Catecholaminergic effects on inhibitory control depend on the interplay of prior task experience and working memory demands

Background: Catecholamines affect response inhibition, but the effects of methylphenidate on inhibitory control in healthy subjects are heterogenous. Theoretical considerations suggest that working memory demands and learning/familiarization processes are important factors to consider regarding catecholaminergic effects on response inhibition. Aims: The purpose of this study was to examine the role of working memory demands and familiarization for methylphenidate effects on response inhibition. Methods: Twenty-eight healthy adults received a single dose of methylphenidate (0.5 mg/kg) or placebo in a randomised, double-blind, crossover study design. The subjects were tested using a working memory-modulated response inhibition paradigm that combined a Go/Nogo task with a mental rotation task. Results: Methylphenidate effects were largest in the most challenging mental rotation condition. The direction of effects depended on the extent of the participants’ task experience. When performing the task for the first time, methylphenidate impaired response inhibition performance in the most challenging mental rotation condition, as reflected by an increased false alarm rate. In sharp contrast to this, methylphenidate seemed to improve response execution performance in the most challenging condition when performing the task for the second time as reflected by reaction times on Go trials. Conclusion: Effects of catecholamines on inhibitory control processes depend on the interplay of two factors: (a) working memory demands, and (b) learning or familiarization with a task. It seems that the net effect of increases in gain control and decreases in working memory processes determines the methylphenidate effect on response inhibition. Hence, crossover study designs likely underestimate methylphenidate effects on cognitive functions.

Analysis on Processing Boundary of Stepped Shaft during Cross Wedge Rolling Process

With the development of cross-wedge rolling (CWR) process in recent years, the processing boundary of parts by means of CWR has witnessed a great breakthrough, especially in the field of area reduction. Based on abundant experiment, the latest processing boundary is constructed. It is affected by rotation condition and products’ defects, such as necking, tensile failure and internal rarefaction. The relationship between basic process parameters and these defects have been presented in this paper, including reasons behind these phenomena.

The extent of interlimb transfer following adaptation to a novel visuomotor condition does not depend on awareness of the condition

There is a controversy in the literature as to whether transfer of motor learning across the arms occurs because of an individual's cognitive awareness of the learned condition. The purpose of this study was to test whether the extent of interlimb transfer following adaptation to a novel visuomotor rotation with one arm, as well as the rate of learning acquired by the other arm, would vary depending on the subjects' awareness of the rotation condition. Awareness of the condition was varied by employing three experimental conditions. In one condition, visual rotation of the display up to 32° was gradually introduced to minimize the subjects' awareness of the rotation during targeted reaching movement. In another condition, the 32° rotation was abruptly introduced from the beginning of the adaptation session. Finally, the subjects were informed regarding the rotation prior to the adaptation session. After adaptation with the left arm under the three conditions, subjects performed reaching movement with the right arm under the same 32° rotation condition. Our results showed that the amount of initial transfer, and also the changes in performance with the right arm, did not vary significantly across the three conditions. This finding suggests that interlimb transfer of visuomotor adaptation does not occur based on an individual's awareness of the manipulation, but rather as a result of implicit generalization of the obtained visuomotor transformation across the arms.

Evidence for context sensitivity of grasp representations in human parietal and premotor cortices

Grasp-related responses in neurons of the macaque rostral inferior parietal lobule [PF/PFG and the anterior intraparietal area (AIP)] are modulated by task context. Event-related functional MRI was used to determine whether this is true in putative homologs of the human cortex, the rostral inferior parietal lobule (rIPL) and the anterior intraparietal sulcus (aIPS). Fifteen healthy, right-handed adults were required to select prospectively the most comfortable way to grasp a horizontally oriented handle using the cued hand (left or right). In the “no-rotation” condition, the task was simply to grasp the handle, whereas in the “rotation” condition, the goal was to plan to grasp and rotate it into a vertical orientation with the cued end (medial or lateral) pointing downward. In both conditions, participants remained still and indicated their grip preferences by pressing foot pedals. As in overt grasping, participants' grip preferences were significantly influenced by anticipation of the demands associated with handle rotation. Activity within the aIPS and rIPL increased bilaterally in both the rotation and no-rotation conditions. Importantly, these responses were significantly greater in the rotation vs. no-rotation condition. Similar context effects were detected in the presupplementary motor area, caudal intraparietal sulcus/superior parietal lobule, and bilateral dorsal and left ventral premotor cortices. Grasp representations within the rIPL and aIPS are sensitive to predicted task demands and play a role in context-sensitive grip selection. Moreover, the findings provide additional evidence that areas involved in the sensorimotor control of grasp also contribute to feedforward planning.