Biomedical subjects

J C Gore

Publications and source records attributed to J C Gore.

At least 55 records · Page 3Linked to original sources

PubMed2000

The angular gyrus in developmental dyslexia: task-specific differences in functional connectivity within posterior cortex.

Converging evidence from neuroimaging studies of developmental dyslexia reveals dysfunction at posterior brain regions centered in and around the angular gyrus in the left hemisphere. We examined functional connectivity (covariance) between the angular gyrus and related occipital and temporal lobe sites, across a series of print tasks that systematically varied demands on phonological assembly. Results indicate that for dyslexic readers a disruption in functional connectivity in the language-dominant left hemisphere is confined to those tasks that make explicit demands on assembly. In contrast, on print tasks that do not require phonological assembly, functional connectivity is strong for both dyslexic and nonimpaired readers. The findings support the view that neurobiological anomalies in developmental dyslexia are largely confined to the phonological-processing domain. In addition, the findings suggest that right-hemisphere posterior regions serve a compensatory role in mediating phonological performance in dyslexic readers.

Adolescent↗

PubMed2000

An event-related neuroimaging study distinguishing form and content in sentence processing.

Two coordinated experiments using functional Magnetic Resonance Imaging (fMRI) investigated whether the brain represents language form (grammatical structure) separately from its meaning content (semantics). While in the scanner, 14 young, unimpaired adults listened to simple sentences that were either nonanomalous or contained a grammatical error (for example, *Trees can grew.), or a semantic anomaly (for example, *Trees can eat.). A same&frasl;different tone pitch judgment task provided a baseline that isolated brain activity associated with linguistic processing from background activity generated by attention to the task and analysis of the auditory input. Sites selectively activated by sentence processing were found in both hemispheres in inferior frontal, middle, and superior frontal, superior temporal, and temporo-parietal regions. Effects of syntactic and semantic anomalies were differentiated by some nonoverlapping areas of activation: Syntactic anomaly triggered significantly increased activity in and around Broca's area, whereas semantic anomaly activated several other sites anteriorly and posteriorly, among them Wernicke's area. These dissociations occurred when listeners were not required to attend to the anomaly. The results confirm that linguistic operations in sentence processing can be isolated from nonlinguistic operations and support the hypothesis of a specialization for syntactic processing.

Adult↗

PubMed2000

The fusiform "face area" is part of a network that processes faces at the individual level.

According to modular models of cortical organization, many areas of the extrastriate cortex are dedicated to object categories. These models often assume an early processing stage for the detection of category membership. Can functional imaging isolate areas responsible for detection of members of a category, such as faces or letters? We consider whether responses in three different areas (two selective for faces and one selective for letters) support category detection. Activity in these areas habituates to the repeated presentation of one exemplar more than to the presentation of different exemplars of the same category, but only for the category for which the area is selective. Thus, these areas appear to play computational roles more complex than detection, processing stimuli at the individual level. Drawing from prior work, we suggest that face-selective areas may be involved in the perception of faces at the individual level, whereas letter-selective regions may be tuning themselves to font information in order to recognize letters more efficiently.

Adult↗

PubMed2000

Performance on indirect measures of race evaluation predicts amygdala activation.

We used fMRI to explore the neural substrates involved in the unconscious evaluation of Black and White social groups. Specifically, we focused on the amygdala, a subcortical structure known to play a role in emotional learning and evaluation. In Experiment 1, White American subjects observed faces of unfamiliar Black and White males. The strength of amygdala activation to Black-versus-White faces was correlated with two indirect (unconscious) measures of race evaluation (Implicit Association Test [IAT] and potentiated startle), but not with the direct (conscious) expression of race attitudes. In Experiment 2, these patterns were not obtained when the stimulus faces belonged to familiar and positively regarded Black and White individuals. Together, these results suggest that amygdala and behavioral responses to Black-versus-White faces in White subjects reflect cultural evaluations of social groups modified by individual experience.

Black or African American↗

PubMed2000

Preliminary evidence of improved verbal working memory performance and normalization of task-related frontal lobe activation in schizophrenia following cognitive exercises.

OBJECTIVE: The authors' goal was to evaluate the possibility of treating brain and behavioral aspects of verbal memory dysfunction in patients with schizophrenia through cognitive exercises. METHOD: Eight patients did daily verbal memory exercises that became progressively more difficult over a 10-week training period. Memory performance and regional brain activations during a verbal memory task were assessed before and after these exercises. RESULTS: Verbal but not nonverbal memory performance improved after training; three patients made substantial gains, and five showed little change. Performance gains were correlated with increases in task-related activation of the left inferior frontal cortex. One patient given 5 extra weeks of training 6 weeks after the initial training period showed maintenance of initial performance gains 6 weeks after training, further improvement after the second period of training, and normalization of task-related activation of the left inferior frontal cortex. CONCLUSIONS: Verbal memory deficits can be ameliorated by memory exercises in some patients with schizophrenia. Performance improvements are associated with increased task-related activation of the same brain region that is activated during verbal memory tasks in healthy individuals.

Adult↗

PubMed1999

An fMRI study of Stroop word-color interference: evidence for cingulate subregions subserving multiple distributed attentional systems.

BACKGROUND: The goal of this study was to model the functional connectivity of the neural systems that subserve attention and impulse control. Proper performance of the Stroop Word-Color Interference Task requires both attention and impulse control. METHODS: Word-color interference was studied in 34 normal adult subjects using functional magnetic resonance imaging. RESULTS: Interregional correlation analyses suggested that the anterior cingulate is coupled functionally with multiple regions throughout the cerebrum. A factor analysis of the significant regional activations further emphasized this functional coupling. The cingulate or related mesial frontal cortices loaded on each of the seven factors identified in the factor analysis. Other regions that loaded significantly on these factors have been described previously as belonging to anatomically connected circuits believed to subserve sensory tuning, receptive language, vigilance, working memory, response selection, motor planning, and motor response functions. These seven factors appeared to be oriented topographically within the anterior cingulate, with sensory, working memory, and vigilance functions positioned more rostrally, and response selection, motor planning, and motor response positioned progressively more caudally. CONCLUSIONS: These findings support a parallel distributed processing model for word-color interference in which portions of the anterior cingulate cortex modify the strengths of multiple neural pathways used to read and name colors. Allocation of attentional resources is thought to modify pathway strengths by reducing cross-talk between information processing modules that subserve the competing demands of reading and color naming. The functional topography of these neural systems observed within the cingulate argues for the presence of multiple attentional subsystems, each contributing to improved task performance. The topography also suggests a role for the cingulate in coordinating and integrating the activity of these multiple attentional subsystems.

Adolescent↗

PubMed1999

Effect of estrogen on brain activation patterns in postmenopausal women during working memory tasks.

CONTEXT: Preclinical studies suggest that estrogen affects neural structure and function in mature animals; clinical studies are less conclusive with many, but not all, studies showing a positive influence of estrogen on verbal memory in postmenopausal women. OBJECTIVE: To investigate the effects of estrogen on brain activation patterns in postmenopausal women as they performed verbal and nonverbal working memory tasks. DESIGN: Randomized, double-blind, placebo-controlled, crossover trial from 1996 through 1998. SETTING: Community volunteers tested in a hospital setting. PATIENTS: Forty-six postmenopausal women aged 33 to 61 years (mean [SD] age, 50.8 [4.7] years). INTERVENTION: Twenty-one-day treatment with conjugated equine estrogens, 1.25 mg/d, randomly crossed over with identical placebo and a 14-day washout between treatments. MAIN OUTCOME MEASURES: Brain activation patterns measured using functional magnetic resonance imaging during tasks involving verbal and nonverbal working memory. RESULTS: Treatment with estrogen increased activation in the inferior parietal lobule during storage of verbal material and decreased activation in the inferior parietal lobule during storage of nonverbal material. Estrogen also increased activation in the right superior frontal gyrus during retrieval tasks, accompanied by greater left-hemisphere activation during encoding. The latter pattern represents a sharpening of the hemisphere encoding/retrieval asymmetry (HERA) effect. Estrogen did not affect actual performance of the verbal and nonverbal memory tasks. CONCLUSIONS: Estrogen in a therapeutic dosage alters brain activation patterns in postmenopausal women in specific brain regions during the performance of the sorts of memory function that are called upon frequently during any given day. These results suggest that estrogen affects brain organization for memory in postmenopausal women.

Adult↗

PubMed1999

In vivo measurement of ADC change due to intravascular susceptibility variation.

The apparent diffusion coefficient (ADC) of extravascular tissue water in rat brains was measured in response to step-wise injections of the superparamagnetic intravascular contrast agent AMI-227. These data were normalized and compared with measured changes in R2* and blood magnetic susceptibility. Linear regression showed that ADC changes 33%/ppm shift of intravascular susceptibility and 0.43% s(-1) change in R2*. These changes correspond to a predicted ADC change of approximately 6% for a change between fully oxygenated and fully deoxygenated blood. The source of these ADC changes was confirmed to be background gradients within the sample by the use of diffusion weighting with bipolar gradients of odd symmetry designed to cancel such background gradient effects on ADC. The results suggest that diffusion-weighted imaging is sensitive to blood-oxygenation and may provide a means of measuring changes in blood oxygen. They also provide estimates of the potential contribution of susceptibility changes to changes in ADC that occur, for example, in stroke and seizure.

Animals↗

PubMed1999

Quantitative imaging of magnetization transfer using multiple selective pulses.

New spectroscopic and imaging methods have been developed for quantitatively measuring magnetization transfer (MT). These methods use trains of radiofrequency (rf) pulses with pulse separations much longer than 1/k(mf) and pulse durations much shorter than 1/k(mf), where k(mf) is the rate of MT from the immobile (macromolecular) protons to the mobile (free water) protons. Signal sensitivity to MT occurs when these pulses affect the mobile and immobile proton pools to different degrees. The signal from water may be quantitatively related to the macromolecular content of the sample using theory. The method has been used to make quantitative measurements of macromolecular content in cross-linked bovine serum albumin and employed in conjunction with echoplanar imaging to produce maps of the spatial distribution of the macromolecular content.

Algorithms↗

PubMed1999

Analysis of J coupling-induced fat suppression in DIET imaging.

The DIET (or dual interval echo train) sequence, a modification of the fast spin echo (FSE) sequence that selectively reduces signal from fat in MR images, has been investigated. The DIET sequence uses an initial echo spacing longer than that of a conventional FSE sequence, thus allowing J coupling-induced dephasing to take effect. The sequence is evaluated theoretically, and its effectiveness on a hydrocarbon (1-pentene) is demonstrated numerically using density matrix calculations. The sequence is also evaluated experimentally using in vitro solutions and in vivo imaging. The efficacy of the sequence is compared for different lipid chemical structures, field strengths, and pulse sequence parameters.

Adipose Tissue↗

PubMed1999

Density matrix simulations of the effects of J coupling in spin echo and fast spin echo imaging.

A computer simulation has been used to calculate the effects of J coupling on the amplitudes of echoes produced by CPMG sequences. The program computes the evolution of the density matrix for different pulse intervals and can predict the signals obtainable from spin systems of any size and complexity. Results from the simulation confirm the prediction that a decrease in the effects of J coupling is largely responsible for the bright fat signal seen in fast spin echo imaging at high pulse rates. The effects of J coupling on CPMG echotrains are examined for A3B2 and A3B2C2 spin systems over a wide range of J coupling and chemical shift values and pulse spacings. The effects of J coupling on the point spread function obtained with fast spin echo imaging are also discussed.

Algorithms↗

PubMed1999

Construction and implementation of NMR quantum logic gates for two spin systems.

The implementation of small prototype quantum computers has been studied through ensemble quantum computing via NMR measurements. In such laboratory studies it is convenient to have access to a wide array of logic gates. Here a systematic approach to reduce the logic gate to an NMR pulse sequence is introduced. This approach views the truth table for a quantum logic operation as a permutation matrix that corresponds to a propagator for an NMR transition. This propagator is then used as the starting point for the derivation of a pulse sequence. Pulse sequences for all the permutations of a four level system are reported along with implementations of representative examples on a two spin-1/2 system, 13C-labeled chloroform.

Magnetic Resonance Spectroscopy↗

PubMed1999

ROC analysis of statistical methods used in functional MRI: individual subjects.

The complicated structure of fMRI signals and associated noise sources make it difficult to assess the validity of various steps involved in the statistical analysis of brain activation. Most methods used for fMRI analysis assume that observations are independent and that the noise can be treated as white gaussian noise. These assumptions are usually not true but it is difficult to assess how severely these assumptions are violated and what are their practical consequences. In this study a direct comparison is made between the power of various analytical methods used to detect activations, without reference to estimates of statistical significance. The statistics used in fMRI are treated as metrics designed to detect activations and are not interpreted probabilistically. The receiver operator characteristic (ROC) method is used to compare the efficacy of various steps in calculating an activation map in the study of a single subject based on optimizing the ratio of the number of detected activations to the number of false-positive findings. The main findings are as follows: Preprocessing. The removal of intensity drifts and high-pass filtering applied on the voxel time-course level is beneficial to the efficacy of analysis. Temporal normalization of the global image intensity, smoothing in the temporal domain, and low-pass filtering do not improve power of analysis. Choices of statistics. the cross-correlation coefficient and t-statistic, as well as nonparametric Mann-Whitney statistics, prove to be the most effective and are similar in performance, by our criterion. Task design. the proper design of task protocols is shown to be crucial. In an alternating block design the optimal block length is be approximately 18 s. Spatial clustering. an initial spatial smoothing of images is more efficient than cluster filtering of the statistical parametric activation maps.

Brain↗

PubMed1999

An event-related fMRI study of implicit phrase-level syntactic and semantic processing.

Most neuroimaging studies of language function to date use a block-subtraction paradigm in which images acquired during relatively long periods of target stimuli are compared to those acquired during a control period. These studies typically require an overt response on the part of the subject, usually some type of discrimination or grammatical judgment by button press, or silent word generation. Results from studies of syntactic and semantic processing have generally been compatible with the classical correlation to Broca's area and Wernicke's area, respectively. Recently, functional magnetic resonance imaging (fMRI) studies departing from the block-subtraction paradigm in favor of event-related fMRI paradigms have been reported. We have extended the use of this approach to examine implicit (i.e., without an explicit task on the part of the subject) syntactic and semantic processing at the phrasal level, using visually presented verb phrases. Left BA 44 is more strongly activated for the syntactic condition than the semantic condition. BA 45, 10, and 46 show laterality differences: mostly left-lateralized for the syntactic condition and right-lateralized for the semantic condition. We also find activations of the inferior parietal lobe, consistent with a visual oddball response reported previously, and the anterior cingulate gyrus (BA 32), implicated for attention and memory-related processes in numerous studies.

Adolescent↗

PubMed1999

Activation of the middle fusiform 'face area' increases with expertise in recognizing novel objects.

Part of the ventral temporal lobe is thought to be critical for face perception, but what determines this specialization remains unknown. We present evidence that expertise recruits the fusiform gyrus 'face area'. Functional magnetic resonance imaging (fMRI) was used to measure changes associated with increasing expertise in brain areas selected for their face preference. Acquisition of expertise with novel objects (greebles) led to increased activation in the right hemisphere face areas for matching of upright greebles as compared to matching inverted greebles. The same areas were also more activated in experts than in novices during passive viewing of greebles. Expertise seems to be one factor that leads to specialization in the face area.

Adult↗

PubMed1999

Predicting midsagittal pharynx shape from tongue position during vowel production.

The shape of the pharynx has a large effect on the acoustics of vowels, but direct measurement of this part of the vocal tract is difficult. The present study examines the efficacy of inferring midsagittal pharynx shape from the position of the tongue, which is much more amenable to measurement. Midsagittal magnetic resonance (MR) images were obtained for multiple repetitions of 11 static English vowels spoken by two subjects (one male and one female). From these, midsagittal widths were measured at approximately 3-mm intervals along the entire vocal tract. A regression analysis was then used to assess whether the pharyngeal widths could be predicted from the locations and width measurements for four positions on the tongue, namely, those likely to be the locations of a receiver coil for an electromagnetometer system. Predictability was quite high throughout the vocal tract (multiple r> 0.9), except for the extreme ends (i.e., larynx and lips) and small decreases for the male subject in the uvula region. The residuals from this analysis showed that the accuracy of predictions was generally quite high, with 89.2% of errors being less than 2 mm. The extremes of the vocal tract, where the resolution of the MRI was poorer, accounted for much of the error. For languages like English, which do not use advanced tongue root (ATR) distinctively, the midsagittal pharynx shape of static vowels can be predicted with high accuracy.

Female↗

PubMed1999

Functional magnetic resonance imaging identifies abnormal visual cortical function in patients with occipital lobe epilepsy.

PURPOSE: To determine whether functional magnetic resonance imaging (fMRI) can reliably identify lateralized cortical dysfunction in patients with suspected occipital lobe epilepsy. METHODS: We compared visual cortical function of 10 patients with intractable occipital lobe epilepsy with nine control subjects' fMRI. Visual stimulation by using an alternating checkerboard pattern results in transient increases in the intensity of the proton magnetic resonance signal of water in the occipital lobes during echo-planar imaging. We used these stimulus-dependent changes in signal intensity to construct functional activation maps, which we registered onto anatomic images. RESULTS: After full-field stimulation, none of the patients with occipital lobe epilepsy had normal activation patterns, whereas eight of the nine control subjects had normal patterns (p = 0.001). Abnormalities consisted of either a markedly asymmetric activation pattern in six of 10 patients (p = 0.04), or a complete absence of activation in four of 10 patients (p = 0.05). The abnormal side of activation was concordant with the side of seizure onset in all six patients with asymmetric activation maps. Half-field stimulation produced less reliable results. Although more patients had abnormal activation maps than did controls with half-field stimulation (p = 0.04), the abnormal side was discordant with the side of seizure onset in three of the five patients who had markedly asymmetric activation patterns. CONCLUSIONS: These results suggest that fMRI with full-field stimulation is a reliable, noninvasive method for identifying areas of abnormal visual cortical function ipsilateral to the epileptogenic region in patients with occipital lobe epilepsy.

Adolescent↗

PubMed1998

Temporal cortex activation in humans viewing eye and mouth movements.

We sought to determine whether regions of extrastriate visual cortex could be activated in subjects viewing eye and mouth movements that occurred within a stationary face. Eleven subjects participated in three to five functional magnetic resonance imaging sessions in which they viewed moving eyes, moving mouths, or movements of check patterns that occurred in the same spatial location as the eyes or mouth. In each task, the stimuli were superimposed on a radial background pattern that continually moved inward to control for the effect of movement per se. Activation evoked by the radial background was assessed in a separate control task. Moving eyes and mouths activated a bilateral region centered in the posterior superior temporal sulcus (STS). The moving check patterns did not appreciably activate the STS or surrounding regions. The activation by moving eyes and mouths was distinct from that elicited by the moving radial background, which primarily activated the posterior-temporal-occipital fossa and the lateral occipital sulcus-a region corresponding to area MT/V5. Area MT/V5 was also strongly activated by moving eyes and to a lesser extent by other moving stimuli. These results suggest that a superior temporal region centered in the STS is preferentially involved in the perception of gaze direction and mouth movements. This region of the STS may be functionally related to nearby superior temporal regions thought to be involved in lip-reading and in the perception of hand and body movement.

Adult↗