An Unusual Location of Deep Venous Thrombosis Associated with Ischemic Stroke and Persistent Foramen Ovale

Up to 40% of ischemic strokes have no known cause (cryptogenic). The prevalence of persistent foramen ovale (PFO) amongst patients with cryptogenic stroke (CS) is twice as high as that of the normal population, therefore suggesting a causal relationship between the two entities. However, PFO by itself is not sufficient to cause stroke, as an embolic source is needed. This source is often unknown, making the causal relationship between CS and PFO hard to demonstrate. The most frequent, although still seldom, identifiable cause of embolism in an otherwise cryptogenic stroke associated with PFO is a deep venous thrombosis (DVT) of the lower extremities. Here, we present a unique case of brachiocephalic venous DVT associated with PFO and ischemic stroke in a young patient. As the search for DVT in patients with PFO and stroke is often limited to the lower extremities, this case may suggest that an unspecified number of DVTs are overlooked. Our report lends support to paradoxical embolism as a mechanism of stroke in patients with PFO and does, at least in selected cases, suggest a more detailed search for DVT beyond the lower extremities

The neural correlates of social attention: automatic orienting to social and nonsocial cues

Previous evidence suggests that directional social cues (e.g., eye gaze) cause automatic shifts in attention toward gaze direction. It has been proposed that automatic attentional orienting driven by social cues (social orienting) involves a different neural network from automatic orienting driven by nonsocial cues. However, previous neuroimaging studies on social orienting have only compared gaze cues to symbolic cues, which typically engage top-down mechanisms. Therefore, we directly compared the neural activity involved in social orienting to that involved in purely automatic nonsocial orienting. Twenty participants performed a spatial cueing task consisting of social (gaze) cues and automatic nonsocial (peripheral squares) cues presented at short and long stimulus (cue-to-target) onset asynchronies (SOA), while undergoing fMRI. Behaviorally, a facilitation effect was found for both cue types at the short SOA, while an inhibitory effect (inhibition of return: IOR) was found only for nonsocial cues at the long SOA. Imaging results demonstrated that social and nonsocial cues recruited a largely overlapping fronto-parietal network. In addition, social cueing evoked greater activity in occipito-temporal regions at both SOAs, while nonsocial cueing recruited greater subcortical activity, but only for the long SOA (when IOR was found). A control experiment, including central arrow cues, confirmed that the occipito-temporal activity was at least in part due to the social nature of the cue and not simply to the location of presentation (central vs. peripheral). These results suggest an evolutionary trajectory for automatic orienting, from predominantly subcortical mechanisms for nonsocial orienting to predominantly cortical mechanisms for social orienting

Visual Stability and the Motion Aftereffect: A Psychophysical Study Revealing Spatial Updating

Eye movements create an ever-changing image of the world on the retina. In particular, frequent saccades call for a compensatory mechanism to transform the changing visual information into a stable percept. To this end, the brain presumably uses internal copies of motor commands. Electrophysiological recordings of visual neurons in the primate lateral intraparietal cortex, the frontal eye fields, and the superior colliculus suggest that the receptive fields (RFs) of special neurons shift towards their post-saccadic positions before the onset of a saccade. However, the perceptual consequences of these shifts remain controversial. We wanted to test in humans whether a remapping of motion adaptation occurs in visual perception

Cross-frequency coupling of brain oscillations indicates the success in visual motion discrimination

Cortical activity such as recorded by EEG or MEG is characterized by ongoing rhythms that encompass a wide range of temporal and spatial scales. Recent studies have suggested an oscillatory hierarchy with faster oscillations being locked to preferred phases of underlying slower waves, a functional principle applied up to the level of action potential generation. We here tested the idea that amplitude-phase coupling between frequencies might serve the detection of weak sensory signals. To this end we recorded neuromagnetic responses during a motion discrimination task using near-threshold stimuli. Amplitude modulation of occipital high-frequency oscillations in the gamma range (63+/-5 Hz) was phase locked to a slow-frequency oscillation in the delta band (1-5 Hz). Most importantly, the strength of gamma amplitude modulation reflected the success in visual discrimination. This correlation provides evidence for the hypothesis that coupling between low- and high-frequency brain oscillations subserves signal detection

Differential Coherency Dependency in Subregions of the Human MT+ Complex

A functional hallmark of cortical neurons sensitive to visual motion is the dependency of their firing rate on motion strength. Specifically, single unit activity in macaque areas MT and MST is known to monotonically increase with motion strength such as motion coherence defined by the percentage of dot elements of a random dot kinematogram (RDK) moving in the same direction. Despite the strong similarities of the visual cortex of human and nonhuman primates, human area MT+, located in the posterior part of the inferior temporal sulcus (pITS) and probably comprising both areas MT and MST, has not consistently been found to respond stronger to coherent as compared to incoherent motion. A first goal of the present functional MRI study was to assess the responses to coherent and incoherent visual motion for both areas, separately. To this end, we exploited the fact that area MST lays immediately anterior to area MT and that only the first receives signals from both visual hemifields. A second goal was to test the influence of stimulus size. Blood oxygenation level depend (BOLD) responses were obtained from eleven human subjects who observed a RDK (stationary dots, incoherent motion, or coherent motion) in the right visual hemifield during stationary fixation. For a fixed eccentricity the stimulus extensions were varied in such a way to cover an area either equaling, exceeding, or falling below the mean MT receptive field size of macaque area MT [1]. Unlike the posterior part of left-hemisphere pITS, the anterior part and its right-hemisphere homolog showed significantly stronger responses to coherent as compared to incoherent motion. These differences were only present for stimuli larger than the estimated MT receptive field size. Based on these findings, we suggest that functional MRI may reveal stronger responses to coherent visual motion in human area MST provided that the stimulus allows for sufficient summation within the receptive fields. In contrast fMRI may fail to reveal the same dependency for area MT

Visual motion perception deficits due to cerebellar lesions are paralleled by specific changes in cerebro-cortical activity

Recent anatomical studies have revealed strong cerebellar projections into parietal and prefrontal cortex. These findings suggest that the cerebellum might not only play a functional role in motor control but also cognitive domains, an idea also supported by neuropsychological testing of patients with cerebellar lesions that has revealed specific deficits. The goal of the present study was to test whether or not cognitive impairments after cerebellar damage are resulting from changes in cerebro-cortical signal processing. The detection of global visual motion embedded in noise, a faculty compromised after cerebellar lesions, was chosen as a model system. Using magnetoencephalography, cortical responses were recorded in a group of patients with cerebellar lesions (n = 8) and controls (n = 13) who observed visual motion of varied coherence, i.e., motion strength, presented in the peripheral visual field during controlled stationary fixation. Corroborating earlier results, the patients showed a significant impairment in global motion discrimination despite normal fixation behavior. This deficit was paralleled by qualitative differences in responses recorded from parieto-temporal cortex, including a reduced responsiveness to coherent visual motion and a striking loss of bilateral representations of motion coherence. Moreover, the perceptual thresholds correlated with the cortical representation of motion strength on single subject basis. These results demonstrate that visual motion processing in cerebral cortex critically depends on an intact cerebellum and establish a correlation between cortical activity and impaired visual perception resulting from cerebellar damage

Cerebrocerebellar Circuits for the Perceptual Cancellation of Eye-movement-induced Retinal Image Motion

Despite smooth pursuit eye movements, we are unaware of resultant retinal image motion. This example of perceptual invariance is achieved by comparing retinal image slip with an internal reference signal predicting the sensory consequences of the eye movement. This prediction can be manipulated experimentally, allowing one to vary the amount of self-induced image motion for which the reference signal compensates and, accordingly, the resulting percept of motion. Here we were able to map regions in CRUS I within the lateral cerebellar hemispheres that exhibited a significant correlation between functional magnetic resonance imaging signal amplitudes and the amount of motion predicted by the reference signal. The fact that these cerebellar regions were found to be functionally coupled with the left parieto-insular cortex and the supplementary eye fields points to these cortical areas as the sites of interaction between predicted and experienced sensory events, ultimately giving rise to the perception of a stable world despite self-induced retinal motion

Biobleaching of high quality pulps with laccase mediator system: Influence of treatment time and oxygen supply

6 páginas, 10 figuras -- PAGS bros. 193-198In this study we examined the influence of the treatment time and addition of oxygen on the efficiency of a laccase mediator system (L) applied to flax pulp at atmospheric pressure. The redox potential and the dissolved oxygen concentration during L tests are measured. After L stage, an alkaline extraction (E) is carried out. The pulp properties (kappa number, brightness and viscosity) and the effluents properties (color and COD) were measured in order to evaluate the environmental impact of this enzymatic treatment. The biotreatment involves two distinct stages in both L and LE sequences; in the beginning the pulp exhibits a fast delignification and a slow viscosity decrease that is followed by slow delignification in the second. Pulp brightness changed differently during L stage and LE sequence. Initially brightness after the L stage decreased with respect to the initial pulp; then, it increased rapidly and eventually leveled off. After the LE sequence, brightness increased rapidly in the beginning and more gradually afterwards. The results show that supplying the medium with oxygen and increasing the oxygen concentration in it, influence the kinetics of the process. Based on CIE L*a*b* color coordinates study, the enzyme treatment not only removes lignin, but also alters the structure of the pulp by causing the formation of chromophoric groups giving color. Such groups are removed in an E stage.Spanish MEC ENZPULP Project (CTQ2005-08925-C02-01) and a BIORENEW Integrated European Project (NMP2-CT-2006-026456). Department of University, Research and Society of the Information of the Generalitat de Catalunya and the Social European Fund for the research fellowship (2005 FI grant)Peer reviewe