Biomedical subjects

Leyla deToledo-Morrell

Publications and source records attributed to Leyla deToledo-Morrell.

8 recordsLinked to original sources

PubMed2006

Hippocampal disconnection contributes to memory dysfunction in individuals at risk for Alzheimer's disease.

The concept of amnestic mild cognitive impairment (MCI) describes older people who show a decline predominantly in memory function, but who do not meet criteria for dementia. Because such individuals are at high risk for developing Alzheimer's disease, they are of great interest for understanding the prodromal stages of the disease process. The mechanism underlying memory dysfunction in people with MCI is not fully understood. The present study uses quantitative, high-resolution structural MRI techniques to investigate, in vivo, the anatomical substrate of memory dysfunction associated with MCI. Changes in brain structures were assessed with two imaging techniques: (i) whole-brain, voxel-based morphometry to determine regions of reduced white matter volume and (ii) sensitive volumetric segmentation of the entorhinal cortex and hippocampus, gray matter regions that are critically important for memory function. In participants with amnestic MCI, compared with age-matched controls, results showed a significant decrease in white matter volume in the region of the parahippocampal gyrus that includes the perforant path. There was also significant atrophy in both the entorhinal cortex and the hippocampus. Regression models demonstrated that both hippocampal volume and parahippocampal white matter volume were significant predictors of declarative memory performance. These results suggest that, in addition to hippocampal atrophy, disruption of parahippocampal white matter fibers contributes to memory decline in elderly individuals with MCI by partially disconnecting the hippocampus from incoming sensory information.

Aged↗

PubMed2005

Basic research in epilepsy and aging.

A PubMed search of the years 1965 to 2003 found only 30 articles that were directly related to modeling seizures or epilepsy in aged animals. This lack of research is disturbing but explainable because of the high cost of aged animals and their increasing infirmity. Many changes occur in the older brain: cell loss in the hippocampal formation, changes in long-term potentiation maintenance, alteration in kindling, increased susceptibility to status epilepticus, and neuronal damage from stroke. The effect of aging on voltage-gated sodium and calcium channels has not been studied sufficiently. With increasing numbers of elderly persons with epilepsy needing appropriate treatment, the need to better understand the basic mechanisms of epilepsy is crucial.

Aged↗

PubMed2005

Longitudinal changes in white matter following ischemic stroke: a three-year follow-up study.

Information on longitudinal changes in white matter after stroke is limited. The aim of the present study was to quantitatively investigate longitudinal changes in the microstructural integrity of non-lesioned white matter at 1-3 years following ischemic stroke. In a sample of 80 ischemic stroke patients, we obtained diffusion tensor imaging (DTI) measures of fractional anisotropy (FA), an apparent measure of white matter integrity, in radiologically normal-appearing white matter at baseline and 3 years of follow-up. Mixed model regression analysis results showed a significant improvement in FA from baseline during the first 2 years of follow-up that stabilized by the third year of follow-up. These results demonstrate a long-term improvement in apparent white matter integrity following ischemic stroke that continues, at least, into the second year following the insult.

Aged↗

PubMed2005

Relating medial temporal lobe volume to frontal fMRI activation for memory encoding in older adults.

Neuroimaging research on the brain basis of memory decline in older adults typically has examined age-related changes either in structure or in function. Structural imaging studies have found that smaller medial temporal lobe (MTL) volumes are associated with lower memory performance. Functional imaging studies have found that older adults often exhibit bilateral frontal-lobe activation under conditions where young adults exhibit unilateral frontal activation. As yet, no one has examined whether these MTL structural and frontal-lobe functional findings are associated. In this study, we tested whether these findings were correlated in a population of healthy older adults in whom we previously demonstrated verbal memory performance was positively associated with left entorhinal cortex volume in the MTL (Rosen et al., 2003) and right frontal lobe activation during memory encoding (Rosen et al., 2002). Thirteen, non-demented, community-dwelling older adults participated both in a functional MRI (fMRI) study of verbal memory encoding and structural imaging. MRI-derived left entorhinal volume was measured on structural images and entered as a regressor against fMRI activation during verbal memory encoding. Right frontal activation (Brodmann's Area 47/insula) was positively correlated with left entorhinal cortex volume. These findings indicate a positive association between MTL volume and right frontal-lobe function that may underlie variability in memory performance among the elderly, and also suggest a two-stage model of memory decline in aging.

Aged↗

PubMed2004

MRI-derived entorhinal volume is a good predictor of conversion from MCI to AD.

With high-resolution quantitative magnetic resonance imaging (MRI) techniques, it is possible to examine alterations in brain anatomy in vivo and to identify regions affected in the earliest stages of Alzheimer's disease (AD). In the present study, 27 patients diagnosed with mild cognitive impairment (MCI) received a high-resolution MRI scan at baseline and were followed with yearly clinical evaluations. Ten of the 27 patients converted to AD during a 36-month period following the baseline clinical evaluation. Hippocampal and entorhinal cortex volumes derived from the baseline scan were compared to determine which of these two regions, known to be pathologically involved very early in the course of AD, could best differentiate MCI converters from non-converters. Although both entorhinal and hippocampal volumes were found to be independent predictors of the likelihood of conversion to AD, it was the right hemisphere entorhinal volume that best predicted conversion with a concordance rate of 93.5%.

Aged↗

PubMed2004

The pattern of neuropsychological deficits in Vascular Cognitive Impairment-No Dementia (Vascular CIND).

We examined the pattern of neuropsychological deficits in Vascular Cognitive Impairment-No Dementia (Vascular CIND) by comparing the cognitive and behavioral performance of 41 post-stroke Vascular CIND patients to that of 62 post-stroke patients with no cognitive impairment (NCI). Neuropsychological test scores were grouped into seven cognitive and four behavioral domains, then converted to standardized, weighted principle component scores (PCS) for each domain. Multivariate logistic regression models built on cognitive domains found the immediate recall and psychomotor domains to best predict diagnostic group membership. In a separate model limited to behavioral data, the depressed mood domain best predicted group membership. The combination of immediate memory deficits, psychomotor slowness and depression have also been found in Vascular Dementia (VaD), suggesting that the pattern of deficits in Vascular CIND and VaD neuropsychological deficits are similar. This cognitive and behavioral pattern similarity supports the hypothesis that Vascular CIND lies on a continuum between NCI and VaD.

Activities of Daily Living↗

PubMed2003

Differential associations between entorhinal and hippocampal volumes and memory performance in older adults.

Magnetic resonance imaging-derived entorhinal and hippocampal volumes were measured in 14 nondemented, community-dwelling older adults. Participants were selected so that memory scores from 2 years prior to scanning varied widely but were not deficient relative to age-appropriate norms. A median split of these memory scores defined high-memory and low-memory groups. Verbal memory scores at the time of imaging were lower, and entorhinal and hippocampal volumes were smaller, in the low-memory group than in the high-memory group. Left entorhinal cortex volume showed the strongest correlation (r= .79) with immediate recall of word lists. Left hippocampal volume showed the strongest correlation (r= .57) with delayed paragraph recall. These results suggest that entorhinal and hippocampal volumes are related to individual differences in dissociable kinds of memory performance among healthy older adults.

Aged↗

PubMed2002

The localizing yield of sphenoidal and anterior temporal electrodes in ictal recordings: a comparison study.

PURPOSE: To compare the localizing yield of sphenoidal electrodes placed under fluoroscopic guidance (SEs) and anterior temporal electrodes (ATEs) in ictal recordings from a group of patients with seizure disorders of anterior temporal origin. METHODS: We compared ictal recordings of 156 seizures obtained with SEs and ATEs from 40 consecutive patients with seizures of anterior temporal origin. Four electroencephalographers reviewed ictal recordings independently and blind to the patients' identity, presurgical data, and inclusion of ATEs or SEs. Outcome variables included (a) number of correctly localized seizures with SE and ATE recordings by at least three raters; (b) number of ictal foci in which all seizures were localized only with SEs; and (c) number of seizures in which SEs identified the ictal onset > or =5 s earlier than ATEs. RESULTS: Interrater agreement among the four raters was significantly greater with SE than with ATE recordings (p < 0.0001). The number of seizures correctly localized was significantly greater with SEs (n = 144) than with ATEs (n = 99; p < 0.0001). All the seizures [n = 36 (23%)] originating from 14 ictal foci (29%) in 11 patients (27.5%) were localized only with SEs. Finally, the ictal onset was detected at SEs > or =5 s earlier than at ATEs in 67 (43%) seizures originating from 33 (69%) foci in 30 (75%) patients. CONCLUSIONS: SEs improve interrater agreement in the localization of seizures of anterior temporal origin, and in about one fourth of patients, SEs add ictal data not identified by ATEs.

Adolescent↗