the effectiveness of a voluntary online discussion forum on improving students’ course performance

The purpose of this study was to evaluate the effectiveness of voluntary discussion forums in a higher education setting. Specifically, we examined intrinsic forum participation and investigated its relation to course performance across two experiments. In Experiment 1 (N = 1284) an online discussion forum was implemented at the beginning of an undergraduate introductory psychology course, and measures of course performance (i.e., writing assignment grades, exam grades, and extra-credits obtained) were compared with measures of forum participation. In Experiment 2 (N = 1334) an online discussion forum was implemented halfway through a second undergraduate introductory psychology course, after an initial measure of course performance was obtained, to control for the potential confound of student engagement (e.g., students who perform better in the course use the forum more). Overall, the results showed that students who participated in the forum tended to have better performance in the course, and furthermore that participating in the discussion forum, particularly reading posts on the forum, slightly improved exam performance. This study provides empirical support for the theoretical proposition that there is a facilitation effect of discussion forum participation on course performance. The results also suggest that implementation of an online discussion forum is beneficial even if a teacher only invests minimal time on the forum.     

Independence or redundancy? Two models of conscious and unconscious influences.

L. L. Jacoby et al (1993) assume that the conscious and unconscious processes make independent contributions to task performance. As an alternative to the independence model, it is suggested that a redundancy model based on the assumption that conscious processes are always associated with correlated unconscious processes can also be used to dissociate the separate influences of these processes. Using data reported by Jacoby et al, it is shown that each model leads to different but equally plausible estimates of conscious and unconscious influences, following both variations in attention (i.e., focused vs divided) and in encoding (i.e., read vs generate). Given these results, both the dependence and redundancy models must be considered plausable models of the underlying relation between conscious and unconscious processes. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Investigation a memory-based account of negative priming: Support for selection-feature mismatch.

Using typical and modified negative priming tasks, the selection-feature mismatch account of negative priming was tested. In the modified task, participants performed selections on the basis of a semantic feature (e.g., referent size). This procedure has been shown to enhance negative priming (P. A. MacDonald, S. Joordens, & K. N. Seergobin, 1999). Across 3 experiments, negative priming occurred only when the repeated item mismatched in terms of the feature used as the basis for selections. When the repeated item was congruent on the selection feature across the prime and probe displays, positive priming arose. This pattern of results appeared in both the ignored- and the attended-repetition conditions. Negative priming does not result from previously ignoring an item. These findings strongly support the selection-feature mismatch account of negative priming and refute both the distractor inhibition and the episodic-retrieval explanations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The similarities (and familiarities) of pseudowords and extremely high-frequency words: Examining a familiarity-based explanation of the pseudoword effect.

The pseudoword effect is the finding that pseudowords (i.e., rare words or pronounceable nonwords) give rise to more hits and false alarms than words. Using the retrieving effectively from memory (REM) model of recognition memory, we tested a familiarity-based account of the pseudoword effect: Specifically, the pseudoword effect arises because pseudowords lack distinctive semantic meanings. Because semantics can differentiate orthographically similar words (e.g., horse vs. house), by lacking distinctive semantics, pseudowords have greater interitem similarity than words, and hence more familiarity, which gives rise to the pseudoword effect. Across two sets of simulations, we demonstrate that this account explains the pseudoword effect in addition to accounting for why the pseudoword effect is absent when irregular nonwords are compared with words. Furthermore, our modeling efforts suggest a novel experiment that leads us to the discovery of a new concordant effect. Namely, extremely high-frequency words behave like pseudowords (giving rise to more hits and false alarms than high-frequency words) and also have less distinctive semantics than high-frequency words. We conclude that our work provides strong evidence in favor of the familiarity-based accounts of the pseudoword effect. We discuss the implications of our research with regard to various issues surrounding the pseudoword effect and REM model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The rate ratio of injury and aggressive incident for alcohol alone,cocaine alone and simultaneous use before the event: A case–crossover study

Objectives

(i) To estimate the rate ratio (RR) of use of alcohol alone, cocaine alone, and both substances simultaneously on acute injury or an aggressive incident, (ii) to compare the RRs for simultaneous use within 3 or 6 h of the event; and (iii) to compare the RRs of two measures of exposure, “hours of feeling effects” vs estimates based on self-reported quantity and frequency of use.

Methods

The study employed a case–crossover design with the frequency approach. Clients (N = 616) in substance abuse treatment for alcohol or cocaine issues from 2009 to 2012 completed a self-administered questionnaire on their substance use within 3 and 6 h before a recent injury or physically aggressive incident. Clients also reported detailed quantity and frequency information in relation to their typical substance use, as well as information on “feeling effects”. The RR of acute harms due to substance use was estimated using the Mantel–Haenszel estimator.

Results

In the 6-h window before the event, use of cocaine alone, alcohol alone and simultaneous alcohol and cocaine use were each significantly (P < 0.05) related to a recent injury and aggressive incident. Simultaneous use was not significantly greater than use of either drug alone. Estimates of RR based on simultaneous use for a 3-h window before the event were consistently larger than those based on a 6-h window, and comparisons were significant (P < 0.05) for an aggressive incident but not an injury. With reference to the two measures of exposure, three of eight comparisons of RRs were significantly larger for feeling the effects of the substance in comparison to quantity and frequency of substance use.

Conclusion

These findings are consistent with increased likelihood of harms related to the acute effects of alcohol alone, cocaine alone or simultaneous use. The results are suggestive that the acute effects of these drugs may be better measured within a 3-h time window than a 6-h window. Finally, we found that “hours of feeling effects” yielded higher estimates of RR than the quantity–frequency approach; however both measures support the overall findings.     

Selective attention: A reevaluation of the implications of negative priming.

The notion that inhibitory processes play a critical role in selective attention has gained wide support. Much of this support derives from studies of negative priming. The authors note that the attribution of negative priming to an inhibitory mechanism of attention draws its support from a common assumption underlying priming procedures, together with the procedure that has been used to measure negative priming. The results from a series of experiments demonstrate that selection between 2 competing prime items is not required to observe negative priming. This result is demonstrated across several experiments in which participants named 1 of 2 items in a second display following presentation of a single-item prime. The implications of these results for existing theories of negative priming are discussed, and a theoretical framework for interpreting negative priming and several related phenomena is forwarded. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term semantic priming: A computational account and empirical evidence.

Semantic priming is traditionally viewed as an effect that rapidly decays. A new view of long-term word priming in attractor neural networks is proposed. The model predicts long-term semantic priming under certain conditions. That is, the task must engage semantic-level processing to a sufficient degree. The predictions were confirmed in computer simulations and in 3 experiments. Experiment 1 showed that when target words are each preceded by multiple semantically related primes, there is long-lag priming on a semantic decision task but not on a lexical-decision task. Experiment 2 replicated the long-term semantic priming effect for semantic decisions with only one prime per target. Experiment 3 demonstrated semantic priming with much longer word lists at lags of 0, 4, and 8 items. These are the first experiments to demonstrate a semantic priming effect spanning many intervening items and lasting much longer than a few seconds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)