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Biomedical subjects

John C Gore

Publications and source records attributed to John C Gore.

At least 19 recordsLinked to original sources
PubMed2003

Neural systems for compensation and persistence: young adult outcome of childhood reading disability.

BACKGROUND: This study examined whether and how two groups of young adults who were poor readers as children (a relatively compensated group and a group with persistent reading difficulties) differed from nonimpaired readers and if there were any factors distinguishing the compensated from persistently poor readers that might account for their different outcomes. METHODS: Using functional magnetic resonance imaging, we studied three groups of young adults, ages 18.5-22.5 years, as they read pseudowords and real words: 1) persistently poor readers (PPR; n = 24); 2) accuracy improved (compensated) readers (AIR; n = 19); and 3) nonimpaired readers (NI, n = 27). RESULTS: Compensated readers, who are accurate but not fluent, demonstrate a relative underactivation in posterior neural systems for reading located in left parietotemporal and occipitotemporal regions. Persistently poor readers, who are both not fluent and less accurate, activate posterior reading systems but engage them differently from nonimpaired readers, appearing to rely more on memory-based rather than analytic word identification strategies. CONCLUSIONS: These findings of divergent neural outcomes as young adults are both new and unexpected and suggest a neural basis for reading outcomes of compensation and persistence in adults with childhood dyslexia.

Adult↗
PubMed2003

Cluster analysis of muscle functional MRI data.

Muscle functional magnetic resonance imaging (mfMRI) is frequently used to determine spatial patterns of muscle involvement in exercising humans. A frequent finding in mfMRI is that, even within synergistic muscle groups, signal intensity (SI) data from individual voxels can be quite heterogeneous. The purpose of this study was to develop a novel method for organizing heterogeneous mfMRI data into clusters whose members behave similarly to each other but distinctly from members of other clusters and apply it in studies of functional compartmentalization in the anterior compartment of the leg. An algorithm was developed that compared the SI time courses of adjacent voxels and grouped together voxels that were sufficiently similar. The algorithm's performance was verified by using simulated data sets with known regional differences in SI time courses that were then applied to experimental mfMRI data acquired from six male subjects (age 22.6 +/- 0.9 yr, mean +/- SE) who sustained isometric contractions of the dorsiflexors at 40% of maximum voluntary contraction. The experimental data were also characterized by using a traditional analysis (user-specified regions of interest from a single image), in which the relative change in SI and the contrast-to-noise ratio [CNR; 100%x(SI(RESTING) - SI(ACTIVE)/(noise standard deviation)] were measured. In general, clusters were found in areas in which the CNR exceeded 5. Cluster analysis made functional distinctions between regions of muscle that were not seen with traditional analysis. In conclusion, cluster analysis's use of the full SI time course provides more sensitivity to muscle functional compartmentation than traditional analysis.

Adult↗
PubMed2003

A functional magnetic resonance imaging study of bipolar disorder: state- and trait-related dysfunction in ventral prefrontal cortices.

BACKGROUND: Abnormalities in prefrontal and anterior cingulate cortices are implicated in disturbances of attention, cognition, and impulse regulation in bipolar disorder. Acute episodes have been associated with dysfunction in these brain regions, and more enduring trait-related dysfunction has been implicated by volumetric and cellular abnormalities in these regions. The relative contributions of prefrontal regions to state and trait disturbances in bipolar disorder, however, have not been defined. We sought to characterize state- and trait-related functional impairment in frontal systems in bipolar disorder. METHODS: Thirty-six individuals with bipolar disorder I (11 with elevated, 10 with depressed, and 15 with euthymic mood states) and 20 healthy control subjects matched for handedness and sex participated in an event-related functional magnetic resonance imaging study of the color-word Stroop to determine mean percentage of regional task-related signal change. RESULTS: Signal increased during the Stroop task similarly across diagnostic groups in a distribution that included dorsal anterior cingulate and prefrontal cortices, consistent with previously reported activations in this task. Signal changes associated with specific mood states in bipolar disorder were detected in ventral prefrontal cortex, with a blunted increase in signal on the right side in the elevated mood group (P =.005) and an exaggerated increase in signal on the left side in the depressed group (P =.02) compared with the euthymic group. Patients (vs healthy controls) demonstrated blunted activation in a spatially distinct, rostral region of left ventral prefrontal cortex that was independent of mood state (P<.005). CONCLUSIONS: Bipolar disorder is associated with a trait abnormality in left ventral prefrontal cortex. Additional ventral prefrontal abnormalities may be associated with specific acute mood states. The hemispheric laterality of the abnormality and the directions of signal change may relate to the valence of the mood episode.

Adult↗
PubMed2003

Gambling urges in pathological gambling: a functional magnetic resonance imaging study.

BACKGROUND: Gambling urges in pathological gambling (PG) often immediately precede engagement in self-destructive gambling behavior. An improved understanding of the neural correlates of gambling urges in PG would advance our understanding of the brain mechanisms underlying PG and would help direct research into effective treatments. METHODS: Echoplanar functional magnetic resonance imaging was used to assess brain function during viewing of videotaped scenarios with gambling, happy, or sad content. Participants rated the quality and magnitude of their emotional and motivational responses. RESULTS: Men with PG (n = 10) reported mean +/- SD greater gambling urges after viewing gambling scenarios vs control subjects (n = 11) (5.20 +/- 3.43 vs 0.32 +/- 0.60; chi21,19 = 21.71; P<.001). The groups did not differ significantly in their subjective responses to the happy (P =.56) or sad (P =.81) videotapes. The most pronounced between-group differences in neural activities were observed during the initial period of viewing of the gambling scenarios: PG subjects displayed relatively decreased activity in frontal and orbitofrontal cortex, caudate/basal ganglia, and thalamus compared with controls. Distinct patterns of regional brain activity were observed in specific temporal epochs of videotape viewing. For example, differences localized to the ventral anterior cingulate during the final period of gambling videotape viewing, corresponding to the presentation of the most provocative gambling stimuli. Although group differences in brain activity were observed during viewing of the sad and happy scenarios, they were distinct from those corresponding to the gambling scenarios. CONCLUSIONS: In men with PG, gambling cue presentation elicits gambling urges and leads to a temporally dynamic pattern of brain activity changes in frontal, paralimbic, and limbic brain structures. When viewing gambling cues, PG subjects demonstrate relatively decreased activity in brain regions implicated in impulse regulation compared with controls.

Adolescent↗
PubMed2003

Oscillating gradient measurements of water diffusion in normal and globally ischemic rat brain.

Oscillating gradients were used to probe the diffusion-time/frequency dependence of water diffusion in the gray matter of normal and globally ischemic rat brain. In terms of a conventional definition of diffusion time, the oscillating gradient measurements provided the apparent diffusion coefficient (ADC) of water with diffusion times between 9.75 ms and 375 micros, an order of magnitude shorter than previously studied in vivo. Over this range, ADCs increased as much as 24% in vivo and 50% postmortem, depending on the nature of the oscillating gradient waveform used. Novel waveforms were employed to sample narrow frequency bands of the so-called diffusion spectrum. This spectral description of ADC includes the effects of restriction and/or flow, and is independent of experimental parameters, such as diffusion time. The results in rat brain were found to be consistent with restricted diffusion and the known micro-anatomy of gray matter. Differences between normal and postmortem data were consistent with an increase in water restriction and/or a decrease in flow, and tentatively suggest that physical changes following the onset of ischemia occur on a scale of about 2 microm, similar to a typical cellular dimension in gray matter.

Animals↗
PubMed2003

Quantitative imaging of magnetization transfer using an inversion recovery sequence.

A new imaging method has been developed for quantitatively measuring magnetization transfer (MT). It uses a simple inversion recovery sequence, although one with very short (milliseconds) inversion times, and thus can be implemented on clinical imaging systems with little modification to existing pulse sequences. The sequence requires an inversion pulse with a length much longer than T(2m) (typically 10 micros) and much shorter than T(2f) (typically tens of ms) and 1/k(mf) (typically tens of ms), where T(2m) and T(2f) are the transverse relaxation times of the immobile macromolecular and free water protons, respectively, and k(mf) is the rate of MT between these populations. The resultant NMR signal is sensitive to MT when this inversion pulse affects the mobile and immobile proton pools to different degrees and by appropriate analysis of the signals obtained for different inversion times, quantitative information can be derived on the macromolecular content and exchange rates within the sample. The method has been used in conjunction with echo planar imaging to produce maps of the spatial distribution of the macromolecular content and MT rate in cross-linked bovine serum albumin. Comparisons between this method and other quantitative MT techniques are discussed.

Echo-Planar Imaging↗
PubMed2003

Classification and quantification of neuronal fiber pathways using diffusion tensor MRI.

Quantitative characterization of neuronal fiber pathways in vivo is of significant neurological and clinical interest. Using the capability of MR diffusion tensor imaging to determine the local orientations of neuronal fibers, novel algorithms were developed to bundle neuronal fiber pathways reconstructed in vivo with diffusion tensor images and to quantify various physical and geometric properties of fiber bundles. The reliability of the algorithms was examined with reproducibility tests. Illustrative results show that consistent physical and geometric measurements of novel properties of neuronal tissue can be obtained, which offer considerable potential for the quantitative study of fiber pathways in vivo.

Algorithms↗
PubMed2003

Frontostriatal abnormalities in adolescents with bipolar disorder: preliminary observations from functional MRI.

OBJECTIVE: This study investigated whether the functional abnormalities in prefrontal systems observed in adult bipolar disorder are manifested in adolescents with this illness. METHOD: Ten adolescents with bipolar disorder and 10 healthy comparison subjects participated in a color-naming Stroop task during event-related functional magnetic resonance imaging. RESULTS: Signal increases in the left putamen and thalamus were significantly greater in the bipolar disorder group than in the healthy group. Age correlated positively with signal increases in the bilateral rostroventral prefrontal cortex and the striatum in the healthy group but not in the bipolar disorder group. In the bipolar disorder subjects, depressive symptoms correlated positively with signal increases in the ventral striatum. CONCLUSIONS: These findings suggest the presence of dysfunction in the subcortical portions of the frontostriatal circuits in adolescents with bipolar disorder. The absence of the prefrontal abnormalities that were observed previously in adults and the absence of the age-related increases in prefrontal activity observed in normal comparison subjects suggest that a developmental disturbance in prefrontal function may emerge in bipolar disorder over the course of adolescence.

Adolescent↗
PubMed2003

Regional brain volumes and their later neurodevelopmental correlates in term and preterm infants.

OBJECTIVE: To compare regional brain volumes measured in term and preterm infants, and to correlate regional volumes with measures of neurodevelopmental outcome. METHODS: High-contrast, high-resolution magnetic resonance imaging scans were acquired in 10 preterm and 14 term infants who were scanned near term. The cerebrum was segmented into cortical gray matter, white matter, cerebral ventricles, subcortical gray matter, cerebellum, and brainstem. The cortical gray matter, white matter, and ventricles were further divided into specific anatomic subregions, and the volumes were compared across groups. Measures of cognitive and motor development were acquired between 18 and 20 months of corrected age. Correlations of regional brain volumes with developmental outcome were assessed in the preterm group. RESULTS: Volumes in preterm infants were reduced in parieto-occipital gray matter and increased in the midbody, occipital horn, and temporal horns of the lateral ventricles. Gray matter volumes were also less prominently reduced in the sensorimotor and inferior occipital cortices. Normal lateralization of white matter volumes were altered in the parieto-occipital region in the preterm infants, who had significantly larger left-sided and smaller right-sided structures. White matter volumes in the sensorimotor and midtemporal regions correlated strongly with measures of neurodevelopmental outcome. CONCLUSIONS: These findings of reduced volumes in sensorimotor and parieto-occipital regions in preterm infants, and the prospective correlations of regional volumes with cognitive outcome, confirm and extend findings previously reported in a cross-sectional study of 8-year-old prematurely born children. The data suggest that regional brain volumes near term are a promising marker for predicting disturbances of cognitive outcome in preterm infants. Further prospective, longitudinal studies of neonatal brain volumes and developmental indices into later childhood are required to confirm the utility of regional brain volumes as predictors of longer term outcome.

Anatomy, Cross-Sectional↗
PubMed2003

Quantity determination and the distance effect with letters, numbers, and shapes: a functional MR imaging study of number processing.

BACKGROUND AND PURPOSE: The ability to quantify, or to determine magnitude, is an important part of number processing, and the extent to which language and other cognitive abilities are involved with number processing is an area of interest. We compared activation patterns, reaction times, and accuracy as subjects determined stimulus magnitude by ordering letters, numbers, and shapes. A second goal was to define the brain regions involved in the distance effect (the farther apart numbers are, the faster subjects are at judging which number is larger) and whether this effect depended on stimulus type. METHODS: Functional MR images were acquired in 19 healthy subjects. The order task required the subjects to judge whether three stimuli were in order according to their position in the alphabet (letters), position in the number line (numbers), or size (shapes). In the control (identify task), subjects judged whether one of the three stimuli was a particular letter, number, or shape. Each stimulus type was divided into near trials (quantity difference of three or less) and far trials (quantity difference of at least five) to assess the distance effect. RESULTS: Subjects were less accurate and slower with letters than with numbers and shapes. A distance effect was present with shapes and numbers, as subjects ordered the near trials slower than far trials. No distance effect was detected with letters. The occipital lobes and intraparietal sulci were active with all three stimuli. Shapes required no additional areas, although analysis of the distance effect revealed that near shapes involved other brain regions, including the frontal lobes. Letters activated a large network comprising the frontal lobes, the anterior cingulate gyrus, and basal ganglia, but few additional areas were engaged by the distance effect. Numbers involved a smaller network including the inferior and middle frontal gyri. The left supramarginal gyrus and both inferior frontal gyri were active in the distance effect with numbers. CONCLUSION: Numbers and letters, which are stimuli more associated with abstract symbolism compared with shapes, resulted in slower reaction times and an increased number of active brain regions. Shapes and numbers, but not letters, elicited a distance effect, indicating access to a mental continuum of quantity. The left supramarginal gyrus and both inferior frontal gyri were involved in the distance effect with numbers. The intraparietal sulci were important in determining stimulus magnitude for all stimuli.

Adult↗
PubMed2002

The role of the parietal cortex in visual feature binding.

When multiple objects are simultaneously present in a scene, the visual system must properly integrate the features associated with each object. It has been proposed that this "binding problem" is solved by selective attention to the locations of the objects [Treisman, A.M. & Gelade, E. (1980) Cogn. Psychol. 12, 97-136]. If spatial attention plays a role in feature integration, it should do so primarily when object location can serve as a binding cue. Using functional MRI (fMRI), we show that regions of the parietal cortex involved in spatial attention are more engaged in feature conjunction tasks than in single feature tasks when multiple objects are shown simultaneously at different locations but not when they are shown sequentially at the same location. These findings suggest that the spatial attention network of the parietal cortex is involved in feature binding but only when spatial information is available to resolve ambiguities about the relationships between object features.

Adult↗
PubMed2002

Disruption of posterior brain systems for reading in children with developmental dyslexia.

BACKGROUND: Converging evidence indicates a functional disruption in the neural systems for reading in adults with dyslexia. We examined brain activation patterns in dyslexic and nonimpaired children during pseudoword and real-word reading tasks that required phonologic analysis (i.e., tapped the problems experienced by dyslexic children in sounding out words). METHODS: We used functional magnetic resonance imaging (fMRI) to study 144 right-handed children, 70 dyslexic readers, and 74 nonimpaired readers as they read pseudowords and real words. RESULTS: Children with dyslexia demonstrated a disruption in neural systems for reading involving posterior brain regions, including parietotemporal sites and sites in the occipitotemporal area. Reading skill was positively correlated with the magnitude of activation in the left occipitotemporal region. Activation in the left and right inferior frontal gyri was greater in older compared with younger dyslexic children. CONCLUSIONS: These findings provide neurobiological evidence of an underlying disruption in the neural systems for reading in children with dyslexia and indicate that it is evident at a young age. The locus of the disruption places childhood dyslexia within the same neurobiological framework as dyslexia, and acquired alexia, occurring in adults.

Adolescent↗
PubMed2002

BOLD activity during mental rotation and viewpoint-dependent object recognition.

We measured brain activity during mental rotation and object recognition with objects rotated around three different axes. Activity in the superior parietal lobe (SPL) increased proportionally to viewpoint disparity during mental rotation, but not during object recognition. In contrast, the fusiform gyrus was preferentially recruited in a viewpoint-dependent manner in recognition as compared to mental rotation. In addition, independent of the effect of viewpoint, object recognition was associated with ventral areas and mental rotation with dorsal areas. These results indicate that the similar behavioral effects of viewpoint obtained in these two tasks are based on different neural substrates. Such findings call into question the hypothesis that mental rotation is used to compensate for changes in viewpoint during object recognition.

Analysis of Variance↗
PubMed2002

Detection of functional connectivity using temporal correlations in MR images.

Functional connectivity among brain regions has been investigated via an analysis of correlations between regional signal fluctuations recorded in magnetic resonance (MR) images obtained in a steady state. In comparison with studies of functional connectivity that utilize task manipulations, the analysis of correlations in steady state data is less susceptible to confounds arising when functionally unrelated brain regions respond in similar ways to changes in task. A new approach to identifying interregional correlations in steady state data makes use of two independent data sets. Regions of interest (ROIs) are defined and hypotheses regarding their connectivity are generated in one data set. The connectivity hypotheses are then evaluated in the remaining (independent) data set by analyzing low frequency temporal correlations between regions. The roles of the two data sets are then reversed and the process repeated, perhaps multiple times. This method was illustrated by application to the language system. The existence of a functional connection between Broca's area and Wernicke's area was confirmed in healthy subjects at rest. An increase in this functional connection when the language system was actively engaged (when subjects were continuously listening to narrative text) was also confirmed. In a second iteration of analyses, a correlation between Broca's area and a region in left premotor cortex was found to be significant at rest and to increase during continuous listening. These findings suggest that the proposed methodology can reveal the presence and strength of functional connections in high-level cognitive systems.

Adult↗
PubMed2002

Compartmental study of T(1) and T(2) in rat brain and trigeminal nerve in vivo.

The integrated T(1)-T(2) characteristics of rat brain and trigeminal nerve water were studied in vivo using a rapid method for acquiring a series of images that depend on T(1) and T(2) relaxation times. Gray matter regions showed only one signal component in both the T(1) and T(2) domains. Trigeminal nerve, however, which has been shown previously to exhibit three T(2) components, was found to also exhibit three T(1) components. The correlations between these T(1) and T(2) components were demonstrated by uniquely filtering out each of the three T(2) components using an inversion-recovery preparation, as determined by the component T(1) values. Based on previous works, it is postulated that each of these three signal components is derived from a unique microanatomical region of the nerve. Knowledge of these T(1) components may thus prove valuable in devising novel methods of identifying the presence and quantifying the volume of tissue subtypes such as myelin.

Animals↗
PubMed2002

Validation of diffusion tensor MRI-based muscle fiber tracking.

Diffusion-tensor (DT) MRI fiber tracking may potentially be used for in vivo structural analysis. The purpose of this study was to assess quantitatively the ability of a DT-MRI fiber-tracking algorithm to measure the fiber orientation (pennation) in skeletal muscle in vivo. In five adult Sprague-Dawley rats, the pennation angle (theta) was measured in the rat lateral gastrocnemius with DT-MRI (theta(DT-MRI)) and by direct anatomical inspection (DAI) (theta(DAI)). The mean theta(DT-MRI) was not significantly different from the mean theta(DAI). In addition, the two methods were highly correlated (r = 0.89) and the regression of theta(DT-MRI) on theta(DAI) resulted in a slope not significantly different from 1 and an intercept not significantly different from zero. These data indicate that DT-MRI-based fiber tracking as implemented here is a valid tool for in vivo structural analysis of small-animal skeletal muscle.

Animals↗
PubMed2002

Changes in CBF-BOLD coupling detected by MRI during and after repeated transient hypercapnia in rat.

The effect of hypercapnia on the cerebral metabolic rate of oxygen consumption (CMRO(2)) remains incompletely understood. This study examined the relationship between susceptibility (blood oxygenation level dependent (BOLD)) and perfusion-weighted (flow-sensitive alternating inversion recovery (FAIR)) MRI techniques both during induction of repeated transient hypercapnia (THC) and after return to normocapnia during whisker barrel functional activation. During induction of THC the FAIR signal became significantly elevated over control after 100 s of hypercapnia (P = 0.039), with a trend of increasing significance to 5 min (P = 0.000008). The FAIR signal in the activated cortex during subsequent normocapnia was significantly increased compared to pre-THC control after each successive period of THC. The mean grouped FAIR signal increased by 81% +/- 63% after one exposure (P = 0.021), by 163% +/- 55% after the second exposure (P = 0.0002), and by 240% +/- 54% after the third exposure (P = 0.000002). The mean grouped BOLD signal trended upward, but did not increase significantly during or after exposure 1, 2, or 3. These data demonstrate increased uncoupling of perfusion-weighted from susceptibility imaging techniques, both in nonactivated cortex during hypercapnia, and with activation after multiple exposures to THC. These results are consistent with saturation of BOLD contrast as well as with increases in CMRO(2) with stimulation after multiple exposures to THC.

Animals↗