Biomedical subjects

David C Zhu

Publications and source records attributed to David C Zhu.

7 recordsLinked to original sources

PubMed2006

Cortical activation to indoor versus outdoor scenes: an fMRI study.

Prior studies identify two cortical areas, posterior parahippocampal cortex and retrosplenial cortex, that preferentially activate to images of real-world scenes compared to images of other meaningful visual stimuli such as objects and faces. Behavioral and computational studies suggest that sub-categories of real-world scenes differ in their visual and semantic properties. It is presently unknown whether the cortical areas that have been implicated in scene analysis similarly activate differentially to behaviorally relevant scene sub-categories. To examine this issue, we directly compared cortical activation to indoor and outdoor scenes in an fMRI study with a large number of non-repeated images in each condition. Activation in posterior parahippocampal cortex, including parahippocampal place area, was significantly greater for indoor than outdoor scenes. In contrast, no such difference was observed in retrosplenial cortex, though this region preferentially activated to scenes over faces. These findings suggest differences in function in these two areas. The results are consistent with the view that posterior parahippocampal cortex is functional in processing local space.

Adolescent↗

PubMed2006

Changes in the amplitude and timing of the hemodynamic response associated with prepulse inhibition of acoustic startle.

Disruption of the early stages of information processing in limbic brain circuits may underlie symptoms of severe neuropsychiatric disorders. Prepulse inhibition of acoustic startle (PPI) is diminished in many of these disorders and may reflect the disruption of this CNS function. PPI is associated with brain activity in many of the same regions in humans as it is in laboratory animals, suggesting that neuroimaging studies in humans may help localize deficits that can then be elucidated in animal models. In this article, we employed a rapid presentation event-related design during continuous EPI BOLD scanning to examine hemodynamic response functions (HRFs) associated with PPI. Fourteen healthy participants listened to 100 pulse alone and 100 prepulse combined with pulse (prepulse-pulse) trials. PPI is the normalized difference in the startle response to the two trial types. Following the prepulse-pulse trials, the amplitudes of the HRFs in auditory cortices and in the anterior insula were increased, while in the cerebellum, thalamus and anterior cingulate, they were decreased, relative to the pulse alone trials. In addition, the timing of the prepulse-pulse responses was delayed in the auditory cortices, anterior insula and cerebellum. Finally, PPI measured outside the scanner was predicted by the difference in BOLD responses between trial types in the anterior insula and in the cerebellum. The results suggest that prepulse inhibition, and by extension early stages of information processing, modulate both the amplitude as well as timing of neural activity.

Acoustic Stimulation↗

PubMed2006

Dynamics of lateral ventricle and cerebrospinal fluid in normal and hydrocephalic brains.

PURPOSE: To develop quantitative MRI techniques to measure, model, and visualize cerebrospinal fluid (CSF) hydrodynamics in normal subjects and hydrocephalic patients. MATERIALS AND METHODS: Velocity information was obtained using time-resolved (CINE) phase-contrast imaging of different brain regions. A technique was developed to measure the change of lateral ventricle (LV) size. The temporal relationships between the LV size change, CSF movement, and blood flow could then be established. The data were incorporated into a first-principle CSF hydrodynamic model. The model was then used to generate specific predictions about CSF pressure relationships. To better-visualize the CSF flow, a color-coding technique based on linear transformations was developed that represents the magnitude and direction of the velocity in a single cinematic view. RESULTS: The LV volume change of the eight normal subjects was 0.901+/-0.406%. Counterintuitively, the LV decreases as the choroid plexus expands, so that they act together to produce the CSF oscillatory flow. The amount of oscillatory flow volume is 21.7+/-10.6% of the volume change of the LV from its maximum to its minimum. CONCLUSION: The quantification and visualization techniques, together with the mathematical model, provide a unique approach to understanding CSF flow dynamics.

Adult↗

PubMed2005

Full-brain T1 mapping through inversion recovery fast spin echo imaging with time-efficient slice ordering.

Brain T1 mapping has important clinical applications in detecting brain disorders. Conventional T1 mapping techniques are usually based on inversion recovery spin echo (IRSE) imaging or its more time-efficient counterpart inversion recovery fast spin echo (IRFSE) imaging because they can deliver good image quality. Multiple inversion times are required to accurately estimate T1 over a wide range of values. Without acquisition optimization, both the IRSE and the IRFSE T1 mapping techniques require long scan times to image the whole brain. To reduce the scan time and maintain the quality of the T1 maps, we propose a new full-brain T1 mapping pulse sequence based on a multislice inversion recovery fast spin echo imaging using a time-efficient slice ordering technique.

Adult↗

PubMed2005

Pulsatile cerebrospinal fluid dynamics in the human brain.

Disturbances of the cerebrospinal fluid (CSF) flow in the brain can lead to hydrocephalus, a condition affecting thousands of people annually in the US. Considerable controversy exists about fluid and pressure dynamics, and about how the brain responds to changes in flow patterns and compression in hydrocephalus. This paper presents a new model based on the first principles of fluid mechanics. This model of fluid-structure interactions predicts flows and pressures throughout the brain's ventricular pathways consistent with both animal intracranial pressure (ICP) measurements and human CINE phase-contrast magnetic resonance imaging data. The computations provide approximations of the tissue deformations of the brain parenchyma. The model also quantifies the pulsatile CSF motion including flow reversal in the aqueduct as well as the changes in ICPs due to brain tissue compression. It does not require the existence of large transmural pressure differences as the force for ventricular expansion. Finally, the new model gives an explanation of communicating hydrocephalus and the phenomenon of asymmetric hydrocephalus.

Brain↗

PubMed2004

The interaction of social and emotional processes in the brain.

Social stimuli function as emotional barometers for the immediate environment are the catalysts for many emotional reactions, and have inherent value for relationships and survival independent of their current emotional content. We, therefore, propose that the neural mechanisms underlying social and emotional information processing may be interconnected. In the current study, we examined the independent and interactive effects of social and emotional processes on brain activation. Whole-brain images were acquired while participants viewed and categorized affective pictures that varied on two dimensions: emotional content (i. e., neutral, emotional) and social content (i. e., faces/people, objects/scenes). Patterns of activation were consistent with past findings demonstrating that the amygdala and part of the visual cortex were more active to emotionally evocative pictures than to neutral pictures and that the superior temporal sulcus was more active to social than to nonsocial pictures. Furthermore, activation of the superior temporal sulcus and middle occipito-temporal cortex showed evidence of the interactive processing of emotional and social information, whereas activation of the amygdala showed evidence of additive effects. These results indicate that interactive effects occur early in the stream of processing, suggesting that social and emotional information garner greater attentional resources and that the conjunction of social and emotional cues results in synergistic early processing, whereas the amygdala appears to be primarily implicated in processing biologically or personally relevant stimuli, regardless of the nature of the relevance (i. e., social, emotional, or both).

Adolescent↗

PubMed2003

Breast tissue differentiation using arterial spin tagging.

An arterial spin tagging (AST) pulse sequence has been developed to measure T(1) and relative blood perfusion. This full sequence is composed of three sequences: selective tagging, nonselective tagging, and nontagging. Perfusion quantification error resulting from imperfect inversion and acquisition slice profiles has been addressed in the literature. In this work, the error is reduced through the application of optimized Shinnar-Le Roux (SLR) RF pulses and a semi-log linear regression data-processing technique. A threshold approach based on the breast tissue T(1) and relative blood perfusion is introduced to show that these two parameters can be applied to breast tissue differentiation and potentially to cancer detection.

Breast↗