Surface Termination of Fe3O4(111) Films Studied by CO Adsorption Revisited.

Although the (111) surface of Fe3O4 (magnetite) has been investigated for more than 20 years, substantial controversy remains in the literature regarding the surface termination proposed based on structural and adsorption studies. The present article provides density functional theory results that allow to rationalize experimental results of infrared reflection-absorption spectroscopy and temperature-programmed desorption studies on CO adsorption, thus leading to a unified picture in which the Fe3O4(111) surface is terminated by a 1/4 monolayer of tetrahedrally coordinated Fe3+ ions on top of a close-packed oxygen layer as previously determined by low energy electron diffraction. However, surface defects play a crucial role in adsorption properties and may dominate chemical reactions on Fe3O4(111) when exposed to the ambient.

Hyperthermic intraperitoneal chemotherapy with paclitaxel or cisplatin in patients with stage III-C/IV ovarian cancer. Is there any difference?

OBJETIVE: To compare the results of the administration of HIPEC with Paclitaxel or Cisplatin after cytoreduction in patients with stage IIIC-IV ovarian cancer, especially focused on disease-free survival. PATIENTS: We retrospectively analyzed a consecutive series of patients operated after being diagnosed with stage III-C/IV serous epithelial ovarian carcinoma. Patients included in the study were treated between January 2008 and March 2015. After cytoreduction, Paclitaxel (doses of 60 mg/m(2)O or Cisplatin (doses of 75 mg/m(2)) were used. RESULTS: A total of 111 patients were included. Median age was 61 years. In 60 of them (54%) Paclitaxel was used during HIPEC treatment and 51 patients (46%) were treated with Cisplatin. PCI was similar between groups (PCI = 11 in both cases). Median follow up was 34 months (12-96 months). The median disease free survival in Paclitaxel Group was 27 months and 33 months in Cisplatin Group (p = 0.551). In patients treated with Paclitaxel disease free survival rates at 1, 2, and 3 years were 79%, 60% and 46%. In patients treated with Cisplatin disease free survival at 1, 2, and 3 years were 64%, 50% and 40% respectively. After a multivariate analysis, incomplete cytoreduction (HR: 6.54, 95% CI 2.98-10.17, p < 0.01) and PCI >11 (HR: 2.15, 95% CI 1.42-6.68, p < 0.05) were identified as independent factors associated with a reduced disease-free survival. Cystotatic used was not relevant regarding disease free survival analysis. CONCLUSION: HIPEC with paclitaxel or cisplatin after cytoreduction in patients with ovarian cancer IIIC-IV has not shown different results in disease-free survival outcomes.

Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix.

While nanoparticles are being pursued actively for a number of applications, dispersed atomic species have been explored far less in functional materials architectures, primarily because composites comprising dispersed atoms are challenging to synthesize and difficult to stabilize against sintering or coarsening. Here we show that room temperature oxidation of Au-Sn alloys produces nanostructures whose surface is terminated by a reducible amorphous oxide that contains atomically dispersed Au. Analysis of the oxidation process shows that the dispersal of Au in the oxide can be explained by predominant oxygen anion diffusion and kinetically limited metal mass transport, which restrict phase separation due to a preferential oxidation of Sn. Nanostructures prepared by oxidation of nanoscale Au-Sn alloys with intermediate Au content (30-50%) show high activity in a CO-oxidation probe reaction due to a cooperative mechanism involving Au atoms as sites for CO adsorption and reaction to CO2 embedded in a reducible oxide that serves as a renewable oxygen reservoir. Our results demonstrate a reliable approach toward nanocomposites involving oxide-embedded, atomically dispersed noble metal species.

Correction: Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix.

Correction for 'Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix' by P. Sutter et al., Nanoscale Horiz., 2016, 1, 212-219.

COMT and ANKK1 gene-gene interaction modulates contextual updating of mental representations.

The differential expression of the dopamine transmitter through its prefrontostriatal pathway has been proposed to account for individual differences in the updating of higher order task representations. Here we examined the interaction between two polymorphic variations of genes involved in the regulation of prefrontal and striatal dopamine (catechol-O-methyltransferase-COMT and ANKK1) on the neural mechanisms of task-set switching. A task-cueing paradigm was employed to measure behavioral costs and a scalp-recorded specific brain potential (novelty-P3) associated to distinct context updating operations in the face of either sensory or task novelty. The interaction between the COMT and ANKK1 genes was evidenced by corresponding specific behavioral costs and novelty-P3 amplitude enhancements reflecting task-set updating mechanisms. This effect was found only in individuals combining genes that yielded a balance between dopamine concentrations and receptor densities. Individuals displaying a putative "unbalance" showed enhanced novelty-P3 responses to all sensory changes, indicative of a task-set updating to sensory cues in a task-context independent fashion. These results support the epistasis of COMT and ANKK1 phenotypes in the flexible control of contextual information in humans.

The role of DAT1 gene on the rapid detection of task novelty.

In an environment with a myriad of different stimuli, the fast detection of novel and behaviorally relevant signals becomes crucial for an adaptive behavior. The detection of task-novelty has been related to striatum-prefrontal cortex (PFC) pathways involving dopaminergic (DA) neurotransmission. Here we thus tested the hypothesis that DA regulates the detection of task novelty through the modulation of the auditory N1 potential, an auditory potential peaking at 100 ms and previously shown to be modulated by the detection of sensory novelty. Thirty-five healthy volunteers were divided in two groups according to the presence or absence of the 9-repetition allele (9R) of the SLC6A3/DAT1 gene for the dopamine transporter. Participants performed a cued task-switching paradigm that dissociated the effects of exogenous sensory novelty from those of endogenous task novelty. Individuals with the 9R allele showed an amplitude enhancement of the auditory N1 elicited to sensory changes requiring a task-set reconfiguration as compared to sensory changes with no task novelty. In contrast, individuals without the 9R allele did not have their N1 waveform modulated by task novelty. The present results suggest that individuals homozygous for the 10-repeat allele fail to detect the behavioral relevance of new stimuli at early stages.

The role of the dopamine transporter DAT1 genotype on the neural correlates of cognitive flexibility.

Cognitive flexibility, the ability to adapt goal-oriented behaviour in response to changing environmental demands, varies widely amongst individuals, yet its underlying neural mechanisms are not fully understood. Neuropharmacological and human clinical studies have suggested a critical role for striatal dopaminergic function mediated by the dopamine transporter (DAT). The present study aimed at revealing the role of the DAT in the individual brain response stereotypy underlying cognitive flexibility. A task-switching protocol was administered to a sample divided according to the presence or absence of the 9-repeat (9R) allele of the DAT1 polymorphism, while registering behavioural and electrophysiological novelty-P3 responses. The absence of the 9R (higher gene expression) is related to less striatal DA availability. Individuals lacking the 9R (9R-) showed specific response time (RT) increases for sensory change and task-set reconfiguration, as well as brain modulations not observed in participants with the 9R allele (9R+), suggesting that task performance of the former group depended on immediate local context. In contrast, individuals displaying high striatal DA showed larger RT costs than 9R- individuals to any sensory change, with no further increase for task-set reconfiguration, and a larger early positive brain response irrespective of the task condition, probably reflecting larger inhibition of any previous interference as well as stronger activation of the current task set. However, the polymorphic groups did not differ in their mean RTs in trials requiring task-set reconfiguration. This distinct stereotypy of cerebral responses reveals different patterns of cognitive control according to the DAT1 gene polymorphism.

Construct validity of the Trail Making Test: role of task-switching, working memory, inhibition/interference control, and visuomotor abilities.

The aim of this study was to clarify which cognitive mechanisms underlie Trail Making Test (TMT) direct and derived scores. A comprehensive review of the literature on the topic was carried out to clarify which cognitive factors had been related to TMT performance. Following the review, we explored the relative contribution from working memory, inhibition/interference control, task-switching ability, and visuomotor speed to TMT performance. Forty-one healthy old subjects participated in the study and performed a battery of neuropsychological tests including the TMT, the Digit Symbol subtest [Wechsler Adult Intelligence Scale (Third Version) (WAIS-III)], a Finger Tapping Test, the Digits Forward and Backward subtests (WAIS-III), Stroop Test, and a task-switching paradigm inspired in the Wisconsin Card Sorting Test. Correlation and regression analyses were used in order to clarify the joint and unique contributions from different cognitive factors to the prediction of TMT scores. The results suggest that TMT-A requires mainly visuoperceptual abilities, TMT-B reflects primarily working memory and secondarily task-switching ability, while B-A minimizes visuoperceptual and working memory demands, providing a relatively pure indicator of executive control abilities.

Decreased brain coordinated activity in autism spectrum disorders during executive tasks: reduced long-range synchronization in the fronto-parietal networks.

Current theories of brain function propose that the coordinated integration of transient activity patterns in distinct brain regions is the essence of brain information processing. The behavioural manifestations of individuals with autism spectrum disorders (ASD) suggest that their brains have a different style of information processing. Specifically, a current trend is to invoke functional disconnection in the brains of individuals with ASD as a possible explanation for some atypicalities in the behaviour of these individuals. Our observations indicate that the coordinated activity in brains of children with autism is lower than that found in control participants. Disruption of long-range phase synchronization among frontal, parietal and occipital areas was found, derived from magnetoencephalographic (MEG) recordings, in high-functioning children with ASD during the performance of executive function tasks and was associated with impaired execution, while enhanced long-range brain synchronization was observed in control children. Specifically, a more significant prefrontal synchronization was found in control participants during task performance. In addition, a robust enhancement in synchrony was observed in the parietal cortex of children with ASD relative to controls, which may be related to parietal lobe abnormalities detected in these individuals. These results, using synchronization analysis of brain electrical signals, provide support for the contention that brains of individuals with autism may not be as functionally connected as that of the controls, and may suggest some therapeutic interventions to improve information processing in specific brain areas, particularly prefrontal cortices.

Structure-effect relation of C18 long-chain fatty acids in the reduction of body weight in rats.

OBJECTIVE: To investigate the relationship between chemical structure and physiological effect, the efficacy and the molecular mechanisms involved in the reduction of body weight by C18 fatty acids (stearic, elaidic, oleic, linoleic and 2-hydroxyoleic acids (2-OHOA)). DESIGN: Ad libitum fed, lean Wistar Kyoto rats treated orally with up to 600 mg kg(-1) of the fatty acids or vehicle every 12 h for 7 days. Besides, starved rats and rats pairfed to the 2-OHOA-treated group served as additional controls under restricted feeding conditions. MEASUREMENTS: Body weight, food intake, weight of various fat depots, plasma leptin, hypothalamic neuropeptides, uncoupling proteins (UCP) in white (WAT) and brown adipose tissue (BAT) and phosphorylation level of cyclic AMP (cAMP) response element-binding protein (CREB) in WAT. RESULTS: Only treatment with oleic acid and 2-OHOA induced body weight loss (3.3 and 11.4%, respectively) through reduction of adipose fat mass. Food intake in these rats was lower, although hypothalamic neuropeptide and plasma leptin levels indicated a rise in orexigenic status. Rats pairfed to the 2-hydroxyoleic group only lost 6.3% body weight. UCP1 expression and phosphorylation of CREB was drastically increased in WAT, but not BAT of 2-OHOA-treated rats, whereas no UCP1 expression could be detected in WAT of rats treated with oleic acid. CONCLUSION: Both cis-configured monounsaturated C18 fatty acids (oleic acid and 2-OHOA) reduce body weight, but the introduction of a hydroxyl group in position 2 drastically increases loss of adipose tissue mass. The novel molecular mechanism unique to 2-hydroxyoleic, but not oleic acid, implies induction of UCP1 expression in WAT by the cAMP/PKA pathway-dependent transcription factor CREB, most probably as part of a transdifferentiation process accompanied by enhanced energy expenditure.

Trail Making Test in traumatic brain injury, schizophrenia, and normal ageing: sample comparisons and normative data.

The Trail Making Test (TMT) has been a useful assessment tool to investigate executive function. Several studies have recently improved the existing TMT norms by mean of large samples of healthy individuals stratified by a number of demographic variables from different populations. In contrast, criticisms have been raised about the utility of norms from healthy samples to detect changes across time in clinical samples where TMT performance used to be altered. In addition, few studies have compared groups of patients with deficits in TMT performance, making it difficult to decide whether a single set of norms is sufficient to assess different clinical populations. We provide normative data from three large samples of patients with traumatic brain injury (TBI) (n=90), schizophrenia spectrum disorders (n=127), and healthy Spanish speakers (n=223). Differences between healthy participants and patients in all TMT direct (TMT-A, TMT-B) and derived (B-A, B:A, B-A/A) scores were found. TMT performance was poorer in TBI patients than in schizophrenia patients except for the B:A and B-A/A scores, suggesting a similar underlying executive deficit. Normal ageing impaired both direct and derived TMT indices, as revealed by lower scores in the healthy elderly group (55-80 years old) as compared with young (16-24) and middle-aged (25-54) healthy participants. Three different sets of norms stratified by age, education, or both are presented for clinical use. Recommendations on TMT scores are made for future research.

[Electrophysiology of executive functions]. / Electrofisiología de las funciones ejecutivas.

INTRODUCTION: In neuropsychology, executive functions have been defined as those that coordinate the flow of information processing in the brain. In the last decade its study has undergone an important development, partly due to the use of functional neuroimaging. DEVELOPMENT: Electrophysiological techniques have also provided a link between two specific components of the event related brain potential (ERP) and certain control and monitoring processes, as those described in theoretical frameworks of executive functioning (i.e., Norman & Shallice). On the one hand, attentional set shifting paradigms allow us to relate the anteriorly (P3a; latency 300-350 ms) and posteriorly (P3b; latency 450-600 ms) distributed components of the so called 'novelty P3', with a more general mechanism of attentional set shifting that could account for both stimulus and task novelty. On the other hand, 'error related negativity' (ERN or En) has shown its sensitivity to action monitoring (i.e., error detection and error correction processes), during the execution of response selection RT tasks. CONCLUSIONS: The comprehension of these two executive processes represents critical aspects in our understanding of brain function, and has direct applications to the design of both theoretical models and assessment and rehabilitation programs for patients with dysexecutive disorders.

Electrofisiología de las funciones ejecutivas / Electrophysiology of executive functions

Introducción. La Neuropsicología define las funciones ejecutivas cerebrales como aquellas que coordinan el procesamiento de la información en el cerebro. Su estudio ha experimentado un importante avance en la última década promovido por la utilización de las técnicas de neuroimagen funcional. Desarrollo. Las técnicas de medición electrofisiológica han permitido establecer una relación entre dos componentes específicos del potencial evocado (PE) cerebral y determinados procesos de control y monitorización descritos en modelos teóricos sobre funcionamiento ejecutivo, como el de Norman y Shallice. Por un lado, los aspectos anterior (P3a; latencia 300350 ms) y posterior (P3b; latencia 450-600 ms) del componente P3 a la novedad (del inglés, novelty P3), se han vinculado con un sistema genérico de cambio atencional ante las demandas novedosas del entorno y de la tarea, gracias al empleo de los paradigmas experimentales de cambio de set atencional. Por otro lado, el PE denominado negatividad relacionada con los errores (del inglés, error related negativity o ERN) se ha mostrado sensible a los procesos de monitorización de la conducta (p. ej., detección de errores y generación de acciones correctivas), durante la ejecución de tareas de selección de respuesta con tiempo de reacción. Conclusiones. La comprensión de estos dos subprocesos ejecutivos supone un elemento clave en el concepto del funcionamiento del cerebro con aplicaciones directas sobre la generación, tanto de modelos teóricos como de protocolos de evaluación y rehabilitación de pacientes con alteraciones disejecutivas (AU)

Introduction. In neuropsychology, executive functions have been defined as those that coordinate the flow of information processing in the brain. In the last decade its study has undergone an important development, partly due to the use of functional neuroimaging. Development. Electrophysiological techniques have also provided a link between two specific components of the event related brain potential (ERP) and certain control and monitoring processes, as those described in theoretical frameworks of executive functioning (i.e., Norman & Shallice). On the one hand, attentional set shifting paradigms allow us to relate the anteriorly (P3a; latency 300-350 ms) and posteriorly (P3b; latency 450-600 ms) distributed components of the so-called ‘novelty P3’, with a more general mechanism of attentional set shifting that could account for both stimulus and task novelty. On the other hand, ‘error related negativity’ (ERN or En) has shown its sensitivity to action-monitoring (i.e., error detection and error correction processes), during the execution of response-selection RT tasks. Conclusions. The comprehension of these two executive processes represents critical aspects in our understanding of brain function, and has direct applications to the design of both theoretical models and assessment and rehabilitation programs for patients with dysexecutive disorders (AU)

Fragile-X syndrome and skewed X-chromosome inactivation within a family: a female member with complete inactivation of the functional X chromosome.

Fragile X syndrome is the most common form of inherited mental retardation. It is caused by the increase in length of a stretch of CGG triplet repeats within the FMR1 gene. A full mutation (> 200 repeats) leads to methylation of the CpG island and silencing of the FMR1 gene. We present here two sisters that are compound heterozygotes for a full mutation and a 53 repeat intermediate allele, one of them showing mental retardation and clinical features of an affected male (speech delay, hyperactivity, large ears, prominent jaw, gaze aversion), while the other is borderline normal (mild delay). Southern blot and FMRP expression analysis showed that the sister with mental retardation had the normal FMR1 gene totally methylated and no detectable protein, while her sister had 70% of her cells with the normal FMR1 gene unmethylated and normal FMRP levels. We found that the observed phenotypic differences between both sisters who are cytogenetically normal, are caused by extreme skewed X-chromosome inactivation. Analysis of the extended family showed that most of the other female family members that carry a pre-mutation or a full mutation showed some degree of skewing in their X-chromosome inactivation. The presence of several family members with skewed X inactivation and the direction and degree of skewing is inconsistent with a mere selection during development, and suggests a genetic origin for this phenomenon.

Does the Wisconsin Card Sorting Test measure prefontral function?

This review describes a research program aimed at evaluating the validity and specificity of the Wisconsin Card Sorting Test (WCST), one of the most widely used tests of prefrontal function in clinical and experimental neuropsychology. In spite of its extensive use, voices of caution have arisen against the use of WCST scores as direct markers of prefrontal damage or dysfunction. Adopting a cognitive neuroscience approach, the present research program integrates behavioral, physiological, and anatomical information to investigate the cognitive and neural mechanisms behind WCST performance. The results show that WCST performance evokes conspicuous physiological changes over frontal as well as posterior brain regions. Moreover, WCST scores confound very heterogeneous cognitive and neural processes. This confounding effect may have led many authors to overlook the relative importance of certain dysfunctional states such as those indexed by random errors. These findings strongly suggest that WCST scores cannot be regarded as valid nor specific markers of prefrontal lobe function. However, they do provide some relevant clues to update our current knowledge about prefrontal function. In the long run, the integrative approach of cognitive neuroscience may help us design and develop more valid and sensitive tools for neuropsychological assessment.

Adaptación Madrid del test de clasificación de cartas de Wisconsin:un estudio comparativo de consistencia interna / Madrid adaptation of the Wiscosisn card sorting test: a comparative study of internal consistency

Introducción. El test de clasificación de cartas de Wisconsin (WCST, del inglés Wisconsin Card Sorting Test) sigue siendo una prueba neuropsicológica muy utilizada para evaluar la patología del lóbulo frontal. Estudios recientes han cuestionado la validez del WCST como marcador de disfunción frontal. Objetivos. Presentamos una adaptación simplificada del WCST especialmente diseñada para valorar la capacidad de cambiar el criterio atencional. Nuestros objetivos son examinar las diferencias normativas y en la consistencia interna entre nuestra adaptación y el WCST convencional. Sujetos y métodos. Ambas pruebas fueron administradas a una grupo de 60 sujetos jóvenes sin patología cerebral. A las puntuaciones de ambos tests se aplicó un análisis de componentes principales para obtener su estructura interna. Resultados. Se detectaron diferencias estadísticas significativas entre las puntuaciones de los sujetos españoles y los datos normativos del WCST. Los análisis de componentes principales mostraron una solución de dos componentes en el WCST convencional y una solución de tres componentes en nuestra adaptación. Conclusiones. Los baremos americanos subestimaron el nivel de ejecución de la muestra española. El análisis de la consistencia interna reveló una estructura factorial excesivamente redundante y simple del WCST convencional. Nuestra adaptación mostró una estructura interna más rica, con una ordenación de las puntuaciones de error más acorde con el tipo de proceso cognitivo implicado. Estas ventajas son atribuibles a un análisis más preciso de los errores no perseverativos, subclasificados en errores eficientes (i.e., ligados al contraste de hipótesis) y errores aleatorios (i.e., ligados a la pérdida de criterio atencional) (AU)

Heterogeneous DNA binding modes of berenil.

Isothermal titration calorimetry (ITC) profiles of berenil bound to different DNAs show that, despite the strong preference of berenil for AT-rich regions in DNA, it can bind to other DNA sequences significantly. The ITC results were used to quantify the binding of berenil, and the thermodynamic profiles were obtained using natural DNAs as well as synthetic polynucleotides. ITC binding isotherms cannot be simply described when a single set of identical binding sites is considered, except for poly[d(A-T)2]. Ultraviolet melting of DNA and differential scanning calorimetry were also used to quantify several aspects of the binding of berenil to salmon testes DNA. We present evidence for secondary binding sites for berenil in DNA, corresponding to G+C rich sites. Berenil binding to poly[d(G-C)2] is also observed. Circular dichroism experiments showed that binding to GC-rich sites involves drug intercalation. Using a molecular modeling approach we demonstrate that intercalation of berenil into CpG steps is sterically feasible.

Free radical activity of natural and heat treated amphibole asbestos.

The amphibole minerals amosite and crocidolite were subjected to calcination and to hydrothermal treatment in order to study the effect of these heat treatments on the ability of the minerals to trigger formation of free radicals, which is known to be a main factor causing asbestosis and other asbestos-induced diseases. Free radical activity of the natural and heat treated minerals was studied by using supercoiled DNA (pUC18 plasmid) as a target molecule, and also by means of EPR spectroscopy. It was shown that after calcination of the natural minerals at 1073 K their free radical activity was strongly decreased These results, which may have relevant consequences for asbestos technology, were correlated with concomitant alteration of the structure and surface chemistry of the minerals during calcination.

[Madrid adaptation of the Wisconsin card sorting test: a comparative study of internal consistency]. / Adaptación Madrid del test de clasificación de cartas de Wisconsin: un estudio comparativo de consistencia interna.

INTRODUCTION: WCST (Wisconsin Card Sorting Test) is still a widely used neuropsychological test for evaluation of disorders of the frontal lobes. Recent studies have cast doubt on the validity of WCST as a marker for frontal dysfunction. OBJECTIVES: We present a simplified version of WCST specially designed to evaluate the capacity to change the criteria for attention. Our objectives were to examine the difference in standards and in internal consistency between our adaptation and the conventional WCST. SUBJECTS AND METHODS: The two tests were applied to a group of 60 young persons with no cerebral disorders. The principal components of both tests were analysed for determine their internal structure. RESULTS: We found statistically significant differences between the scores of Spanish persons and the standard data for WCST. Analysis of the main components showed a solution of two components in the conventional WCST and a solution of three components in our adaptation. CONCLUSIONS: The American rating system underestimated the level of performance in the Spanish sample. Analysis of the internal consistency showed the excessively redundant and simple factorial structure of the conventional WCST. Our adaptation was shown to have a richer internal structure, with the order of error scores more in accord with the type of cognitive process involved. These advantages may be attributed to more exact analysis of non perseverant errors, subclassified as efficient errors (i.e. linked to comparison of hypotheses) and random errors (i.e. linked to loss of criteria for attention).

Attentional set shifting modulates the target P3b response in the Wisconsin card sorting test.

For years the Wisconsin card sorting test (WCST) has been used as a test of frontal lobe function. Recent event-related potential (ERP) research has shown large differences in the amplitude of P3b responses evoked by early and late trials within each WCST series ([8]: Barceló F., Sanz M., Molina V., Rubia FJ. The Wisconsin Card Sorting Test and the assessment of frontal function: A validation study with event-related potentials. Neuropsychologia 1997;35:399-408). In this study, 16 normal subjects performed a WCST adaptation to investigate the role of attentional set shifting in these WCST P3b effects. Two control tasks were designed to examine whether early-late WCST P3b changes reflect category selection (attention) or category storage (memory) operations. Results suggest both a sharp P3b attenuation during shift WCST trials, followed by a gradual P3b build-up during post-shift trials. This P3b modulation could not be attributed to selection or storage of simple sensory stimulus dimensions, nor was it observed when the new rule was externally prompted by the first card in the WCST series. Instead, WCST P3b changes seem related to the endogenously generated shift in the perceptual rule used to sort the cards (i.e., the shift in set). The gradual build-up in P3b amplitude paralleled a progressive improvement in sorting efficiency over several post-shift WCST trials. A model based on formal theories of visual attention and attentional set shifting is proposed to account for these effects. The model offers firm grounds for prediction and bridges the gap between related clinical and experimental evidence.