Practice-induced visual perceptual learning is thought to reflect the plasticity of sensory brain regions. The hypothesis that changes in early visual areas may depend on top-down modulation from ...higher level brain regions by attentional mechanisms is still debated. We used a causal approach by repetitive transcranial magnetic stimulation (rTMS) to evaluate the role of primary visual cortex (V1) and posterior parietal cortex (PPC) in visual perceptual learning. Twelve healthy volunteers performed a forced-choice orientation discrimination task of gabor patches (consisting of 500 trials in five blocks) without any intervention or immediately after a conditioning inhibitory 1-Hz rTMS protocol delivered over the V1, the right PPC, and the vertex (control area), in four different days. Conditioning inhibition by 1-Hz rTMS over the V1 produced an overall worsening of the performance accuracy but no effect in the learning rate, as measured by the slope of the learning curve. The learning rate was lower after right PPC inhibition compared to the other conditions, when evaluated during the first two blocks (200 trials) where occurred most of the learning. These preliminary findings suggest that higher level brain regions may be involved in the mechanisms underlying perceptual learning.
The cortical silent period (CSP) following transcranial magnetic stimulation reflects GABAB-mediated inhibition in the primary motor cortex (M1), and could contribute to understand the ...pathophysiological substrates of epilepsies. Increased CSP duration has been reported in idiopathic generalized epilepsy (IGE) and in partial epilepsy (PE) involving the M1, although other studies yielded discordant findings. In this meta-analysis we systematically assessed the consistency of CSP changes in untreated epileptic patients. We searched for controlled studies evaluating the CSP in drug-naïve or drug-free patients with IGE or PE. The mean difference between CSP duration obtained in patients and controls was calculated. Fourteen studies (267 patients and 234 controls) were included. A significant mean difference was found, with longer CSP in patients than in controls. The difference was still greater if IGE patients only were analyzed. CSP modifications did not depend from differences in motor threshold between patients and controls. Meta-analysis confirms CSP modifications in epilepsies, with enhancement of this cortical inhibitory measure in most IGE patients. This provides a rationale for investigations aiming to verify the hypotheses that increased CSP reflects compensatory neural phenomena counteracting transition from the interictal to ictal state, and that CSP variability reflects the pathophysiological heterogeneity of epileptic syndromes.
The paper deals with Gibbs samplers that include high-dimensional conditional Gaussian distributions. It proposes an efficient algorithm that only requires a scalar Gaussian sampling. The algorithm ...relies on a random excursion along a random direction. It is proved to converge, i.e. the drawn samples are asymptotically under the target distribution. Our original motivation is in unsupervised inverse problems related to general linear observation models and their solution in a hierarchical Bayesian framework implemented through sampling algorithms. The paper provides an illustration focused on 2-D simulations and on the super-resolution problem.
Ca and Co substitutions in (Ca,Co)(OH)2 hydroxides Delorme, F.; Giovannelli, F.; Autret-Lambert, C. ...
Materials research bulletin,
October 2013, 2013-10-00, 2013-10, Letnik:
48, Številka:
10
Journal Article
Recenzirano
•No solid solution exists between Ca(OH)2) and β-Co(OH)2.•The substitution limit of calcium in β-Co(OH)2 is lower than 12%.•The substitution limit of cobalt in portlandite is lower than 7%.
According ...to DFT simulation, no mixed hydroxide containing calcium and a small divalent cation with the brucite structure is possible. This experimental study confirms that between portlandite (Ca(OH)2) and β-Co(OH)2, a solid solution does not exist. Samples have been synthesized by coprecipitation under flowing nitrogen at room temperature. However, XRD, TEM and DTA/TG analyses show that a partial solubility exists and that the substitution limit of calcium in β-Co(OH)2 is lower than 12% and lower than 7% for cobalt in Ca(OH)2. The two kinds of particles exhibit similar plate-like morphology with a size between 50 and 200nm and a thickness of about 10nm. The origin of such low substitution limits could be the difference in radii between calcium and cobalt generating local stresses. Substitutions by small amounts of different cations to reduce the local stresses such as Al, Sr or Cu have failed to allow improving significantly the substitution limits. An alternative synthesis route consisting in contacting the first cation oxide in a solution containing a salt of the second cation has also failed to reach a complete solid solution between portlandite and β-Co(OH)2.
The relationship between left ventricular ejection fraction (LVEF) and cognitive performance in patients with coronary artery disease (CAD) without overt heart failure is still under debate. In the ...present study we combine behavioural measures and event-related potentials (ERPs) to verify whether electrophysiological correlates of recognition memory (Old/New effect) is modulated differently as a function of LVEF. Twenty-five male patients with CAD (13 without LVEF > 55% and 12 with LVEF < 40% left ventricular dysfunction), and a Mini Mental State Examination score > 25 were enrolled. ERPs were recorded while participants performed a visual word recognition task consisting of a test phase in which they were asked to judge whether visual stimuli were previously presented in a learning phase (‘old’) or not (‘new’). ERPs responses from the test phase were analyzed. A late positive ERP component between 300 and 500 ms was differentially modulated in the two groups: a clear old/new effect (enhanced mean amplitude for old respect to new items) was observed in patients without LVEF dysfunction; whereas patients with overt LVEF dysfunction did not show such old/new effect. These data suggest that ERPs may reveal possible functional brain abnormalities that might be not observed at behavioural levels.
In healthy humans, the execution of linguistic tasks modifies the excitability of the hand area of the dominant primary motor cortex (M1), as tested by TMS. Our aim was to investigate the effect of ...linguistic tasks on the excitability of the M1 in patients with adductor type-spasmodic dysphonia (ASD), before and after Botulinum Neurotoxin Type A (BoNT-A) injections. We studied 10 patients with ASD and 10 age-matched healthy subjects. All participants were right handed. The excitability of either M1 hand area was evaluated at the baseline and during different linguistic and non-linguistic tasks: (1) reading aloud of single words; (2) silent reading; (3) looking at meaningless non-letter strings; (4) oral movements without vocalization; (5) producing simple syllabic phonation. In healthy controls, the motor evoked potential (MEP) elicited by TMS of the dominant M1 were significantly larger during reading aloud. In ASD patients, MEP enhancement in the dominant hand emerged not only during reading aloud but also during syllabic phonation. BoNT-A injections restored the neurophysiologic abnormalities. We conclude that ASD is characterized by an abnormal excitability of the hand area of the dominant M1 during specific linguistic tasks. This likely reflects an altered functional connectivity between cortical speech network and M1.
In this work, spark plasma sintering of La2Mo2O9 powder was used to achieve dense ceramics of La7Mo7O30 and explore their thermoelectric properties. SPS sintering of La2Mo2O9 powder at 973 K for ...10 min under 90 MPa leads to a bicoloured sample with white and black faces. XRD patterns of white and black faces are attributed to La2Mo2O9 and La7Mo7O30 phases, respectively. These experimental conditions allow observing the in-situ reduction of La2Mo2O9 during the SPS process. With a longer sintering time of 30 min, a ceramic of La7Mo7O30 is obtained. Its electrical conductivity exhibits a semiconducting behaviour and reaches a value of 1000 Sm-1 at 1000 K. The negative Seebeck coefficient show a n-type conduction in this phase. La7Mo7O30 exhibits a very low thermal conductivity, less than 1 Wm−1K−1 from room temperature up to 1000 K, similar to the values reported for La2Mo2O9. A figure of merit of 0.04 is reached at 1000 K.
•We analyze dysprosody in patients with idiopathic Parkinson's disease using a sentence repetition task.•We perform an automatic analysis of speech signals.•PD patients exhibit longer pauses between ...each sentence repetition.•PD patients show a lower percentage of “speech time” during a whole repetition period.
Parkinson's disease (PD) involves impairments of voice and speech (hypokinetic dysarthria). Dysprosody is one of the most common features of PD speech that includes alterations of rhythm and velocity of articulation. The aim of this study is the evaluation of dysprosody patterns in Parkinsonian patients during a sentence repetition task by means of a fully automated tool.
Twenty PD patients (14 male and 6 female) and 19 healthy controls (9 male and 10 female) were tested. Results show significant differences between the two groups as far as the time interval between each sentence repetition (Tinter), the percent of speech time with respect to sentence duration (D%) and the Net Speech Rate (NSR – defined as the number of syllables of the sentence divided by the effective speech time) are concerned. In particular, Tinter is larger in PD patients while D% is higher in the control group. These results show that PD patients may exhibit longer pauses between each sentence repetition and a lower percentage of “speech time” during a whole repetition period. Thus, the decrease of D% leads to an increase of NSR. Other acoustic parameters (noise and F0 variability) did not show any significant difference. This study confirms that speech in PD patients is characterized by short rushes followed by unorthodox pauses. These results may lead to the development of a system for the automatic acoustic analysis which could significantly reduce the processing time in particular during pre-processing, that to date is a time-consuming and operator-dependent step especially in case of recordings of long duration.
Highlights • We evaluate the role of the lateral occipital cortex (LOC) in audio–visual integration. • Facilitation induced by coherent audio–visual integration was reduced with TMS on LOC. • ...Audio–visual interaction may occur at early stage of object recognition process.
Conventional solid state mixed oxide route using manual and ball milling is investigated for the preparation of K
0·5
Na
0·5
NbO
3
(KNN) ceramics. Microstructure engineering was made using two ...milling methods and sintering techniques, and the crystal growth; then electromechanical properties were investigated as a function of sintering temperature, densification and grain size. The sintering conditions were set at 920°C/5 min for spark plasma sintering and 1090-1120°C/10 and 48 h for classical sintering. KNN crystal was grown using floating zone technique under nitrogen gas, where the translation and rotation speeds were fixed at 3 mm h
−1
and 20 rev min
−1
respectively. Piezoelectric and dielectric performances were measured and related to the microstructure. High k
t
(33 to 48%), k
p
of 18 to 48% and d
33
of 127-140 pC N
−1
were reached for relative densities of 84 to 96%. KNN ceramics are now available for the design of ultrasonic sensors.
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