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BACKGROUND: X-ray computed tomography (CT) can non-destructively examine objects by producing three-dimensional images of their internal structure. Although the availability of biomedical micro-CT offers the increased access to scanners, CT images of dense objects are susceptible to artifacts particularly due to beam hardening. OBJECTIVE: This study proposes and evaluates a simple semi-empirical correction method for beam hardening and scatter that can be applied to biomedical scanners. METHODS: Novel calibration phantoms of varying diameters were designed and built from aluminum and poly[methyl-methacrylate]. They were imaged using two biomedical micro-CT scanners. Absorbance measurements made through different phantom sections were fit to polynomial and inversely exponential functions and used to determine linearization parameters. Corrections based on the linearization equations were applied to the projection data before reconstruction. RESULTS: Correction for beam hardening was achieved when applying both scanners with the correction methods to all test objects. Among them, applying polynomial correction method based on the aluminum phantom provided the best improvement. Correction of sample data demonstrated a high agreement of percent-volume composition of dense metallic inclusions between using the Bassikounou meteorite from the micro-CT images (13.7%) and previously published results using the petrographic thin sections (14.6% 8% metal and 6.6% troilite). CONCLUSIONS: Semi-empirical linearization of X-ray projection data with custom calibration phantoms allows accurate measurements to be obtained on the radiodense samples after applying the proposed correction method on biomedical micro-CT images.
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Procesamiento de Imagen Asistido por Computador/métodos , Microtomografía por Rayos X/métodos , Algoritmos , Artefactos , Calibración , Imagenología Tridimensional , Meteoroides , Fantasmas de ImagenRESUMEN
OBJECTIVE: Low-amplitude, high-frequency whole-body vibration (WBV) has been adopted for the treatment of musculoskeletal diseases including osteoarthritis (OA); however, there is limited knowledge of the direct effects of vibration on joint tissues. Our recent studies revealed striking damage to the knee joint following exposure of mice to WBV. The current study examined the effects of WBV on specific compartments of the murine tibiofemoral joint over 8 weeks, including microarchitecture of the tibia, to understand the mechanisms associated with WBV-induced joint damage. DESIGN: Ten-week-old male CD-1 mice were exposed to WBV (45 Hz, 0.3 g peak acceleration; 30 min/day, 5 days/week) for 4 weeks, 8 weeks, or 4 weeks WBV followed by 4 weeks recovery. The knee joint was evaluated histologically for tissue damage. Architecture of the subchondral bone plate, subchondral trabecular bone, primary and secondary spongiosa of the tibia was assessed using micro-CT. RESULTS: Meniscal tears and focal articular cartilage damage were induced by WBV; the extent of damage increased between 4 and 8-week exposures to WBV. WBV did not alter the subchondral bone plate, or trabecular bone of the tibial spongiosa; however, a transient increase was detected in the subchondral trabecular bone volume and density. CONCLUSIONS: The lack of WBV-induced changes in the underlying subchondral bone suggests that damage to the articular cartilage may be secondary to the meniscal injury we detected. Our findings underscore the need for further studies to assess the safety of WBV in the human population to avoid long-term joint damage.
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Cartílago Articular/lesiones , Traumatismos de la Rodilla/patología , Tibia/patología , Vibración/efectos adversos , Animales , Biopsia con Aguja , Cartílago Articular/patología , Modelos Animales de Enfermedad , Inmunohistoquímica , Traumatismos de la Rodilla/fisiopatología , Masculino , Ratones , Ratones Endogámicos , Valores de Referencia , Microtomografía por Rayos XRESUMEN
Methyl jasmonate (MeJA) was tested by seed treatment for its ability to protect tomato seedlings against fusarium wilt caused by the soil-borne fungal pathogen Fusarium oxysporum f.sp. lycopersici. Isolated from Solanum lycopersicon L. seeds, cv. Beta fungus was identified as F. oxysporum f.sp. lycopersici Race 3 fungus by using phytopathological and molecular methods. MeJA applied at 0.01, 0.1 and 1 mM reduced spore germination and mycelial growth in vitro. Soaking of tomato seeds in MeJA solution at 0.1 mM for 1 h significantly enhanced the resistance level against the tested fungus in tomato seedlings 4 weeks after inoculation. The extracts from leaves of 15-day-old seedlings obtained from previously MeJA soaked seeds had the ability to inhibit in vitro spore germination of tested fungus. In these seedlings a significant increase in the levels phenolic compounds such as salicylic acid (SA), kaempferol and quercetin was observed. Up-regulation of phenylalanine ammonia-lyase (PAL5) and benzoic acid/salicylic acid carboxyl methyltransferase (BSMT) genes and down-regulation of the isochorysmate synthase (ICS) gene in response to exogenous MeJA application indicate that the phenylalanine ammonia-lyase (PAL), not the isochorismate (IC) pathway, is the primary route for SA production in tomato. Moreover, the increased accumulation of the flavonols quercetin and kaempferol appears closely related to the increase of PAL5, chalcone synthase (CHS) and flavonol synthase/flavanone 3-hydroxylase-like (FLS) genes. Elevated levels of salicylic acid in seedlings raised from MeJA-soaked seeds were simultaneously accompanied by a decrease of jasmonic acid, the precursor of MeJA, and an increase of 12-oxo-phytodienoic acid (OPDA), the precursor of jasmonic acid. The present results indicate that the priming of tomato seeds with 0.1mM MeJA before sowing enables the seedlings grown from these seeds to reduce the attack of the soil-borne fungal pathogen F. oxysporum f.sp. lycopersici, so it can be applied in practice.
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Acetatos/farmacología , Ciclopentanos/farmacología , Resistencia a la Enfermedad/efectos de los fármacos , Ácidos Grasos Insaturados/metabolismo , Flavonoles/metabolismo , Fusarium/fisiología , Oxilipinas/farmacología , Ácido Salicílico/metabolismo , Semillas/microbiología , Solanum lycopersicum/microbiología , Vías Biosintéticas/efectos de los fármacos , Vías Biosintéticas/genética , Fusarium/efectos de los fármacos , Fusarium/aislamiento & purificación , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Genes de Plantas , Solanum lycopersicum/efectos de los fármacos , Solanum lycopersicum/genética , Fenoles/metabolismo , Enfermedades de las Plantas/microbiología , Extractos Vegetales/farmacología , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/microbiología , Plantones/efectos de los fármacos , Plantones/microbiología , Semillas/efectos de los fármacos , Esporas Fúngicas/efectos de los fármacos , Esporas Fúngicas/fisiologíaRESUMEN
INTRODUCTION: Bone mineral density (BMD) is an important factor in the examination of the performance of bone instrumentation both in and ex vivo, and until now, there has not existed a reliable technique for determining BMD at the precise location of such hardware. This paper describes such a technique, using cadaveric human sacra as a model. METHODS: Nine fresh-frozen sacra had solid and hollow titanium screws placed into the S1 pedicles from a posterior approach. High-resolution micro-computed tomography (CT) was performed on each specimen before and after screw placement. All images were reconstructed with an isotropic spatial resolution of 308 mum, reoriented, and the pre-screw and post-screw scans were registered and transformed using a six-degree rigid-body transformation matrix. Once registered, two points, corresponding to the center of the screw at the cortex and at the screw tip, were determined in each scan. These points were used to generate cylindrical regions of interest (ROI) with the same trajectory and dimensions as the screw. BMD measurements were obtained within each of the ROI in the pre-screw scan. To examine the effect of artefact on BMD measurements around the titanium screws, annular ROI of 1 mm thickness were created expanding from the surface of the screws, and BMD was measured within each in both the pre- and post-screw scans. RESULTS: The registration process was accurate to 190 mum, with a precision of 189 mum and error in BMD measurement of +/-2% in repeated scans. BMD values in the cylindrical ROI corresponding to screw trajectories were not statistically different from side to side of each specimen (p=0.23). Metal artefact created significant differences in BMD values (p=0.001) and followed an exponential decay curve as distance from the screws increased, approaching a low value of approximately 20 mg HA cm(-3), but not disappearing completely. SUMMARY: CT in the presence of metal creates artefact, making measured BMD values near implants unreliable. This technique is accurate for determination of BMD, non-destructive, and eliminates the problem of this metal artefact through the use of co-registered scans. This technique has applications both in vitro and in vivo.
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Densidad Ósea , Tornillos Óseos , Microtomografía por Rayos X/métodos , Anciano , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Técnicas In Vitro , MasculinoRESUMEN
BACKGROUND: Peptidylarginine deiminase 4 (PAD4) may generate epitopes targeted by anticitrullinated protein antibodies in rheumatoid arthritis (RA). A subset of patients with RA has serum autoantibodies to human recombinant PAD4 (hPAD4). Here, we assessed whether anti-hPAD4 status in RA predicted disease outcome after antitumour necrosis factor (anti-TNF)-alpha therapy. METHODS: We analysed RA sera obtained at baseline (n = 40) and after 1 year on anti-TNF-alpha therapy (n = 33) for anti-hPAD4 IgG. Association analyses between baseline anti-hPAD status and disease progression were performed. RESULTS: We found that 17 of 40 patients (42.5%) were serum anti-hPAD4 positive at baseline, and the anti-hPAD4 IgG levels were stable over 1 year on anti-TNF-alpha therapy. At baseline, there were indications that anti-hPAD4 positive patients had more severe disease than the negative patients. After 1 year on anti-TNF-alpha therapy, the anti-hPAD4 positive patients displayed a persistently elevated disease activity score using 28 joint counts score and increased progression in the van der Heijde-modified Sharp erosion score. Accordingly, more anti-hPAD4 positive than negative patients presented an increase in van der Heijde-modified Sharp erosion scores >0 over 1 year. CONCLUSIONS: Anti-hPAD4 IgG can be detected in a subset of RA sera and the levels are stable after initiation of anti-TNF-alpha therapy. Serum anti-hPAD4 may predict persistent disease activity and radiographic progression in patients with RA receiving anti-TNF-alpha therapy.
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Antirreumáticos/uso terapéutico , Artritis Reumatoide/inmunología , Autoanticuerpos/sangre , Hidrolasas/inmunología , Factor de Necrosis Tumoral alfa/antagonistas & inhibidores , Adalimumab , Anticuerpos Monoclonales/uso terapéutico , Anticuerpos Monoclonales Humanizados , Artritis Reumatoide/diagnóstico por imagen , Artritis Reumatoide/tratamiento farmacológico , Progresión de la Enfermedad , Etanercept , Femenino , Humanos , Inmunoglobulina G/sangre , Inmunoglobulina G/uso terapéutico , Infliximab , Masculino , Persona de Mediana Edad , Pronóstico , Arginina Deiminasa Proteína-Tipo 4 , Desiminasas de la Arginina Proteica , Radiografía , Receptores del Factor de Necrosis Tumoral/uso terapéutico , Índice de Severidad de la Enfermedad , Resultado del TratamientoRESUMEN
Micro-CT has become a powerful tool for small animal research, having the ability to obtain high-resolution in vivo and ex vivo images for analyzing bone mineral content, organ vasculature, and bone microarchitecture extraction. The use of exogenous contrast agents further extends the use of micro-CT techniques, but despite advancements in contrast agents, single-energy micro-CT is still limited in cases where two different materials share similar grey-scale intensity values. This study specifically addresses the development of multiple-energy cone-beam micro-CT, for applications where bone must be separated from blood vessels filled with a Pb-based contrast material (Microfil) in ex vivo studies of rodents and tissue specimens. The authors report the implementation of dual- and triple-energy CT algorithms for material-specific imaging using postreconstruction decomposition of micro-CT data; the algorithms were implemented on a volumetric cone-beam micro-CT scanner (GE Locus Ultra). For the dual-energy approach, extrinsic filtration was applied to the x-ray beam to produce spectra with different proportions of x rays above the K edge of Pb. The optimum x-ray tube energies (140 kVp filtered with 1.45 mm Cu and 96 kVp filtered with 0.3 mm Pb) that maximize the contrast between bone and Microfil were determined through numerical simulation. For the triple-energy decomposition, an additional low-energy spectrum (70 kVp, no added filtration) was used. The accuracy of decomposition was evaluated through simulations and experimental verification of a phantom containing a cortical bone simulating material (SB3), Microfil, and acrylic. Using simulations and phantom experiments, an accuracy greater than 95% was achieved in decompositions of bone and Microfil (for noise levels lower than 11 HU), while soft tissue was separated with accuracy better than 99%. The triple-energy technique demonstrated a slightly higher, but not significantly different, decomposition accuracy than the dual-energy technique for the same achieved noise level in the micro-CT images acquired at the multiple energies. The dual-energy technique was applied to the decomposition of an ex vivo rat specimen perfused with Microfil; successful decomposition of the bone and Microfil was achieved, enabling the visualization and characterization of the vasculature both in areas where the vessels traverse soft tissue and when they are surrounded by bone. In comparison, in single energy micro-CT, vessels surrounded by bone could not be distinguished from the cortical bone, based on grey-scale intensity alone. This work represents the first postreconstruction application of material-specific decomposition that directly takes advantage of the K edge characteristics of a contrast material injected into an animal specimen; the application of the technique resulted in automatic, accurate segmentation of 3D micro-CT images into bone, vessel, and tissue components. The algorithm uses only reconstructed images, rather than projection data, and is calibrated by an operator with signal values in regions identified as being comprised entirely of either cortical bone, contrast-enhanced vessel, or soft tissue; these required calibration values are observed directly within reconstructed CT images acquired at the multiple energies. These features facilitate future implementation on existing research micro-CT systems.
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Tomografía Computarizada de Haz Cónico/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Microtomografía por Rayos X/métodos , Angiografía , Animales , Huesos/diagnóstico por imagen , Medios de Contraste/química , Imagenología Tridimensional , Plomo , Fantasmas de Imagen , Dosis de Radiación , Ratas , Ratas Sprague-DawleyRESUMEN
BACKGROUND: Antibodies targeting citrullinated antigens are specific for rheumatoid arthritis (RA). Citrullination is catalysed by the peptidylarginine deiminase (PAD) enzyme family. Critical enzymes are often targeted by disease-specific antibodies in complex immune-mediated diseases. Here, we have tested for autoantibodies against human recombinant PAD4 (hPAD4) in Caucasian RA patients. METHODS: A time-resolved fluorometric immunoassay based on hPAD4 was developed to analyse sera from two RA cohorts (n = 237 and n = 177), one systemic lupus erythaematosus (SLE) cohort (n = 84) and 148 healthy controls. Simple and multiple analyses were performed to examine possible associations between anti-hPAD4 and disease variables. RESULTS: Raised levels of anti-hPAD4 IgG were found in both RA cohorts compared to the controls, and 23% of the RA patients were anti-hPAD4 IgG positive. Anti-hPAD4 was associated with anti-cyclic citrullinated peptide (CCP) and rheumatoid factor (RF), as well as increased physical disability. Anti-hPAD4 was also associated with higher longitudinal radiographic damage scores and increased clinical joint pathology, but weaker than anti-CCP. No associations were found between anti-hPAD4 and selected Human leukocyte antigen (HLA)-DRB1 variants. CONCLUSIONS: Approximately 23% of Caucasian RA patients have serum IgG antibodies against hPAD4. The presence of serum anti-hPAD4 IgG was in simple analyses associated with a more severe disease phenotype, and the association with physical disability was maintained in multiple analyses.
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Artritis Reumatoide/inmunología , Autoanticuerpos/sangre , Hidrolasas/inmunología , Inmunoglobulina G/sangre , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Artritis Reumatoide/diagnóstico por imagen , Artritis Reumatoide/patología , Estudios de Cohortes , Femenino , Fluorometría , Humanos , Lupus Eritematoso Sistémico/inmunología , Masculino , Persona de Mediana Edad , Péptidos Cíclicos/inmunología , Arginina Deiminasa Proteína-Tipo 4 , Desiminasas de la Arginina Proteica , Radiografía , Proteínas Recombinantes/inmunología , Factor Reumatoide/sangre , Índice de Severidad de la EnfermedadRESUMEN
The left lateral frontopolar (LFP) cortex showed dimension change-related activation in previous event-related functional magnetic resonance imaging studies of visual singleton feature search with non-brain-lesioned participants. Here, we tested the hypothesis that LFP actively supports changes of attention from the old to the new target-defining dimension in singleton feature search. Singleton detection was selectively slowed in this task when the target-defining dimension changed in patients with left LFP lesions, compared with patients with frontomedian lesions as well as with matched controls without brain lesions. We discuss a potential role of LFP in change detection when the optimal allocation of dimension-based attention is not clearly defined by the task.
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Trastornos del Conocimiento/etiología , Trastornos del Conocimiento/psicología , Corteza Prefrontal/lesiones , Percepción Visual/fisiología , Adulto , Anciano , Aneurisma Roto/psicología , Atención/fisiología , Lesiones Encefálicas/psicología , Neoplasias Encefálicas/complicaciones , Neoplasias Encefálicas/psicología , Trastornos del Conocimiento/patología , Femenino , Lateralidad Funcional/fisiología , Humanos , Aneurisma Intracraneal/psicología , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Estimulación Luminosa , Corteza Prefrontal/patologíaRESUMEN
Recent progress in understanding the biosynthesis of the auxin, indole-3-acetic acid (IAA) in Arabidopsis thaliana is reviewed. The current situation is characterized by considerable progress in identifying, at the molecular level and in functional terms, individual reactions of several possible pathways. It is still too early to piece together a complete picture, but it becomes obvious that A. thaliana has multiple pathways of IAA biosynthesis, not all of which may operate at the same time and some only in particular physiological situations. There is growing evidence for the presence of an indoleacetamide pathway to IAA in A. thaliana, hitherto known only from certain plant-associated bacteria, among them the phytopathogen Agrobacterium tumefaciens.
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Arabidopsis/metabolismo , Ácidos Indolacéticos/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Amidohidrolasas/fisiología , Aminohidrolasas/fisiología , Arabidopsis/enzimología , Indoles/metabolismo , Complejos Multienzimáticos/fisiología , Oximas/metabolismo , Triptaminas/metabolismoRESUMEN
The aim of this study was to investigate the neural correlates of the functional distinction underlying attentional mechanisms of endogenous-sustained and exogenous-transient spatial selection. We recorded event related potentials (ERPs) and used functional magnetic resonance imaging (fMRI) in separate experiments while subjects performed a simple reaction time (RT) to the same visual stimulus displayed to one of several field locations. Endogenous-sustained or exogenous-transient focusing of attention onto target location were obtained by presenting the stimulus in blocks of same-point vs. randomised-point trials, respectively. Same-point stimuli yielded overall faster RT than randomised stimuli, indicating a facilitating effect of endogenous-sustained spatial attention on the perceptual processing of the impending stimulus. Moreover, same-point vs. randomised presentations revealed significant increases in the fMRI signal in the bilateral lingual and fusiform gyri as well as in the right calcarine sulcus, in conjunction with a larger amplitude of the posterior P1 component of ERPs, but no modulation of the amplitude of the N1 component. Rather, a larger amplitude of N1 was found in the reverse contrast, randomised minus same-point trials, which revealed increases in the fMRI signal along the posterior left superior frontal sulcus and bilaterally in the superior precuneus. These findings indicate that N1 indexes exogenous orienting of attention and is likely to represent the activity of frontal and parietal components of the attention network involved in eliciting attention changes. In contrast, the effects of those changes, resulting in a modulation of activation in visual occipital areas, are indexed by P1.
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Atención/fisiología , Encéfalo , Potenciales Evocados/fisiología , Imagen por Resonancia Magnética , Percepción Espacial/fisiología , Adolescente , Adulto , Análisis de Varianza , Encéfalo/anatomía & histología , Encéfalo/irrigación sanguínea , Encéfalo/fisiología , Mapeo Encefálico , Electroencefalografía/métodos , Femenino , Lateralidad Funcional , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Masculino , Oxígeno/sangre , Estimulación Luminosa/métodos , Tiempo de Reacción/fisiologíaRESUMEN
Patients with lesions of the splenium showed higher validity effects of visuospatial cues than did patients with partial lesions of the corpus callosum anterior to the splenium and control participants. Many of the patients tested had also shown a left-ear suppression for consonant-vowel syllables in a previous dichotic listening study. The authors interpret these parallel findings as evidence for the disruption of signals that normally alert the individual to the presence of behaviorally relevant stimuli, possibly originating in the temporoparietal junction area. After splenial lesions, these signals may not reach the contralateral hemisphere, leading to supramodal deficits in target detection, especially under distracting conditions.
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Lesiones Encefálicas/fisiopatología , Corteza Cerebral/fisiopatología , Percepción Espacial/fisiología , Percepción Visual/fisiología , Adulto , Corteza Cerebral/patología , Cuerpo Calloso , Señales (Psicología) , Femenino , Lateralidad Funcional/fisiología , Humanos , Masculino , Persona de Mediana Edad , Tiempo de Reacción/fisiología , Reproducibilidad de los Resultados , Factores de TiempoRESUMEN
Successful survival in a competitive world requires the employment of efficient procedures for selecting new in preference to old information. Recent behavioral studies have shown that efficient selection is dependent not only on properties of new stimuli but also on an intentional bias that we can introduce against old stimuli. Event-related analysis of functional magnetic resonance imaging data from a task involving visual search across time as well as space indicates that the superior parietal lobule is specifically involved in processes leading to the efficient segmentation of old from new items, whereas the temporoparietal junction area and the ascending limb of the right intraparietal sulcus are involved in the detection of salient new items and in response preparation. The study provides evidence for the functional segregration of brain regions within the posterior parietal lobe.
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Atención/fisiología , Aprendizaje Discriminativo/fisiología , Lóbulo Parietal/fisiología , Reconocimiento Visual de Modelos/fisiología , Adulto , Mapeo Encefálico , Percepción de Color/fisiología , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Memoria a Corto Plazo/fisiología , Orientación/fisiología , Consumo de Oxígeno/fisiología , Lóbulo Parietal/irrigación sanguínea , Tiempo de Reacción/fisiología , Flujo Sanguíneo Regional/fisiología , Lóbulo Temporal/fisiología , Vías Visuales/fisiologíaRESUMEN
Target detection in visual singleton feature search is slowed when consecutive targets are defined in different visual dimensions. Behavioral data provide evidence that attentional weight needs to be shifted between dimension-specific processing modules. We found similar dimension-specific change effects in a conjunction search task, in which observers searched for an odd-one-out target defined by a unique combination of size and color or, respectively, size and motion direction. Changes of the secondary target dimension (color or motion) across trials, but not target feature changes within a dimension, increased the time required to detect the target. Dimensional change costs were greatly increased for singleton conjunction search compared to singleton feature search. This suggests involvement of top-down control processes in dimensional change in conjunction search, in contrast to stimulus-driven dimensional change in singleton feature search. The functional anatomical correlates of top-down controlled visual dimension changes were investigated in two event-related functional magnetic resonance imaging (fMRI) experiments. In Experiment 1, dimensional change in singleton conjunction search was accompanied by transient activations in a fronto-posterior network of brain areas that was largely non-overlapping with the general network activated during visual search. Experiment 2, which contrasted singleton feature and conjunction search within the same session, revealed a double dissociation in anterior prefrontal cortex: left frontopolar cortex was selectively involved in stimulus-driven dimension changes but not in top-down controlled dimension changes, whereas the reverse was observed in frontomedian cortex.
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Imagen por Resonancia Magnética , Reconocimiento Visual de Modelos/fisiología , Corteza Prefrontal/fisiología , Corteza Visual/fisiología , Adulto , Cognición/fisiología , Femenino , Humanos , Masculino , Estimulación LuminosaRESUMEN
We review event-related fMRI data regarding the role of the left lateral frontopolar cortex (LFPC) in attentional switching processes. We found LFPC activation when subjects had to reallocate attentional resources, either between visual dimensions (color and motion) or between locations. However, LFPC activation during these dimension or location switches was observed only when subjects had to counteract stimulus-driven attention to an invalid dimension or location. LFPC was not activated following changes of stimulus-response associations. Further experiments will have to show whether LFPC is actively involved in the reallocation of attentional resources or whether it rather has a monitoring function.
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Atención/fisiología , Percepción de Color/fisiología , Lóbulo Frontal/fisiología , Percepción de Movimiento/fisiología , Orientación/fisiología , Desempeño Psicomotor/fisiología , Mapeo Encefálico , Humanos , Imagen por Resonancia Magnética , Vías Nerviosas/fisiologíaRESUMEN
An extinction-like effect in normal subjects was previously elicited when a low-salience target in the left was simultaneously presented with a highly salient distractor in the right visual hemifield, but not vice versa (Pollmann, 1996). We investigated in four experiments whether this extinction-like effect depends on (a) explicit localization and (b) response competition. It was found that the extinction-like effect could be replicated in the absence of both. In contradistinction to our previous results, low-salience distractors had no effect on pop-out target search. This showed that explicit spatial localization demands lead to low-salience distractor interference on pop-out search.
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Campos Visuales/fisiología , Percepción Visual/fisiología , Adulto , Femenino , Fijación Ocular/fisiología , Humanos , Masculino , Tiempo de ReacciónRESUMEN
A cognitive task can often be subdivided into several subprocesses, which follow a specific temporal order. Here, we report an event-related functional magnetic resonance imaging (fMRI) experiment on memory search, in which the temporal onset of search in primary memory was varied relative to retrieval from secondary memory. Furthermore, previous behavioral studies demonstrated that search times in primary memory depend on the number of items in a memory set, whereas retrieval from secondary memory is a set-size independent process. We analyzed the dependency of the blood oxygenation level dependent (BOLD)-response on the temporal onset of memory search on the one hand and on memory set size on the other hand to differentiate the contribution of retrieval from secondary memory, maintenance in primary memory, item search in primary memory, and response-related processes. The timing of activation followed cue presentation bilaterally in the middle frontal gyri (Brodmann area (BA) 9,46) and the inferior parts of the precentral gyri (BA6). In all other regions of interest (ROI), supplementary motor area (SMA), posterior parietal cortex, antero-superior insula, and primary motor cortex, the onset of activation was delayed with delayed probe presentation, ruling out participation in retrieval from secondary memory. The amplitude of the BOLD-response increased with increasing memory set size in all ROI except primary motor cortex and left posterior parietal cortex. All areas with cue-associated BOLD onset, suggesting involvement in retrieval, showed prolonged BOLD activation, suggesting that they also support maintenance of the retrieved information.
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Encéfalo/fisiología , Imagen por Resonancia Magnética/métodos , Memoria/fisiología , Recuerdo Mental/fisiología , Adulto , Encéfalo/irrigación sanguínea , Mapeo Encefálico , Circulación Cerebrovascular , Cognición , Femenino , Hemodinámica , Humanos , Oxígeno/sangre , Consumo de OxígenoRESUMEN
We report an event-related functional magnetic-resonance-imaging (fMRI) experiment that investigates the relationship of transient visual object memory, visuospatial orienting, and object recognition. Delayed object matching and visuospatial orienting involved a highly overlapping network of brain areas. Common areas were the frontal eye fields (FEF), the pre-supplementary motor area (pre-SMA)/SMA complex, the precentral gyri, and the horizontal and descending branches of the intraparietal sulcus (IPS). Selective delay activation was observed anterior to the FEF and in the ascending part of the IPS. Right dorsolateral prefrontal cortex was involved in goal-directed visual search, but showed no delay activity.
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Corteza Cerebral/fisiología , Imagen por Resonancia Magnética , Memoria a Corto Plazo/fisiología , Reconocimiento Visual de Modelos/fisiología , Adulto , Corteza Cerebral/anatomía & histología , Potenciales Evocados/fisiología , Femenino , Humanos , MasculinoRESUMEN
Objects characterized by a unique visual feature may pop out of their environment. When participants have to search for such "odd-one-out" targets, detection is facilitated when targets are consistently defined within the same feature dimension (e.g., color) compared with when the target dimension is uncertain (e.g., color or motion). Further, with dimensional uncertainty, there is a cost when a given target is defined in a different dimension to the preceding target, relative to when the critical dimension remains the same. Behavioral evidence suggests that a target dimension change involves a shift of attention to the new dimension. The present fMRI study revealed increased activation in the left frontopolar cortex, as well as in posterior visual areas of the dorsal and ventral streams, specific to changes in the target dimension. In contrast, activation in the striate cortex was decreased. This pattern suggests control of cross-dimensional attention shifts by the frontopolar cortex, modulating visual cortical processing by increased activation in higher-tier visual areas and suppression of activation in lower-tier areas.
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Atención/fisiología , Percepción de Color/fisiología , Lóbulo Frontal/fisiología , Percepción de Movimiento/fisiología , Campos Visuales/fisiología , Adolescente , Adulto , Femenino , Giro del Cíngulo/fisiología , Hipocampo/fisiología , Humanos , Imagen por Resonancia Magnética , Masculino , Giro Parahipocampal/fisiología , Estimulación LuminosaRESUMEN
When a switch between two tasks has to be carried out, performance is slower than in trials where the same task is performed repeatedly. This finding has been attributed to time-consuming control processes required for task switching. Previous results of other paradigms investigating cognitive control processes suggested that prefrontal cortex is involved in executive control. We used event-related fMRI to investigate prefrontal cortex involvement in task switching. Regions in the lateral prefrontal and premotor cortex bilaterally, the anterior insula bilaterally, the left intraparietal sulcus, the SMA/pre-SMA region and the cuneus/precuneus were activated by the task repetition condition and showed additional activation in the task switch condition. This confirmed the hypothesis that lateral prefrontal cortex is involved in task switching. However, the results also showed that this region is neither the only region involved in task switching nor a region specifically involved in task switching.
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Imagen por Resonancia Magnética , Corteza Prefrontal/fisiología , Desempeño Psicomotor/fisiología , Adulto , Mapeo Encefálico , Potenciales Evocados/fisiología , Femenino , Lateralidad Funcional/fisiología , Humanos , Masculino , Corteza Motora/fisiologíaRESUMEN
Recently, event-related fMRI-experiments have been reported in which subsequent trials were separated by only 2 sec or less. Because the BOLD response needs 10 sec and longer to return to baseline, the event-related signal in these experiments has to be extracted from the overlapping responses elicited by successive trials. Usually it is assumed that this convolved signal is a summation of the overlapping BOLD responses. We tested this assumption by comparing event-related signals in conditions with little and with substantial BOLD overlap in two fMRI experiments of a task-switching paradigm. We analyzed the difference in the activational time course elicited by a critical task and a baseline task when trials of both tasks were separated by intertrial intervals of 15 sec or when the critical trials were embedded in a stream of baseline trials with ISI = 1 sec. The change of the BOLD signal elicited by the critical trials showed a high correspondence between both experiments in five out of six cortical ROI. Our data support the view that BOLD overlap leads to largely linear signal changes. In the present study, task-related increases in the BOLD response were detected equally well with substantial BOLD overlap as with mostly nonoverlapping BOLD responses.