Reproducibility in the absence of selective reporting : An illustration from large-scale brain asymmetry research

Altres ajuts: Max Planck Society (Germany).The problem of poor reproducibility of scientific findings has received much attention over recent years, in a variety of fields including psychology and neuroscience. The problem has been partly attributed to publication bias and unwanted practices such as p-hacking. Low statistical power in individual studies is also understood to be an important factor. In a recent multisite collaborative study, we mapped brain anatomical left-right asymmetries for regional measures of surface area and cortical thickness, in 99 MRI datasets from around the world, for a total of over 17,000 participants. In the present study, we revisited these hemispheric effects from the perspective of reproducibility. Within each dataset, we considered that an effect had been reproduced when it matched the meta-analytic effect from the 98 other datasets, in terms of effect direction and significance threshold. In this sense, the results within each dataset were viewed as coming from separate studies in an "ideal publishing environment," that is, free from selective reporting and p hacking. We found an average reproducibility rate of 63.2% (SD = 22.9%, min = 22.2%, max = 97.0%). As expected, reproducibility was higher for larger effects and in larger datasets. Reproducibility was not obviously related to the age of participants, scanner field strength, FreeSurfer software version, cortical regional measurement reliability, or regional size. These findings constitute an empirical illustration of reproducibility in the absence of publication bias or p hacking, when assessing realistic biological effects in heterogeneous neuroscience data, and given typically-used sample sizes

Cross-sensory inhibition or unisensory facilitation: A potential neural architecture of modality switch effects

In a simple reaction time task in which auditory and visual stimuli are presented in random sequence alone (A or V) or together (AV), there is a so-called reaction time (RT) cost on trials in which sensory modality switches (A\u2192V) compared to when it repeats (A\u2192A). This is always true for unisensory trials, whereas RTs to AV stimuli preceded by unisensory stimuli are statistically comparable with the Repeat condition (AV\u2192AV). Neural facilitation for Repeat trials or neural inhibition for Switch trials could both account for these effects. Here we used a neural network model (Multisensory Integration with Crossed Inhibitory Dynamics (MICID) model) to test the ability of these two distinct mechanisms, inhibition and facilitation, to produce the specific patterns of behavior that we see experimentally, modeling switch and repeat trials as well as the influence of the interval between the present and the previous trial. The model results are consistent with an inhibitory account in which there is competition between the different sensory modalities, instead of a facilitation account in which the preceding stimulus sensitizes the neural system to its particular sensory modality. Moreover, the model shows that multisensory integration can explain the results in case of multisensory stimuli, where the preceding stimulus has little effect. This is due to faster dynamics for multisensory facilitation compared to cross-sensory inhibition. These findings link the cognitive framework delineated by the empirical results to a plausible neural implementation

Alpha modulation during working memory encoding predicts neurocognitive impairment in ADHD

BackgroundAttention-deficit/hyperactivity disorder (ADHD) is associated with working memory (WM) deficits. However, WM is a multiprocess construct that can be impaired through several pathways, leaving the source of WM impairments in ADHD unresolved. In this study, we aim to replicate, in an independent sample, previously reported deficits in component processes of WM deficits in ADHD and expand to consider their implications for neurocognitive outcomes.MethodsIn 119 children (7-14 years old, 85 with ADHD), we used electroencephalography measures to quantify component processes during performance of a spatial working memory task. We quantified stimulus encoding using alpha range (8-12 Hz) power; vigilance by the P2 event-related potential to cues; and WMmaintenance by occipital-alpha and frontal-theta (4-7 Hz) power. These measures were evaluated against metrics of executive function, ADHD symptoms, and academic achievement.ResultsEncoding alpha-power decreases and cue P2 amplitude were attenuated in ADHD, whereas occipital-alpha power during maintenance was significantly greater in ADHD, consistent with a compensatory response to weak encoding. Weak alpha modulation during encoding was associated with poorer reading comprehension and executive function, as well as enhanced ADHD symptoms. Previously reported effects in frontal-theta power failed to replicate.ConclusionsStimulus encoding, a component process of WM coupled to alpha modulation, is impaired in ADHD, and, unlike WM maintenance or vigilance processes, has implications outside of the laboratory via a relationship with executive function, and, to a weaker extent, reading comprehension

Mega-analysis of gray matter volume in substance dependence: General and substance-specific regional effects

Objective: Although lower brain volume has been routinely observed in individuals with substance dependence compared with nondependent control subjects, the brain regions exhibiting lower volume have not been consistent across studies. In addition, it is not clear whether a common set of regions are involved in substance dependence regardless of the substance used or whether some brain volume effects are substance specific. Resolution of these issues may contribute to the identification of clinically relevant imaging biomarkers. Using pooled data from 14 countries, the authors sought to identify general and substance-specific associations between dependence and regional brain volumes. Method: Brain structure was examined in a mega-analysis of previously published data pooled from 23 laboratories, including 3,240 individuals, 2,140 of whom had substance dependence on one of five substances: alcohol, nicotine, cocaine, methamphetamine, or cannabis. Subcortical volume and cortical thickness in regions defined by FreeSurfer were compared with nondependent control subjects when all sampled substance categories were combined, as well as separately, while controlling for age, sex, imaging site, and total intracranial volume. Because of extensive associations with alcohol dependence, a secondary contrast was also performed for dependence on all substances except alcohol. An optimized split-half strategy was used to assess the reliability of the findings. Results: Lower volume or thickness was observed in many brain regions in individuals with substance dependence. The greatest effects were associated with alcohol use disorder. A set of affected regions related to dependence in general, regardless of the substance, included the insula and the medial orbitofrontal cortex. Furthermore, a support vector machine multivariate classification of regional brain volumes successfully classified individuals with substance dependence on alcohol or nicotine relative to nondependent control subjects. Conclusions: The results indicate that dependence on a range of different substances shares a common neural substrate and that differential patterns of regional volume could serve as useful biomarkers of dependence on alcohol and nicotine