113 research outputs found

    Revisiting Multi-Subject Random Effects in fMRI: Advocating Prevalence Estimation

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    Random Effects analysis has been introduced into fMRI research in order to generalize findings from the study group to the whole population. Generalizing findings is obviously harder than detecting activation in the study group since in order to be significant, an activation has to be larger than the inter-subject variability. Indeed, detected regions are smaller when using random effect analysis versus fixed effects. The statistical assumptions behind the classic random effects model are that the effect in each location is normally distributed over subjects, and "activation" refers to a non-null mean effect. We argue this model is unrealistic compared to the true population variability, where, due to functional plasticity and registration anomalies, at each brain location some of the subjects are active and some are not. We propose a finite-Gaussian--mixture--random-effect. A model that amortizes between-subject spatial disagreement and quantifies it using the "prevalence" of activation at each location. This measure has several desirable properties: (a) It is more informative than the typical active/inactive paradigm. (b) In contrast to the hypothesis testing approach (thus t-maps) which are trivially rejected for large sample sizes, the larger the sample size, the more informative the prevalence statistic becomes. In this work we present a formal definition and an estimation procedure of this prevalence. The end result of the proposed analysis is a map of the prevalence at locations with significant activation, highlighting activations regions that are common over many brains

    Freeze or Forget? Virtual Attack Effects in an Emotional Sternberg Task

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    Emotionally salient stimuli have the ability to disrupt cognitive processing. This kind of disruption involves effects on working memory and may be related to mental health problems. To explore the nature of such emotional interference on working memory, a Virtual Attack Emotional Sternberg Task (VAEST) was used. Neutral faces were presented as distractors and warning signals, which were sometimes followed by a virtual attack, created by having the neutral face turn angry while the image was enlarged. The attack was hypothesized to have one of two effects: to disrupt cognitive processing and thereby increase interference effects, or to terminate a state of freezing and thereby reduce interference effects. The task was successfully completed online by a sample of 59 students. Results clearly show that the virtual attack caused a reduction of interference relative to no-attack trials. The apparent cognitive disruption caused by emotional distractors may thus reflect freezing, which can be reversed by a freeze-terminating stimulus

    Anticipated attack slows responses in a cued virtual attack emotional sternberg task

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    Threatening stimuli have varying effects, including reaction time increase in working memory tasks. This could reflect disruption of working memory or, alternatively, a reversible state of freezing. In the current series of experiments, reversible slowing due to anticipated threat was studied using the cued Virtual Attack Emotional Sternberg Task (cVAEST). In this task visually neutral cues indicate whether a future virtual attack could or could not occur during the maintenance period of a Sternberg task. Three studies (N = 47, 40, and 40, respectively) were performed by healthy adult participants online. The primary hypothesis was that the cVAEST would evoke anticipatory slowing. Further, the studies aimed to explore details of this novel task, in particular the interval between the cue and probe stimuli and the memory set size. In all studies it was found that threat anticipation slowed RTs on the working memory task. Further, Study 1 (memory set size 3) showed a decrease in RT when the attack occurred over all CSIs. In Study 2 a minimal memory set of one item was used, under which circumstances RTs following attacks were only faster shortly after cue presentation (CSI 200 and 500 ms), when RTs were high for both threat and safe cues. Study 3 replicated results of Study 2 with more fine-grained time intervals. The results confirm that anticipation of attack stimuli can reversibly slow responses on an independent working memory task. The cVAEST may provide a useful method to study such threat-induced response slowing

    Spatial anticipatory attentional bias for threat: reliable individual differences with RT-based online measurement

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    Cues that predict the future location of emotional stimuli may evoke an anticipatory form of automatic attentional bias. The reliability of this bias towards threat is uncertain: experimental design may need to be optimized or individual differences may simply be relatively noisy in the general population. The current study therefore aimed to determine the split-half reliability of the bias, in a design with fewer factors and more trials than in previous work. A sample of 63 participants was used for analysis, who performed the cued Visual Probe Task online, which aims to measure an anticipatory attentional bias. The overall bias towards threat was tested and split-half reliability was calculated over even and odd blocks. Results showed a significant bias towards threat and a reliability of around 0.7. The results support systematic individual differences in anticipatory attentional bias and demonstrate that RT-based bias scores, with online data collection, can be reliable

    Alcohol-related attentional bias variability and conflicting automatic associations

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    Attentional bias variability is related to alcohol abuse. Of potential use for studying variability is the anticipatory attentional bias: Bias due to the locations of predictively-cued rather than already-presented stimuli. The hypothesis was tested that conflicting automatic associations are related to attentional bias variability. Further, relationships were explored between anticipatory biases and individual differences related to alcohol use. 74 social drinkers performed a cued Visual Probe Task and univalent Single-Target Implicit Associations Tasks. Questionnaires were completed on risky drinking, craving, and motivations to drink or refrain from drinking. Ambiguity was related to attentional bias variability at the 800 ms Cue-Stimulus Interval. Further, a bias related to craving and risky drinking was found at the 400 ms Cue-Stimulus Interval. Thus, the selection of attentional responses was biased by predicted locations of expected salient stimuli. The results support a role of conflicting associations in attentional bias variability

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    OBJECTIVE: Functional MRI has thus far demonstrated that HIV has an impact on frontal-striatal systems involved in executive functioning. The potential impact of HIV on frontal-striatal systems involved in reward processing has yet to be examined by functional MRI. This study therefore aims to investigate the effects of HIV infection on reward processing by examining the function of the ventral-striatal reward system during a monetary incentive delay task. DESIGN: This is a cross-sectional case-control study. METHODS: Eighteen combined antiretroviral therapy-naive HIV-positive (HIV+) participants, as well as 16 matched healthy controls, performed a monetary incentive delay task. This paradigm assesses behaviour as well as functional brain activity-associated reward anticipation and reward outcome. RESULTS: HIV+ participants showed a general decrease in activation associated with both neutral as well as potentially rewarding cues in their ventral striatum. We found normal activity related to reward outcome in the orbito-frontal cortex. Despite HIV+ participants' reaction times being significantly slower when independently measured from the reward paradigm, this performance deficit normalized during the performance of the reward task. CONCLUSION: HIV caused a decrease in activity during cue processing in the ventral striatum, with normal cortical functioning during reward outcome processing. Our results therefore suggest that HIV not only has an impact on fronto-striatal systems involved in executive functioning, but also has a direct impact on the function of the ventral-striatal reward system

    Аудит як процедура контролю за станом платіжної системи суб’єкта господарської діяльності

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    У статті розглядаються питання аудиту розрахункових операцій. Виділено різні види аудиторських процедур – аналітичні та альтернативні. Визначено порядок проведення аудиторської перевірки розрахунків.В статье рассматриваются вопросы аудита расчетных операций. Выделены различные виды аудиторских процедур – аналитические и альтернативные. Определен порядок проведения аудиторской проверки.In the article the issues of audit of payments are revealed. Various types of audit procedures – analytical and alternative are identified. The procedure for conducting the audit is stipulated

    Disrupted upregulation of salience network connectivity during acute stress in siblings of schizophrenia patients

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    BACKGROUND: An adaptive neural stress response is essential to adequately cope with a changing environment. It was previously argued that sympathetic/noradrenergic activity during acute stress increases salience network (SN) connectivity and reduces executive control network (ECN) connectivity in healthy controls, with opposing effects in the late aftermath of stress. Altered temporal dynamics of these networks in response to stress are thought to play a role in the development of psychopathology in vulnerable individuals. METHODS: We exposed male healthy controls (n = 40, mean age = 33.9) and unaffected siblings of schizophrenia patients (n = 39, mean age = 33.2) to the stress or control condition of the trier social stress test and subsequently investigated resting state functional connectivity of the SN and ECN directly after and 1.5 h after stress. RESULTS: Acute stress resulted in increased functional connectivity within the SN in healthy controls, but not in siblings (group × stress interaction pfwe < 0.05). In the late aftermath of stress, stress reduced functional connectivity within the SN in both groups. Moreover, we found increased functional connectivity between the ECN and the cerebellum in the aftermath of stress in both healthy controls and siblings of schizophrenia patients. CONCLUSIONS: The results show profound differences between siblings of schizophrenia patients and controls during acute stress. Siblings lacked the upregulation of neural resources necessary to quickly and adequately cope with a stressor. This points to a reduced dynamic range in the sympathetic response, and may constitute a vulnerability factor for the development of psychopathology in this at-risk group
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