Association between cognitive performance and cortical glucose metabolism in patients with mild Alzheimer's disease

Background: Neuronal and synaptic function in Alzheimer's disease (AD) is measured in vivo by glucose metabolism using positron emission tomography (PET). Objective: We hypothesized that neuronal activation as measured by PET is a more sensitive index of neuronal dysfunction than activity during rest. We investigated if the correlations between dementia severity as measured with the Mini Mental State Examination (MMSE) and glucose metabolism are an artifact of brain atrophy. Method: Glucose metabolism was measured using {[}F-18]fluorodeoxyglucose PET during rest and activation due to audiovisual stimulation in 13 mild to moderate AD patients (MMSE score >= 17). PET data were corrected for brain atrophy. Results: In the rest condition, glucose metabolism was correlated with the MMSE score primarily within the posterior cingulate and parietal lobes. For the activation condition, additional correlations were within the primary and association audiovisual areas. Most local maxima remained significant after correcting for brain atrophy. Conclusion: PET activity measured during audiovisual stimulation was more sensitive to functional alterations in glucose metabolism in AD patients compared to the resting PET. The association between glucose metabolism and MMSE score was not dependent on brain atrophy. Copyright (C) 2005 S. Karger AG, Basel

Non-Thermal Emission from AGN Coronae

Accretion disk coronae are believed to account for X-ray emission in Active Galactic Nuclei (AGNs). In this paper the observed emission is assumed to be due to a population of relativistic, non-thermal electrons (e.g. produced in a flare) injected at the top of an accretion disk magnetic loop. While electrons stream along magnetic field lines their energy distribution evolves in time essentially because of inverse Compton and synchrotron losses. The corresponding time dependent emission due, in the X-ray energy range, to the inverse Compton mechanism, has been computed. Since the typical decay time of a flare is shorter than the integration time for data acquisition in the X-ray domain, the resulting spectrum is derived as the temporal mean of the real, time-dependent, emission, as originated by a series of consecutive and identical flares. The model outcome is compared to both the broad band BeppoSAX X-ray data of the bright Seyfert 1 NGC 5548, and to a few general X-ray spectral properties of Seyfert 1s as a class. The good agreement between model and observations suggests that the presently proposed non-thermal, non-stationary model could be a plausible explanation of AGN X-ray emission, as an alternative to thermal coronae models.Comment: 15 pages, 4 postscript figure

COVID-19 and Biomedical Experts: When Epistemic Authority is (Probably) Not Enough

This critical essay evaluates the potential integration of distinct kinds of expertise in policymaking, especially during situations of critical emergencies, such as the COVID-19 pandemic. This article relies on two case studies: (i) herd immunity (UK) and (ii) restricted access to ventilators for disabled people (USA). These case studies are discussed as examples of experts’ recommendations that have not been widely accepted, though they were made within the boundaries of expert epistemic authority. While the fundamental contribution of biomedical experts in devising public health policies during the COVID-19 pandemic is fully recognized, this paper intends to discuss potential issues and limitations that may arise when adopting a strict expert-based approach. By drawing attention to the interests of minorities (disenfranchized and underrepresented groups), the paper also claims a broader notion of “relevant expertise.” This critical essay thus calls for the necessity of wider inclusiveness and representativeness in the process underlying public health policymaking

Verb Semantics modulates neural activity in the left Lateral Temporal Cortex

Here we show that the implicit processing of telicity, dynamicity and agentivity differentially modulate neural activity across different brain clusters and, in particular, within lMTG. We found that selectivity for state and telic verbs identified the most anterior and the most posterior portion of lMTG, respectively. Furthermore, dynamicity and agentivity modulated brain responses in parietal and ventral extrastriate regions. The role of each property was clearly isolated, as the stimuli were specifically controlled for and the task design covertly assessed the representation of those properties. Different event types are differentially mapped based on their semantic representation and, in particular, lMTG represents conceptual semantic properties of verbs: specifically, that kind of conceptual information which is relevant to morphosyntax, that is, telicity, stativity and agentivity, that, unlike referential semantic features, and independently of them, govern morphosyntax in a specified way

New light from the dark: What blindness can teach us about brain function

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Are supramodality and cross-modal plasticity the yin and yang of brain development? From blindness to rehabilitation

Research in blind individuals has primarily focused for a long time on the brain plastic reorganization that occurs in early visual areas. Only more recently, scientists have developed innovative strategies to understand to what extent vision is truly a mandatory prerequisite for the brain’s fine morphological architecture to develop and function. As a whole, the studies conducted to date in sighted and congenitally blind individuals have provided ample evidence that several ‘visual’ cortical areas develop independently from visual experience and do process information content regardless of the sensory modality through which a particular stimulus is conveyed: a property named supramodality. At the same time, lack of vision leads to a structural and functional reorganization within 'visual' brain areas, a phenomenon known as cross-modal plasticity. Cross-modal recruitment of the occipital cortex in visually deprived individuals represents an adaptative compensatory mechanism that mediates processing of non-visual inputs. Supramodality and cross-modal plasticity appear to be the 'yin and yang' of brain development: supramodal is what takes place despite the lack of vision, whereas cross-modal is what happens because of lack of vision. Here we provide a critical overview of the research in this field and discuss the implications that these novel findings have for the development of educative/rehabilitation approaches and sensory substitution devices in sensory-impaired individuals