18 research outputs found

    Neuronal Generator Patterns At Scalp Elicited By Lateralized Aversive Pictures Reveal Consecutive Stages Of Motivated Attention

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    Event-related potential (ERP) studies have provided evidence for an allocation of attentional resources to enhance perceptual processing of motivationally salient stimuli. Emotional modulation affects several consecutive components associated with stages of affective-cognitive processing, beginning as early as 100ā€“200 ms after stimulus onset. In agreement with the notion that the right parietotemporal region is critically involved during the perception of arousing affective stimuli, some ERP studies have reported asymmetric emotional ERP effects. However, it is difļ¬cult to separate emotional from non-emotional effects because differences in stimulus content unrelated to affective salience or task demands may also be associated with lateralized function or promote cognitive processing. Other concerns pertain to the operational deļ¬nition and statistical independence of ERP component measures, their dependence on an EEG reference, and spatial smearing due to volume conduction, all of which impede the identiļ¬cation of distinct scalp activation patterns associated with affective processing. Building on prior research using a visual half-ļ¬eld paradigm with highly controlled emotional stimuli (pictures of cosmetic surgery patients showing disordered [negative] or healed [neutral] facial areas before or after treatment), 72channel ERPs recorded from 152 individuals (ages 13ā€“68 years; 81 female) were transformed into reference-free current source density (CSD) waveforms and submitted to temporal principal components analysis (PCA) to identify their underlying neuronal generator patterns. Using both nonparametric randomization tests and repeated measures ANOVA, robust effects of emotional content were found over parietooccipital regions for CSD factors corresponding to N2 sink (212 ms peak latency), P3 source (385 ms) and a late centroparietal source (630 ms), all indicative of greater positivity for negative than neutral stimuli. For the N2 sink, emotional effects were right-lateralized and modulated by hemiļ¬eld, with larger amplitude and asymmetry for left hemiļ¬eld (right hemisphere) presentations. For all three factors, more positive amplitudes at parietooccipital sites were associated with increased ratings of negative valence and greater arousal. Distributed inverse solutions of the CSDPCA-based emotional effects implicated a sequence of maximal activations in right occipitotemporal cortex, bilateral posterior cingulate cortex, and bilateral inferior temporal cortex. These ļ¬ndings are consistent with hierarchical activations of the ventral visual pathway reļ¬‚ecting subsequent processing stages in response to motivationally salient stimuli

    Motivated Attention And Family Risk For Depression: Neuronal Generator Patterns At Scalp Elicited By Lateralized Aversive Pictures Reveal Blunted Emotional Responsivity

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    Behavioral and electrophysiologic evidence suggests that major depression (MDD) involves right parietotemporal dysfunction, a region activated by arousing aļ¬€ective stimuli. Building on prior event-related potential (ERP) ļ¬ndings (Kayser et al. 2016 NeuroImage 142:337ā€“350), this study examined whether these abnormalities also characterize individuals at clinical high risk for MDD. We systematically explored the impact of family risk status and personal history of depression and anxiety on three distinct stages of emotional processing comprising the late positive potential (LPP). ERPs (72 channels) were recorded from 74 high and 53 low risk individuals (age 13ā€“59 years, 58 male) during a visual half-ļ¬eld paradigm using highly-controlled pictures of cosmetic surgery patients showing disordered (negative) or healed (neutral) facial areas before or after treatment. Reference-free current source density (CSD) transformations of ERP waveforms were quantiļ¬ed by temporal principal components analysis (tPCA). Component scores of prominent CSD-tPCA factors sensitive to emotional content were analyzed via permutation tests and repeated measures ANOVA for mixed factorial designs with unstructured covariance matrix, including gender, age and clinical covariates. Factor-based distributed inverse solutions provided descriptive estimates of emotional brain activations at group level corresponding to hierarchical activations along ventral visual processing stream. Risk status aļ¬€ected emotional responsivity (increased positivity to negative-than-neutral stimuli) overlapping early N2 sink (peak latency 212 ms), P3 source (385 ms), and a late centroparietal source (630 ms). High risk individuals had reduced right-greater-thanleft emotional lateralization involving occipitotemporal cortex (N2 sink) and bilaterally reduced emotional eļ¬€ects involving posterior cingulate (P3 source) and inferior temporal cortex (630 ms) when compared to those at low risk. While the early emotional eļ¬€ects were enhanced for left hemiļ¬eld (right hemisphere) presentations, hemiļ¬eld modulations did not diļ¬€er between risk groups, suggesting top-down rather than bottom-up eļ¬€ects of risk. Groups did not diļ¬€er in their stimulus valence or arousal ratings. Similar eļ¬€ects were seen for individuals with a lifetime history of depression or anxiety disorder in comparison to those without. However, there was no evidence that risk status and history of MDD or anxiety disorder interacted in their impact on emotional responsivity, suggesting largely independent attenuation of attentional resource allocation to enhance perceptual processing of motivationally salient stimuli. These ļ¬ndings further suggest that a deļ¬cit in motivated attention preceding conscious awareness may be a marker of risk for depression

    Methods of estimating shale gas resources - Comparison, evaluation and implications

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    Estimates of technically recoverable shale gas resources remain highly uncertain, even in regions with a relatively long history of shale gas production. This paper examines the reasons for these uncertainties, focusing in particular on the methods used to derive resource estimates. Such estimates can be based upon the extrapolation of previous production experience in developed areas, or from the geological appraisal of undeveloped areas. The paper assesses the strengths and weaknesses of these methods, the level of uncertainty in the results and the implications of this for current policy debates. We conclude that there are substantial difficulties in assessing the recoverable volumes of shale gas and that current resource estimates should be treated with considerable caution. Most existing studies lack transparency or a rigorous approach to assessing uncertainty and provide estimates that are highly sensitive to key variables that are poorly defined - such as the assumed ratio of gas-in-place to recovered gas (the ā€˜recovery factorā€™) and the assumed ultimate recovery from individual wells. To illustrate the uncertainties both within and between different methodological approaches, we provide case studies of resource estimates for the Marcellus shale in the US and three basins in India
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