Biomedical subjects

Michael A Kraut

Publications and source records attributed to Michael A Kraut.

At least 19 recordsLinked to original sources

PubMed2006

Neural correlates of the object-recall process in semantic memory.

The recall of an object from features is a specific operation in semantic memory in which the thalamus and pre-supplementary motor area (pre-SMA) are integrally involved. Other higher-order semantic cortices are also likely to be involved. We used the object-recall-from-features paradigm, with more sensitive scanning techniques and larger sample size, to replicate and extend our previous results. Eighteen right-handed healthy participants performed an object-recall task and an association semantic task, while undergoing functional magnetic resonance imaging. During object-recall, subjects determined whether words pairs describing object features combined to recall an object; during the association task they decided if two words were related. Of brain areas specifically involved in object recall, in addition to the thalamus and pre-SMA, other regions included the left dorsolateral prefrontal cortex, inferior parietal lobule, and middle temporal gyrus, and bilateral rostral anterior cingulate and inferior frontal gyri. These regions are involved in semantic processing, verbal working memory and response-conflict detection and monitoring. The thalamus likely helps to coordinate activity of these different brain areas. Understanding the circuit that normally mediates this process is relevant for schizophrenia, where many regions in this circuit are functionally abnormal and semantic memory is impaired.

Adult↗

PubMed2006

Inverse correlation between cerebral blood flow measured by continuous arterial spin-labeling (CASL) MRI and neurocognitive function in children with sickle cell anemia (SCA).

Overt stroke, clinically "silent" cerebral infarct, and neurocognitive impairment are frequent complications of sickle cell anemia (SCA). Current imaging techniques have limited sensitivity and specificity to identify children at risk for neurocognitive impairment. We prospectively evaluated 24 children with SCA with a neurologic exam, complete blood count, transcranial Doppler ultrasound (TCD), measurement of intelligence quotient (IQ), and magnetic resonance imaging (MRI) with measurement of cerebral blood flow (CBF) using continuous arterial spin-labeling (CASL) MRI. Average CBF to gray matter was 112 +/- 36 mL/100 g/min. We identified a strong inverse relationship between performance IQ and CBF (-1.5 points per 10 mL/100 g/min increase in CBF, P = .013). Elevated steady-state white blood cell count (> or = 14 x 10(9)/L [14,000/microL]) was associated with lower full scale IQ (86 +/- 9 vs 99 +/- 10, P = .005). CASL MRI may identify children with neurocognitive impairment, before damage is evident by structural MRI or TCD.

Anemia, Sickle Cell↗

PubMed2006

The Semantic Object Retrieval Test (SORT) in normal aging and Alzheimer disease.

OBJECTIVE: To characterize performance on a test of semantic object retrieval (Semantic Object Retrieval Test-SORT) in healthy, elderly subjects and patients with Alzheimer disease (AD). BACKGROUND: Although the initial presentation of patients with AD often reflects impairment in delayed recall for verbally encoded memory, common complaints of patients with early AD are actually related to semantic memory impairment. DESIGN: Thirty-eight AD patients and 121 healthy aging controls enrolled in an Alzheimer's Disease Center received a battery of standard neuropsychologic tests including the SORT. RESULTS: Compared with normal controls, AD patients had SORT memory impairments with significantly more false positive memory errors, fewer correctly produced names, and more substitutions in the name production aspect of the test. SORT had robust test-retest reliability in normals. CONCLUSIONS: The SORT task provides a direct, specific assessment of semantic memory, and has now been administered to 121 healthy, aging controls for normative ranges of performance, and to AD patients. The task detected semantic memory deficits in approximately half of patients with mild-moderate AD, which is comparable to other studies assessing semantic deficits in AD with less specific measures.

Aged↗

PubMed2006

Neuroanatomic organization of sound memory in humans.

The neural interface between sensory perception and memory is a central issue in neuroscience, particularly initial memory organization following perceptual analyses. We used functional magnetic resonance imaging to identify anatomic regions extracting initial auditory semantic memory information related to environmental sounds. Two distinct anatomic foci were detected in the right superior temporal gyrus when subjects identified sounds representing either animals or threatening items. Threatening animal stimuli elicited signal changes in both foci, suggesting a distributed neural representation. Our results demonstrate both category- and feature-specific responses to nonverbal sounds in early stages of extracting semantic memory information from these sounds. This organization allows for these category-feature detection nodes to extract early, semantic memory information for efficient processing of transient sound stimuli. Neural regions selective for threatening sounds are similar to those of nonhuman primates, demonstrating semantic memory organization for basic biological/survival primitives are present across species.

Acoustic Stimulation↗

PubMed2005

Cross-sectional and longitudinal analyses of anatomical sulcal changes associated with aging.

Imaging studies of the human brain indicate that the cortex undergoes anatomic changes during the aging process. With the ability to study the human brain in vivo using magnetic resonance imaging, understanding the nature and location of these changes is of increasing interest. In this work, we investigate cross-sectional and longitudinal age effects on the geometric shape and gray matter (GM) volume for regions of interest on the cortical surface. Each of the regions corresponds to the buried cortex surrounding the sulcal spaces and is termed a "sulcal region." The study consists of 35 older adults scanned three times over a 4-year time span. The group includes 19 women and 16 men ranging in ages from 59 to 84 years (mean 70.9, standard deviation 6.2). We analyze 8 sulcal regions-the buried cortex surrounding the left and right central, superior frontal, cingulate, and parietooccipital sulci. We examine surface area, GM thickness, GM volume, sulcal depth, local gyrification index, and measures of curvature. Results indicate cross-sectional age effects in mean thickness, GM volume, sulcal depth, and curvature characteristics of sulcal regions. In addition, we found longitudinal decreases in surface area, mean thickness, GM volume, and sulcal depth measures as well as changes in sulcal curvature.

Aged↗

PubMed2005

Cortical reconstruction using implicit surface evolution: accuracy and precision analysis.

Two different studies were conducted to assess the accuracy and precision of an algorithm developed for automatic reconstruction of the cerebral cortex from T1-weighted magnetic resonance (MR) brain images. Repeated scans of three different brains were used to quantify the precision of the algorithm, and manually selected landmarks on different sulcal regions throughout the cortex were used to analyze the accuracy of the three reconstructed surfaces: inner, central, and pial. We conclude that the algorithm can find these surfaces in a robust fashion and with subvoxel accuracy, typically with an accuracy of one third of a voxel, although this varies with brain region and cortical geometry. Parameters were adjusted on the basis of this analysis in order to improve the algorithm's overall performance.

Algorithms↗

PubMed2005

Abnormal object recall and anterior cingulate overactivation correlate with formal thought disorder in schizophrenia.

BACKGROUND: The neural basis of formal thought disorder (FTD) is unknown. An influential theory is that FTD results from impaired semantic memory processing. We explored the neural correlates of semantic memory retrieval in schizophrenia using an imaging task assessing semantic object recall. METHOD: Sixteen healthy control subjects and sixteen schizophrenia patients whose FTD symptoms were measured with the Thought Disorder Index completed a verbal object-recall task during functional magnetic resonance imaging. Participants viewed two words describing object features that either evoked (object recall) or did not evoke a semantic concept. RESULTS: Schizophrenia patients tended to overrecall objects for feature pairs that did not describe the same object. Functionally, rostral anterior cingulate cortex (ACC) activation in patients positively correlated with FTD severity during both correct recalled and overrecalled trials. Compared with control subjects, during object recalling, patients overactivated bilateral ACC, temporooccipital junctions, temporal poles and parahippocampi, right inferior frontal gyrus, and dorsolateral prefrontal cortex, but underactivated inferior parietal lobules. CONCLUSIONS: Our results support impaired semantic memory retrieval as underlying FTD pathophysiology. Schizophrenia patients showed abnormal activations of brain areas involved in semantic memory, verbal working memory, and initiation and suppression of conflicting responses, which were associated with semantic overrecall and FTD.

Adult↗

PubMed2004

Longitudinal evolution of unidentified bright objects in children with neurofibromatosis-1.

Neurofibromatosis type-1 (NF-1) is the most common autosomal dominant disorder affecting the central nervous system. Magnetic resonance imaging (MRI) has revealed distinctive T2-weighted hyperintense foci (termed unidentified bright objects, UBOs) which appear to represent spongiform changes in the white matter. Cross-sectional and longitudinal analyses suggest that UBOs disappear over time; however, none of these studies have examined comprehensively these foci. We conducted a quantitative MRI longitudinal study of number of affected regions, number of UBOs per region, and UBO volume per region, in a sample of 12 children with NF-1. We applied semi-automatic morphometric methods and comprehensive statistical approaches, within a detailed anatomical parcellation framework. Our data demonstrate that, despite a similar UBO regional distribution (e.g., prevalent globus pallidus/internal capsule (GP/IC) location), UBO evolution was more complex than previously reported. In some subjects, the total number of UBO-occupied locations demonstrated a decrease between approximately ages 7 and 12 years, followed by a progressive increase during adolescence. This pattern was also found for UBO number and/or volume for all regions, with the exception of the cerebellar hemispheres. This REGIONAL distinction may reflect differences in white matter structure between affected long tract fiber bundles and that of cerebral and cerebellar myelinated fibers. The findings are also discussed in the context of previous MR and behavioral studies. We conclude that studies like the present one, in association with other MR modalities, are necessary to characterize more completely the nature and evolution of UBOs and their role in the cognitive phenotype of NF-1.

Adolescent↗

PubMed2004

Neural mechanisms of semantic memory.

Using previously published functional magnetic resonance imaging work studying object recall as a framework, we describe the spatial and temporal properties of brain activation as one plausible model of visually triggered access to semantic memory. We suggest that interactions between the dorsomedial thalamus and Brodmann area 6 facilitate the setting of object search criteria and perhaps drive the search. The pulvinar nucleus of the thalamus, in concert with ventral temporal and occipital cortical regions, become active later, perhaps when the criteria are met or the target object is identified.

Brain↗

PubMed2003

Semantic memory deficit with a left thalamic infarct.

Previous studies of patients with thalamic lesions have reported consistent word finding difficulties without a proposed etiology. The authors describe a patient with a focal left thalamic infarct, pronounced word finding problems, and a relatively selective impairment in semantic memory for object recall from features. The thalamus is proposed to facilitate electrical activity between brain regions that encode object features, resulting in object recall. Thalamic dysfunction disrupting object recall is a plausible etiology for impaired word finding in some patients.

Brain Infarction↗

PubMed2003

Longitudinal magnetic resonance imaging studies of older adults: a shrinking brain.

Age-related loss of brain tissue has been inferred from cross-sectional neuroimaging studies, but direct measurements of gray and white matter changes from longitudinal studies are lacking. We quantified longitudinal magnetic resonance imaging (MRI) scans of 92 nondemented older adults (age 59-85 years at baseline) in the Baltimore Longitudinal Study of Aging to determine the rates and regional distribution of gray and white matter tissue loss in older adults. Using images from baseline, 2 year, and 4 year follow-up, we found significant age changes in gray (p < 0.001) and white (p < 0.001) volumes even in a subgroup of 24 very healthy elderly. Annual rates of tissue loss were 5.4 +/- 0.3, 2.4 +/- 0.4, and 3.1 +/- 0.4 cm3 per year for total brain, gray, and white volumes, respectively, and ventricles increased by 1.4 +/- 0.1 cm3 per year (3.7, 1.3, 2.4, and 1.2 cm3, respectively, in very healthy). Frontal and parietal, compared with temporal and occipital, lobar regions showed greater decline. Gray matter loss was most pronounced for orbital and inferior frontal, cingulate, insular, inferior parietal, and to a lesser extent mesial temporal regions, whereas white matter changes were widespread. In this first study of gray and white matter volume changes, we demonstrate significant longitudinal tissue loss for both gray and white matter even in very healthy older adults. These data provide essential information on the rate and regional pattern of age-associated changes against which pathology can be evaluated and suggest slower rates of brain atrophy in individuals who remain medically and cognitively healthy.

Age Factors↗

PubMed2003

Nontuberculous mycobacterial lymphadenitis of the head and neck: radiologic observations and clinical context.

OBJECTIVE: To summarize the radiologic findings in our series of immunocompetent children with NTMA and to review the clinical and laboratory findings, as well as the treatment and clinical courses, in these patients. MATERIALS AND METHODS: We reviewed the computed tomographic (CT) studies, as well as the clinical courses of eleven patients with laboratory-confirmed diagnosis of NTMA, and recorded the anatomic locations of the affected lymph nodes. RESULTS: In 10 of 11 patients, there were peripherally enhancing, centrally cystic nodes. In 7 of the patients, there was (usually mild) inflammation of the regional fat and overlying skin thickening. Adenopathy in the parotid and submandibular regions was most common. In 4 of the patients, there was more than one nodal group involved. CONCLUSION: In a child who presents with enlarging neck masses and with radiologically demonstrated centrally cystic nodal masses exhibiting relatively little mass effect or inflammatory change in the surrounding fat, the diagnosis of NTMA should be entertained.

Child↗

PubMed2003

fMRI evidence that the neural basis of response inhibition is task-dependent.

Event-related fMRI was used to investigate the hypothesis that neural activity involved in response inhibition depends upon the nature of the response being inhibited. Two different Go/No-go tasks were compared-one with a high working memory load and one with low. The 'simple' Go/No-go task with low working memory load required subjects to push a button in response to green spaceships but not red spaceships. A 'counting' Go/No-go task (high working memory load) required subjects to respond to green spaceships as well as to those red spaceships preceded by an even number of green spaceships. In both tasks, stimuli were presented every 1.5 s with a 5:1 ratio of green-to-red spaceships. fMRI group data for each task were analyzed using random effects models to determine signal change patterns associated with Go events and No-go events (corrected P< or =0.05). For both tasks, Go responses were associated with signal change in the left primary sensorimotor cortex, supplementary motor area (SMA) proper, and anterior cerebellum (right>left). For the simple task, No-go events were associated with activation in the pre-SMA; the working memory-loaded 'counting' task elicited additional No-go activation in the right dorsolateral prefrontal cortex. The findings suggest that neural contributions to response inhibition may be task dependent; the pre-SMA appears necessary for inhibition of unwanted movements, while the dorsolateral prefrontal cortex is recruited for tasks involving increased working memory load.

Adult↗

PubMed2003

Neural hybrid model of semantic object memory: implications from event-related timing using fMRI.

Previous studies by our group have demonstrated fMRI signal changes and synchronized gamma rhythm EEG oscillations between thalamus and cortical regions as subjects recall objects from visually presented features. Here, we extend this work by estimating the time course of fMRI signal changes in the cortical and subcortical regions found to exhibit evidence for task-related activation. Our results indicate that there are separate loci of signal changes in the thalamus (dorsomedial and pulvinar) that exhibit notable differences in times of onset, peak and return to baseline of signal changes. The signal changes in the pulvinar demonstrate the slowest transients of all the cortical and subcortical regions we examined. Evaluation of cortical regions demonstrated salient differences as well, with the signal changes in Brodmann area 6 (BA6) rising, peaking, and returning to baseline earlier than those detected in other regions. We conclude that BA6 mediates early designation or refinement of search criteria, and that the pulvinar may be involved in the binding of feature stimuli for an integrated object memory.

Adult↗

PubMed2003

Correlation of functional MR imaging activation data with simple reaction times.

PURPOSE: To determine the relationship between subject reaction times (RTs) and activation volume in the brain during visuomotor functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twenty-four subjects performed a simple RT task during single-event functional MR imaging, and RTs were recorded. The six subjects with the fastest RTs were designated the fast RT group, and the six subjects with the slowest RTs were designated the slow RT group. The data were processed with noncorrected height threshold (P <.001) for individual comparisons and corrected height threshold (P <.05) for group comparisons (t tests). The activation volumes in both occipital lobes, the left sensorimotor cortex, and the supplemental motor cortices were compared for the two groups. RESULTS: The mean RT +/- SD was 342 msec +/- 20.15 for the fast RT group and 475 msec +/- 36.17 for the slow RT group (P <.0001). More voxels of activation were seen in the fast RT group than in the slow RT group in the occipital lobes, left sensorimotor cortices, and supplemental motor cortices on individual and group maps. This difference was statistically significant in the left sensorimotor (P =.03) and left visual (P =.05) cortices. In the right visual cortex, a trend toward more activation in the fast RT group was noted (P =.15). There was a negative correlation between RTs and activation volume in the left sensorimotor cortex (P =.048). CONCLUSION: There was a greater activation volume in motor and visual cortices in the fast RT group than in the slow RT group.

Adult↗

PubMed2003

Lack of sex effect on brain activity during a visuomotor response task: functional MR imaging study.

BACKGROUND AND PURPOSE: As more individuals are enrolled in clinical functional MR imaging (fMRI) studies, an understanding of how sex may influence fMRI-measured brain activation is critical. METHODS: We used fixed- and random-effects models to study the influence of sex on fMRI patterns of brain activation during a simple visuomotor reaction time task in the group of 26 age-matched men and women. We evaluated the right visual, left visual, left primary motor, left supplementary motor, and left anterior cingulate areas. RESULTS: Volumes of activations did not significantly differ between the groups in any defined regions. Analysis of variance failed to show any significant correlations between sex and volumes of brain activation in any location studied. Mean percentage signal-intensity changes for all locations were similar between men and women. A two-way t test of brain activation in men and women, performed as a part of random-effects modeling, showed no significant difference at any site. CONCLUSION: Our results suggest that sex seems to have little influence on fMRI brain activation when we compared performance on the simple reaction-time task. The need to control for sex effects is not critical in the analysis of this task with fMRI.

Adult↗

PubMed2003

Early characteristics of Sturge-Weber syndrome shown by perfusion MR imaging and proton MR spectroscopic imaging.

We report the case of a 9-month-old boy with Sturge-Weber syndrome and new onset of seizure. Perfusion MR imaging showed early changes compatible with impaired venous drainage in the affected hemisphere, whereas proton MR spectroscopic imaging revealed a focal parietal area of elevated choline without significant alteration of N-acetylaspartate levels. The perfusion and subtle metabolic abnormalities are comparable with the extent of the overlying leptomeningeal enhancement, illustrating the early pathophysiological manifestation of this disease.

Aspartic Acid↗

PubMed2002

Interactions between thalamic and cortical rhythms during semantic memory recall in human.

Human scalp electroencephalographic rhythms, indicative of cortical population synchrony, have long been posited to reflect cognitive processing. Although numerous studies employing simultaneous thalamic and cortical electrode recording in nonhuman animals have explored the role of the thalamus in the modulation of cortical rhythms, direct evidence for thalamocortical modulation in human has not, to our knowledge, been obtained. We simultaneously recorded from thalamic and scalp electrodes in one human during performance of a cognitive task and found a spatially widespread, phase-locked, low-frequency rhythm (7-8 Hz) power decrease at thalamus and scalp during semantic memory recall. This low-frequency rhythm power decrease was followed by a spatially specific, phase-locked, fast-rhythm (21-34 Hz) power increase at thalamus and occipital scalp. Such a pattern of thalamocortical activity reflects a plausible neural mechanism underlying semantic memory recall that may underlie other cognitive processes as well.

Brain Mapping↗