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Biomedical subjects

J A Fiez

Publications and source records attributed to J A Fiez.

At least 19 recordsLinked to original sources
PubMed2000

Lesion segmentation and manual warping to a reference brain: intra- and interobserver reliability.

The study of subjects with acquired brain damage has been an invaluable tool for exploring human brain function, and the description of lesion locations within and across subjects is an important component of this method. Such descriptions usually involve the separation of lesioned from nonlesioned tissue (lesion segmentation) and the description of the lesion location in terms of a standard anatomical reference space (lesion warping). The objectives of this study were to determine the sources and magnitude of variability involved in lesion segmentation and warping using the MAP-3 approach. Each of two observers segmented the lesion volume in ten brain-damaged subjects twice, so as to permit pairwise comparisons of both intra- and interobserver agreement. The segmented volumes were then warped to a reference brain using both a manual (MAP-3) and an automated (AIR-3) technique. Observer agreement between segmented and warped volumes was analyzed using four measures: volume size, distance between the volume surfaces, percentage of nonoverlapping voxels, and percentage of highly discrepant voxels. The techniques for segmentation and warping produced high agreement within and between observers. For example, in most instances, the warped volume surfaces created by different observers were separated by less than 3 mm. The performance of the automated warping technique compared favorably to the manual technique in most subjects, although important exceptions were found. Overall, these results establish benchmark parameters for expert and automated lesion transfer, and indicate that a high degree of confidence can be placed in the detailed anatomical interpretation of focal brain damage based upon the MAP-3 technique.

Brain Damage, Chronic↗
PubMed1999

A comment on the functional localization of the phonological storage subsystem of working memory.

Working memory, as defined by Baddeley and Hitch, is an interactive set of cognitive processes responsible for holding information online and available for analysis. Part of that system is a specialized subsystem devoted to maintaining verbal information; the verbal "slave" subsystem has as a core component a phonological store. For many years, the anatomical locus of the phonological store has been thought to be in the supramarginal and angular gyri of the speech dominant hemisphere, and functional neuroimaging studies provide broad support for this localization. However, a finer grained analysis of published experiments reveals two possible foci for the phonological store within the parietal lobe, neither of which has a pattern of functional activation that is fully consistent with the Baddeley and Hitch model. The purpose of the present paper is to review several studies relevant to the question of the localization of the phonological store and to suggest possible reasons the results are discrepant.

Humans↗
PubMed1999

Effects of lexicality, frequency, and spelling-to-sound consistency on the functional anatomy of reading.

Functional neuroimaging was used to investigate three factors that affect reading performance: first, whether a stimulus is a word or pronounceable non-word (lexicality), second, how often a word is encountered (frequency), and third, whether the pronunciation has a predictable spelling-to-sound correspondence (consistency). Comparisons between word naming (reading) and visual fixation scans revealed stimulus-related activation differences in seven regions. A left frontal region showed effects of consistency and lexicality, indicating a role in orthographic to phonological transformation. Motor cortex showed an effect of consistency bilaterally, suggesting that motoric processes beyond high-level representations of word phonology influence reading performance. Implications for the integration of these results into theoretical models of word reading are discussed.

Adult↗
PubMed1998

The effects of practice on the functional anatomy of task performance.

The effects of practice on the functional anatomy observed in two different tasks, a verbal and a motor task, are reviewed in this paper. In the first, people practiced a verbal production task, generating an appropriate verb in response to a visually presented noun. Both practiced and unpracticed conditions utilized common regions such as visual and motor cortex. However, there was a set of regions that was affected by practice. Practice produced a shift in activity from left frontal, anterior cingulate, and right cerebellar hemisphere to activity in Sylvian-insular cortex. Similar changes were also observed in the second task, a task in a very different domain, namely the tracing of a maze. Some areas were significantly more activated during initial unskilled performance (right premotor and parietal cortex and left cerebellar hemisphere); a different region (medial frontal cortex, "supplementary motor area") showed greater activity during skilled performance conditions. Activations were also found in regions that most likely control movement execution irrespective of skill level (e.g., primary motor cortex was related to velocity of movement). One way of interpreting these results is in a "scaffolding-storage" framework. For unskilled, effortful performance, a scaffolding set of regions is used to cope with novel task demands. Following practice, a different set of regions is used, possibly representing storage of particular associations or capabilities that allow for skilled performance. The specific regions used for scaffolding and storage appear to be task dependent.

Brain↗
PubMed1998

Neuroimaging studies of word reading.

This review discusses how neuroimaging can contribute to our understanding of a fundamental aspect of skilled reading: the ability to pronounce a visually presented word. One contribution of neuroimaging is that it provides a tool for localizing brain regions that are active during word reading. To assess the extent to which similar results are obtained across studies, a quantitative review of nine neuroimaging investigations of word reading was conducted. Across these studies, the results converge to reveal a set of areas active during word reading, including left-lateralized regions in occipital and occipitotemporal cortex, the left frontal operculum, bilateral regions within the cerebellum, primary motor cortex, and the superior and middle temporal cortex, and medial regions in the supplementary motor area and anterior cingulate. Beyond localization, the challenge is to use neuroimaging as a tool for understanding how reading is accomplished. Central to this challenge will be the integration of neuroimaging results with information from other methodologies. To illustrate this point, this review will highlight the importance of spelling-to-sound consistency in the transformation from orthographic (word form) to phonological (word sound) representations, and then explore results from three neuroimaging studies in which the spelling-to-sound consistency of the stimuli was deliberately varied. Emphasis is placed on the pattern of activation observed within the left frontal cortex, because the results provide an example of the issues and benefits involved in relating neuroimaging results to behavioral results in normal and brain damaged subjects, and to theoretical models of reading.

Brain↗
PubMed1997

Standardized stimuli and procedures for investigating the retrieval of lexical and conceptual knowledge for actions.

We have developed a set of naming and recognition tests for evaluating the retrieval of lexical and conceptual knowledge for actions. As a first step, normative information about 280 items was collected for the following variables: (1) the naming responses elicited by each item, (2) the degree to which the image of each item agreed with a target name, (3) the familiarity to each depicted action, and (4) the visual complexity of each item. This information was used to develop administration and scoring procedures for a standardized test of action naming. The effectiveness and reliability of these procedures were evaluated in a second experiment. In a third experiment, five tests were developed to probe the retrieval of conceptual knowledge: (1) independently of the production of a naming response, (2) in response to pictorial and nonpictorial stimuli, (3) in terms of the attributes associated with specific actions, and (4) in terms of similarities and differences between various actions.

Humans↗
PubMed1996

A positron emission tomography study of the short-term maintenance of verbal information.

Positron emission tomography (PET) was used to investigate the functional brain anatomy associated with the short-term maintenance of linguistic information. Subjects were asked to retain five related words, unrelated words, or pseudowords silently for the duration of a 40 sec PET scan. When brain activity during these short-term maintenance tasks was compared with a visual fixation control task, increases were found bilaterally in the dorsolateral prefrontal cortex and cerebellum, and medially in the supplementary motor area. Furthermore, effects of stimulus condition and recall performance were found in the left frontal operculum. To investigate the role of articulatory systems in the maintenance of verbal information, regional activation was compared across the maintenance tasks and a covert articulation task (silent counting). The cerebellum was active in both task conditions, whereas activation in prefrontal regions was specific to the maintenance condition. Conversely, greater activation was found in a left middle insular region in the silent counting than in the maintenance tasks. Based on converging results in this and previous studies, dorsolateral prefrontal cortical areas appear to contribute to the maintenance of both verbal and nonverbal information, whereas left frontal opercular regions appear to be involved specifically in the rehearsal of verbal material. Contrary to results found in other studies of working memory, activation was not found in the inferior parietal cortex, suggesting that this area is involved in aspects of stimulus encoding and retrieval, which were minimized in the present study.

Adult↗
PubMed1992

Neuroimaging.

Recent advances in neuroimaging have led to an increase in the types of studies possible in the field of cognitive neuroscience. Researchers are now using neuroimaging to enhance classic approaches, such as lesion-behavior studies, as well as provide information about normal functions at levels that were previously difficult to assess.

Animals↗
PubMed1992

Impaired non-motor learning and error detection associated with cerebellar damage. A single case study.

A previously conducted positron emission tomography (PET) study of normal humans suggested that the cerebellum makes important non-motor contributions to language processing. Beginning with the task which produced right cerebellar PET activation, we studied a 49-yr-old male (RC1) with right cerebellar damage on a variety of tasks involving complex non-motor processing. Whereas RC1's performance on standard tests of memory, intelligence, 'frontal function' and language skills was excellent, he had profound deficits in two areas: (1) practice-related learning; (2) detection of errors. Considered in relation to cerebellar contributions to motor tasks, the results suggest some functions performed by the cerebellum may be generalized beyond a purely motor domain.

Cerebellar Diseases↗
PubMedDate not supplied

Practice-related changes in human brain functional anatomy during nonmotor learning.

Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

Adult↗
PubMedDate not supplied

PET activation of posterior temporal regions during auditory word presentation and verb generation.

Previous studies using positron emission tomography (PET) report blood flow changes in superior and middle temple gyri associated with auditory and language tasks (Petersen et al., 1988, 1989; Wise et al., 1991; Demonet et al., 1992; Howard et al., 1992; Sergent et al., 1992; Zatorre et al., 1992; Petrides et al., 1993; Raichle et al., 1994; Fiez et al., 1995). An important issue is whether these changes reflect the activation of a single functional region or multiple regions with distinct functional contributions. In the present study, we examined this issue by focusing upon two tasks for which we have previously reported posterior temporal blood flow changes: listening to auditorily presented words (Petersen et al., 1988, 1989), and generation of a verb in response to a visually presented noun (Raichle et al., 1994); see also Wise et al. (1991). We began by further characterizing a left temporoparietal region of change previously associated with auditory word presentation. This previously reported response was replicated, and the results were extended by demonstrating presentation of pseudowords also produced activation. We next asked whether the activation associated with auditory word presentation could be distinguished from that associated with the generation of verbs in response to visually presented nouns. It was found that the activations associated with these two tasks could be both functionally and spatially dissociated. Thus, two posterior temporal areas associated with auditory word presentation and verb generation appear to represent distinct areas concerned with word processing. More generally, the results demonstrate an approach for assessing the independence of two activated areas.

Acoustic Stimulation↗