RESUMEN
In vivo measurements of human brain deformation during mild acceleration are needed to help validate computational models of traumatic brain injury and to understand the factors that govern the mechanical response of the brain. Tagged magnetic resonance imaging is a powerful, noninvasive technique to track tissue motion in vivo which has been used to quantify brain deformation in live human subjects. However, these prior studies required from 72 to 144 head rotations to generate deformation data for a single image slice, precluding its use to investigate the entire brain in a single subject. Here, a novel method is introduced that significantly reduces temporal variability in the acquisition and improves the accuracy of displacement estimates. Optimization of the acquisition parameters in a gelatin phantom and three human subjects leads to a reduction in the number of rotations from 72 to 144 to as few as 8 for a single image slice. The ability to estimate accurate, well-resolved, fields of displacement and strain in far fewer repetitions will enable comprehensive studies of acceleration-induced deformation throughout the human brain in vivo.
Asunto(s)
Aceleración , Encéfalo/patología , Cabeza/fisiología , Imagen por Resonancia Magnética/métodos , Adulto , Lesiones Encefálicas/patología , Simulación por Computador , Femenino , Humanos , Masculino , Reproducibilidad de los Resultados , RotaciónRESUMEN
Huntington's Disease (HD) is a neurodegenerative disorder caused by a cytosine-adenine-guanine (CAG) triplet repeat-expansion in the Huntingtin (HTT) gene. Diagnosis of HD is classically defined by the presence of motor symptoms; however, cognitive and depressive symptoms frequently precede motor manifestations, and may occur early in the prodromal phase. There are sparse data so far on functional brain correlates of depressive symptoms in prodromal HD. A Stroop color-naming test was administered to 32 subjects in the prodromal phase of HD and 52 expansion-negative controls while performing functional magnetic resonance imaging at 3Tesla. Networks of functional connectivity were identified using group independent component analysis, followed by an analysis of functional network interactions. A contrast of temporal regression-based beta-weights was calculated as a reflection of Stroop-interference related activity and correlated with Center for Epidemiologic Studies Depression (CES-D) scores. For secondary analysis, patients were stratified into two subgroups by median split of CAG repeat-length. Stroop performance was independent of HTT mutation-carrier status and CES-D score. Stroop-interference-related activity of the ventromedial prefrontal cortex-node of the default-mode network, calculated by temporal-regression beta-weights, was more highly correlated with depressive symptoms in subjects in the prodromal phase of HD than in controls, differing significantly. The strength of this correlation and its difference from controls increased when a subgroup of patients with longer CAG repeat lengths was analyzed. These findings suggest that depressive symptoms in prodromal HD subjects may reflect altered functional brain network activity in the context of early HD-related brain alterations.
Asunto(s)
Trastorno Depresivo/fisiopatología , Enfermedad de Huntington/fisiopatología , Interpretación de Imagen Asistida por Computador , Imagen por Resonancia Magnética , Red Nerviosa/fisiopatología , Corteza Prefrontal/fisiopatología , Síntomas Prodrómicos , Test de Stroop , Adenina , Adulto , Citosina , Análisis Mutacional de ADN , Trastorno Depresivo/diagnóstico , Trastorno Depresivo/genética , Trastorno Depresivo/psicología , Femenino , Carga Genética , Guanina , Giro del Cíngulo/fisiopatología , Humanos , Proteína Huntingtina , Enfermedad de Huntington/diagnóstico , Enfermedad de Huntington/genética , Enfermedad de Huntington/psicología , Masculino , Persona de Mediana Edad , Proteínas del Tejido Nervioso/genética , Estadística como Asunto , Expansión de Repetición de TrinucleótidoRESUMEN
Increasing evidence suggests that abnormal white matter is central to the pathophysiology and, potentially, the pathogenesis of schizophrenia (SCZ). The spatial distribution of observed abnormalities and the type of white matter involved remain to be elucidated. Seventeen chronically ill individuals with SCZ and 17 age- and gender-matched controls were studied using a 3T magnetic resonance imaging diffusion tensor imaging protocol designed to examine the abnormalities of white matter by region and by level of architectural infrastructure as assessed by fractional anisotropy (FA) in native space. After assessing whole-brain FA, FA was divided into quartiles, capturing all brain regions with FA values from 0 to 0.25, 0.25 to 0.5, 0.5 to 0.75, and 0.75 to 1.0. Mean whole-brain FA was 4.6% smaller in the SCZ group than in healthy controls. This difference was largely accounted for by FA values from the second quartile (between 0.25 and 0.5). Second quartile FA was decreased in all 130 brain regions of the template in the SCZ group, with the difference reaching statistical significance in 41 regions. Correspondingly, the amount of brain tissue with an FA of â¼0.4 was significantly reduced in the SCZ group, while the amount of brain tissue falling in the lowest quartile of FA was increased. These findings strongly imply a diffuse loss of white matter integrity in SCZ. Our finding that the loss of integrity disproportionately involves white matter of low to moderate organization suggests an approach to the specificity of white matter abnormalities in SCZ based on microstructure rather than spatial distribution.
Asunto(s)
Imagen de Difusión por Resonancia Magnética/métodos , Fibras Nerviosas Mielínicas/patología , Esquizofrenia/patología , Adulto , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
We measured brain activation in six anorexia nervosa patients and six healthy controls performing a novel emotional Stroop task using Fat, Thin, and Neutral words, and words made of XXXXs. Reaction times increased in the patient group in Thin and Fat conditions. In the Thin-XXXX contrast, patients showed greater activation than controls at the junction of left insula, frontal and temporal lobes and in left middle and medial frontal gyri. In the Fat-XXXX contrast, controls showed greater activation in left dorsolateral prefrontal cortex and right parietal areas. Mechanisms underlying attentional bias in anorexia nervosa likely differ under conditions of positive and negative valence. This paradigm is a promising tool to examine neural mediation of emotional response in anorexia nervosa.
Asunto(s)
Anorexia Nerviosa/fisiopatología , Encéfalo/fisiopatología , Emociones/fisiología , Pruebas de Asociación de Palabras , Adulto , Anorexia Nerviosa/psicología , Corteza Cerebral/fisiopatología , Femenino , Lóbulo Frontal/fisiopatología , Lateralidad Funcional/fisiología , Humanos , Imagen por Resonancia Magnética , Persona de Mediana Edad , Pruebas Neuropsicológicas/estadística & datos numéricos , Lóbulo Parietal/fisiopatología , Desempeño Psicomotor/fisiología , Lóbulo Temporal/fisiopatologíaRESUMEN
The effects of variable-interval (VI) and fixed-ratio (FR) schedules of reinforcement for work-related behavior and an organizer for the work materials (behavioral prosthesis) were evaluated with 3 adults with severe or profound mental retardation. The participants had been recommended for study because of high rates of off-task and aberrant behavior in their daily vocational training programs. For 2 participants, VI and FR schedules resulted in the same outcome: more aberrant behavior than on-task and off-task behavior combined. The FR schedule nearly eliminated emission of aberrant and off-task behavior by the 3rd participant. Combining the behavioral prosthesis with FR reinforcement (FR+O) increased the proportion of time spent in on-task behavior by all participants under certain FR schedule parameters. Second-by-second analyses of the observation records revealed that FR schedules reduced off-task and aberrant behavior during work sequences (i.e., ratio runs), and FR+O led to a further reduction of these behaviors during postreinforcement pauses. Overall, the results show how organizer and schedule parameters can be adjusted to produce an optimized balance between productivity and reinforcement while undesirable behavior is minimized.