Imma C. Clemente

MRI and genetic correlates of cognitive function in elders with memory impairment

The present study investigated the relationship between genetic variation, MRI measurements and neuropsychological function in a sample of 58 elders exhibiting memory decline. In agreement with previous reports, we found that the epsilon4 allele of the apolipoprotein E (APOE) and the D allele of the angiotensin converting enzyme (ACE) polymorphisms negatively modulated the cognitive performance. Further, we found an association between the A allele of the apolipoprotein C1 (APOC1) polymorphism and poorer memory and frontal lobe function. No clear associations emerged between MRI measures of white matter lesions (WML) or hippocampal sulcal cavities (HSC) and the cognitive performance after controlling for age effects. Further, the degree of WML or HSC lesions was in general not predisposed genetically except for the presence of the A allele of the APOC1 polymorphism that was related to a higher severity of HSC scores. Our results suggest that WML or HSC do not represent important brain correlates of genetic influences on cognitive performance in memory impaired subjects.

Angiotensin I converting enzyme polymorphism in humans with age-associated memory impairment: relationship with cognitive performance.

We compared the distribution of an insertion (I)/deletion (D) polymorphism coding for the angiotensin I converting enzyme (ACE) gene in 100 subjects fulfilling NIMH criteria for Age-associated memory impairment (AAMI) and 124 controls. We found significantly reduced prevalences of the ACE I/I genotype together with increases of the ACE D allele in the AAMI group. We further compared the neuropsychological performance of the AAMI group according to their ACE genotype. Those AAMI subjects presenting the ACE I/I genotype exhibited better performance on a measure of frontal lobe function. Our results suggest that the lack of the ACE I/I genotype and the presence of the ACE D allele are associated with memory impairment in the elderly.

Neuropsychological and Genetic Differences Between Age‐Associated Memory Impairment and Mild Cognitive Impairment Entities

OBJECTIVE: To neuropsychologically and genetically compare age‐associated memory impairment (AAMI) and mild cognitive impairment (MCI) entities and to determine what proportion of AAMI diagnosed individuals could also receive a MCI diagnosis. To compare the distribution of a previously known genetic risk factor for Alzheimers disease (apolipoprotein E common polymorphism) associated with these two conditions with a sample of the normal aging.

Apo E influences declarative and procedural learning in age-associated memory impairment.

Age-associated memory impairment (AAMI) is a clinical entity which was originally described to define memory problems linked to normal aging. Apolipoprotein E and ACE genes have both been associated with cognitive impairment in aging and dementia. The purpose of this study was to investigate memory and executive functions in AAMI according to the genetic background. We found that subjects carrying the Apo E epsilon4 allele exhibit lower memory performance on tests of both declarative and procedural memory. We did not find differences on frontal lobe tests. These findings give further support to the hypothesis concerning a genetic susceptibility for cognitive impairment in aging.

Task-dependent Activity and Connectivity Predict Episodic Memory Network-based Responses to Brain Stimulation in Healthy Aging

BACKGROUND Transcranial magnetic stimulation (TMS) can affect episodic memory, one of the main cognitive hallmarks of aging, but the mechanisms of action remain unclear. OBJECTIVES To evaluate the behavioral and functional impact of excitatory TMS in a group of healthy elders. METHODS We applied a paradigm of repetitive TMS - intermittent theta-burst stimulation - over left inferior frontal gyrus in healthy elders (n = 24) and evaluated its impact on the performance of an episodic memory task with two levels of processing and the associated brain activity as captured by a pre and post fMRI scans. RESULTS In the post-TMS fMRI we found TMS-related activity increases in left prefrontal and cerebellum-occipital areas specifically during deep encoding but not during shallow encoding or at rest. Furthermore, we found a task-dependent change in connectivity during the encoding task between cerebellum-occipital areas and the TMS-targeted left inferior frontal region. This connectivity change correlated with the TMS effects over brain networks. CONCLUSIONS The results suggest that the aged brain responds to brain stimulation in a state-dependent manner as engaged by different tasks components and that TMS effect is related to inter-individual connectivity changes measures. These findings reveal fundamental insights into brain network dynamics in aging and the capacity to probe them with combined behavioral and stimulation approaches.

Relationship among 1H-magnetic resonance spectroscopy, brain volumetry and genetic polymorphisms in humans with memory impairment

We investigated the relationship among neuroanatomical, neurochemical and genetic variables in 44 subjects with age-related memory impairment. Hydrogen magnetic resonance spectroscopy was used to determine N-acetyl/creatine (NAA/Cr) concentrations in basal ganglia and medial temporal regions. Volumetric measures were obtained for caudate nucleus and hippocampus. Genetic polymorphisms examined included apolipoproteins (APO) E and CI, angiotensin converting enzyme and dopamine D2 receptor TaqI genes. Age was found to be negatively correlated with hippocampal and basal ganglia volumes, but not with neurochemical values. Multiple regression analyses showed that the APOC1 polymorphism was the only variable which predicted NAA/Cr values in basal ganglia. NAA/Cr metabolites in the medial temporal lobe but not in the basal ganglia region were related with lower performance in verbal memory.

APOE status modulates the changes in network connectivity induced by brain stimulation in non-demented elders.

Behavioral consequences of a brain insult represent an interaction between the injury and the capacity of the rest of the brain to adapt to it. We provide experimental support for the notion that genetic factors play a critical role in such adaptation. We induced a controlled brain disruption using repetitive transcranial magnetic stimulation (rTMS) and show that APOE status determines its impact on distributed brain networks as assessed by functional MRI (fMRI).Twenty non-demented elders exhibiting mild memory dysfunction underwent two fMRI studies during face-name encoding tasks (before and after rTMS). Baseline task performance was associated with activation of a network of brain regions in prefrontal, parietal, medial temporal and visual associative areas. APOE ε4 bearers exhibited this pattern in two separate independent components, whereas ε4-non carriers presented a single partially overlapping network. Following rTMS all subjects showed slight ameliorations in memory performance, regardless of APOE status. However, after rTMS APOE ε4-carriers showed significant changes in brain network activation, expressing strikingly similar spatial configuration as the one observed in the non-carrier group prior to stimulation. Similarly, activity in areas of the default-mode network (DMN) was found in a single component among the ε4-non bearers, whereas among carriers it appeared disaggregated in three distinct spatiotemporal components that changed to an integrated single component after rTMS. Our findings demonstrate that genetic background play a fundamental role in the brain responses to focal insults, conditioning expression of distinct brain networks to sustain similar cognitive performance.

Thalamic diffusion differences related to cognitive function in white matter lesions

Cerebral white matter lesions (WMLs) are related to cognitive deficits, probably due to a disruption of frontal-subcortical circuits. We explored thalamic diffusion differences related to white matter lesions (WMLs) and their association with cognitive function in middle-aged individuals. Ninety-six participants from the Barcelona-AsIA Neuropsychology Study were included. Participants were classified into groups based on low grade and high grade of periventricular hyperintensities (PVHs) and deep white matter hyperintensities (DWMHs). Tract-Based Spatial Statistics was used to study thalamic diffusion differences between groups. Mean fractional anisotropy (FA) values in significant areas were calculated for each subject and correlated with cognitive performance. Participants with high-grade PVHs and DWMHs showed lower FA thalamic values compared to those with low-grade PVHs and DWMHs, respectively. Decreased FA thalamic values in high-grade DWMHs, but not high-grade PVH, were related to lower levels of performance in psychomotor speed, verbal fluency, and visuospatial skills. Thalamic diffusion differences are related to lower cognitive function only in participants with high-grade DWMHs. These results support the hypothesis that fronto-subcortical disruption is associated with cognitive function only in DWMHs.

Angiotensin I converting enzyme polymorphism effects in patients with normal pressure hydrocephalus syndrome before and after surgery.

Previous reports have suggested an association between the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE), cardiovascular disease, and cognitive performance. Normal pressure hydrocephalus (NPH) is considered to be an example of reversible dementia although the clinical improvement after shunting varies from subject to subject. An association has been suggested between vascular risk factors and the development of NPH. The ACE plays a major role in vascular pathology and physiology. In the present study we investigated the distribution of an ACE gene insertion/deletion polymorphism in 112 patients diagnosed with NPH and in 124 controls. We also evaluated the role of this genetic polymorphism in cognitive functioning before and following surgery in a subgroup of 72 patients. No differences in genetic or allele distributions were found between patients and healthy subjects, but among patients, carriers of D/D or D/I genotypes obtained less cognitive benefit following shunt surgery, especially on measures of memory and frontal function. Our data support previous findings in other conditions indicating that possession of at least one D allele is associated with poorer cognitive performance.