Poststimulation time interval-dependent effects of motor cortex anodal tDCS on reaction-time task performance

Anodal transcranial direct current stimulation (tDCS) induces long-term potentiation-like plasticity, which is associated with long-lasting effects on different cognitive, emotional, and motor performances. Specifically, tDCS applied over the motor cortex is considered to improve reaction time in simple and complex tasks. The timing of tDCS relative to task performance could determine the efficacy of tDCS to modulate performance. The aim of this study was to compare the effects of a single session of anodal tDCS (1.5 mA, for 15 min) applied over the left primary motor cortex (M1) versus sham stimulation on performance of a go/no-go simple reaction-time task carried out at three different time points after tDCS—namely, 0, 30, or 60 min after stimulation. Performance zero min after anodal tDCS was improved during the whole course of the task. Performance 30 min after anodal tDCS was improved only in the last block of the reaction-time task. Performance 60 min after anodal tDCS was not significantly different throughout the entire task. These findings suggest that the motor cortex excitability changes induced by tDCS can improve motor responses, and these effects critically depend on the time interval between stimulation and task performance.     

Hippocampal PKA/CREB pathway is involved in the improvement of memory induced by spermidine in rats

Spermidine (SPD) is an endogenous polyamine that modulates N-methyl-D-aspartate (NMDA) receptor function, and has been reported to facilitate memory formation. In the current study we determined whether or not the PKA/CREB signaling pathway is involved in SPD-induced facilitation of memory of inhibitory avoidance task in adult rats. The post-training administration of the cAMP-dependent protein kinase (PKA) inhibitor, N-[2-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide [H-89, 0.5 ρmol intrahippocampal (ih)] or the antagonist of the NMDA receptor polyamine-binding site (arcaine, 0.02 nmol ih) with SPD (0.2 nmol ih) prevented memory improvement induced by SPD. Intrahippocampal administration of SPD (0.2 nmol) facilitated PKA and cAMP response element-binding protein (CREB) phosphorylation in the hippocampus 180 min, but not 30 min, after administration, and increased translocation of the catalytic subunit of PKA into the nucleus. Arcaine (0.02 nmol) and H-89 (0.5 ρmol) prevented the stimulatory effect of SPD on PKA and CREB phosphorylation. These results suggest that memory enhancement induced by the ih administration of SPD involves the PKA/CREB pathways in rats.     

Instruction and load effects on high-skill and low-skill individuals: A study in the domain of mental arithmetic

What happens when people are asked to respond as quickly or as accurately as possible? This study tested the effects of speed/accuracy instructions and working-memory load on people's strategy efficiency and strategy selection. Adult participants solved simple addition problems (Experiment 1) and simple multiplication problems (Experiment 2) under load and no-load conditions and provided trial-by-trial strategy reports. High-skill participants were more efficient than low-skill participants, but the underlying causes of these skill-related effects differed across experiments. In the addition experiment, high-skill participants responded adaptively to the changing situations by changing their strategy choices, which resulted in smaller effects on their actual performance. Low-skill participants in contrast, did not change their strategy choices as adaptively, which resulted in less efficient performance—and especially so under load conditions. In the multiplication experiment, high-skill and low-skill participants differed in strategy efficiencies rather than in strategy choices. In the discussion, the results are further interpreted and future adaptations for the adaptive strategy choice model (ASCM; Siegler & Jenkins, 1989) are suggested.     

Stimulus- and response-conflict-induced cognitive control in the flanker task

Recently, several studies have been conducted to investigate the top-down adjustments made after incongruent trials during conflict tasks. In the present study, we investigated conflict monitoring with different types of conflict. In a modified version of the flanker task, a distinction was made between stimulus—stimulus conflict and stimulus—response conflict. Six colors were mapped to three responses in order to exclude all sequences in which a relevant or an irrelevant stimulus- or response-related feature was repeated from trialn−1 to trialn. An analysis of the effect of the congruency of the previous trial demonstrated that conflict adaptation was present. The stimulus congruency effect was reduced after both a stimulus-incongruent trial and a response-incongruent trial. The response congruency effect did not vary as a function of previous congruency. These findings are discussed in relation to the distinction between conflict detection and conflict regulation.     

Model‐related factor score predictors for confirmatory factor analysis

The present paper introduces model‐related (MR) factor score predictors, which reflect specific aspects of confirmatory factor models. The development is mainly based on Schönemann and Steiger's regression score components, but it can also be applied to the factor score coefficients. It is shown that the rotation of factor score predictors has no impact on the covariance matrix reproduced from the corresponding regression component patterns. Thus, regression score components or factor score coefficients can be rotated in order to obtain the required properties. This idea is the basis for MR factor score predictors, which are computed by means of a partial Procrustes rotation towards a target pattern representing the interesting properties of a confirmatory factor model. Two examples demonstrate the construction of MR factor score predictors reflecting specific constraints of a factor model.     

Macbeth and the Joystick: Evidence for moral cleansing after playing a violent video game

The “Macbeth effect” denotes the phenomenon that people wish to cleanse themselves physically when their moral self has been threatened. In this article we argue that such a threat to one's moral self may also result from playing a violent video game, especially when the game involves violence against humans. The cleansing effect should be particularly strong among inexperienced players who do not play video games on a regular basis, because frequent players may apply other strategies to alleviate any moral concerns. Seventy students played one of two violent video games and were then asked to select 4 out of 10 gift products, half of which were hygiene products. Inexperienced players reported more moral distress when the game involved violence against humans (compared to violence against objects), and selected more hygiene products in this condition than frequent video game players. Frequent players, on the other hand, reported less moral distress, irrespective of the game they played.     

Is judgment of random time intervals biased and capacity-limited?

 Recently, random generation of time intervals has been proposed as a procedure to impair executive processing in a dual-task paradigm without substantial interference with phonological and visuo-spatial working memory resources. A fundamental assumption of this procedure is that humans are able to distinguish time sequences on their degree of randomness. The present study tests this assumption. To this end, non-biased, repetition-biased, alternation-biased sequences and repetitive rhythms were judged under conditions of higher or lower executive load. In Exp. 1, load depended on the presentation speed, while in Exp. 2, a dual-task condition was used with either a concurrent number-copying task or an arithmetic task. It was found that the participants could distinguish repetitive rhythms from more or less random sequences, and that both accuracy of this judgment and latency were affected by the concurrent load. The findings are taken as a first indication that random time judgment is capacity-limited. Received: 9 September 1999 / Accepted: 1 October 1999