ABSTRACT
BACKGROUND AND PURPOSE: Previous investigations show that bilinguals exhibit the first symptoms of dementia 4-5 years later than monolinguals. Therefore, bilingualism has been proposed as a cognitive reserve mechanism. Recent studies have advanced towards an understanding of the brain mechanisms underlying bilingualism's protection against dementia, but none of them deals with white matter (WM) diffusion. METHODS: In this study, the topic was investigated by measuring WM integrity in a sample of 35 bilinguals and 53 passive bilinguals with mild cognitive impairment. RESULTS: No significant differences were found between the groups in cognitive level, education, age or sex. However, bilinguals showed higher mean diffusivity in the fornix, but higher fractional anisotropy, lower mean diffusivity, axial diffusivity and radial diffusivity in the parahippocampal cingulum, and lower radial diffusivity in the right uncinate fasciculus. Significant correlations were also found between WM integrity in the left parahippocampal cingulum and the Boston Naming Test in passive bilinguals. CONCLUSIONS: These results suggest that bilingualism contributes to a differential pattern of WM disintegration due to mild cognitive impairment in fibers related to bilingualism and memory.
Subject(s)
Brain/drug effects , Cognitive Dysfunction/diagnostic imaging , Multilingualism , White Matter/diagnostic imaging , Aged , Anisotropy , Atrophy/diagnostic imaging , Atrophy/pathology , Brain/pathology , Cognitive Dysfunction/pathology , Cognitive Reserve , Diffusion Tensor Imaging/methods , Female , Humans , Male , Nerve Net/diagnostic imaging , Nerve Net/pathology , White Matter/pathologyABSTRACT
BACKGROUND: Previous studies to determine memory lateralization with functional MR imaging (fMRI) have used encoding or recall tasks. The convergence between the results of both tasks, however, is unknown. OBJECTIVE: The objective of this study was to investigate hemispheric asymmetries of temporal lobe activity (parahippocampus and fusiform gyri) in patients with temporal lesions by using both kinds of fMRI tasks. METHODS: By using blood oxygenation level-dependent fMRI, hemispheric asymmetries of 25 consecutive patients admitted for presurgical evaluation of memory and 12 healthy control participants were studied. Activation was induced by using the picture-encoding task (processing of complex scenes) and the hometown-walking task (requiring mental navigation through one's hometown by using landmarks given by participants themselves). RESULTS: Results in the control group showed that both tasks activated the parahippocampus similarly. The picture-encoding task, however, yielded greater posterior activations in the parahippocampus than did the hometown-walking task. As observed in other studies, more than half the patients showed contralesional representation of memory in each task. It is important to note that estimated memory lateralization from each task was different in 30% of patients, and several cases showed clear discrepancies between both tasks. CONCLUSION: Although previous studies showed that both tasks were useful for evaluating memory lateralization, the present study suggested that the administration of both tasks is necessary for presurgical evaluation of memory lateralization in patients with lesions in the temporal lobe. Therefore, both encoding and recall processes should at least be considered in the evaluation of memory.
Subject(s)
Brain Neoplasms/physiopathology , Functional Laterality , Magnetic Resonance Imaging , Memory , Temporal Lobe/physiopathology , Adult , Aged , Female , Humans , Male , Middle AgedABSTRACT
La evaluación de las funciones de memoria relacionadas con estructuras del lóbulo temporal medial se ha convertido en uno de los pilares más importantes en la Neuropsicología actual, dada su extrema relevancia en enfermedades como las demencias y las epilepsias temporales. En esta comunicación revisaremos los resultados que nuestro grupo de investigación ha obtenido con la utilización de sendos protocolos de evaluación de la memoria mediante resonancia magnética funcional (RMf): la tarea de `Paseo por tu Ciudad' (PPTC) y la tarea de `codificación/recuerdo' de imágenes complejas. La tarea de PPTC se ha aplicado a un grupo de nueve pacientes candidatos a neurocirugía por lesiones en el lóbulo temporal, y se obtuvo en todos ellos una representación bilateral o contralesional de la memoria. Los resultados coinciden con los obtenidos en el estudio original de Jokeit, Okujava y Woermann (2001) y parecen mostrar que este protocolo sirve para determinar la preservación o no de la función mnésica en el hemisferio lesionado. Por su parte, la tarea de codificación/recuerdo de imágenes se ha administrado a un grupo de cuatro pacientes con enfermedad de Alzheimer, cuatro con deterioro cognitivo leve y cinco participantes controles. De acuerdo con nuestras hipótesis, los resultados han mostrado una menor activación en la circunvolución parahipocampal izquierda en el grupo con deterioro cognitivo leve que en el grupo control, así como una menor activación bilateral en esas estructuras en el grupo con enfermedad de Alzheimer, si se compara con el grupo control. Nuestros resultados, en conjunto, muestran la importancia que en el futuro tendrá la RMf en la evaluación neuropsicológica de la memoria, y en el diagnóstico de las enfermedades del sistema nervioso central (AU)
he assessment of memory functions related to medial temporal lobe has become one of the most important issues on current neuropsychology. On this communication, we review the results which our research group has achieved using two functional magnetic resonance Image procedures to assess memory function: Hometown walking task and an encoding/retrieval task using complex images. Nine patients with tumoural temporal lesions performed the hometown walking task. The results of these patients showed either a bilateral or contralesional representation of memory function. These results confirm those obtained by Jokeit, Okujava y Woermann (2001), and they seem to prove that this protocol is useful to determine the preservation of memory function in the non-damaged hemisphere. On the other hand, the images encoding/retrieval task has been run by two groups of four patients diagnosed as Alzheimer disease and mild cognitive impairment, and another group of five patients who participated as a control group. According to our hypothesis, the results have shown a lower activation at the left parahippocampal gyrus in mild cognitive impairment and Alzheimer disease patients than controls, just as a lower bilateral activation in the same structure for the Alzheimer group than the control group. As a whole, our results show how important may become functional magnetic resonance image for neuropsychological assessment of memory, and as a diagnostic tool for CNS diseases (AU)
