Biomedical subjects

C Lacadie

Publications and source records attributed to C Lacadie.

9 recordsLinked to original sources

PubMed2001

The functional neural architecture of components of attention in language-processing tasks.

Using functional magnetic resonance imaging we examined three important dimensions of attentional control (selective attention, divided attention, and executive function) in 25 neurologically normal, right-handed men and women, using tasks involving the perception and processing of printed words, spoken words, or both. In the context of language-processing manipulations: selective attention resulted in increased activation at left hemisphere parietal sites as well as at inferior frontal sites, divided attention resulted in additional increases in activation at these same left hemisphere sites and was also uniquely associated with increased activation of homologous sites in the right hemisphere, and executive function (measured during a complex task requiring sequential decision-making) resulted in increased activation at frontal sites relative to all other conditions. Our findings provide support for the belief that specific functional aspects of attentional control in language processing involve widely distributed but distinctive cortical systems, with mechanisms associated with the control of perceptual selectivity involving primarily parietal and inferior frontal sites and executive function engaging specific sites in frontal cortex.

Adult↗

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

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

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↗

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↗

PubMed1998

Functional disruption in the organization of the brain for reading in dyslexia.

Learning to read requires an awareness that spoken words can be decomposed into the phonologic constituents that the alphabetic characters represent. Such phonologic awareness is characteristically lacking in dyslexic readers who, therefore, have difficulty mapping the alphabetic characters onto the spoken word. To find the location and extent of the functional disruption in neural systems that underlies this impairment, we used functional magnetic resonance imaging to compare brain activation patterns in dyslexic and nonimpaired subjects as they performed tasks that made progressively greater demands on phonologic analysis. Brain activation patterns differed significantly between the groups with dyslexic readers showing relative underactivation in posterior regions (Wernicke's area, the angular gyrus, and striate cortex) and relative overactivation in an anterior region (inferior frontal gyrus). These results support a conclusion that the impairment in dyslexia is phonologic in nature and that these brain activation patterns may provide a neural signature for this impairment.

Brain↗

PubMed1998

Quantifying and comparing region-of-interest activation patterns in functional brain MR imaging: methodology considerations.

The general aims of functional brain magnetic resonance imaging (fMRI) studies are to ascertain which areas of the brain are activated during a specific task, the extent of this activation, whether different groups of subjects demonstrate different patterns of activation, and how these groups behave in different tasks. Many steps are involved in answering such questions and if each step is not carefully controlled the results may be influenced. This work has three objectives. Firstly, to present a technique for quantitatively evaluating methods used in functional imaging data analysis. While receiver-operator-characteristic (ROC) analysis has been used effectively to evaluate the ability of post-processing algorithms to detect true activations while rejecting false activations, it is difficult to adapt such a technique for comparisons of methods for quantitating activations. We present a technique based on the ANOVA, between two or more regions of interest (ROIs), subject groups, or activation tasks, over a range of statistical thresholds, which reveals the sensitivity of different activation quantification metrics to noise and other variables. Secondly, we use this technique to compare two methods of quantifying localized brain activation. There are numerous ways of quantifying the amount of activation present in a specific region of the brain in an individual subject. We compare the pixel count approach, which simply counts the number of pixels above an arbitrary statistical threshold, with an approach based on the sum of t-values above the same arbitrary t-value threshold. Finally, we examine the sensitivity of the results from an analysis of variance, to user defined parameters such as threshold and region of interest size. Both simulated and real functional magnetic resonance data are used to demonstrate these techniques.

Analysis of Variance↗

PubMed1997

Predicting reading performance from neuroimaging profiles: the cerebral basis of phonological effects in printed word identification.

This study linked 2 experimental paradigms for the analytic study of reading that heretofore have been used separately. Measures on a lexical decision task designed to isolate phonological effects in the identification of printed words were examined in young adults. The results were related to previously obtained measures of brain activation patterns for these participants derived from functional magnetic resonance imaging (fMRI). The fMRI measures were taken as the participants performed tasks that were designed to isolate orthographic, phonological, and lexical-semantic processes in reading. Individual differences in the magnitude of phonological effects in word recognition, as indicated by spelling-to-sound regularity effects on lexical decision latencies and by sensitivity to stimulus length effects, were strongly related to differences in the degree of hemispheric lateralization in 2 cortical regions.

Adult↗

PubMed1996

Auditory selective attention: an fMRI investigation.

In the present experiment, 25 adult subjects discriminated speech tokens ([ba]/[da]) or made pitch judgments on tone stimuli (rising/falling) under both binaural and dichotic listening conditions. We observed that when listeners performed tasks under the dichotic conditions, during which greater demands are made on auditory selective attention, activation within the posterior (parietal) attention system and at primary processing sites in the superior temporal and inferior frontal regions was increased. The cingulate gyrus within the anterior attention system was not influenced by this manipulation. Hemispheric differences between speech and nonspeech tasks were also observed, both at Broca's Area within the inferior frontal gyrus and in the middle temporal gyrus.

Adult↗