Effects of fimbria lesions on trace two-way active avoidance acquisition and retention in rats

The fimbria-fornix (FF) is the main subcortical input to the hippocampus. It has been shown that FF lesions facilitate performance on a standard-delay two-way active avoidance task (AA2), thought to involve implicit memory. The hippocampal region is required for explicit or relational memory. It has been proposed that the hippocampus and related structures might associate events that are separated in space or time and detect elements shared in common by such discontiguous episodes. Therefore, FF lesions would be expected to impair performance on a trace paradigm, which introduces an interval between the CS (conditioned stimulus) and the US (unconditioned stimulus) and is generally considered a model of explicit memory. We predicted that FF lesions would impair memory in a trace AA2 procedure, while the same lesions would facilitate memory in a standard delay version of the task. To test this hypothesis, two experiments were carried out in 102 male Wistar rats. The first experiment characterized the trace paradigm using this kind of conditioning and demonstrated that control rats were able to acquire and retrieve (24 h and 11 days postacquisition) the association between the CS (tone) and the US (electric foot shock) when a trace interval (5, 10, or 20 s) was interposed between both stimuli. In the second experiment, we investigated the effects of FF electrolytic lesions on the same task using delay and trace (10-s trace interval) paradigms. Surprisingly, FF lesions facilitated the acquisition and the 24-h retention of the AA2 not only on the standard delay paradigm, but also with the trace paradigm. We suggest that facilitative effects could be a result of impairment in contextual learning.     

Co-occurrence of non-suicidal self-injury and impulsivity in extreme weight conditions

The aims of the present study were to determine the prevalence of non-suicidal self-injury (NSSI) in different eating disorder (ED) groups and morbid obesity, and to investigate whether NSSI in different ED/obesity groups co-occur with impulsivity. We assessed 535 individuals (365 ED and 170 obese patients) by means of a single item assessing lifetime NSSI and the Barratt Impulsivity Scale, which measures different dimensions of impulsivity. The results showed that 19.1% of the ED patients engaged in at least one act of NSSI during their life-time. NSSI was more prevalent in Bulimia Nervosa, Binge Eating Disorder, Eating Disorder Not Otherwise Specified compared to Anorexia Nervosa, Restrictive type and morbid obesity. Finally, ED/obese patients who engaged in NSSI scored significantly higher on the attentional, motor and non-planning subscales than patients without NSSI. The implications of these findings for the treatment of NSSI in binge/purging ED patients are discussed.     

The effect of skewness and kurtosis on the robustness of linear mixed models

This study analyzes the robustness of the linear mixed model (LMM) with the Kenward–Roger (KR) procedure to violations of normality and sphericity when used in split-plot designs with small sample sizes. Specifically, it explores the independent effect of skewness and kurtosis on KR robustness for the values of skewness and kurtosis coefficients that are most frequently found in psychological and educational research data. To this end, a Monte Carlo simulation study was designed, considering a split-plot design with three levels of the between-subjects grouping factor and four levels of the within-subjects factor. Robustness is assessed in terms of the probability of type I error. The results showed that (1) the robustness of the KR procedure does not differ as a function of the violation or satisfaction of the sphericity assumption when small samples are used; (2) the LMM with KR can be a good option for analyzing total sample sizes of 45 or larger when their distributions are normal, slightly or moderately skewed, and with different degrees of kurtosis violation; (3) the effect of skewness on the robustness of the LMM with KR is greater than the corresponding effect of kurtosis for common values; and (4) when data are not normal and the total sample size is 30, the procedure is not robust. Alternative analyses should be performed when the total sample size is 30.     

Parental Psychopathology Levels as a Moderator of Temperament and Oppositional Defiant Disorder Symptoms in Preschoolers

Oppositional Defiant Disorder (ODD) is among the most prevalent disorders in preschoolers. It has been linked to temperament, since characteristics such as elevated surgency and negative affect, as well as low levels of effortful control, contribute to the development of this disorder. Evidence also indicates that parental psychopathology can accentuate temperamental traits. Our aim was to assess whether the levels of psychopathology of mothers and fathers acts as a moderator of the relationship between temperament and ODD symptoms in preschoolers, both cross-sectionally at ages 3, 4 and 5, and longitudinally between ages 3 and 5. The sample included 550 children evaluated at ages 3, 4 and 5 through questionnaires and a semi-structured diagnostic interview with parents. Parents also answered a questionnaire about their own psychopathology. The results indicated that negative affect and effortful control are associated with higher levels of ODD symptoms in preschoolers. At child age 5, higher levels of paternal depression and anxiety increased the effect of low effortful control on ODD. High levels of negative affect and low levels of effortful control at age 3 were statistical predictors of ODD levels at age 5, and this relationship was also moderated by paternal anxiety and depression. The results have important clinical implications for the proper orientation of interventions, suggesting that interventions should integrate the paternal caregiver in the treatment.     

The spatial correspondence hypothesis and orienting in response to central and peripheral spatial cues

Two experiments examined visual orienting in response to spatial precues. In Experiment 1A participants were informed that targets usually (p =.8) appeared on the same side as cues in a particular colour (e.g., red). Rapid orienting was observed, with both central and peripherally presented cues. In Experiment IB cue displays were spatially symmetric. Participants were informed that target location (left or right) was usually predicted (p =.8) by cue colour (red or green). Orienting effects were observed, but these were slower to develop and much weaker than in Experiment 1 A. In Experiment 2A and 2B the cue was a single, centrally presented letter. We compared effects of spatially symmetric (T, X, v, o) and asymmetric (d, b) letter cues. Validity effects were present for asymmetric cues, but entirely absent for symmetric cues. These finding are discussed in terms of Lambert and Duddy's (2002) proposal that spatial correspondence learning plays a critical role in spatial precueing. Implications of the results for the distinction between endogenous and exogenous orienting are also considered.     

Using the linear mixed model to analyze nonnormal data distributions in longitudinal designs

Using a Monte Carlo simulation and the Kenward–Roger (KR) correction for degrees of freedom, in this article we analyzed the application of the linear mixed model (LMM) to a mixed repeated measures design. The LMM was first used to select the covariance structure with three types of data distribution: normal, exponential, and log-normal. This showed that, with homogeneous between-groups covariance and when the distribution was normal, the covariance structure with the best fit was the unstructured population matrix. However, with heterogeneous between-groups covariance and when the pairing between covariance matrices and group sizes was null, the best fit was shown by the between-subjects heterogeneous unstructured population matrix, which was the case for all of the distributions analyzed. By contrast, with positive or negative pairings, the within-subjects and between-subjects heterogeneous first-order autoregressive structure produced the best fit. In the second stage of the study, the robustness of the LMM was tested. This showed that the KR method provided adequate control of Type I error rates for the time effect with normally distributed data. However, as skewness increased—as occurs, for example, in the log-normal distribution—the robustness of KR was null, especially when the assumption of sphericity was violated. As regards the influence of kurtosis, the analysis showed that the degree of robustness increased in line with the amount of kurtosis.     

Evaluating effects in short time series: alternative models of analysis

In the applied context, short time-series designs are suitable to evaluate a treatment effect. These designs present serious problems given autocorrelation among data and the small number of observations involved. This paper describes analytic procedures that have been applied to data from short time series, and an alternative which is a new version of the generalized least squares method to simplify estimation of the error covariance matrix. Using the results of a simulation study and assuming a stationary first-order autoregressive model, it is proposed that the original observations and the design matrix be transformed by means of the square root or Cholesky factor of the inverse of the covariance matrix. This provides a solution to the problem of estimating the parameters of the error covariance matrix. Finally, the results of the simulation study obtained using the proposed generalized least squares method are compared with those obtained by the ordinary least squares approach. The probability of Type I error associated with the proposed method is close to the nominal value for all values of rho1 and n investigated, especially for positive values of rho1. The proposed generalized least squares method corrects the effect of autocorrelation on the test's power.     

Autocorrelation problems in short time series

The work of Huitema (1985) on autocorrelation in behavioral data suggests that the use of conventional statistical methods is justified. The present study restates the problem of autocorrelation by analyzing 100 baselines of small samples designs published in the Journal of Applied Behavior Analysis during 1992. The results show a negative bias in the autocorrelations, especially with very small samples. The autocorrelation values are normally distributed, and the method of Davies, Trigg, and Newbold (1977) is the most accurate in calculating the standard deviation.     

Trajectories of Oppositional Defiant Disorder Irritability Symptoms in Preschool Children

This study traces the developmental course of irritability symptoms in oppositional defiant disorder (ODD) from ages 3–5 and examines the psychopathological outcomes of the different trajectories at age 6. Method. A sample of 622 3-year-old preschoolers (311 were boys), followed up until age 6, was assessed yearly with a semi-structured diagnostic interview with parents and at age 6 with questionnaires answered by parents, teachers and children. Results. Growth-Mixture-Modeling yielded five trajectories of irritability levels for the whole sample (high-persistent 3.5 %, decreasing 3.8 %, increasing 2.6 %, low-persistent 44.1 % and null 46.0 %). Among the children who presented with ODD during preschool age, three trajectories of irritability symptoms resulted (high-persistent 31.9 %, decreasing 34.9 % and increasing 33.2 %). Null, low-persistent and decreasing irritability courses in the sample as a whole gave very similar discriminative capacity for children’s psychopathological state at age 6, while the increasing and high-persistent categories involved poorer clinical outcomes than the null course. For ODD children, the high-persistent and increasing trajectories of irritability predicted disruptive behavior disorders, comorbidity, high level of functional impairment, internalizing and externalizing problems and low anger control at age 6. Conclusions. Irritability identifies a subset of ODD children at high risk of poorer longitudinal psychopathological and functional outcomes. It might be clinically relevant to identify this subset of ODD children with a high number of irritability symptoms throughout development with a view to preventing comorbid and future adverse longitudinal outcomes.