Temperature influence on DXA measurements: bone mineral density acquisition in frozen and thawed human femora

<p>Abstract</p> <p>Background</p> <p>Determining bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) is an established and widely used method that is also applied prior to biomechanical testing. However, DXA is affected by a number of factors. In order to delay decompositional processes, human specimens for biomechanical studies are usually stored at about -20°C; similarly, bone mineral density measurements are usually performed in the frozen state. The aim of our study was to investigate the influence of bone temperature on the measured bone mineral density.</p> <p>Methods</p> <p>Using DXA, bone mineral density measurements were taken in 19 fresh-frozen human femora, in the frozen and the thawed state. Water was used to mimic the missing soft tissue around the specimens. Measurements were taken with the specimens in standardized internal rotation. Total-BMD and single-BMD values of different regions of interest were used for evaluation.</p> <p>Results</p> <p>Fourteen of the 19 specimens showed a decrease in BMD after thawing. The measured total-BMD of the frozen specimens was significantly (1.4%) higher than the measured BMD of the thawed specimens.</p> <p>Conclusion</p> <p>Based on our findings we recommend that the measurement of bone density, for example prior to biomechanical testing, should be standardized to thawed or frozen specimens. Temperature should not be changed during measurements. When using score systems for data interpretation (e.g. T- or Z-score), BMD measurements should be performed only on thawed specimens.</p

Modulating proactive cognitive control by reward:Differential anticipatory effects of performance contingent and non-contingent rewards

The present study investigated the influences of two different forms of reward presentation in modulating cognitive control. In three experiments, participants performed a flanker task for which one-third of trials were precued for a chance of obtaining a reward (reward trials). In Experiment 1, a reward was provided if participants made the correct response on reward trials, but a penalty was given if they made an incorrect response on these trials. The anticipation of this performance-contingent reward increased response speed and reduced the flanker effect, but had little influence on the sequential modulation of the flanker effect after incompatible trials. In Experiment 2, participants obtained a reward randomly on two-thirds of the precued reward trials and were given a penalty on the remaining one-third, regardless of their performance. The anticipation of this non-contingent reward had little influence on the overall response speed or flanker effect, but reduced the sequential modulation of the flanker effect after incompatible trials. Experiment 3 also used performance non-contingent rewards, but participants were randomly penalized more often than they were rewarded; non-contingent penalty had little influence on the sequential modulation of the flanker effect. None of the three experiments showed a reliable influence of the actual acquisition of rewards on task performance. These results indicate anticipatory effects of performance-contingent and non-contingent rewards on cognitive control with little evidence of aftereffects

Supplement for: The role of affective evaluation in conflict adaptation: An LRP study

Supplemental analyses with all trials, including direct repetitions and response repetitions

Bottom-up influences on voluntary task switching in different reward contexts?

In humans, voluntary task switching is susceptible to bottom-up influences like a switch of the target stimulus identity (Mayr & Bell, 2006). A recent study with ants (Czaczkes, Koch, Fro center dot ber, & Dreisbach, 2018) has shown that even irrelevant cue changes increase switching behavior, but only if they are presented within a high-reward context. To investigate whether a reward context would also increase switching behavior in response to meaningless cue changes in humans, we conducted two voluntary task switching experiments. On each trial, participants chose between two tasks preceded by one of two different color cues. Reward prospect was manipulated between blocks (Experiment 1: no vs. high reward; Experiment 2: low vs. high reward). In both experiments, the cue change did not modulate the voluntary switch rate. However, the voluntary switch rate was significantly lower in high-reward blocks as compared to no-reward or low-reward blocks. This suggests that bottom-up influences on deliberate task switching in humans are limited to task-relevant information. Moreover, the finding of a decreased voluntary switch rate within a high-reward context further supports the claim that unchanged high reward prospect promotes cognitive stability

Biomechanische Studie zur Versorgung von Fibulafrakturen mittels biodegradierbarer Implantate

Photograph of Wally Shufflebottom on the left and his wife Cissie Shufflebottom nee Rosaire on the right - The Texans - with a show girl in the middle, practising for their Wild West Show

The dynamic balance between cognitive flexibility and stability: the influence of local changes in reward expectation and global task context on voluntary switch rate

Current theories describe cognitive control as a dynamic balance between two antagonistic control functions, namely cognitive stability and flexibility. Recent evidence suggests that this balance between these control modes is modulated by changing reward prospects on the one side and contextual parameters on the other. In the present study, we aim to investigate how both factors interact. In a between-subjects design, we manipulated the context by the ratio of free- to forced-choice trials (80:20, 50:50, 20:80) in a hybrid task-switching paradigm, combining forced- and free-choice task switching. In addition, two reward magnitudes changed randomly from trial to trial. Results showed an overall increase in voluntary switch rate (VSR) with increasing forced-choice frequency, demonstrating a robust context effect. Moreover, the trial-by-trial reward manipulation interacted with this global context effect: with a stability bias (80% free:20% forced), only an increase in reward expectation increased VSR, whereas with a more flexible global bias (in the 50:50 or 20:80 conditions) VSR increased when reward expectation changed and reduced when reward expectation remained high. Taken together, results suggest that the cognitive system is able to adapt to global context parameters and to respond to rapid changes in reward expectation at the same time