Biomedical subjects

J C Gore

Publications and source records attributed to J C Gore.

At least 37 records · Page 2Linked to original sources

PubMed2000

Regional brain volume abnormalities and long-term cognitive outcome in preterm infants.

CONTEXT: Preterm infants have a high prevalence of long-term cognitive and behavioral disturbances. However, it is not known whether the stresses associated with premature birth disrupt regionally specific brain maturation or whether abnormalities in brain structure contribute to cognitive deficits. OBJECTIVE: To determine whether regional brain volumes differ between term and preterm children and to examine the association of regional brain volumes in prematurely born children with long-term cognitive outcomes. DESIGN AND SETTING: Case-control study conducted in 1998 and 1999 at 2 US university medical schools. PARTICIPANTS: A consecutive sample of 25 eight-year-old preterm children recruited from a longitudinal follow-up study of preterm infants and 39 term control children who were recruited from the community and who were comparable with the preterm children in age, sex, maternal education, and minority status. MAIN OUTCOME MEASURES: Volumes of cortical subdivisions, ventricular system, cerebellum, basal ganglia, corpus callosum, amygdala, and hippocampus, derived from structural magnetic resonance imaging scans and compared between preterm and term children; correlations of regional brain volumes with cognitive measures (at age 8 years) and perinatal variables among preterm children. RESULTS: Regional cortical volumes were significantly smaller in the preterm children, most prominently in sensorimotor regions (difference: left, 14.6%; right, 14.3% [P<.001 for both]) but also in premotor (left, 11.2%; right, 12.6% [P<.001 for both]), midtemporal (left, 7.4% [P =.01]; right, 10.2% [P<.001]), parieto-occipital (left, 7.9% [P =.01]; right, 7.4% [P =.005]), and subgenual (left, 8.9% [P =.03]; right, 11.7% [P =.01]) cortices. Preterm children's brain volumes were significantly larger (by 105. 7%-271.6%) in the occipital and temporal horns of the ventricles (P<. 001 for all) and smaller in the cerebellum (6.7%; P =.02), basal ganglia (11.4%-13.8%; P</=.005), amygdala (left, 20.2% [P =.001]; right, 30.0% [P<.001]), hippocampus (left, 16.0% [P =.001]; right, 12.0% [P =.007]), and corpus callosum (13.1%-35.2%; P</=.01 for all). Volumes of sensorimotor and midtemporal cortices were associated positively with full-scale, verbal, and performance IQ scores (P<.01 for all). CONCLUSIONS: Our data indicate that preterm birth is associated with regionally specific, long-term reductions in brain volume and that morphological abnormalities are, in turn, associated with poorer cognitive outcome. JAMA. 2000;284:1939-1947.

Brain↗

PubMed2000

Network analysis of brain activations in working memory: behavior and age relationships.

Forty-six middle-aged female subjects were scanned using functional Magnetic Resonance Imaging (fMRI) during performance of three distinct stages of a working memory task-encoding, rehearsal, and recognition-for both printed pseudowords and visual forms. An expanse of areas, involving the inferior frontal, parietal, and extrastriate cortex, was active in response to stimuli during both the encoding and recognition periods. Additional increases during memory recognition were seen in right prefrontal regions, replicating a now-common finding [for reviews, see Fletcher et al. (1997) Trends Neurosci 20:213-218; MacLeod et al. (1998) NeuroImage 7:41-48], and broadly supporting the Hemispheric Encoding/Retrieval Asymmetry hypothesis [Tulving et al. (1994) Proc Natl Acad Sci USA 91:2016-2020]. Notably, this asymmetry was not qualified by the type of material being processed. A few sites demonstrated higher activity levels during the rehearsal period, in the absence of any new stimuli, including the medial extrastriate, precuneus, and the medial temporal lobe. Further analyses examined relationships among subjects' brain activations, age, and behavioral scores on working memory tests, acquired outside the scanner. Correlations between brain scores and behavior scores indicated that activations in a number of areas, mainly frontal, were associated with performance. A multivariate analysis, Partial Least Squares [McIntosh et al. (1996) NeuroImage 3:143-157, (1997) Hum Brain Map 5:323-327], was then used to extract component effects from this large set of univariate correlations. Results indicated that better memory performance outside the scanner was associated with higher activity at specific sites within the frontal and, additionally, the medial temporal lobes. Analysis of age effects revealed that younger subjects tended to activate more than older subjects in areas of extrastriate cortex, medial frontal cortex, and the right medial temporal lobe; older subjects tended to activate more than younger subjects in the insular cortex, right inferior temporal lobe, and right inferior frontal gyrus. These results extend recent reports indicating that these regions are specifically involved in the memory impairments seen with aging.

Adult↗

PubMed2000

Functional neuroanatomy of executive processes involved in dual-task performance.

The subjective experience of allocating one's attentional resources among competing tasks is nearly universal, and most current models of cognition include a mechanism that performs this allocation; examples include the central executive system and the supervisory attentional system. Yet, the exact form that an executive system might take and even its necessity for cognition are controversial. Dual-task paradigms have commonly been used to investigate executive function. The few neuroimaging studies of these paradigms have yielded contradictory findings. Using functional MRI, we imaged brain function during two dual-task paradigms, each with a common auditory component task (NOUN task) but varying with respect to a visual component task (SPACE or FACE tasks). In each of the two dual-task paradigms, the results showed that the activated areas varied with the component tasks, that all of the areas activated during dual task performance were also activated during the component tasks, and that surplus activation within activated areas during DUAL conditions was parsimoniously accounted for by the addition of the second task. These findings suggest that executive processes may be mediated by interactions between anatomically and functionally distinct systems engaged in performance of component tasks, as opposed to an area or areas dedicated to a generic executive system.

Brain↗

PubMed2000

Abnormal ventral temporal cortical activity during face discrimination among individuals with autism and Asperger syndrome.

BACKGROUND: Recognition of individual faces is an integral part of both interpersonal interactions and successful functioning within a social group. Therefore, it is of considerable interest that individuals with autism and related conditions have selective deficits in face recognition (sparing nonface object recognition). METHOD: We used functional magnetic resonance imaging (fMRI) to study face and subordinate-level object perception in 14 high-functioning individuals with autism or Asperger syndrome (the autism group), in comparison with 2 groups of matched normal controls (normal control group ] [NC1] and normal control group 2 [NC2]) (n = 14 for each). Regions of interest (ROIs) were defined in NC1 and then applied in comparisons between NC2 and the autism group. Regions of interest were also defined in NC2 and then applied to comparisons between NC1 and the autism group as a replication study. RESULTS: In the first set of comparisons, we found significant task x group interactions for the size of activation in the right fusiform gyrus (FG) and right inferior temporal gyri (ITG). Post hoc analyses showed that during face (but not object) discrimination, the autism group had significantly greater activation than controls in the right ITG and less activation of the right FG. The replication study showed again that the autism group used the ITG significantly more for processing faces than the control groups, but for these analyses, the effect was now on the left side. Greater ITG activation was the pattern found in both control groups during object processing. CONCLUSIONS: Individuals with autism spectrum disorders demonstrate a pattern of brain activity during face discrimination that is consistent with feature-based strategies that are more typical of nonface object perception.

Adult↗

PubMed2000

Preliminary findings of antistreptococcal antibody titers and basal ganglia volumes in tic, obsessive-compulsive, and attention deficit/hyperactivity disorders.

BACKGROUND: Previous studies have provided preliminary serological evidence supporting the theory that symptoms of tic disorders or obsessive-compulsive disorder (OCD) may be sequelae of prior streptococcal infection. It is unclear, however, whether previously reported associations with streptococcal infection were obscured by the presence of diagnostic comorbidities. It is also unknown whether streptococcal infection is associated in vivo with anatomical alterations of the brain structures that have been implicated in the pathophysiology of these disorders. METHODS: Antistreptococcal antibody titers were measured in 105 people diagnosed as having CTD, OCD, or attention-deficit/hyperactivity disorder (ADHD) and in 37 community controls without a disorder. Subjects were unselected with regard to their history of streptococcal exposure. Basal ganglia volumes were measured in 113 of these subjects (79 patients and 34 controls). RESULTS: A DSM-IV diagnosis of ADHD was associated significantly with titers of 2 distinct antistreptococcal antibodies, antistreptolysin O and anti-deoxyribonuclease B. These associations remained significant after controlling for the effects of CTD and OCD comorbidity. No significant association was seen between antibody titers and a diagnosis of either CTD or OCD. When basal ganglia volumes were included in these analyses, the relationships between antibody titers and basal ganglia volumes were significantly different in OCD and ADHD subjects compared with other diagnostic groups. Higher antibody titers in these subjects were associated with larger volumes of the putamen and globus pallidus nuclei. CONCLUSIONS: These findings suggest that the prior reports of an association between antistreptococcal antibodies and either CTD or OCD may have been confounded by the presence of ADHD. They also support the hypothesis that in susceptible persons who have ADHD or OCD, chronic or recurrent streptococcal infections are associated with structural alterations in basal ganglia nuclei.

Adult↗

PubMed2000

Complications of nonlinear echo time spacing for measurement of T (2).

Some consequences of using nonlinear echo spacing in multi-echo sequences for measuring T(2) were investigated under the conditions of imperfect RF refocusing or diffusion losses. Although using nonlinear echo spacing has previously been shown to estimate T(2) more accurately, the effect of such spacing is shown to be detrimental when sequences use imperfect RF refocusing pulses. The progressive loss of transverse magnetization that results from imperfect refocusing will alter estimates of T(2) regardless of the echo spacing. However, when the echo spacing is nonlinear, this loss of magnetization also introduces non-mono-exponential T(2) components. Such an effect may distort relative amplitudes of a multi-component T(2) distribution or generate multiple T(2) components where they do not exist. Diffusion through inhomogeneous magnetic fields results in a similar loss of magnetization and T(2) distortion. For these reasons, the use of nonlinearly spaced echoes, while providing in theory a more appropriate sampling of transverse relaxation, is not appropriate for many imaging situations.

Diffusion↗

PubMed2000

Compartmental study of diffusion and relaxation measured in vivo in normal and ischemic rat brain and trigeminal nerve.

The correlation between the apparent diffusion coefficient (ADC) and T(2) of water in rat brain and trigeminal nerve was investigated using a hybrid diffusion-weighted-CPMG imaging sequence. Little dependence of ADC on T(2) was found in brain regions of interest, which is postulated to be due to rapid exchange between intra- and extracellular water. Conversely, the ADC of water in trigeminal nerve was found to change significantly with echo time (TE). Parallel to the nerve and with a constant diffusion time (t(diff) = 10.8 ms), the ADC increased by approximately 30% between TEs of 25 ms and 185 ms; perpendicular to the nerve, the ADC decreased by a similar amount over the same range of TE. Measurements made following the onset of global ischemia yielded lower ADCs, with similar dependence on TE. Observations that transverse relaxation of water in nerves is multiexponential have previously been interpreted in terms of microanatomical compartments in slow exchange. In the context of this interpretation, our data suggest that diffusional anisotropy is greater outside than within the myelinated axons. Further, data following the onset of global ischemia suggest that the mechanism(s) by which ADC is reduced affect most or all microanatomical environments of nerve, at least insofar as they are represented over the TE domain investigated. Magn Reson Med 43:837-844, 2000.

Animals↗

PubMed2000

Intravascular susceptibility agent effects on tissue transverse relaxation rates in vivo.

Since vascular architecture differs among tissues, it was hypothesized that the change in transverse relaxation rate produced by a given tissue concentration of susceptibility contrast agent also varies by tissue. This is relevant to strategies to map regional blood volume by MRI using indicator dilution techniques. R*(2) was measured in rat organs over a range of susceptibility agent concentrations at 1.5 T. Rat red blood cells loaded with dysprosium-DTPA-BMA served as an intravascular susceptibility agent. Tissue samples were frozen in vivo and dysprosium concentrations were independently measured using inductively coupled plasma atomic emission spectroscopy. The slope (k) of R*(2) vs. tissue dysprosium concentration in sec(-1) mM(-1) for myocardium was 97.1 (95% C.I. 77. 0-117.2), liver 122.6 (108.3-136.9), spleen 22.5 (8.8-36.3), kidney 68.1 (58.6-77.6), and skeletal muscle 77.9 (4.1-151.6); k was significantly different (P < 0.05) for all pairings except those with skeletal muscle. Therefore, relative values of tissue blood volume derived from dynamic images of first pass contrast effects may be in error because k is not constant for different conditions.

Acetylcysteine↗

PubMed2000

Rapid acquisition transverse relaxometric imaging.

Segmented echo-planar acquisitions have been incorporated into a multiecho imaging sequence to produce a MRI method for rapid transverse relaxometry. The method is demonstrated on gel phantoms and rat brain and found to produce unbiased estimates of T(2). Gradient performance can be a limiting factor for the implementation of this technique and there is a cost in signal-to-noise ratio resulting from the higher bandwidth required, as is typical for echo-planar acquisitions.

Animals↗

PubMed2000

Measurements of restricted diffusion using an oscillating gradient spin-echo sequence.

An oscillating gradient spin-echo (OGSE) pulse sequence was used to measure the apparent diffusion coefficient (D(app)) of water in the short diffusion time regime in the presence of restrictions. The diffusion coefficients of water in a simple water sample and a water and oil mixture were measured to be the same for different periods of the gradient oscillation, as expected when there are no restriction effects. The D(app) of water in the spaces between closely packed beads was also measured as a function of the gradient oscillation periods in the range 11 to 80 ms. The D(app) of water in restricted systems varies with the period of the gradient oscillation and the dispersion depends on the scale of the restriction. For a sample of packed beads of diameter 9.1 +/- 0.7 microm, the pore surface-to-volume ratio was estimated experimentally by this method to be 1.3 +/- 0.1 microm(-1), corresponding to a mean pore diameter of 6.4 +/- 0.7 microm. A Monte Carlo computer simulation of the NMR OGSE signal from the spins diffusing in a system of compartments was also implemented and the D(app) demonstrated similar behavior with gradient oscillation periods.

Computer Simulation↗

PubMed2000

Event-related fMRI of auditory and visual oddball tasks.

Functional magnetic resonance imaging (fMRI) was used to investigate the spatial distribution of cortical activation in frontal and parietal lobes during auditory and visual oddball tasks in 10 healthy subjects. The purpose of the study was to compare activation within auditory and visual modalities and identify common patterns of activation across these modalities. Each subject was scanned eight times, four times each for the auditory and visual conditions. The tasks consisted of a series of trials presented every 1500 ms of which 4-6% were target trials. Subjects kept a silent count of the number of targets detected during each scan. The data were analyzed by correlating the fMRI signal response of each pixel to a reference hemodynamic response function that modeled expected responses to each target stimulus. The auditory and visual targets produced target-related activation in frontal and parietal cortices with high spatial overlap particularly in the middle frontal gyrus and in the anterior cingulate. Similar convergence zones were detected in parietal cortex. Temporal differences were detected in the onset of the activation in frontal and parietal areas with an earlier onset in parietal areas than in the middle frontal areas. Based on consistent findings with previous event-related oddball tasks, the high degree of spatial overlap in frontal and parietal areas appears to be due to modality independent or amodal processes related to procedural aspects of the tasks that may involve memory updating and non-specific response organization.

Acoustic Stimulation↗

PubMed2000

Effects of cell volume fraction changes on apparent diffusion in human cells.

Diffusion-weighted imaging was used to study the relationship between apparent diffusion coefficient (ADC) and cell volume fraction in cell suspensions and packed arrays. Cell volume fraction was varied by changing extracellular fluid osmolarity (for human glial cells) and by changing cell density (for human glial and red blood cells). In packed arrays of glial cells, ADC increased 10% when cells shrank and decreased 13% when cells swelled. ADC decreased 34% as cell density increased from 0 to 72%. In erythrocyte suspensions, ADC decreased 90% as the cell density increased from 0 to 89%. These results agree with theoretical predictions.

Adult↗

PubMed2000

Neural correlates of the attentional blink.

Attending to a visual event can lead to functional blindness for other events in the visual field. This limit in our attentional capacities is exemplified by the attentional blink (AB), which refers to the transient but severe impairment in perceiving the second of two temporally neighboring targets. Using functional magnetic resonance imaging (fMRI), we observed predominantly right intraparietal and frontal cortex activations associated with the AB. We further demonstrate that an AB can be elicited by both temporal and spatial distractor interference on an attended target and that both of these interference mechanisms activate the same neural circuit. These results suggest that a (right) parietofrontal network previously implicated in attentional control and enhancement is also a locus of capacity-limited processing of visual information.

Adult↗

PubMed2000

A stimulus-driven approach to object identity and location processing in the human brain.

The primate visual system is considered to be segregated into ventral and dorsal streams specialized for processing object identity and location, respectively. We reexamined the dorsal/ventral model using a stimulus-driven approach to object identity and location processing. While looking at repeated presentations of a standard object at a standard location, subjects monitored for any infrequent "oddball" changes in object identity, location, or identity and location (conjunction). While the identity and location oddballs preferentially activated ventral and dorsal brain regions respectively, each oddball type activated both pathways. Furthermore, all oddball types recruited the lateral temporal cortex and the temporo-parietal junction. These findings suggest that a strict dorsal/ventral dual-stream model does not fully account for the perception of novel objects in space.

Attention↗

PubMed2000

Expertise for cars and birds recruits brain areas involved in face recognition.

Expertise with unfamiliar objects ('greebles') recruits face-selective areas in the fusiform gyrus (FFA) and occipital lobe (OFA). Here we extend this finding to other homogeneous categories. Bird and car experts were tested with functional magnetic resonance imaging during tasks with faces, familiar objects, cars and birds. Homogeneous categories activated the FFA more than familiar objects. Moreover, the right FFA and OFA showed significant expertise effects. An independent behavioral test of expertise predicted relative activation in the right FFA for birds versus cars within each group. The results suggest that level of categorization and expertise, rather than superficial properties of objects, determine the specialization of the FFA.

Adult↗

PubMed2000

A model for susceptibility artefacts from respiration in functional echo-planar magnetic resonance imaging.

Respiration causes variations in the signals acquired during magnetic resonance imaging (MRI) and therefore is a significant source of noise in functional brain imaging. A primary component of respiratory noise may arise from variations of bulk susceptibility or air volume in the chest. Here we investigate the nature of the image artefacts that can be caused by such changes. We develop a simple model which attempts to mimic the effects of variations in susceptibility and volume during respiration. Theoretical calculations, computer simulations and imaging experiments with this model show that small variations in susceptibility within the thorax from alterations in the paramagnetism of cavity gas may lead to a shift of the image on the order of 0.1 pixels as well as a shading of the intensity by +/-1%. These effects are observed to be predominant in the phase-encoding direction. They may lead to the production of spurious activations in functional MRI and are likely to be of more importance at higher field strengths.

Algorithms↗

PubMed2000

An event-related functional MRI study of the stroop color word interference task.

In this study we have attempted to define the neural circuits differentially activated by cognitive interference. We used event-related functional magnetic resonance imaging (fMRI) to identify areas of the brain that are activated by the Stroop word-color task in two experiments. In the first experiment, we used infrequent, incongruent colored word stimuli to elicit strong Stroop interference (the 'conventional Stroop' paradigm). In the second experiment, we used infrequent, congruent colored words (the 'inverse Stroop' paradigm) to confirm that the regions identified in the first experiment were in fact specifically related to the Stroop effect and not to nonspecific oddball effects associated with the use of infrequent stimuli. Performance of the conventional Stroop specifically activated the anterior cingulate, insula, premotor and inferior frontal regions. These activated regions in the current experiment are consistent with those activated in fMRI experiments that use a more traditional block design. Finally, analysis of the time course of fMRI signal changes demonstrated differential onset and offset of signal changes in these activated regions. The time course results suggest that the action of various brain areas can be temporally dissociated.

Adult↗

PubMed2000

Effects of hypoglycemia on functional magnetic resonance imaging response to median nerve stimulation in the rat brain.

The authors studied the effects of a standardized mild-moderate hypoglycemic stimulus (glucose clamp) on brain functional magnetic resonance imaging (fMRI) responses to median nerve stimulation in anesthetized rats. In the baseline period (plasma glucose 6.6 +/- 0.3 mmol/L), the MR signal changes induced by median nerve activation were determined within a fixed region of the somatosensory cortex from preinfusion activation maps. Subsequently, insulin and a variable glucose infusion were administered to decrease plasma glucose. The goal was to produce a stable hypoglycemic plateau (2.8 +/- 0.2 mmol/L) for 30 minutes. Thereafter, plasma glucose was restored to euglycemic levels (6.0 +/- 0.3 mmol/L). In the early phase of insulin infusion (15 to 30 minutes), before hypoglycemia was reached (4.7 +/- 0.3 mmol/L), the activation signal was unchanged. However, once the hypoglycemic plateau was achieved, the activation signal was significantly decreased to 57 +/- 6% of the preinfusion value. Control regions in the brain that were not activated showed no significant changes in MR signal intensity. Upon return to euglycemia, the activation signal change increased to within 10% of the original level. No significant activation changes were noted during euglycemic hyperinsulinemic clamp experiments. The authors concluded that fMRI can detect alterations in cerebral function because of insulin-induced hypoglycemia. The signal changes observed in fMRI activation experiments were sensitive to blood glucose levels and might reflect increases in brain metabolism that are limited by substrate deprivation during hypoglycemia.

Animals↗