Biomedical subjects

Todd B Parrish

Publications and source records attributed to Todd B Parrish.

14 recordsLinked to original sources

PubMed2025

The Consortium for Clarity in ADRD Research Through Imaging (CLARiTI): Overview of consortium sites and anticipated enrollment.

INTRODUCTION: The Consortium for Clarity in Alzheimer's disease related dementias (ADRD) Research Through Imaging (CLARiTI) is a study that aims to collect standardized imaging and plasma biomarkers on 2000 Clinical Core participants enrolled across all Alzheimer's Disease Research Centers (ADRC) sites. We sought to summarize the known heterogeneity across centers regarding scientific focus and initial enrollment plans for CLARiTI. METHODS: We developed and distributed a survey capturing information on the 36 CLARiTI site's theme/expertise, recruitment plans, and the intersection of CLARiTI with other ADRC imaging efforts. RESULTS: Anticipated CLARiTI enrollees spanned 11 different categories of suspected etiologies underlying impairment. A wide range of risk factors were endorsed across sites regarding the enrollment of unimpaired individuals. Variability also existed regarding site-level strategies in enrollment into CLARiTI versus other imaging efforts. DISCUSSION: We anticipate that the 2000 individuals that will enroll into CLARiTI will reflect the clinical heterogeneity already in place across the ADRC network. HIGHLIGHTS: The ADRC Consortium for Clarity in ADRD Research Through Imaging (CLARiTI) will leverage and contribute to the existing Alzheimer's Disease Research Centers (ADRC) program by supporting standardized imaging and plasma collection across all centers. We summarize the variation in scientific focus and enrollment plans across ADRC sites participating in CLARiTI. The anticipated CLARiTI cohort will reflect the clinical heterogeneity that already exists across the ADRC network. CLARiTI will contribute to scientific goals related to the detection of multi-etiological signatures relevant for Alzheimer's disease and related disorders (ADRDs).

Humans↗

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

Primary progressive aphasia: PPA and the language network.

Primary Progressive Aphasia (PPA) is a behaviorally focal dementia syndrome with deterioration of language functions but relative preservation of other cognitive domains for at least the first two years of disease. In this study, PPA patients with impaired word finding but intact comprehension of conversational speech and their matched control subjects were examined using voxel-based morphometry (VBM) and functional magnetic resonance imaging (fMRI). fMRI compared signal changes during phonological and semantic language tasks with those during a control task (matching letters). PPA patients showed longer reaction times and reduced accuracy versus controls on the language tasks, but no performance differences on the control task. VBM demonstrated reduced gray matter in left superior temporal and inferior parietal regions in the PPA group. However, these patients showed a normal pattern of activation within the classical language regions. In addition, PPA patients showed activations, not seen in normals, in fusiform gyrus, precentral gyrus, and intra-parietal sulcus. These activations were found to correlate negatively with measures of naming and task performance. The additional activations in PPA may therefore represent a compensatory spread of language-related neural activity or a failure to suppress activity in areas normally inhibited during language tasks.

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

Brain networks for analyzing eye gaze.

The eyes convey a wealth of information in social interactions. This information is analyzed by multiple brain networks, which we identified using functional magnetic resonance imaging (MRI). Subjects attempted to detect a particular directional cue provided either by gaze changes on an image of a face or by an arrow presented alone or by an arrow superimposed on the face. Another control condition was included in which the eyes moved without providing meaningful directional information. Activation of the superior temporal sulcus accompanied extracting directional information from gaze relative to directional information from an arrow and relative to eye motion without relevant directional information. Such selectivity for gaze processing was not observed in face-responsive fusiform regions. Brain activations were also investigated while subjects viewed the same face but attempted to detect when the eyes gazed directly at them. Most notably, amygdala activation was greater during periods when direct gaze never occurred than during periods when direct gaze occurred on 40% of the trials. In summary, our results suggest that increases in neural processing in the amygdala facilitate the analysis of gaze cues when a person is actively monitoring for emotional gaze events, whereas increases in neural processing in the superior temporal sulcus support the analysis of gaze cues that provide socially meaningful spatial information.

Adult↗

PubMed2002

Neural correlates of successful encoding identified using functional magnetic resonance imaging.

Neural activity that occurs during the creation of a new memory trace can be observed using functional magnetic resonance imaging (fMRI). Event-related designs have been used to demonstrate that activity in prefrontal and medial temporal lobe areas is associated with successful memory storage. Here we contrasted activity associated with encoding success and encoding effort. Participants viewed a series of 150 words but attempted to remember only half of them. Encoding effort was manipulated using a cue in the form of a letter (R or F) presented after each word to instruct participants either to remember or to forget that word. Increased activity in left inferior prefrontal cortex was observed when words were followed by the cue to remember. In contrast, increased left medial temporal lobe activity was observed for words that were successfully recalled later. These results show that fMRI correlates of the intention to encode a word are different from fMRI correlates of whether that encoding is successful. Prefrontal activation was strongly associated with intentional verbal encoding, whereas left medial temporal activation was crucial for the encoding that actually led to successful memory on the subsequent test.

Adolescent↗

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

On the use of caffeine as a contrast booster for BOLD fMRI studies.

This study explored the possible use of caffeine as an agent to improve the BOLD (blood oxygen level-dependent) signal response in fMRI. Previous research has demonstrated that caffeine has the ability to reset the level of coupling between blood flow and neuronal activity. In the present study, it has been shown that caffeine causes a decrease in cerebral perfusion by as much as 13.2% without a change in performance. Caffeine is a cerebral vasoconstrictor that causes an increase in the concentration of deoxyhemoglobin and thus a decrease in the BOLD baseline resting signal by 4.4%. During activation, the vasculature responds from below-normal baseline levels with a normal increase in blood flow and volume, resulting in an overall increase in the BOLD contrast. This increase can be as large as 22-37% during the performance of a visually cued motor task. The benefit of such a large increase in the BOLD contrast could be used to improve the image resolution, the acquisition scheme, or the task design of fMRI experiments. Caffeine has the potential to be used as a contrast booster for fMRI experiments.

Adult↗

PubMed2002

Functional anatomy of visual search: regional segregations within the frontal eye fields and effective connectivity of the superior colliculus.

The ability to find targets embedded within complex visual environments requires the dynamic programming of visuomotor search behaviors. Functional magnetic resonance imaging was used to image subjects while they visually searched for targets embedded among foils. Visuomotor search activated the posterior parietal cortex and the frontal eye fields. Both regions showed a greater number of activated voxels on the right, consistent with the known pattern of right hemispheric dominance for spatial attention. The superior colliculus showed prominent activation in the search versus eye movement contrast, demonstrating, for the first time in humans, activation of this region specifically related to an exploratory attentional contingency. An analysis of effective connectivity demonstrated that the search-dependent variance in the activity of the superior colliculus was significantly influenced by the activity in a network of cortical regions including the right frontal eye fields and bilateral parietal and occipital cortices. These experiments also revealed the presence of a mosaic of activated sites within the frontal eye field region wherein saccadic eye movements, covert shifts of attention, and visuomotor search elicited overlapping but not identical zones of activation. In contrast to the existing literature on functional imaging, which has focused on covert shifts of spatial attention, this study helps to characterize the functional anatomy of overt spatial exploration.

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

Reorganization of cortical language areas in patients with aphasia: a functional MRI study.

The purpose of this study is to delineate the pattern of reorganization of cortical language areas using functional magnetic resonance imaging (fMRI) after rehabilitation therapy in patients with aphasia. Six right-handed aphasic patients were investigated. Causes of aphasia were intracerebral hemorrhages of the left basal ganglia in 3 patients, cerebral infarction of the left MCA in 2, and surgical resection of the frontotemporal lobes to control intractable epilepsy in 1. An auditory sentence completion task was used to activate brain language areas during the fMRI. Three patients with left frontal lesions showed activation in the right inferior frontal lobes while performing language tasks, whereas the other 3, whose lesions located at subcortical areas, showed activation in the bilateral frontal and temporal lobes. Our results demonstrated the differences in interhemispheric reorganization of the language network depending on the location of the lesion in aphasic patients. While the patients with subcortical lesion showed tendency of bilateral frontal activation, those with cortical lesion showed activation of the right frontal lobe.

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↗

PubMedDate not supplied

Neural correlates of person recognition.

Rapidly identifying known individuals is an essential skill in human society. To elucidate the neural basis of this skill, we monitored brain activity while experimental participants demonstrated their ability to recognize people on the basis of viewing their faces. Each participant first memorized the faces of 20 individuals who were not known to the participants in advance. Each face was presented along with a voice simulating the individual speaking their name and a biographical fact. Following this learning procedure, the associated verbal information could be recalled accurately in response to each face. These learned faces were subsequently viewed together with new faces in a memory task. Subjects made a yes-no recognition decision in response to each face while also covertly retrieving the person-specific information associated with each learned face. Brain activity that accompanied this retrieval of person-specific information was contrasted to that when new faces were processed. Functional magnetic resonance imaging in 10 participants showed that several brain regions were activated during blocks of learned faces, including left hippocampus, left middle temporal gyrus, left insula, and bilateral cerebellum. Recordings of event-related brain potentials in 10 other participants tracked the time course of face processing and showed that learned faces engaged neural activity responsible for person recognition 300-600 msec after face onset. Collectively, these results suggest that the visual input of a recently learned face can rapidly trigger retrieval of associated person-specific information through reactivation of distributed cortical networks linked via hippocampal connections.

Adult↗