Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Structural MRI”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMed2001

Spatiotemporal mapping of brain activity by integration of multiple imaging modalities.

Functional magnetic resonance imaging (fMRI) and positron emission tomography measure local changes in brain hemodynamics induced by cognitive or perceptual tasks. These measures have a uniformly high spatial resolution of millimeters or less, but poor temporal resolution (about 1s). Conversely, electroencephalography (EEG) and magnetoencephalography (MEG) measure instantaneously the current flows induced by synaptic activity, but the accurate localization of these current flows based on EEG and MEG data alone remains an unsolved problem. Recently, techniques have been developed that, in the context of brain anatomy visualized with structural MRI, use both hemodynamic and electromagnetic measures to arrive at estimates of brain activation with high spatial and temporal resolution. These methods range from simple juxtaposition to simultaneous integrated techniques. Their application has already led to advances in our understanding of the neural bases of perception, attention, memory and language. Further advances in multi-modality integration will require an improved understanding of the coupling between the physiological phenomena underlying the different signal modalities.

Animals↗
PubMed2001

Local Lyapunov exponents detect epileptic zones in spike-less interictal MEG recordings.

OBJECTIVE: In terms of dynamical system theory the rapid alteration of electromagnetic brain signal properties observed with transition from interictal into ictal epileptic activity implies an alteration between at least two dynamical states (attractors). We explored whether such a multistability is reflected also in the dynamical characteristics of the interictal signal. METHODS: A combined method consisting of structural MRI, multichannel magnetoencephalography (MEG) and the non-linear dynamics was applied for the detection of subthreshold interictal activity in temporal lobe epilepsy. Employing multichannel MEG we calculated local Lyapunov exponents (ILE) as a measure of the probability of state transitions in patients with mesiotemporal and extra-mesiotemporal focal epilepsy. RESULTS: The spatial distribution of the variability of ILE was found to be correlated to the side of the epileptic focus, thus, providing a reliable estimate of its localization. CONCLUSION: Our results demonstrate that interictal epileptic activity is characterized by an increase of the number of transitions between different attractors.

Adult↗
PubMed2004

Hippocampal volume and retention in Alzheimer's disease.

This study tested the hypothesis that the hippocampus has a relatively specific role in retaining information over delays. Thirty-seven subjects with probable Alzheimer's disease were evaluated with a verbal memory task and structural MRI. Cortical gray matter but not hippocampal volume predicted immediate free recall. In contrast, hippocampal volume was the best predictor of how well information was retained over a delay, even after controlling for levels of immediate recall. Results suggest that the role of the hippocampus is relatively specific to the consolidation of new memories.

Aged↗
PubMed2005

Correlations of regional cerebral metabolism with memory performance and executive function in patients with herpes encephalitis or frontal lobe lesions.

Cerebral [18F]fluorodeoxyglucose positron emission tomography (18FDG-PET) data from patients suffering amnesia following herpes encephalitis (n=7) or frontal lobe pathology (n=14) were compared with data from age-matched nonamnesic subjects (n=10). All subjects received structural MRI, resting 18FDG-PET scans, and neuropsychological evaluation. PET data were analyzed using complementary statistical parametric mapping and region-of-interest methods. Differential patterns of hypometabolism were found in patients relative to healthy controls. Factor analysis of the neuropsychological data revealed that memory performance was associated with retrosplenial and medial temporal metabolism, and executive function was associated with dorsolateral frontal metabolism. The association between memory performance and retrosplenial metabolism remained statistically significant after accounting for measures of cerebral atrophy using MRI. The significance of the retrosplenium as a major relay station between the thalamus and the medial temporal and frontal lobes--sensitive to changes in either--is discussed in the light of the findings.

Adult↗
PubMed2003

Dementia with Lewy bodies.

The objective was to summarize recent findings about the clinical features, diagnosis and investigation of dementia with Lewy (DLB) bodies, together with its neuropathology, neurochemistry and genetics. Dementia with Lewy bodies (DLB) is a primary, neurodegenerative dementia sharing clinical and pathological characteristics with both Parkinson's disease (PD) and Alzheimer's disease (AD). Antiubiquitin immunocytochemical staining, developed in the early 1990s, allowed the frequency and distribution of cortical LBs to be defined. More recently, alpha-synuclein antibodies have revealed extensive neuritic pathology in DLB demonstrating a neurobiological link with other "synucleinopathies" including PD and multiple system atrophy (MSA). The most significant correlates of cognitive failure in DLB appear to be with cortical LB and Lewy neurites (LNs) rather than Alzheimer type pathology. Clinical diagnostic criteria for DLB, published in 1996, have been subjected to several validation studies against autopsy findings. These conclude that although diagnostic specificity is high (range 79- 100%, mean 92%), sensitivity is lower (range 0- 83 %, mean, 49%). Improved methods of case detection are therefore required. Fluctuating impairments in attention, visual recognition and construction are more indicative of DLB than AD. Relative preservation of medial temporal lobe volume on structural MRI and the use of SPECT tracers for regional blood flow and the dopamine transporter are the most reliable current biomarkers for DLB. There are no genetic or CSF tests recommended for the diagnosis of DLB at present. Between 15 and 20% of all elderly demented cases reaching autopsy have DLB, making it the most common cause of degenerative dementia after AD. Exquisite, not infrequently fatal, sensitivity to neuroleptic drugs and encouraging reports of the effects of cholinesterase inhibitors on cognitive, psychiatric and neurological features, mean that an accurate diagnosis of DLB is more than merely of academic interest. Dementia developing late in the course of PD shares many of the same clinical and pathological characteristics.

Aged↗
PubMed2005

A combined clinical, neuropsychological, and neuroanatomical study of adults with high functioning autism.

INTRODUCTION: Three hypotheses concerning associations between neuroanatomical abnormalities, neuropsychological impairments, and the behavioural manifestations of autism were investigated. The primary hypothesis was that the social interaction impairments diagnostic of autism are associated with deficits of socioemotional perception and abnormalities of the amygdala. One subsidiary hypothesis was that the learning and language impairments that occur in less able individuals with autism are associated with impaired memory, and with abnormalities of hippocampal regions. A second subsidiary hypothesis was that the repetitive behaviour diagnostic of autism is associated with executive deficits and with abnormalities of the prefrontal cortex. Associations between the neuroanatomical regions investigated were also examined. METHODS: Ten adult males with high functioning autism (HFA) were compared with 10 healthy controls matched for age, sex, verbal and nonverbal ability. Hypothesis-driven structural MRI and neuropsychological tests were used to collect neuroanatomical and neuropsychological data on all subjects. A version of the Wing Autism Diagnostic Interview Checklist was used to collect clinical data on the HFA subjects. RESULTS: Strong convergent evidence in support of the amygdala hypothesis was obtained, and preliminary support for the hippocampal/parahippocampal hypothesis. No clear evidence was obtained in support of the prefrontal hypothesis. Patterns of associations amongst volume measures within and between medial temporal and prefrontal regions suggest stronger within-region and weaker between-region associations in the HFA group compared with controls. CONCLUSIONS: These findings are discussed in terms of a model of autism in which selective abnormalities of the amygdala and hippocampus (in all cases) and of the parahippocampal gyrus (in lower functioning cases) are implicated, and in which a disruption of coordinated limbic and prefrontal activity may be critical.

Journal Article↗
PubMed1998

Parieto-occipital cortex activation during self-generated eye movements in the dark.

A number of extrastriate visual areas in the parieto-occipital cortex are known from single-cell recordings of the macaque monkey to be involved in the coding of eye-position signals in the brain. These are important for the accurate location of visual objects in extrapersonal space. It can be predicted that these areas will show increased activation during the performance of eye movements at high frequency. In the present study PET and measurements of the regional distribution of cerebral blood flow (rCBF) were used as indirect measures of neural activity. Two independent groups of normal volunteers performed large-amplitude self-generated eye movements in complete darkness, thus removing the confounding effects of visual stimulation on parieto-occipital activation. The first group (group A; n = 5) served as a hypothesis-generating group and the second group (group B; n = 4) served as a hypothesis-testing group. The data were analysed using statistical parametric mapping at a significance level corrected for multiple comparisons (group A, Z > 4.08; group B, Z > 4.04). Significant rCBF increases were found for both groups in the frontal eye fields, supplementary eye fields, cerebellar vermis and putamina/thalami. Additionally, activation was found in the cunei in the posterior bank of the parieto-occipital sulcus. Also, the extraocular muscles were activated and, as a consequence of the partial volume effect, projected to the orbitofrontal cortices. At a less conservative threshold, activation was found close to the intraparietal sulci on the left side (Z = 3.91, P = 0.09) and right side (Z = 3.33, P = 0.42). The locations of these areas were confirmed in group B with reference to high-resolution structural MRI scans. The activation of the parieto-occipital cortex without overt visual stimuli is interpreted as the result of neural activity related to the reception of efferent copies of motor commands and/or the activation of neurons coding for eye position relative to the orbits. These are important constituents for the location and remapping of visual stimuli in space.

Adult↗
PubMed2002

Adolescents who were born very preterm have decreased brain volumes.

Infants born very preterm have an increased risk of brain injury. Given the great increase in the number of such infants that are surviving, it is important to establish whether any resultant brain abnormalities persist into adolescence and adult life. We therefore examined in vivo whole brain, grey matter, white matter and hippocampal volumes, ventricular size and grey/white matter ratios in a series of adolescents who had been born very preterm, and an age-matched full-term control group. Structural MRI was carried out on a cohort of 72 adolescents (mean age 15 years) who were born before 33 weeks, and 48 age-matched full-term controls. Brain measurements were made blind to group affiliation using stereological principles. After controlling for gender and height, the very preterm subjects showed a 6.0% decrease in whole brain volume, and an 11.8% decrease in cortical grey matter volume, as well as a 15.6% decrease in right and a 12.1% decrease in left hippocampal volumes; they also had a 42.0% increase in the size of the lateral ventricles. Therefore, individuals who were born very preterm continue to show noticeable decrements in brain volumes and striking increases in lateral ventricular volume into adolescence. The functional significance of these abnormalities merits further investigation.

Adolescent↗
PubMed2003

Affective blindsight: intact fear conditioning to a visual cue in a cortically blind patient.

Blindsight refers to remarkable residual visual abilities of patients with damage to the primary visual cortex (V1). Recent studies revealed that such residual abilities do not apply only to relatively simple object discriminations, but that these patients can also differentially categorize and respond to emotionally salient stimuli. The current study reports on a case of intact fear conditioning to a visual cue in a male patient with complete bilateral cortical blindness. The patient was admitted to the stroke unit of the neurological department because of complete loss of vision. Both CT and structural MRI scans confirmed lesions in both territories of the posterior cerebral artery. No visual evoked potentials could be detected confirming complete cortical blindness. During fear conditioning, a visual cue predicted the occurrence of an aversive electric shock. Acoustic startle probes were presented during and between the conditioned stimuli. Relative to the control condition, startle reflexes were substantially potentiated when elicited in the presence of the conditioned stimuli. No such potentiation was observed prior to conditioning. These data suggest that fear learning to visual cues does not require a cortical representation of the conditioned stimulus in the primary sensory cortex and that subcortical pathways are sufficient to activate the fear module in humans.

Aged↗
PubMed2003

Neurofilament inclusion body disease: a new proteinopathy?

We describe four cases of a new clinicopathological entity presenting with either a frontotemporal dementia or corticobasal degeneration syndrome with a mean age of onset of 45 years (range 41-50) characterized pathologically by deposition of neurofilament proteins. All four patients had a rapidly progressive course and have become mute and non-ambulatory, and three have died after mean illness duration of only 3 years (range 2 1/2 -4). Both structural (MRI) and functional (PET and SPECT) imaging demonstrated frontal and temporal lobe and basal ganglia involvement. Gross neuropathological examination in the three deceased patients (the fourth patient, still alive, was diagnosed by brain biopsy) revealed changes affecting predominantly the frontal and temporal cortices, basal ganglia and brainstem. There was superficial linear spongiosis affecting the frontal lobes in all three autopsied patients, and severe caudate atrophy was noted in two of them and demonstrated on MRI in the living patient. On routine staining, there were numerous intracytoplasmic inclusions, which ranged from eosinophilic to basophilic. Some had a clearly defined basophilic margin, while others were granular with a hyaline core. With modified Bielschowsky silver technique, a small number of the inclusions were intensely stained. Inclusions were not labelled with other silver stains. Immuno histochemistry revealed that the inclusions were immunoreactive with antibodies to neurofilament heavy and light chain subunits and to ubiquitin, but not with antibodies to tau and alpha-synuclein. These neurofilament- and ubiquitin-positive inclusions were widespread, specific to neurons and occasionally intranuclear. The frequency and distribution of the inclusions and the silver and immunohistochemical profiles in these four cases is novel and has not been described in detail before. We propose the term neurofilament inclusion body disease for this entity.

Adult↗
PubMed2003

Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases.

Epilepsy surgery is based upon the minute assessment of brain tissue generating epileptic activity. A number of diagnostic methods are employed in the process of presurgical evaluation, supplying information on various morphological and functional aspects, ultimately integrated into the general result fundamental to the final treatment decision. Magnetic source imaging (MSI), combining structural (MRI) and functional (MEG) data, has been playing an increasingly important role among the tools of presurgical epilepsy evaluation. However, in spite of a considerable number of publications, the samples used have hardly exceeded 50 cases. Therefore, we present a synopsis of 455 epilepsy patients who underwent MSI investigations. Analysis of this substantial data revealed that the average sensitivity of MEG for specific epileptic activity was 70%. Among 131 patients who underwent surgical therapy in addition to antiepileptic drug medication, MSI identified the lobe to be treated in 89%, with results for extratemporal cases being even superior to those with temporal lobe surgery. Introducing a measure to quantify the contribution of MSI to the general result of presurgical evaluation that was applied to 104 patients, the results showed that MSI supplied additional information in 35% and information crucial to final decision making in 10%. Accuracy as well as contribution findings underlined MSI appropriateness even for extratemporal epilepsies, which otherwise frequently prove difficult with respect to focus localization.

Adolescent↗
PubMed2003

Metabolic changes and electro-clinical patterns in mesio-temporal lobe epilepsy: a correlative study.

Interictal hypometabolism is commonly found in mesio-temporal lobe epilepsy (MTLE), but its pathophysiology remains incompletely understood. We hypothesized that metabolic changes reflect the preferential networks involved by ictal discharges. We analysed the topography of interictal hypometabolism according to electro-clinical patterns in 50 patients with unilateral hippocampal sclerosis (HS) and consistent features of MTLE. Based on electro-clinical correlations, we identified four groups: (i) mesial group (13 cases) characterized by mesial seizure onset without evidence of early spread beyond the temporal lobe; (ii) anterior mesio-lateral group (AML; 18 cases) with early anterior spread involving the anterior lateral temporal cortex and insulo-fronto-opercular areas; (iii) widespread mesio-lateral group (WML; 15 cases) with wide spread (involving both anterior and posterior lateral temporal and perisylvian areas); and (iv) bitemporal (BT) group (four cases) with early contralateral temporal spread. Results of [18F]fluorodeoxyglucose-PET imaging in each group were compared with those of 10 control subjects using statistical parametric mapping software (SPM99). MRI data and surgical outcome in each group were compared with metabolic findings. Hypometabolism was limited to hippocampal gyrus, temporal pole and insula in the mesial group. Gradual involvement of lateral temporal cortex, insula and perisylvian areas was observed in the AML and WML groups. The BT group differed from the others with mild bitemporal involvement, bilateral insular hypometabolism and longer epilepsy duration. MRI structural abnormalities outside of the mesial formations were detected in 65% of the cases. Neither the severity of HS nor temporal atrophy appeared related to the topography of hypometabolism. However, temporal hypometabolism was more extended when temporo-polar signal changes were detected. Among operated patients (n = 43), seizure-free outcome was obtained in 82%. Surgical outcome appeared more favourable in the mesial group. However, the difference between the four groups was not significant. Our results suggest that hypometabolism in MTLE may be related to ictal discharge generation and spread pathways, even if structural changes and epilepsy duration may also play a role.

Adolescent↗
PubMed2004

Corpus callosum size and very preterm birth: relationship to neuropsychological outcome.

Thinning of the corpus callosum (CC) is often observed in individuals who were born very preterm. Damage to the CC during neurodevelopment may be associated with poor neuropsychological performance. This study aimed to explore any evidence of CC pathology in adolescents aged 14-15 years who were born very preterm, and to investigate the relationship between CC areas and verbal skills. Seventy-two individuals born before 33 weeks of gestation and 51 age- and sex-matched full-term controls received structural MRI and neuropsychological assessment. Total CC area in very preterm adolescents was 7.5% smaller than in controls, after adjusting for total white matter volume (P = 0.015). The absolute size of callosal subregions differed between preterm and full-term adolescents: preterm individuals had a 14.7% decrease in posterior (P < 0.0001) and an 11.6% decrease in mid-posterior CC quarters (P = 0.029). Preterm individuals who had experienced periventricular haemorrhage and ventricular dilatation in the neonatal period showed the greatest decrease in CC area. In very preterm boys only, verbal IQ and verbal fluency scores were positively associated with total mid-sagittal CC size and mid-posterior surface area. These results suggest that very preterm birth adversely affects the development of the CC, particularly its posterior quarter, and this impairs verbal skills in boys.

Adolescent↗
PubMed2006

Amygdala dysfunction in men with the fragile X premutation.

Premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene are associated with autism spectrum disorder in childhood, premature ovarian failure, and the neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). FXTAS, and perhaps the other clinical presentations among carriers, are thought to be due to toxic gain-of-function of elevated levels of the expanded-repeat FMR1 mRNA. Previous structural MRI studies have implicated the amygdala as a potential site of dysfunction underlying social deficits and/or risk for FXTAS. As a preliminary investigation of this possible association, adult males with the premutation, and male controls matched for IQ, age and education, completed three protocols that probe amygdala and sympathetic function: (i) a functional MRI paradigm that measures brain response to fearful faces; (ii) a fear-potentiated startle paradigm that differentiates responses to fearful faces and fearful non-social images and (iii) measurement of skin conductance level during a brief social encounter. Compared with controls, men with the FMR1 premutation demonstrated diminished brain activation in the amygdala and several brain areas that mediate social cognition while viewing fearful faces. The reduced amygdala activation in the premutation group was significantly associated with self-report of psychological symptoms on the Symptom Checklist-90--Revised. These men also displayed a lack of startle potentiation while viewing fearful faces and showed reduced skin conductance response when greeting an unfamiliar experimenter in comparison with the control group. The current findings may be related to social cognition deficits reported previously in children and adults with the premutation. The aetiology for this dysfunction may be elevated FMR1 mRNA or reduced FMR1 protein that occurs in carriers with higher premutation CGG repeat alleles.

Adult↗
PubMed1998

Left planum temporale surface correlates with functional dominance during story listening.

The relationship between anatomical asymmetry of the planum temporale (PT) and functional lateralization for language comprehension was studied in 14 normal volunteers, including five left-handers (LH). PT surfaces and asymmetry were measured in each subject using structural MRI, while functional lateralization was assessed on individual regional cerebral blood flow (rCBF) difference images of a PET-H2(15)O activation protocol in which a story listening condition was contrasted with a control state. Significant positive correlations were found between the left PT surface and the amount of NrCBF increase during the story listening in the left superior temporal gyrus as well as with the left-right activation index in the superior temporal and the temporal pole. Functional imaging data were correlated neither with the right PT surface nor with the right-left PT surface asymmetry index. However the latter index was correlated with handedness scores. The present results indicate that the size of the left PT is the relevant anatomical landmark for language dominance, and demonstrate that anatomical asymmetries are part of the functional variability for language.

Adult↗
PubMed2000

Lateralization of movement-related potentials and the size of corpus callosum.

Using structural MRI and whole-head EEG recordings, we analyzed the correlations between the anatomical parameters of the corpus callosum and the hemispheric distribution of the cortical movement-related potentials during right finger and shoulder movements in nine right-handed men. Statistically significant correlation was found only in finger movements. A relatively large genu and the anterior part of the truncus of the corpus callosum correlated with enhanced pre-movement EEG potential over the ipsilateral M1/S1 area. The lateralization of the movement-related potentials correlates with the size of those callosal regions which connect the homologous areas of the primary sensorimotor and frontal cortices.

Adult↗
PubMed2000

A lesion of cortical area V2 selectively impairs the perception of the direction of first-order visual motion.

Lesions of area MT/V5 in monkeys and its presumed homologue, the motion area, in humans impair motion perception, including the discrimination of the direction of global motion in random dot kinematograms. Here we report the results of similar tests on patient TF, who has a discrete and very small, unilateral infarct in the medial superior part of the right occipital cortex. Structural MRI, co-registered in software with a standardized human brain atlas, reveals that the lesion involves area V2. The patient was impaired in his retinotopically corresponding left lower quadrant on several motion tasks including discrimination in random dot kinematograms of direction, speed and motion-defined discontinuity. He was also impaired on tasks selectively involving first-order motion based on luminance contrast but not on second-order motion based on texture contrast. The results show that even though area MT/V5 is intact, motion perception is abnormal and, in particular, his perception of first-order motion is impaired.

Cerebral Infarction↗
PubMed2001

Voxel-based morphometric analyses of the brain in children and adolescents prenatally exposed to alcohol.

Children of mothers who abuse alcohol during pregnancy can suffer varying degrees of neurological abnormality, cognitive impairment, and behavioral problems, and in the worst case, are diagnosed with fetal alcohol syndrome (FAS). The purpose of the present study was to localize brain abnormalities in a group of children and adolescents prenatally exposed to alcohol using high resolution, 3D structural MRI data and whole-brain voxel-based morphometry (VBM). Data were collected for 21 children and adolescents with histories of prenatal alcohol exposure (ALC) and 21 normally developing individuals. Statistical parametric maps revealed abnormalities most prominent in the left hemisphere perisylvian cortices of the temporal and parietal lobes where the ALC patients tended to have too much gray matter and not enough white matter. These results provide further support for dysmorphology in temporo-parietal cortices above and beyond the overall microcephaly that results from severe prenatal alcohol exposure.

Adolescent↗