Redes neurales de la atencion en pacientes con esquizofrenia y sus familiares no afectados de primer grado: un endofenotipo potencial / Attentional network task in schizophrenic patients and theirs unaffected first degree relatives: a potential endofenotype

Introducción. Existe un notable incremento de reportes sobre déficit atencionales en pacientes con esquizofrenia y sus familiares de primer grado, incluyendo un gran esfuerzo por la búsqueda de endofenotipos para llegar a genes específicos responsables de la enfermedad. Posner y col. Desarrollaron una prueba para explorar las redes neurales de la atención (ANT). Esta provee mediciones por separado para cada una de las tres redes neurales anatómicamente definidas(alerta, orientación y control ejecutivo).Metodología: Investigamos a través de un estudio de asociación familiar el desempeño atencional en 32 pacientes con esquizofrenia, 29 familiares sanos y 29 controles utilizando el ANT. Examinamos segregadamente la eficiencia para las redes del control ejecutivo, la alerta y la orientación, evaluando como los tiempos de reacción eran modificados por la posición de la señal orientadora (“cue”) y la congruencia contextual del estímulo (“flanker”). También exploramos la asociación familiar de estas alteraciones atencionales. Resultados: Un ANOVA reveló un efecto principal del “flanker” y la condición del “cue” y una interacción significativa entre el “flanker” y los grupos estudiados. Los pacientes con esquizofrenia y sus familiares tienen un tiempo de reacción medio superior al grupo control. Los probandos y sus familiares difieren significativamente del grupo control en términos de resolución de conflictos, sin embargo, la alerta aparece conservada. Conclusiones: Nuestros resultados apoyan la tesis de un déficit atencional específico en la esquizofrenia y evidencian la segregación de las tres redes neuro-atencionales. La asociación familiar de estas alteraciones soporta la idea de un endofenotipo potencial en la esquizofrenia (AU)

Introduction. In recent years, reports of attention deficits in schizophrenic patients and in their biological relatives have rapidly increased, including an important effort to search for the endophenotypes in order to link specific genes to this illness. Posner et al. developed a test, the Attention Network Test (ANT), to study the neural networks. This test provides a separate measure for each one of the three anatomically-defined attention networks (alerting, orienting and executive control). Methodology. In this paper, we investigate the attentional performance in 32 schizophrenic patients, 29 unaffected first degree relatives and 29 healthy controls using the ANT through a study of family association. We have studied the efficiency of the segregated executive control, alerting and orienting networks by measuring how response latencies (reaction time) were modified by the cue position and the flanking stimuli. We also studied the familial association of these attentional alterations. Results. The ANOVA revealed main effects of flanker and cue condition and a significant interaction effect between flanker and groups studied. The schizophrenic patients and their relatives had a longer median reaction time than the control group. The probands and their relatives significantly differed from the healthy controls in terms of their conflict resolution; however, the alerting network appeared to be conserved. Conclusions. Our results support the thesis of a specific attentional deficit in schizophrenia and show the segregation of the three attentional networks. The family association of these reported alterations supports the idea of a potential endophenotype in schizophrenia (AU)

Attentional network task in schizophrenic patients and theirs unaffected first degree relatives: a potential endofenotype.

INTRODUCTION: In recent years, reports of attentional deficits in schizophrenic patients and in their biological relatives have rapidly increased, including an important effort to search for the endophenotypes in order to link specific genes to this illness. Posner et al. developed a test, the Attention Network Test (ANT), to study the neural networks. This test provides a separate measure for each one of the three anatomically-defined attention networks (alerting, orienting and executive control). METHODOLOGY: In this paper, we investigate the attentional performance in 32 schizophrenic patients, 29 unaffected first degree relatives and 29 healthy controls using the ANT through a study of family association. We have studied the efficiency of the segregated executive control, alerting and orienting networks by measuring how response latencies (reaction time) were modified by the cue position and the flanking stimuli. We also studied the familial association of these attentional alterations. RESULTS: The ANOVA revealed main effects of flanker and cue condition and a significant interaction effect between flanker and groups studied. The schizophrenic patients and their relatives had a longer median reaction time than the control group. The probands and their relatives significantly differed from the healthy controls in terms of their conflict resolution; however, the alerting network appeared to be conserved. CONCLUSIONS: Our results support the thesis of a specific attentional deficit in schizophrenia and show the segregation of the three attentional networks. The family association of these reported alterations supports the idea of a potential endophenotype in schizophrenia.

[Family transmission of positive and negative symptoms in familial and sporadic schizophrenia]. / Transmisión familiar de los síntomas positivos y negativos en la esquizofrenia familiar y esporádica.

INTRODUCTION: A genetic component is recognized as a cardinal feature in the etiology of schizophrenia that is presently conceived as a complex disease. However, identifying its molecular bases has become a problem, mainly due to the difficulties that the schizophrenic phenotype presents. The aim of this study is to determine whether the positive and negative symptoms are differentiated from each other according to family history in a family study using familial/sporadic strategy. METHODS: 601 subjects were studied (196 schizophrenics, 205 first degree relatives and 200 controls). A SCAN system and the diagnosis criteria of DSM IV were used. For the familial study the FIGS and PANSS scales were applied. Families were grouped into familial or sporadic groups according to family aggregation. Comparisons were made using the ANOVA. RESULTS: The groups of patients and the first degree relatives with familial schizophrenia showed significantly higher scores in the negative sub-scale than did the sporadic schizophrenia subjects. Behavior of the first degree relatives with sporadic schizophrenia was similar to the control group. Positive sub-scale scores and general psychopathology showed no differences in the patients and their relatives according to familiar aggregation. CONCLUSIONS: This study confirms previous results that negative symptoms are more frequent in schizophrenics and their first degree relatives with familial schizophrenia. Therefore, it can be said that negative symptoms are a clinical phenotype more related to the genetic etiology.

Transmisión familiar de los síntomas positivos y negativos en la esquizofrenia familiar y esporádica / Family transmission of positive and negative symptoms in familial and sporadic schizophrenia

Introducción. Se reconoce un componente genético en la etiología de la esquizofrenia concebida en estos momentos como una enfermedad compleja. Identificar las bases moleculares de esta enfermedad se ha convertido en un problema por las dificultades del fenotipo esquizofrénico. El objetivo de esta investigación fue analizar si existen diferencias relacionadas con la presencia de los síntomas positivos y negativos en un estudio familiar utilizando la estrategia familiar/esporádica. Métodos. Se estudiaron 601 sujetos (196 esquizofrénicos, 205 familiares de primer grado y 200 controles). Se utilizó el sistema SCAN y se usaron los criterios diagnósticos del DSM-IV. Para el estudio familiar se aplicó el FIGS y la Escala PANSS. La esquizofrenia se clasificó en familiar o esporádica de acuerdo al número de esquizofrénicos en la familia. La comparación entre los grupos se realizó con el test de análisis de varianza ANOVA. Resultados. La esquizofrenia familiar presentó mayor puntuación en la subescala negativa en los pacientes y sus familiares de primer grado en relación con la esporádica. Los familiares esporádicos se comportaron de forma similar al grupo control. Los grupos familiar y esporádico se comportaron de forma similar en las subescalas positiva y de psicopatología general. Conclusiones. Este estudio confirma resultados previos, donde se ha descrito que los síntomas negativos se presentan más en la esquizofrenia familiar, en los pacientes y en sus familiares. Por tanto pudiéramos decir que los síntomas negativos son un fenotipo clínico más relacionado con la etiología genética (AU)

Brain potentials reflect residual face processing in a case of prosopagnosia.

Here, ERPs were employed to characterise the residual face processing of FE, a patient with extensive damage to the ventral temporal-occipital cortex and a dense prosopagnosia. Alarge N170 was present in FE and he performed well in tests of face structural processing. Covert recognition of the faces of personal acquaintances was demonstrated with P300 oddball experiments. The onset latency of the P300 effect was normal, indicating fast availability of covert memory. The scalp topography of this component in FE was different from that of the P3b, presenting a centro-frontal maximum. FE also presented larger skin conductance responses to familiar than to unfamiliar faces. The amplitudes of both the single-trial P300s and the SCRs triggered by familiar faces were positively correlated with the degree of person-familiarity that FE had for the poser. He performed at chance when asked to select between the face of a familiar person and that of an unfamiliar person on the basis of explicit recognition, whereas he selected more the previously known face if the forced choice was based on trustworthiness or a vague sense of familiarity. The results suggest that in FE, early face processing was relatively intact and covert recognition was fast. Neural structures involved in the processing of emotional or social cues possibly mediate the covert recognition present in FE.

[Visual extinction: a study by means of potentials evoked with movement]. / Extinción visual: estudio mediante potenciales evocados al movimiento.

INTRODUCTION: The term extinction refers to the phenomenon in which a patient with a lesion of the central nervous system ignores one of two stimuli in conditions of simultaneous bilateral stimuli. Various studies observe this phenomenon as the expression of a deficit in the process of selective attention, but there are few studies with potentials related to events (PRE). OBJECTIVES: To find the possible electrical correlation of the extinction phenomenon and the stage of processing at which this occurs. PATIENTS AND METHODS: We studied a patient with a right parieto occipital lesion and a control person of the same race, age, sex and educational level. We carried out two experiments. The first of these was to determine the direction of movement of two surfaces with red and green spots situated on both sides of a central fixation point. In the second experiment, the same task was carried out, but the two surfaces were superimposed, in the same place. In both cases the first movement occurred in the surface which was being attended to and the second might be this surface or the other. The proportion of correct answers were recorded for both movements. The PRE showed an attention disorder which affected the spatial distribution of attention with conservation of the attention to objects. CONCLUSIONS: The suppression of the P1 N1 components are the electrical correlate of the phenomenon of extinction which should occur during early stages of processing. Further investigations are necessary in a larger number of cases.

Extinción visual:estudio mediante potenciales evocados al movimiento / Visual extinction: a study be means of potentials evoked with movement

Introducción. El término extinción hace referencia al fenómeno en el cual un paciente con lesión del sistema nervioso central ignora uno de dos estímulos en condiciones de estimulación bilateral simultánea. Diversos estudios observan este fenómeno como la expresión de un déficit de los procesos de atención selectiva, pocos son los estudios con potenciales relacionados con eventos (PRE). Objetivos. Conocer el posible correlato eléctrico del fenómeno extinción y en qué etapa del procesamiento ocurre. Pacientes y métodos. Se estudia un paciente con lesión parietoccipital derecha y un sujeto control igual en raza, edad, sexo y nivel educacional. Se realizaron dos experimentos. El primero de ellos quería determinar la dirección del movimiento de dos superficies de puntos de color rojo y verde ubicadas a ambos lados de un punto de fijación central. En el segundo experimento se realizó la misma tarea pero con las superficies de puntos superpuestas, en un mismo lugar del espacio. En ambos casos un primer movimiento ocurría en la superficie atendida y el segundo podía ser esta misma o en la no atendida. Se recogieron los porcentajes de respuestas correctas para ambos movimientos. Se registraron los PRE durante la ejecución del primer experimento. Resultados. Los resultados conductuales y de PRE evidencian un trastorno atencional que afecta la distribución espacial de la atención con preservación de la atención a objetos. Conclusiones. La supresión de los componentes P1-N1 es el correlato eléctrico del fenómeno de extinción, el cual debe ocurrir en etapas tempranas de procesamiento. Resulta necesario extender la investigación a un número mayor de casos (AU)

Attentional shifts between surfaces: effects on detection and early brain potentials.

Two consecutive events transforming the same illusory surface in transparent motion (brief changes in direction) can be discriminated with ease, but a prolonged interference ( approximately 500 ms) on the discrimination of the second event arises when different surfaces are concerned [Valdes-Sosa, M., Cobo, A., & Pinilla, T. (2000). Attention to object files defined by transparent motion. Journal of Experimental Psychology: Human Perception and Performance, 26(2), 488-505]. Here we further characterise this phenomenon and compare it to the attentional blink AB [Shapiro, K.L., Raymond, J.E., & Arnell, K.M. (1994). Attention to visual pattern information produces the attentional blink in RSVP. Journal of Experimental Psychology: Human Perception and Performance, 20, 357-371]. Similar to the AB, reduced sensitivity (d') was found in the two-surface condition. However, the two-surface cost was associated with a reduced N1 brain response in contrast to reports for AB [Vogel, E.K., Luck, S.J., & Shapiro, K. (1998). Electrophysiological evidence for a postperceptual locus of suppression during the attentional blink. Journal of Experimental Psychology: Human Perception and Performance, 24(6), 1656-1674]. The results from this study indicate that the two-surface cost corresponds to competitive effects in early vision. Reasons for the discrepancy with the AB study are considered.

Different scalp topography of brain potentials related to expression and identity matching of faces.

Event-related potentials (ERPs) and behavioral data were recorded while subjects performed two tasks on the same set of faces (presented in pairs). One task was identity matching and the other expression matching. Two groups of subjects participated, one familiar and the other unfamiliar with the faces. Subjects were less accurate in matching expressions than identity. Familiarity facilitated identity but not expression matching. ERPs to mismatches in both tasks elicited a negativity around 400 ms, which was similar in latency and amplitude in the two tasks, but differed in scalp topography. Whereas the mismatch negativity had the same landscape over the left hemisphere for both tasks, the component related to expression had larger amplitudes over the right-temporal regions. Familiarity had no effect on these negativities, although it affected a late positivity (LP). These results support the idea of distinct neural systems subserving face processing, and agree with a role of the right hemisphere for the processing of emotional expressions.

Attention to object files defined by transparent motion.

Two interspersed and differently colored sets of dots were rotated in opposite directions and were perceived as superimposed transparent surfaces. Probes consisting of brief changes in dot motion direction were reported. Two probes affecting the same surface were discriminated accurately. The 2nd probe was discriminated poorly if it affected a surface different from the 1st and if the time between probes was less than 600 ms. This reflects a difficulty in switching attention rapidly between surfaces. Spatial proximity increased the interference. Controls were incompatible with traditional spatial mechanisms (2- or 3-dimensional) or with simple sensory filters. Instead, probes were apparently selected by object files. The interference is not simply due to an inability to process 2 objects at once but requires close spatial proximity of incompatible motion signals.

Making features relevant: learning faces and event-related potentials recording using an analytic procedure.

We present a procedure designed for the learning of faces (represented by realistic drawings) and a task for the subsequent recording of Event-Related Potentials (ERPs), with the aim of investigating the psychobiological mechanisms involved in the recognition of familiar (or known) faces. The learning procedure consisted in a series of six sessions in which subjects familiarized themselves with the faces through a forced-choice features task: after the study of a set of 40 faces, each of these was presented at random in an incomplete way (without the eyes/eyebrows fragment), together with two sets of eyes and eyebrows for the subject to decide which of them corresponded to each face. This procedure is thought to facilitate for subjects the acquisition of the information related to the structural description of the faces (that is, without associated verbal/semantic information) using preferentially analytic processing strategies. The parameter d' of the Theory of Signal Detection allowed us to evaluate in the course of the learning sessions the degree of familiarization achieved with the studied faces. Subsequently, an ERPs' recording session was carried out, during which subjects executed a face-feature matching task. In this task, similar in structure to that carried out in the learning sessions, the subject had to decide whether the automatic completion of the faces that was made was correct or incorrect. ERPs' effects related to mismatching features were obtained, which indicate the existence of specific cerebral mechanisms involved in the recognition of faces.

Visual evoked potentials related to motion-onset are modulated by attention.

The effects of attention on visual evoked potentials triggered by motion-onset were examined in four experiments. A set of randomly oriented bars was used as stimuli. The first experiment showed that responses to motion-onset following pattern-onset by less than 300 ms were suppressed. In the other three experiments, the amplitude of N170 was reduced when attention was drawn away from the moving elements and towards spatially interspersed bars that remained static. The superposition of the two sets made spatial selection unlikely. These results support the existence of an attentional 'motion filter' (separating stationary from moving elements) that can operate at early stages of visual processing.

Transparent motion and object-based attention.

The difficulty in processing two stimuli at once increases with their separation. Therefore to demonstrate constraints in dividing attention between objects, the effects of their spatial separation must be controlled. Duncan used superimposed objects to achieve this, and showed that judging two attributes is more accurate if they concern one object than if they concern two objects (Duncan, J. 1984. Journal of Experimental Psychology: General, 113, 501-517). However, critics claim that differences in the spatial or spatial-frequency extent of attention exist between these conditions. We studied transparent motion defined by two sets of differently colored dots that were interspersed in the same region of space, and matched in spatial and spatial frequency properties. Each set moved in a distinct and randomly chosen direction. We found that simultaneous judgments of speed and direction were more accurate when they concerned only one set than when they concerned different sets. Furthermore, appraisal of the directions taken by two sets of dots is more difficult than judging direction for only one set, a difficulty that increases for briefer motion. We conclude that perceptual grouping by common fate exerted a more powerful constraint than spatial proximity, a result consistent with object-based attention. Evidence that this type of object-based attention operates at early stages of vision is examined.

Switching attention without shifting the spotlight object-based attentional modulation of brain potentials.

Although psychophysical evidence for object-based attention has been reported, corresponding studies with event-related potentials (ERPs) are scarce. Here subjects were presented with perceptual fields containing two superimposed objects (transparent surfaces generated by two sets of dots in rigid rotation around fixation, each set of a different color and direction of motion) or only one object (the same dots but either at rest or all rotating in the same direction). Brief (150-msec) rectilinear displacements affected either of the sets at random ISIs of 350 to 550 msec. Attention was directed to one set of dots, guided by color, in order to discriminate the direction of their displacement. Motion-onset ERPs elicited by these displacements were compared for attended and unattended dots. When the perceptual field consisted of two objects, strong suppression of P1 and N1 was obtained in the ERPs associated with the unattended object. No suppression was found with the field containing a single object, although an enhanced selection negativity was found in ERPs associated with attended dots (selected by color). Since the two objects occupied the same region of visual space, the suppression of P1/N1 cannot be explained by the space-based mechanisms but is consistent with object-based attentional selection at early stages of vision. The results highlight the role of perceptual organizations in enabling alternative attentional mechanisms.

Event related brain potentials to semantically incongruent words in children of different ages.

In this study, developmental changes of N400 elicited by a simple paradigm to semantic incongruity were examined. Subjects were divided in three different age groups and educational levels: Group I (first grade) = 7-8 years, n = 10; Group II (third grade) = 9-10 years, n = 10; and Group III (sixth grade) = 11-12 years, n = 10. EEG activity was recorded from 8 monopolar sites referred to linked earlobes. Data showed that the amplitude of the N400 like component did not change significantly from first to sixth grade, although the onset latency appeared to be shorter in older children. No significant latency and amplitude changes were found among groups.

Semantic matching of pictures in schizophrenia: a cross-cultural ERP study.

In this study the N400 of schizophrenics was compared with that of control subjects in a picture semantic-matching task. The comparison of N400 difference waveforms (subtraction of event-related potentials of congruent from those of incongruent trials) between control and patients was supplemented by separate analysis for congruent and incongruent trials. The N400 latency was delayed in patients. Also, the amplitude of N400 in the difference waveform was reduced in schizophrenics; however only congruent trials were different for patients (more negative) with respect to controls. This result is consistent with the hypothesis that schizophrenics use context poorly, but inconsistent with simple versions of the idea that associations are generally disinhibited in schizophrenia. Since the amplitudes of N400 and an auditory P300 were not correlated, a general processing deficit does not explain the results. Finally, by using picture matching, a cross-cultural comparison of N400 in schizophrenics from Cuba and China was possible, which indicated that the N400 abnormalities were similar in both groups.

Brain potentials and the availability of semantic and phonological codes over time.

ERPs were recorded from subjects performing semantic and rhyme matching tasks using either spoken words, printed words or pictures as stimuli. Mismatches enhanced N400 (in the semantic task) and N450 (in the rhyme task). Onset and peak latencies were shorter for N450 than for N400 with spoken words; this relationship was inverted for pictures. Thus these latencies could index availability of semantic and phonological codes. For printed words, the latencies were shorter for N400 than N450, a result that supports direct-access modes of reading with late phonological code activation. The longer latencies found for N400 and N450 to pictures could suggest longer initial decoding for pictures with respect to words.

An ERP study of expectancy violation in face perception.

Expectancies about face-structure can be induced by viewing parts of faces, which generates constraints due to two types of knowledge: feature-content and configuration. In a first experiment ERPs were recorded when parts of familiar faces were completed with incongruent features (from another face), as opposed to congruent features (from the same face). All features were in the correct configuration. An enhanced negativity was found for incongruent completions (N374) that was larger over the right side of the scalp. This replicates the results of Valdes-Sosa and Bobes (1990). In another two experiments, ERPs were recorded when parts of familiar faces were completed by congruent features, but sometimes placed in an incorrect position. In one experiment the features were jumbled; in the other, the features were slightly displaced. These configuration distortions were associated to late positive components, with a maxima at the centro-parietal region, of equal amplitude for both kinds of configuration anomalies. The N374 component seems to be a non-linguistic analog of the N400. The different ERP signatures for expectancy violations of configuration and feature-content suggest that these types of information are processed separately at some stages.

Associative ERP effects with memories of artificial faces.

A previous study (Valdes-Sosa and Bobes, 1990) described a negative ERP component evoked by mis-matches in a face-feature matching task, using photographs of real faces. This component could be N400 (or an analogue), elicited by associative priming within a non-linguistic domain: that of face structure. To confirm this it is necessary to demonstrate that semantic/linguistic recoding was not a necessary condition in triggering the negativity. This means falsifying what we call the 'priming by proxy' hypothesis, and locating the triggering mis-match within face structure. In this paper subjects studied artificial schematic faces over several sessions, and 1 week later were presented with a face-feature matching task with simultaneous ERP recording. Since no semantic information or verbal labels were available, eliciting a mis-match negativity with these faces contradicts the 'priming by proxy' hypothesis. In a first experiment, in which the subjects learning was controlled through a face familiarity decision task, no significant mis-match negativity was found. However, in a second experiment in which learning was controlled through a forced-choice face-feature match, a significant mis-match negativity was found in the subsequent recording session. This result supports the idea that a component similar to N400 can be elicited by an associative mis-match restricted to the face-structural domain.

Brain potentials in a phonological matching task using Chinese characters.

In readers of English, involved in a rhyme judgement task, mismatch trials are associated with an enhanced N450 component of the Event Related Potentials (ERPs). It has been suggested that N450 is related to orthographic or phonological priming. In this paper ERPs were recorded during a phonological matching task, using pairs of logographically dissimilar Chinese characters. A pair was considered to match if they sounded alike with identical phoneme sequences. The subjects (native Chinese speakers) were instructed to ignore vowel-inflections, which in Chinese have lexical status. Since sublexical assembly of phonology is not used in reading Chinese characters, and the members of each pair were logographically dissimilar, match and mismatch trials did not suffer in the amount of orthographic or sublexical phonological priming. An enhanced negative component (latency near 400 msec), was observed in ERPs elicited by the second character in non-matching pairs. The negativity could be similar to N450. If this were so, then N450 could not be associated with orthographic priming, nor with sublexical phonology, but would probably be associated with postlexical processing. Also, in both readers of Chinese and English, the negativity enhanced in non-match trials is larger over the right side of the scalp, suggesting a similar brain lateralization of the underlying processes.