Effective connectivity during successful and unsuccessful recollection in young and old adults.

Aging effects on regional brain activation have been studied extensively to explain the gradual recollection failure that occurs with advancing age. However, little is known about the consequence of aging on the interaction among brain regions that support recollection. The purpose of this study was to examine effective connectivity at encoding and retrieval during successful and unsuccessful recollection in young and old adults. In particular, we analyzed a recollection network that is characterized by its susceptibility to aging effects by middle age or later, which is comprised of the occipital cortex, hippocampus and orbitofrontal cortex. Participants' brains were scanned using functional magnetic resonance imaging while they performed a spatial source memory task. Dynamic causal modeling and Bayesian model selection revealed that subsequent recollection during encoding and recollection during retrieval modulated the influence of the orbitofrontal cortex on the hippocampus in both age groups; this particular connectivity was not modulated by unsuccessful encoding in either group. Successful encoding and retrieval of item-source associations modulated all connections within the network in old adults. The findings revealed that the orbitofrontal cortex influences processes in the hippocampus to ensure successful recollection, and aging alters the recollection network by engaging non-specialized connections.

Brain activity during source memory retrieval in young, middle-aged and old adults.

We investigated neurofunctional changes associated with source memory decline across the adult life span using functional magnetic resonance imaging (fMRI). Young, middle-aged and old adults carried out a natural/artificial judgment of images of common objects that were randomly presented in one of the quadrants of the screen. At retrieval, the images were displayed at the center of the screen and the participants judged whether each image was new or old and, if old, they indicated in which quadrant of the screen the image had originally been presented. Comparing the items associated with correct versus incorrect source judgments revealed that no regions showed greater activity in young adults than in middle-aged adults; however, in young and middle-aged adults the activity in the left hippocampus and left anterior temporal cortex was of greater magnitude than in the older adults. Several regions also exhibited greater activity in young adults than in old adults. These results suggest that in middle age the recollection neural network, assessable by fMRI, is still preserved.

fMRI subsequent source memory effects in young, middle-aged and old adults.

The ability to remember the spatial context in which our experiences occur declines linearly across the adult lifespan. However, little is known about whether this source memory decline is associated with neural activity changes. In the present study, functional magnetic resonance imaging (fMRI) scans were recorded in young, middle-aged and old adults to investigate brain activity variations across the adult lifespan during encoding of subsequent spatial source memory retrieval. Twelve healthy individuals of both sexes were enrolled in each age group. During encoding, participants performed natural/artificial judgment of images of common objects that were randomly presented in one of the quadrants of the screen. During retrieval, the images presented at encoding were randomly mixed with new ones and displayed at the center of the screen. Participants judged whether each image was new or old and, if an image was old, they were instructed to indicate in which quadrant the image was presented in the encoding session. The contrast between study items that were later recognized and assigned a correct source judgment with those whose sources were subsequently forgotten revealed that positive subsequent memory effects disappear by middle age in the left medial orbitofrontal gyrus and appear in the left superior occipital gyrus. This under-recruitment and over-recruitment brain activity was also present in old adults. The results allowed us to identify the specific brain regions that first fail to encode spatial information into an episodic representation during the adult lifespan.

Espectroscopia cuantitativa de hidrógeno por resonancia magnética de 3 T en pacientes sintomáticos y asintomáticos con enfermedad de Huntington / Hydrogen magnetic resonance quantitative spectroscopy at 3 T in symptomatic and asymptomatic Huntington’s disease patients

Introducción. La enfermedad de Huntington es un trastorno neurodegenerativo hereditario autosómico dominante, caracterizado por síntomas motores, cognitivos y psiquiátricos. Objetivo. Determinar si existen diferencias en las concentraciones de N-acetilaspartato, creatina y compuestos que contienen colina (glucerilfosforilcolina y fosfocolina) en el núcleo caudado, el putamen y la corteza occipital de pacientes con enfermedad de Huntington, sintomáticos y asintomáticos. Sujetos y métodos. Se realizaron estudios de espectroscopia de hidrógeno por resonancia magnética en un equipo de 3 T a 10 individuos con prueba genética para enfermedad de Huntington, incluidos en tres grupos: negativos (control), positivos sintomáticos y positivos asintomáticos. Los estudios se cuantificaron con LCModel y se analizaron mediante análisis de varianza y prueba de Fisher. Resultados. Los pacientes sintomáticos mostraron disminución de creatina y N-acetilaspartato en las regiones estudiadas, y disminución de colina en el putamen (p < 0,05). En el núcleo caudado se encontró diferencia de colina entre sintomáticos y asintomáticos (p < 0,05). Conclusiones. Los resultados reflejan disfunción en el metabolismo neuronal y sugieren que la creatina y la colina, al ser marcadores de membrana, pueden comportarse en forma indirecta como marcadores de la evolución en la enfermedad de Huntington (AU)

Introduction. Huntington’s disease is an hereditary autosomic-dominant neurodegenerative disorder, characterized by motor, cognitive and psychiatric symptoms. Aim. To quantify differences in N-acetylaspartate, creatine and choline in caudate nucleus, putamen and occipital cortex of patients with Huntington’s disease, symptomatics and asymptomatics. Subjects and methods. Hydrogen magnetic resonance spectroscopy was performed with a 3 T scanner in 10 Huntington’s disease gene-tested subjects, included in three groups: negative (control), positive sympomatics and positive asymptomatics. Data was quantified with LCModel and analyzed with ANOVA and Fisher tests. Results. Symptomatic patients showed decreased creatine and N-acetylaspartate in the three regions, and decreasedcholine only in putamen (p < 0.05). Choline difference was found between symptomatics and asymptomatics in the caudate nucleus (p < 0.05). Conclusions. Results may reflect neuronal dysfunction and suggest that creatine and choline may serve as markers for Huntington’s disease progression (AU)

[Hydrogen magnetic resonance quantitative spectroscopy at 3 T in symptomatic and asymptomatic Huntington's disease patients]. / Espectroscopia cuantitativa de hidrógeno por resonancia magnética de 3 T en pacientes sintomáticos y asintomáticoscon enfermedad de Huntington.

INTRODUCTION: Huntington's disease is an hereditary autosomic-dominant neurodegenerative disorder, characterized by motor, cognitive and psychiatric symptoms. AIM: To quantify differences in N-acetylaspartate, creatine and choline in caudate nucleus, putamen and occipital cortex of patients with Huntington's disease, symptomatics and asymptomatics. SUBJECTS AND METHODS: Hydrogen magnetic resonance spectroscopy was performed with a 3 T scanner in 10 Huntington's disease gene-tested subjects, included in three groups: negative (control), positive symptomatics and positive asymptomatics. Data was quantified with LCModel and analyzed with ANOVA and Fisher tests. RESULTS: Symptomatic patients showed decreased creatine and N-acetylaspartate in the three regions, and decreased choline only in putamen (p < 0.05). Choline difference was found between symptomatics and asymptomatics in the caudate nucleus (p < 0.05). CONCLUSIONS: Results may reflect neuronal dysfunction and suggest that creatine and choline may serve as markers for Huntington's disease progression.

Valoración de neoplasias intracraneanas mediante studios de resonancia magnética con técnica BOLD, perfusión y espectroscopia / Evaluation of intracraneal neoplasms utilizing MRI, with BOLD, perfusion and espectroscopy techniques

El estudio de la función cerebral a través de la neuroimagen se aplica en la actualidad de manera rutinaria en una gran variedad de situaciones clínicas, entre las cuales se incluyen las neoplasias intracraneanas. Con el advenimiento de la resonancia magnética funcional (fMRI), se puede obtener información fisiológica de la lesión, al igual que una gran especificidad anatómica, abriéndose así las puertas a nuevas posibilidades diagnósticas. Este trabajo es un estudio prospectivo, longitudinal, realizado en el Departamento de Imagenología del Centro Médico American British Cowdray en el que se analizaron los estudios de resonancia magnética convencional, así como los estudios de fMRI (BOLD, perfusión y espectroscopia) de 20 pacientes con diagnóstico de tumor intracraneal, confirmado mediante estudios de histopatología. Se dan a conocer las características de benignidad o malignidad, así como la diferenciación entre áreas de recidiva, recurrencia o necrosis tumoral

Endoscopia virtual intraluminal por angiorresonancia magnética de arterias carótidas: correlación con ultrasonografía doppler y angiografía digital / Virtual intraluminal endoscopy by angiomagnetic resonance of the carotid arteries: correlation with Doppler ultrasound and digital angiography

La navegación endovascular fue realizada después del estudio de la arteria carótida a través de angiorresonancia. El trayecto que fue reconstruido correspondió a las regiones anatómicas identificadas como estenótica debido a placas, trombos, o a engrosamiento de la pared vascular. Los hallazgos por Doppler color fueron utilizados como un parámetro importante de referencia para el análisis de placas y tipo de flujo a través del área afectada. Basados en reconstrucciones en dos dimensiones con técnica de tiempo de vuelo de resonancia magnética del área problema, se obtuvieron vistas de la pared vascular, facilitando un análisis tanto cualitativo como cuantitativo. Consideramos que esto podría aumentar las posibilidades diagnósticas. Con la ventaja de visualizar el lumen vascular, consideramos que esta técnica podría ser útil en el análisis de la integridad de las prótesis vasculares y seguimiento del paciente luego de colocación de balón de angioplastía en coartaciones

Estenosis aguda de la arteria carótida estudiada con Resonancia Magnética en perros / Acute stenosis of the carotid artery, studied by magnetic resonance in dogs

Se valoró la utilidad de la Angiorresonancia magnética (ARM), para determinar el grado de estenosis producida en nueve perros, a los que se les practicó estenosis de la arteria carótida común mediante plicadura y colocación de injerto de pericardio bovino. Los resultados se compararon entre diferentes modalidades de imagen (ARM, Ultrasonido Doppler, y Angiografía con Subtracción Digital), así como con los hallazgos histopatológicos. Como resultado, se comprobó mediante ARM la permeabilidad de los vasos en siete animales, mientras que por histopatología se demostró que existió permeabilidad en 100 por ciento de los mismos. La ARM es un estudio útil para demostrar el sitio de estenosis y como método de seguimiento no invasivo en cirugía por estenosis carotídea aunque cuando se requiere una valoración cuantitativa es necesario recurrir a otras modalidades de imagen

Demostración de las variantes anatómicas del polígono de Willis por angiorresonancia magnética / Magnetic resonance imaging of the circle of Willis and their anatomical variants

Este estudio tiene como objetivo investigar por medio de Angio Resonancia Magnética (ARM), la frecuencia con la que se presentan variantes anatómicas en el polígono de Willis. En un grupo de cien pacientes a los que se les realizó un estudio de ARM, se identificaron básicamente cuatro variantes más de la forma originalmente descrita por Willis. La más común es la persistencia de la arteria comunicante posterior derecha precedida únicamente por la forma habitual del polígono (ausencia de comunicantes). Es importante considerar que en el polígono de Willis existen trayectos vasculares "virtuales", que posteriormente se pueden permeabilizar o llevar a la formación de un trayecto colateral. Ante un evento isquémico u oclusivo, la ARM brinda la opción de poder identificar la dinámica vascular de manera no invasiva y tiene el potencial de poder demostrar variantes anatómicas en el momento del estudio