P300 amplitude is insensitive to working memory load in schizophrenia

<p>Abstract</p> <p>Background</p> <p>Working memory (WM) tasks usually elicit a P300 ERP component, whose amplitude decreases with increasing WM load. So far, this effect has not been studied in schizophrenics (SZs), a group that is considered to have an aberrant brain connectivity and impairments in WM capacity. The aim of this study was to determine the dependency of the P300 component on WM load in a sample of SZ subjects.</p> <p>Methods</p> <p>We recorded 26 subjects (13 SZ patients and their matched controls) with an 80-channel electroencephalogram. Subjects performed an N-back task, a WM paradigm that manipulates the number of items to be stored in memory.</p> <p>Results</p> <p>In healthy subjects, P300 amplitude was highest in the low WM load condition, and lowest in both the attentional control condition and the high WM load condition. In contrast, SZs evidenced low P300 amplitude in all conditions. A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.</p> <p>Conclusions</p> <p>SZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load. These results are consistent with a general impairment in WM capacity in these patients.</p

Psychophysiological Markers of Vulnerability to Psychopathology in Men with an Extra X Chromosome (XXY)

Studying genetically defined syndromes associated with increased risk for psychopathology may help in understanding neurodevelopmental mechanisms related to risk for psychopathology. Klinefelter syndrome (47,XXY) is one of the most common sex chromosomal aneuploidies (1 in 650 male births) and associated with increased vulnerability for psychopathology, including psychotic symptoms. Yet, it remains unknown whether this increased risk is associated with underlying psychophysiological mechanisms that are typically deficient in individuals with psychotic disorders. The present study assessed three “classic” psychophysiological markers of psychosis in Klinefelter syndrome (KS): smooth pursuit eye movements (SPEM), prepulse inhibition (PPI) and P50 suppression. Fourteen adults with KS and 15 non-clinical adults participated in the study. Data on SPEM (reflecting visuo-motor control) as well as PPI and P50 suppression (reflecting sensory gating) were collected. Dysfunctions in SPEM were observed in individuals with KS, with less smooth pursuit as expressed in lower position gain. Also, reduced sensory gating in individuals with KS was suggested by significantly reduced prepulse inhibition of the startle response (PPI) (effect size 1.6). No abnormalities were found in suppression of the P50 (effect size 0.6). We speculate that impairments in these psychophysiological mechanisms may reflect core brain dysfunctions that may also mediate the described increased vulnerability for psychotic symptoms in KS. Although speculative, such deficit specific, rather than disorder specific, psychophysiological dysfunctions in KS might convey vulnerability to other types of psychopathology as well. As KS already can be diagnosed prenatally, the predictive value of childhood impairments in prepulse inhibition and smooth pursuit for development of psychopathology later in life could be assessed. In sum, studying individuals with KS may prove to be an avenue of research leading to new hypotheses and insights into “at risk” pathways to psychopathology

Saccadic latency in hepatic encephalopathy: a pilot study

Hepatic encephalopathy is a common complication of cirrhosis. The degree of neuro-psychiatric impairment is highly variable and its clinical staging subjective. We investigated whether eye movement response times—saccadic latencies—could serve as an indicator of encephalopathy. We studied the association between saccadic latency, liver function and paper- and pencil tests in 70 patients with cirrhosis and 31 patients after liver transplantation. The tests included the porto-systemic encephalopathy (PSE-) test, critical flicker frequency, MELD score and ammonia concentration. A normal range for saccades was established in 31 control subjects. Clinical and biochemical parameters of liver, blood, and kidney function were also determined. Median saccadic latencies were significantly longer in patients with liver cirrhosis when compared to patients after liver transplantation (244 ms vs. 278 ms p < 0.001). Both patient groups had prolonged saccadic latency when compared to an age matched control group (175 ms). The reciprocal of median saccadic latency (μ) correlated with PSE tests, MELD score and critical flicker frequency. A significant correlation between the saccadic latency parameter early slope (σE) that represents the prevalence of early saccades and partial pressure of ammonia was also noted. Psychometric test performance, but not saccadic latency, correlated with blood urea and sodium concentrations. Saccadic latency represents an objective and quantitative parameter of hepatic encephalopathy. Unlike psychometric test performance, these ocular responses were unaffected by renal function and can be obtained clinically within a matter of minutes by non-trained personnel

EMDR Effects on Pursuit Eye Movements

This study aimed to objectivize the quality of smooth pursuit eye movements in a standard laboratory task before and after an Eye Movement Desensitization and Reprocessing (EMDR) session run on seven healthy volunteers. EMDR was applied on autobiographic worries causing moderate distress. The EMDR session was complete in 5 out of the 7 cases; distress measured by SUDS (Subjective Units of Discomfort Scale) decreased to a near zero value. Smooth pursuit eye movements were recorded by an Eyelink II video system before and after EMDR. For the five complete sessions, pursuit eye movement improved after their EMDR session. Notably, the number of saccade intrusions—catch-up saccades (CUS)—decreased and, reciprocally, there was an increase in the smooth components of the pursuit. Such an increase in the smoothness of the pursuit presumably reflects an improvement in the use of visual attention needed to follow the target accurately. Perhaps EMDR reduces distress thereby activating a cholinergic effect known to improve ocular pursuit

Compressive Sensing for Bridge Damage Detection

Key cost factors in a bridge’s life cycle are its inspection and maintenance. In this context, replacing generalpurpose conservatory approaches with site-specific and ondemand services may help reduce costs. The latter require realtime awareness of the structural conditions of the bridge at hand. However, high installation costs for the necessary monitoring facilities, e.g., due to extensive cabling, may turn selfdefeating in such endeavors. Wireless sensor networks (WSNs) provide deployment flexibility and ease of installation, at the price of limited lifetime due to the battery-driven operation; inaccuracies due to imprecise sensor readings; and unreliability due packet loss. In contrast to many other WSN applications, structural monitoring requires the processing of large amounts of data which need to be transported to a base station which requires energy for communication. By applying compressive sensing to the sensor readings, the communication demands can be greatly reduced which is of particular interest for resource constrained systems such as WSNs. In this short paper we design and evaluate a compressive sensing scheme for bridge monitoring

Modelling of Pot Bearings – A Preliminary Study

Previous research indicates that roller and pot bearings may give rise to considerable non-linear effects in certain bridges. These effects appear as variations in natural frequency, mode shape and modal damping ratio, depending on the amplitude of vibration. At small amplitudes of vibration, it seems reasonable to assume that the rolling or sliding mechanism is inactive, thus yielding a stiffer structure and no additional dissipation of energy due to friction. At slightly larger amplitudes of vibration, although still remaining small with respect to geometrical non-linearity, the rolling or sliding mechanism activates, whereby the corresponding constraints are relieved. At the same time, because of the rolling or sliding friction, a certain amount of energy dissipates to the surroundings. In order to improve our understanding of these mechanisms and their practical implications, a preliminary experimental study has been performed with the aim of developing a simple model of these mechanisms, which can be included in theoretical models of bridges and other structures. In this paper, we give a short description of the outcome of our laboratory tests and the status of our model development process.</p

Separation and localisation of P300 sources and their subcomponents using constrained blind source separation

Separation and localisation of P300 sources and their constituent subcomponents for both visual and audio stimulations is investigated in this paper. An effective constrained blind source separation (CBSS) algorithm is developed for this purpose. The algorithm is an extension of the Infomax BSS system for which a measure of distance between a carefully measured P300 and the estimated sources is used as a constraint. During separation, the proposed CBSS method attempts to extract the corresponding P300 signals. The locations of the corresponding sources are then estimated with some indeterminancy in the results. It can be seen that the locations of the sources change for a schizophrenic patient. The experimental results verify the statistical significance of the method and its potential application in the diagnosis and monitoring of schizophrenia