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Biomedical subjects

M Marsel Mesulam

Publications and source records attributed to M Marsel Mesulam.

13 recordsLinked to original sources
PubMed2005

Larger deficits in brain networks for response inhibition than for visual selective attention in attention deficit hyperactivity disorder (ADHD).

BACKGROUND: Brain activation differences between 12 control and 12 attention deficit hyperactivity disorder (ADHD) children (9- to 12-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI). METHOD: Visual selective attention was measured with the visual search of a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go/no-go task. RESULTS: There were limited group differences in the selective attention task, with control children showing significantly greater intensity of activation in a small area of the superior parietal lobule region of interest. There were large group differences in the response inhibition task, with control children showing significantly greater intensity of activation in fronto-striatal regions of interest including the inferior, middle, superior and medial frontal gyri as well as the caudate nucleus and globus pallidus. CONCLUSION: The widespread hypoactivity for the ADHD children on the go/no-go task is consistent with the hypothesis that response inhibition is a specific deficit in attention deficit hyperactivity disorder.

Attention↗
PubMed2004

Brain-behavior correlation in children depends on the neurocognitive network.

We examined brain-behavior correlations in 12 children (age range 9.3 to 11.7 years) during a selective attention task that required the visual search of a conjunction of features and during a response inhibition task that required the inhibition of a pre-potent response during "no-go" blocks. We found that the association between performance in these tasks and brain activation as measured by functional magnetic resonance imaging (fMRI) depended on the neurocognitive network. Specifically, better performance during the no-go task was associated with greater activation in the response inhibition network including the prefrontal cortex and basal ganglia. In contrast, better performance during the visual search task was associated with less activation in the selective attention network including superior parietal lobule and lateral premotor cortex. These results show that the relation of performance to the magnitude of neural activation is complex and may display differential relationships based on the cognitive domain, anatomical region, and perhaps also developmental stage.

Attention↗
PubMed2004

Development of brain mechanisms for processing orthographic and phonologic representations.

Developmental differences in the neurocognitive networks for lexical processing were examined in 15 adults and 15 children (9- to 12-year-olds) using functional magnetic resonance imaging (fMRI). The lexical tasks involved spelling and rhyming judgments in either the visual or auditory modality. These lexical tasks were compared with nonlinguistic control tasks involving judgments of line patterns or tone sequences. The first main finding was that adults showed greater activation than children during the cross-modal lexical tasks in a region proposed to be involved in mapping between orthographic and phonologic representations. The visual rhyming task, which required conversion from orthography to phonology, produced greater activation for adults in the angular gyrus. The auditory spelling task, which required the conversion from phonology to orthography, also produced greater activation for adults in the angular gyrus. The greater activation for adults suggests they may have a more elaborated posterior heteromodal system for mapping between representational systems. The second main finding was that adults showed greater activation than children during the intra-modal lexical tasks in the angular gyrus. The visual spelling and auditory rhyming did not require conversion between orthography and phonology for correct performance but the adults showed greater activation in a system implicated for this mapping. The greater activation for adults suggests that they have more interactive convergence between representational systems during lexical processing.

Acoustic Stimulation↗
PubMed2003

Dissociation of neural representation of intensity and affective valuation in human gustation.

We used a 2 x 2 factorial design to dissociate regions responding to taste intensity and taste affective valence. Two intensities each of a pleasant and unpleasant taste were presented to subjects during event-related fMRI scanning. The cerebellum, pons, middle insula, and amygdala responded to intensity irrespective of valence. In contrast, valence-specific responses were observed in anterior insula/operculum extending into the orbitofrontal cortex (OFC). The right caudolateral OFC responded preferentially to pleasant compared to unpleasant taste, irrespective of intensity, and the left dorsal anterior insula/operculuar region responded preferentially to unpleasant compared to pleasant tastes equated for intensity. Responses best characterized as an interaction between intensity and pleasantness were also observed in several limbic regions. These findings demonstrate a functional segregation within the human gustatory system. They also show that amygdala activity may be driven by stimulus intensity irrespective of valence, casting doubt upon the notion that the amygdala responds preferentially to negative stimuli.

Adult↗
PubMed2003

Dissociating explicit and implicit category knowledge with fMRI.

Neuroimaging of healthy volunteers identified separate neural systems supporting the expression of category knowledge depending on whether the learning mode was intentional or incidental. The same visual category was learned either intentionally or implicitly by two separate groupsof participants. During a categorization test, functional magnetic resonance imaging (fMRI) was used to compare brain activity evoked by category members and nonmembers. After implicit learning, when participants had learned the category incidentally, decreased occipital activity was observed for novel categorical stimuli compared with noncategorical stimuli. In contrast, after intentional learning, novel categorical stimuli evoked increased activity in the hippocampus, right prefrontal cortex, left inferior temporal cortex, precuneus, and posterior cingulate. Even though the categorization test was identical in the two conditions, the differences in brain activity indicate differing representations of category knowledge depending on whether the category had been learned intentionally or implicitly.

Brain Mapping↗
PubMed2003

Neurofibrillary tangles, amyloid, and memory in aging and mild cognitive impairment.

BACKGROUND: Large numbers of neurofibrillary tangles (NFTs) and amyloid plaques are diagnostic markers for Alzheimer disease (AD), but lesser numbers of these lesions are also seen in nondemented elderly individuals. Much of the existing literature suggests that the NFTs of AD have a closer correlation with cognitive function than do amyloid plaques. Whether a similar relationship exists in normal aging and mild cognitive impairment (MCI), a condition that frequently reflects a preclinical stage of AD, remains unknown. OBJECTIVE: To determine the distribution patterns of beta-amyloid plaques and NFTs and the association of these lesions with memory performance in nondemented individuals. METHODS: We investigated regional distributions and neuropsychological correlates of NFTs and amyloid plaques in cognitively normal elderly persons and subjects with MCI who received neuropsychological testing before death. Subjects Eight nondemented subjects who volunteered to receive annual neuropsychological testing and agreed to brain donation were studied. Five subjects showed no cognitive impairment, and 3 were diagnosed with MCI. RESULTS: Distribution of NFTs followed a rigorous and hierarchical pattern, but distribution of amyloid plaques varied among individuals. Subjects with MCI displayed higher NFT densities than did nonimpaired subjects. In addition, NFT density in the temporal lobe correlated with memory scores, whereas density of amyloid plaques did not. CONCLUSIONS: Neurofibrillary tangles are more numerous in medial temporal lobe regions associated with memory function and show a relationship to performance on memory tests in nondemented individuals. These results suggest that NFTs may constitute a pathological substrate for memory loss not only in AD but also in normal aging and MCI.

Aged↗
PubMed2003

Relation between brain activation and lexical performance.

Functional magnetic resonance imaging (fMRI) was used to determine whether performance on lexical tasks was correlated with cerebral activation patterns. We found that such relationships did exist and that their anatomical distribution reflected the neurocognitive processing routes required by the task. Better performance on intramodal tasks (determining if visual words were spelled the same or if auditory words rhymed) was correlated with more activation in unimodal regions corresponding to the modality of sensory input, namely the fusiform gyrus (BA 37) for written words and the superior temporal gyrus (BA 22) for spoken words. Better performance in tasks requiring cross-modal conversions (determining if auditory words were spelled the same or if visual words rhymed), on the other hand, was correlated with more activation in posterior heteromodal regions, including the supramarginal gyrus (BA 40) and the angular gyrus (BA 39). Better performance in these cross-modal tasks was also correlated with greater activation in unimodal regions corresponding to the target modality of the conversion process (i.e., fusiform gyrus for auditory spelling and superior temporal gyrus for visual rhyming). In contrast, performance on the auditory spelling task was inversely correlated with activation in the superior temporal gyrus possibly reflecting a greater emphasis on the properties of the perceptual input rather than on the relevant transmodal conversions.

Acoustic Stimulation↗
PubMed2003

Neural development of selective attention and response inhibition.

Brain activation differences between 12 children (9- to 12-year-olds) and 12 adults (20- to 30-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI). Spatial selective attention was measured with the visual search for a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go no-go task. There were small developmental differences in the selective attention task, with children showing greater activation than adults in the anterior cingulate and thalamus. There were large developmental differences in the response inhibition task, with children showing greater activation than adults in a fronto-striatal network including middle cingulate, medial frontal gyrus, medial aspects of bilateral superior frontal gyrus, and the caudate nucleus on the left. Children also showed greater bilateral activation for the response inhibition task in posterior cingulate, thalamus and the hippocampo-amygdaloid region. The extensive developmental differences on the response inhibition task are consistent with the prolonged maturation of the fronto-striatal network.

Adult↗
PubMed2002

Functional changes in temporal lobe activity during transient global amnesia.

The integrity of temporal lobe activity during and after recovery from transient global amnesia (TGA) was assessed in a case study using functional MRI. TGA was associated with scene-encoding deficits in a temporolimbic circuit that recovered over time. Frontoparietal areas recruited during the amnesic state may signify a compensatory reliance on visuospatial or working memory strategies. Reduction of extrastriate cortex responses over repeated testing sessions possibly indicates intact visual priming in TGA.

Adult↗
PubMed2002

Modality independence of word comprehension.

Functional magnetic resonance imaging (fMRI) was used to examine the functional anatomy of word comprehension in the auditory and visual modalities of presentation. We asked our subjects to determine if word pairs were semantically associated (e.g., table, chair) and compared this to a reference task where they were asked to judge whether word pairs rhymed (e.g., bank, tank). This comparison showed task-specific and modality-independent activation for semantic processing in the heteromodal cortices of the left inferior frontal gyrus (BA 46, 47) and left middle temporal gyrus (BA 21). There were also modality-specific activations in the fusiform gyrus (BA 37) for written words and in the superior temporal gyrus (BA 22) for spoken words. Our findings are consistent with the hypothesis that word form recognition (lexical encoding) occurs in unimodal cortices and that heteromodal brain regions in the anterior as well as posterior components of the language network subserve word comprehension (semantic decoding).

Adult↗
PubMed2002

Functional anatomy of intra- and cross-modal lexical tasks.

Functional magnetic resonance imaging (fMRI) was used to examine lexical processing in normal adults (20-35 years). Two tasks required only intramodal processing (spelling judgments with visual input and rhyming judgments with auditory input) and two tasks required cross-modal processing between phonologic and orthographic representations (spelling judgments with auditory input and rhyming judgments with visual input). Each task led to greater activation in the unimodal association area concordant with the modality of input, namely fusiform gyrus (BA 19, 37) for written words and superior temporal gyrus (BA 22, 42) for spoken words. Cross-modal tasks generated greater activation in posterior heteromodal regions including the supramarginal and angular gyri (BA 40, 39). Cross-modal tasks generated additional activation in unimodal areas representing the target of conversion, superior temporal gyrus for visual rhyming and fusiform gyrus for auditory spelling. Our findings suggest that the fusiform gyrus processes orthographic word forms, the superior temporal gyrus processes phonologic word forms, and posterior heteromodal regions are involved in the conversion between orthography and phonology.

Adult↗
PubMed2002

Hemodynamic response changes in cerebrovascular disease: implications for functional MR imaging.

BACKGROUND AND PURPOSE: Patients with cerebrovascular occlusive disease may develop compensatory changes in local cerebral vasculature with a resultant loss of vascular reactivity. These alterations can affect the blood oxygen level-dependent (BOLD) signal that is the basis for functional MR imaging. We investigated the BOLD signal in patients with unilateral cerebrovascular disease to ascertain the clinical utility of functional MR imaging in these patients. METHODS: Five healthy volunteers and three patients with cerebro-occlusive disease were imaged with both a block and an event-related design of a visually cued bilateral motor task. Activation maps were calculated, and individual hemodynamic response curves were generated for left and right primary motor cortices. Vascular reserve was determined for the relevant vascular territory by using transcranial Doppler ultrasonography (US). RESULTS: In the event-related data, the amplitude of the BOLD response was significantly decreased in the motor cortex ipsilateral to the stenosis and showed significant delays in the timing of the hemodynamic response. In contrast, the longer duration stimulus and longer TR of the block design showed significant decreases in the BOLD amplitude but no significant interhemispheric temporal differences. Corroborating the hemodynamic status, transcranial Doppler US analysis showed diminished vascular reserve ipsilateral to the lesion. CONCLUSION: Differences in the results between the event-related and block paradigms reflect the sensitivity to alterations in autoregulation or vascular compliance. These changes in the vasculature directly affect the BOLD contrast underlying functional MR imaging. Thus, while this technique remains a useful clinical tool, caution is warranted when studying patients with cerebrovascular disease.

Adult↗