Role of Basal Ganglia Circuits in Resisting Interference by Distracters: A swLORETA Study

BACKGROUND: The selection of task-relevant information requires both the focalization of attention on the task and resistance to interference from irrelevant stimuli. Both mechanisms rely on a dorsal frontoparietal network, while focalization additionally involves a ventral frontoparietal network. The role of subcortical structures in attention is less clear, despite the fact that the striatum interacts significantly with the frontal cortex via frontostriatal loops. One means of investigating the basal ganglia's contributions to attention is to examine the features of P300 components (i.e. amplitude, latency, and generators) in patients with basal ganglia damage (such as in Parkinson's disease (PD), in which attention is often impaired). Three-stimulus oddball paradigms can be used to study distracter-elicited and target-elicited P300 subcomponents. METHODOLOGY/PRINCIPAL FINDINGS: In order to compare distracter- and target-elicited P300 components, high-density (128-channel) electroencephalograms were recorded during a three-stimulus visual oddball paradigm in 15 patients with early PD and 15 matched healthy controls. For each subject, the P300 sources were localized using standardized weighted low-resolution electromagnetic tomography (swLORETA). Comparative analyses (one-sample and two-sample t-tests) were performed using SPM5® software. The swLORETA analyses showed that PD patients displayed fewer dorsolateral prefrontal (DLPF) distracter-P300 generators but no significant differences in target-elicited P300 sources; this suggests dysfunction of the DLPF cortex when the executive frontostriatal loop is disrupted by basal ganglia damage. CONCLUSIONS/SIGNIFICANCE: Our results suggest that the cortical attention frontoparietal networks (mainly the dorsal one) are modulated by the basal ganglia. Disruption of this network in PD impairs resistance to distracters, which results in attention disorders

Acquisition et exploitation d'images morphologiques en conditions stereotaxiques : application a l'irradiation interstitielle des tumeurs cerebrales

SIGLECNRS T 57199 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A statistical study over Europe of the relative locations of lightning and associated energetic burst of electrons from the radiation belt

International audienceThe DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) spacecraft detects short bursts of lightning-induced electron precipitation (LEP) simultaneously with newly injected upgoing whistlers. The LEP occurs within < 1 s of the causative lightning discharge. First in situ observations of the size and location of the region affected by the LEP precipitation are presented on the basis of a statistical study made over Eu-rope using the DEMETER energetic particle detector, wave electric field experiment, and networks of lightning detection (Météorage, the UK Met Office Arrival Time Difference network (ATDnet), and the World Wide Lightning Location Network (WWLLN)). The LEP is shown to occur significantly north of the initial lightning and extends over some 1000 km on each side of the longitude of the lightning. In agreement with models of electron interaction with obliquely propagating lightning-generated whistlers, the distance from the LEP to the lightning decreases as lightning proceed to higher latitudes. Keywords. Ionosphere (particle precipitation; wave– particle interactions) – meteorology and atmospheric dynamics (lightning

Intracerebral study of gamma rhythm reactivity in the sensorimotor cortex.

International audienceThe generators and functional correlates of gamma oscillations within the sensorimotor cortex remain unclear. With the goal of locating the oscillations' sources precisely and then studying the relationship between oscillatory reactivity and ongoing movement, we recorded stereoelectroencephalograms with intracerebral electrodes in eight epileptic subjects awaiting surgical treatment. The sensorimotor cortex was free of lesions and was exhaustively explored with the electrodes. Subjects were asked to perform various self-paced movements contralateral to the exploration zone, brief and sustained, distal movements and a pointing movement. We used the event-related desynchronization method to quantify the reactivity of the 40-60-Hz band before, during and after the performance of movement. A very focused, event-related synchronization of gamma rhythms was found in all subjects. It was predominantly observed in the primary sensorimotor area and its distribution was consistent with the functional map established using electrical stimulations. Two different temporal patterns were observed, the event-related synchronization of gamma rhythms was related either to movement onset or to movement offset but was never recorded before movement. This observation suggests that gamma oscillations are more probably related to movement execution than to motor planning. The different patterns argue in favour of multiple functional roles; it has been shown that gamma oscillations may support the efferent drive to the muscles and here we show that they are also likely to be related to somatosensory integration. We therefore suggest that gamma oscillations in the 40-60-Hz band may support afferent sensory feedback to the sensorimotor cortex during the performance of movement

Relationship between intracerebral gamma oscillations and slow potentials in the human sensorimotor cortex.

International audienceChanges in sensorimotor rhythms (mu, beta and gamma) and movement-related cortical potentials (MRCPs) are both generated principally by the contralateral sensorimotor areas during the execution of self-paced movement. They appear to reflect movement control mechanisms, which remain partially unclear. With the aim of better understanding their sources and significance, we recorded MRCPs and sensorimotor rhythms during and after self-paced movement using intracerebral electrodes in eight epileptic subjects investigated by stereoelectroencephalography. The results showed that: (i) there is a strong spatial relationship between the late components of movement--the so-called motor potential (MP) and post-movement complex (PMc)--and gamma event-related synchronization (ERS) within the 40-60 Hz band, as the MP/PMc always occurred in contacts displaying gamma ERS (the primary sensorimotor areas), whereas mu and beta reactivities were more diffuse; and (ii) MPs and PMc are both generated by the primary motor and somatosensory areas, but with distinct sources. Hence, this could mean that kinesthesic sensory afferences project to neurons other than those firing during the pyramidal tract volley. The PMc and low gamma ERS represent two electrophysiological facets of kinesthesic feedback from the joints and muscles involved in the movement to the sensorimotor cortex. It could be suggested that gamma oscillations within the 40-60 Hz band could serve to synchronize the activities of the various neuronal populations involved in control of the ongoing movement

Kinematic angular parameters in PD: reliability of joint angle curves and comparison with healthy subjects,”

Abstract Background: Most previous biomechanical studies of Parkinson&apos;s disease (PD) have been restricted to the description of spatiotemporal parameters and certain peak values for angular parameters. The reliability of joint angle curves and comparisons with control data are of major interest in PD, since variability in gait cycle timing is a feature of this pathology. Methods: We used a video motion analysis system to record kinematic, spatiotemporal and angular parameters in 32 &apos;off-drug&apos; PD patients. The reliability of the patients&apos; lower limb joint angle curves in the sagittal plane were analysed using the intra-class correlation coefficient (ICC), together with fast Fourier transform (FFT) analysis and hierarchical classification for discarding deviant curves. Lastly, we compared average curves (using a mixed model and the bootstrap method) for the less-affected and more-affected sides of PD patients and then compared the patient data with the results from 30 age-matched controls. Results: The ICC-based procedure was easily applicable. Only 9.4% and 12.5% of the patients&apos; hip and knee curves (respectively) were deemed to be unreliable. However, the PD patients&apos; very high cycle-to-cycle variability in the sagittal plane ankle curves prevented us from applying to this joint. For the knee joint, the curves for the most disabled patients (who walked at below 0.5 m/s) were not reliable. We did not find any differences between the less and more disabled sides. The differences between patient and control curves concerned the doublesupport time during the stance phase and the time point for maximum knee flexion during the swing phase. Patients and controls differed in terms of the hip extension phase, with lower values in PD. Conclusion: We have developed the use of validated statistic tools for unambiguously comparing PD patients and controls in terms of joint angle curve differences.

Impaired Early Attentional Processes in Parkinson’s Disease: A High-Resolution Event-Related Potentials Study

<div><p>Introduction</p><p>The selection of task-relevant information requires both the focalization of attention on the task and resistance to interference from irrelevant stimuli. A previous study using the P3 component of the event-related potentials suggested that a reduced ability to resist interference could be responsible for attention disorders at early stages of Parkinson’s disease (PD), with a possible role of the dorsolateral prefrontal cortex (DLPFC).</p><p>Methods</p><p>Our objective was to better determine the origin of this impairment, by studying an earlier ERP component, the N2, and its subcomponents, as they reflect early inhibition processes and as they are known to have sources in the anterior cingulate cortex (ACC), which is involved together with the DLPFC in inhibition processes. Fifteen early-stage PD patients and 15 healthy controls (HCs) performed a three-stimulus visual oddball paradigm, consisting in detecting target inputs amongst standard stimuli, while resisting interference from distracter ones. A 128-channel electroencephalogram was recorded during this task and the generators of the N2 subcomponents were identified using standardized weighted low-resolution electromagnetic tomography (swLORETA).</p><p>Results</p><p>PD patients displayed fewer N2 generators than HCs in both the DLPFC and the ACC, for all types of stimuli. In contrast to controls, PD patients did not show any differences between their generators for different N2 subcomponents.</p><p>Conclusion</p><p>Our data suggest that impaired inhibition in PD results from dysfunction of the DLPFC and the ACC during the early stages of attentional processes.</p></div

Between-group statistical maps of the N200 components' grey matter current densities, with the permutation method (p<0.05).

<p>Top panel (4A-C): healthy controls vs. PD patients (4A: standard N200, 4B: distracter N200, 4C: target N200). Bottom panel (4D-F): PD patients vs. healthy controls (4D: standard N2, 4E: distracter N2, 4F: target N2).</p

Clinical and demographic features of the Parkinson's disease (PD) patients and healthy controls.

<p>Mean (standard deviation). p values were determined in t-tests (except for the gender ratio, to which a χ² test was applied).</p><p>Clinical and demographic features of the Parkinson's disease (PD) patients and healthy controls.</p

A schematic representation of the three-stimulus visual oddball paradigm.

<p>The circle task is on the left and the square task on the right.</p