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M Mentis

Publications and source records attributed to M Mentis.

14 recordsLinked to original sources
PubMed2002

Parametric mapping of [18F]FPCIT binding in early stage Parkinson's disease: a PET study.

We have shown that fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane ([(18)F]FPCIT) and PET offer a valuable means of quantifying regional abnormality in dopamine transporter (DAT) imaging associated with Parkinson's disease (PD). The objective of this study was to delineate the topographic distribution of DAT binding in early stage idiopathic PD using statistical parametric analysis of [(18)F]FPCIT PET data. We performed dynamic PET studies in 15 hemi-parkinsonian (Hoehn & Yahr I) patients and 10 age-matched normal volunteers over 100 min and calculated images of [(18)F]FPCIT binding ratios on a pixel-by-pixel basis. Statistical parametric mapping (SPM) was then used to localize binding reductions in PD and to compute the absolute change relative to normal. [(18)F]FPCIT binding decreased significantly in the contralateral posterior putamen of the PD group (P < 0.001, corrected). A significant reduction was also seen in the ipsilateral putamen, which was smaller in extent but localized more posteriorly. A quantitative comparison of DAT binding in the two clusters showed that the onset of motor symptoms in PD was associated with an approximate 70% loss relative to the normal mean in the contralateral posterior putamen. These results suggest that SPM analysis of [(18)F]FPCIT PET data can be used to quantify and map abnormalities in DAT activity within the human striatum. This method provides a useful tool to track the onset and progression of PD at its earliest stages.

Aged↗
PubMed2001

Functional networks in motor sequence learning: abnormal topographies in Parkinson's disease.

We examined the neural circuitry underlying the explicit learning of motor sequences in normal subjects and patients with early stage Parkinson's disease (PD) using 15O-water (H2 15O) positron emission tomography (PET) and network analysis. All subjects were scanned while learning motor sequences in a task emphasizing explicit learning, and during a kinematically controlled motor execution reference task. Because different brain networks are thought to subserve target acquisition and retrieval during motor sequence learning, we used separate behavioral indices to quantify these aspects of learning during the PET experiments. In the normal cohort, network analysis of the PET data revealed a significant covariance pattern associated with acquisition performance. This topography was characterized by activations in the left dorsolateral prefrontal cortex (PFdl), rostral supplementary motor area (preSMA), anterior cingulate cortex, and in the left caudate/putamen. A second independent covariance pattern was associated with retrieval performance. This topography was characterized by bilateral activations in the premotor cortex (PMC), and in the right precuneus and posterior parietal cortex. The normal learning-related topographies failed to predict acquisition performance in PD patients and predicted retrieval performance less accurately in the controls. A separate network analysis was performed to identify discrete learning-related topographies in the PD cohort. In PD patients, acquisition performance was associated with a covariance pattern characterized by activations in the left PFdl, ventral prefrontal, and rostral premotor regions, but not in the striatum. Retrieval performance in PD patients was associated with a covariance pattern characterized by activations in the right PFdl, and bilaterally in the PMC, posterior parietal cortex, and precuneus. These results suggest that in early stage PD sequence learning networks are associated with additional cortical activation compensating for abnormalities in basal ganglia function.

Adult↗
PubMed2001

Functional correlates of pallidal stimulation for Parkinson's disease.

We measured regional cerebral blood flow with H2 15O and positron emission tomography (PET) scanning at rest and during a motor task to study the mechanism of motor improvement induced by deep brain stimulation of the internal globus pallidus in Parkinson's disease. Six right-handed patients with Parkinson's disease were scanned while performing a predictable paced sequence of reaching movements and while observing the same screen displays and tones. PET studies were performed ON and OFF stimulation in a medication-free state. Internal globus pallidus deep brain stimulation improved off-state United Parkinson's Disease Rating Scale motor ratings (37%, p < 0.002) and reduced timing errors (movement onset time, 55%, p < 0.01) as well as spatial errors (10%, p < 0.02). Concurrent regional cerebral blood flow recordings revealed a significant enhancement of motor activation responses in the left sensorimotor cortex (Brodmann area [BA] 4), bilaterally in the supplementary motor area (BA 6), and in the right anterior cingulate cortex (BA 24/32). Significant correlations were evident between the improvement in motor performance and the regional cerebral blood flow changes mediated by stimulation. With internal globus pallidus deep brain stimulation, improved movement initiation correlated with regional cerebral blood flow increases in the left sensorimotor cortex and ventrolateral thalamus and in the contralateral cerebellum. By contrast, improved spatial accuracy correlated with regional cerebral blood flow increases in both cerebellar hemispheres and in the left sensorimotor cortex. These results suggest that internal globus pallidus deep brain stimulation may selectively improve different aspects of motor performance. Multiple, overlapping neural pathways may be modulated by this intervention.

Adult↗
PubMed2000

Patterns of regional brain activation associated with different forms of motor learning.

To examine the variations in regional cerebral blood flow during execution and learning of reaching movements, we employed a family of kinematically and dynamically controlled motor tasks in which cognitive, mnemonic and executive features of performance were differentiated and characterized quantitatively. During 15O-labeled water positron emission tomography (PET) scans, twelve right-handed subjects moved their dominant hand on a digitizing tablet from a central location to equidistant targets displayed with a cursor on a computer screen in synchrony with a tone. In the preceding week, all subjects practiced three motor tasks: 1) movements to a predictable sequence of targets; 2) learning of new visuomotor transformations in which screen cursor motion was rotated by 30 degrees -60 degrees; 3) learning new target sequences by trial and error, by using previously acquired routines in a task placing heavy load on spatial working memory. The control condition was observing screen and audio displays. Subtraction images were analyzed with Statistical Parametric Mapping to identify significant brain activation foci. Execution of predictable sequences was characterized by a modest decrease in movement time and spatial error. The underlying pattern of activation involved primary motor and sensory areas, cerebellum, basal ganglia. Adaptation to a rotated reference frame, a form of procedural learning, was associated with decrease in the imposed directional bias. This task was associated with activation in the right posterior parietal cortex. New sequences were learned explicitly. Significant activation was found in dorsolateral prefrontal and anterior cingulate cortices. In this study, we have introduced a series of flexible motor tasks with similar kinematic characteristics and different spatial attributes. These tasks can be used to assess specific aspects of motor learning with imaging in health and disease.

Adult↗
PubMed1998

In utero cocaine exposure and language development.

A growing body of literature suggests that in utero cocaine exposure may place a child at risk for impaired language development. Because the field of gestational drug exposure and its effects on communicative development is young, the research is still limited and the data are contradictory, plagued by many methodological problems. The accumulating evidence, however, suggests that the development of specific aspects of language may be compromised in a percentage of children and that outcome is affected by a wide range of prenatal and postnatal biological and environmental factors. The data also suggest that deficits are best identified through the use of focused test batteries and may be evident only under stressful or difficult conditions. This article provides a critique and general overview of the literature on the early communicative and language development of prenatally cocaine-exposed children. Potential reasons for compromised language development and the clinical implications of these findings are discussed.

Child Language↗
PubMed1995

Discourse topic management in senile dementia of the Alzheimer's type.

The purpose of the study was to provide a detailed evaluation of the topic management abilities of a group of subjects with senile dementia of the Alzheimer's type (SDAT) and to compare their patterns of topic management to that of a normal elderly (NE) subject group. Twenty-four subjects participated in the study: 12 SDAT subjects and 12 NE subjects matched along the variables of age, sex, and education. The evaluation of topic management was based on a 20-minute casual conversational interaction between the subject and a speech-language pathologist that was videotaped and later transcribed orthographically. Topic management was analyzed in terms of a modified version of the multidimensional topic coherence analysis developed by Mentis and Prutting (1991). The results indicated significant differences between the SDAT and NE subjects along a number of parameters of topic introduction and maintenance. The topic management profiles of the SDAT subjects were characterized by a reduced ability to change topics while preserving the discourse flow, difficulty in actively contributing to the propositional development of the topic, and a failure to consistently maintain topic in a clear and coherent manner. These problems appeared to be related to underlying problems across the discourse-pragmatic, linguistic, and cognitive domains; they highlight the need to more fully explore the interactions among deficits in SDAT and their effects on conversational discourse.

Aged↗
PubMed1995

Effects of prenatal exposure to cocaine and associated risk factors on language development.

During the past decade there has been a dramatic increase in the number of children born with prenatal exposure to cocaine. However, there is very little hard data concerning the later development of these children. The purpose of this preliminary study was to compare the language development profiles of 5 children prenatally exposed to cocaine and associated risk factors to the language development profiles of a matched non-exposed control group in terms of analyses of the discourse-pragmatic, semantic, and form components of language. The language evaluation was based on the analysis of a 30-minute language sample. The results suggested differences between the two groups as well as differences within the cocaine-exposed group. The major differences between the two groups were in discourse-pragmatics although less marked differences in syntactic development were also found. The results are discussed in relation to the potential contribution of pertinent medical and environmental risk factors. The study suggests that for children with prenatal exposure to cocaine in combination with multiple associated risk factors, language development may be compromised.

Child Language↗
PubMed1995

Brain metabolic function in older men with chronic essential hypertension.

BACKGROUND AND METHODS. To determine the effects of hypertension on brain function, positron emission tomography (PET) studies using (18F)-2-fluoro-2-deoxy-D-glucose (FDG) were performed on a group of 17 otherwise healthy older hypertensive men (mean age +/- SD = 69 +/- 8 yr) and 25 age- and gender-matched controls. Subjects had medically treated essential hypertension for a minimum of 10 years (range = 10 to 24 yr) with no evidence of end-organ impairment from hypertension by routine clinical screening and by history. All hypertensive and control subjects were determined to be cognitively normal by extensive neuropsychological testing. The hypertensive subjects previously had been reported to have lateral ventricle enlargement and left hemisphere brain atrophy by quantitative MRI. PET data were analyzed using t-tests to look at group differences.

Aged↗
PubMed1991

Analysis of topic as illustrated in a head-injured and a normal adult.

The purpose of this study was to develop a reliable multidimensional topic analysis that would be sensitive to patterns and problems in topic management. Six conversation and four monologue language samples of a closed-head-injured adult and a matched normal adult were compared. High interjudge reliability was found for all frequently occurring parameters of the analysis. Differences between the two subjects were obtained on a number of the topic introduction and maintenance parameters. The results illustrate the potential of the analysis to reliably identify, quantify, and describe differences between subjects in discourse topic management. The potential of the analysis to provide detailed profiles of topic management and describe the influence of such variables as genre and topic complexity on discourse topic was demonstrated.

Adult↗
PubMed1987

Cohesion in the discourse of normal and head-injured adults.

Cohesion strategies used by 3 normal and 3 head-injured adults were examined in both conversational and narrative conditions. Two major findings emerged. First, the head-injured subjects used different cohesion patterns from the normal adults in both conditions. Second, both groups used different cohesion patterns in the conversational and narrative conditions. The study highlights the importance of viewing the language of head-injured adults within the context of discourse. Testing the language system through narrative as well as conversational discourse is important since both conditions are characterized by their own distinctive internal structure and organization.

Adult↗
PubMed1985

Motivation in childhood autism: can they or won't they?

Research in the area of motivation in autistic and other children suggests that autistic children may be capable of performing at a higher level than they typically function. This article describes research in the area of 'learned helplessness' which suggests that autistic children's handicaps may expose them to frequent failure and to an unusual level of non-contingent reinforcement which may produce a 'learned helplessness' state of extremely low motivation, with a consequent abnormally low overall functioning level. The present article also discusses research on strategies which might be employed to improve autistic children's exposure to favourable response-reinforcer contingencies. This would be expected to improve the general level of motivation in such children, with related gains in the acquisition, generalization maintenance of a broad array of target behaviours.

Autistic Disorder↗