Background: Depression is characterized by cognitive impairments, including executive dysfunctions. These executive deficits could reflect impairments of more basic executive processes, such as ...updating, set shifting and inhibition. While shifting and inhibition impairments are often reported, studies on depression have been somewhat obscure about specific deficits of the updating process. The main goal of that study was to assess the updating process in young in-patients with depression.
Methods: We used a verbal
n-back task to assess updating process. Load and mental manipulation within working memory (WM) were incremented by using three different levels of complexity (1,2,3-back). Neuropsychological tests and an attentional task (0-back) were also administered to subjects. Twenty-two individuals meeting DSM-IV criteria for Major Unipolar Depression and 22 healthy control subjects, matched on age, verbal IQ and education, were included in the study.
Results: Subjects with depression showed significant deficits at the
n-back task compared to control subjects. They were normal in tasks assessing the short-term maintenance in WM and attention. This suggests that depressed patients exhibit impairment in the updating process. Depressed patients also showed set shifting and inhibition deficits. Only the
n-back task was correlated with the number of hospitalizations and the longitudinal course of the illness.
Conclusions: Our results suggest that young depressed in-patients have widespread executive dysfunctions, including updating, shifting and inhibition processes. We also found a correlation between a longitudinal measure of depression severity and an updating task performance. We suggest that using multiple executive tasks gives the opportunity to distinguish the specific influence of various executive processes on clinical dimensions in depression.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The dorsolateral prefrontal cortex (DLPFC) plays a key role in working memory (WM). Yet its precise contribution (the storage, manipulation and/or utilization of information for the forthcoming ...response) remains to be determined. To test the hypothesis that the DLPFC is more involved in the preparation of actions than in the maintenance of information in short-term memory (STM), we undertook a functional magnetic resonance imaging investigation in normal subjects performing two delayed response tasks (matching and reproduction tasks) in a visuospatial task sequence (presenta- tion, delay, response). In the two tasks, the presentation and delay phases were similar, but the expected response was different: in the matching task, subjects had to indicate whether a visuospatial sequence matched the sequence presented before the delay period; in the reproduction task, subjects had to reproduce the sequence and, therefore, to mentally organize their response during the delay. Using a fMRI paradigm focusing on the delay period, we observed a significant DLPFC activation when subjects were required to mentally prepare a sequential action based on the information stored in STM. When subjects had only to maintain a visuospatial stimulus in STM, no DLPFC activation was found. These results suggest that a parietal–premotor network is sufficient to store visuospatial information in STM whereas the DLPFC is involved when it is necessary to mentally prepare a forthcoming sequential action based on the information stored in STM.
We test the hypothesis that motivational and cognitive processes are linked by a specific neural system to reach maximal efficiency. We studied six normal subjects performing a working memory ...paradigm (n-back tasks) associated with different levels of monetary reward during an fMRI session. The study showed specific brain activation in relation with changes in both the cognitive loading and the reward associated with task performance. First, the working memory tasks activated a network including the dorsolateral prefrontal cortex Brodmann area (BA) 9/46 and, in addition, in the lateral frontopolar areas (BA 10), but only in the more demanding condition (3-back task). This result suggests that lateral prefrontal areas are organized in a caudo-rostral continuum in relation with the increase in executive requirement. Second, reward induces an increased activation in the areas already activated by working memory processing and in a supplementary region, the medial frontal pole (BA 10), regardless of the level of cognitive processing. It is postulated that the latter region plays a specific role in monitoring the reward value of ongoing cognitive processes. Third, we detected areas where the signal decreases (ventral-BA 11/47 and subgenual prefrontal cortices) in relation with both the increase of cognitive demand and the reward. The deactivation may represent an emotional gating aimed at inhibiting adverse emotional signals to maximize the level of performance. Taken together, these results suggest a balance between increasing activity in cortical cognitive areas and decreasing activity in the limbic and paralimbic structures during ongoing higher cognitive processing.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
“Orbitofrontal” and “cingulate” striatofrontal loops and the mesolimbic dopaminergic system that modulates their function have been implicated in motivation and sensitivity to reinforcement in ...animals. Parkinson’s disease (PD) provides a model to assess their implications in humans. The aims of the study were to investigate motivation and sensitivity to reinforcement in non-demented and -depressed PD patients and to evaluate the influence of dopaminergic therapy by comparing patients in “on” (with
l-Dopa) and “off” (without
l-Dopa) states. Twenty-three PD patients were compared, in both the “on” and “off” states, to 28 controls, using: (1) an Apathy Scale; (2) Stimulus–Reward Learning, Reversal, and Extinction tasks; and (3) a Gambling task. PD patients were found: (1) mildly apathetic; (2) impaired on Stimulus–Reward Learning and Reversal, but not on Extinction; and (3) able to progress in the Gambling task during the first, but not the second assessment. There was no significant correlation between these various deficits.
l-Dopa treatment clearly improved motivation, but had more limited and contrasting effects on other variables, decreasing the number of omission errors in Reversal, but increasing the number of perseveration errors in Extinction. These results suggest: (1) an implication of striatofrontal loops in human motivation and explicit and implicit sensitivity to reinforcement; (2) a positive influence of
l-Dopa treatment on the subjective evaluation of motivation, but contrasting effects on reward sensitivity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract Background Repetitive checking in obsessive-compulsive disorder (OCD) would serve to relieve obsession-related anxiety and/or to compensate memory deficit, but experimental literature on ...this subject is inconsistent. The main objective is to test the influence of obsession-related anxiety and memory on repetitive checking in OCD. Methods Twenty-three OCD checkers, 17 OCD non-checkers and 41 controls performed a delayed-matching-to-sample task with an unrestricted checking option. Some stimuli were obsession-related in order to measure the influence of anxiety on checking. A version of the task without checking possibility was used to assess memory abilities. Results OCD checkers had similar memory performances but checked more than the other groups when presented with non-anxiogenic stimuli. Level of anxiety associated to the stimulus did not influence the number of checks. Conclusions Increased checking in OCD checkers, being independent of memory abilities and primary obsession-related anxiety, would, therefore, be closer to an automated behaviour than a coping strategy.
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma. Since autumn 2009 both telescopes have been working together in stereoscopic mode, ...providing a significant improvement with respect to the previous single-telescope observations. We use observations of the Crab Nebula taken at low zenith angles to assess the performance of the MAGIC stereo system. The trigger threshold of the MAGIC telescopes is 50−60GeV. Advanced stereo analysis techniques allow MAGIC to achieve a sensitivity as good as (0.76±0.03)% of the Crab Nebula flux in 50h of observations above 290GeV. The angular resolution at those energies is better than ∼0.07°. We also perform a detailed study of possible systematic effects which may influence the analysis of the data taken with the MAGIC telescopes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Very high energy (VHE) Delta *g-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation ...(~0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/GeV Delta *g-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE E -- Delta *G with a photon index Delta *G = 3.75 ? 0.27stat ? 0.2syst. The averaged integral flux above 100 GeV is (4.6 ? 0.5) X 10--10 cm--2 s--1 (~1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 ? 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the Delta *g-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE Delta *g-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models.
Context.The small-scale distribution of dark matter in galactic halos is poorly known. Several studies suggest that it could be very clumpy, which is of paramount importance when investigating the ...annihilation signal from exotic particles (e.g. supersymmetric or Kaluza-Klein). Aims.We focus on the annihilation signal in positrons. We estimate the associated uncertainty, that is due to the fact that we do not know exactly how the clumps are distributed in the Galactic halo. Methods.We perform a statistical study based on analytical computations, as well as numerical simulations. We study the average and variance of the annihilation signal over many Galactic halos having the same statistical properties. Results.We find that the so-called boost factor used by many authors should be used with caution, as i) it depends on energy and ii) it may be different for positrons, antiprotons and gamma rays, a fact which has not been discussed before. As an illustration, we use our results to discuss the positron spectrum measurements by the HEAT experiment.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We report on the detection with the MAGIC telescopes of very high energy (VHE) γ-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval 2008 November ...to 2010 February. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6σ in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 ± 0.14. The mean flux above 300 GeV, between 2009 October and 2010 February, (3.1 ± 0.5) × 10-12 cm-2 s-1, corresponds to (2.5 ± 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3σ) of flares in the middle of 2009 October and November, implies that the emission is variable. The MAGIC results favor a scenario with the VHE emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone synchrotron self-Compton (SSC) scenario, e.g., multi-zone SSC, external Compton, or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
We report on the observation of Delta *g-rays above 25 GeV from the Crab pulsar (PSR B0532+21) using the MAGIC I telescope. Two data sets from observations during the winter period 2007/2008 and ...2008/2009 are used. In order to discuss the spectral shape from 100 MeV to 100 GeV, one year of public Fermi Large Area Telescope (Fermi-LAT) data are also analyzed to complement the MAGIC data. The extrapolation of the exponential cutoff spectrum determined with the Fermi-LAT data is inconsistent with MAGIC measurements, which requires a modification of the standard pulsar emission models. In the energy region between 25 and 100 GeV, the emission in the P1 phase (from --0.06 to 0.04, location of the main pulse) and the P2 phase (from 0.32 to 0.43, location of the interpulse) can be described by power laws with spectral indices of --3.1 ? 1.0stat ? 0.3syst and --3.5 ? 0.5stat ? 0.3syst, respectively. Assuming an asymmetric Lorentzian for the pulse shape, the peak positions of the main pulse and the interpulse are estimated to be at phases --0.009 ? 0.007 and 0.393 ? 0.009, while the full widths at half-maximum are 0.025 ? 0.008 and 0.053 ? 0.015, respectively.
PDF
