Biomedical subjects

J Jovicich

Publications and source records attributed to J Jovicich.

5 recordsLinked to original sources

PubMed2002

Abnormal brain activation on functional MRI in cognitively asymptomatic HIV patients.

BACKGROUND/OBJECTIVES: A previous fMRI study demonstrated increased brain activation during working memory tasks in patients with HIV with mild dementia. The current study aims to determine whether patients who are HIV-1 positive and have normal cognitive function also show increased brain activation on fMRI. METHODS: Blood oxygenation level-dependent (BOLD) fMRI was performed in 10 patients with HIV (CD <500) and 10 age-, sex-, education-, and handedness-matched seronegative subjects. Each subject performed a battery of neuropsychological tests and fMRI with three tasks (0-back, 1-back, and 2-back) that required different levels of attention for working memory. RESULTS: Compared with control subjects, patients with HIV showed greater magnitude of brain activation (BOLD signal intensity changes, p <or= 0.001) in the lateral prefrontal cortex, with normal performance during fMRI and on a battery of neuropsychological tests. The patients with HIV also showed increased activated brain volume in the lateral prefrontal cortex (p = 0.007) but not in other activated regions, including the posterior parietal cortex, supplementary motor area, thalamus, caudate, and occipital cortex. The increase in activated brain volume was independent of task difficulty. CONCLUSION: Increased brain activation in subjects who are positive for HIV precedes clinical signs or deficits on cognitive tests. Early injury to the neural substrate may necessitate increased usage of brain reserve to maintain normal cognitive function. BOLD fMRI appears to be more sensitive than clinical and neuropsychological evaluations for detecting early HIV-associated brain injury.

AIDS Dementia Complex↗

PubMed2001

Brain areas specific for attentional load in a motion-tracking task.

Although visual attention is known to modulate brain activity in the posterior parietal, prefrontal, and visual sensory areas, the unique roles of these areas in the control of attentional resources have remained unclear. Here, we report a dissociation in the response profiles of these areas. In a parametric functional magnetic resonance imaging (fMRI) study, subjects performed a covert motion-tracking task, in which we manipulated "attentional load" by varying the number of tracked balls. While strong effects of attention--independent of attentional load--were widespread, robust linear increases of brain activity with number of balls tracked were seen primarily in the posterior parietal areas, including the intraparietal sulcus (IPS) and superior parietal lobule (SPL). Thus, variations in attentional load revealed different response profiles in sensory areas as compared to control areas. Our results suggest a general role for posterior parietal areas in the deployment of visual of attentional resources.

Adult↗

PubMed2001

Neural correlates of attention and working memory deficits in HIV patients.

OBJECTIVES: To evaluate the neural correlates of attention and working memory deficits in patients with HIV-1. METHOD: fMRI was used to evaluate brain activity in 11 patients with HIV and 11 age-, sex-, education-, and handedness-matched seronegative subjects, while performing a battery of tasks that required different levels of attention for working memory. RESULTS: Patients with HIV showed greater brain activation (blood oxygenation level dependent signal changes) in some regions compared with control subjects while performing the same tasks. For the simpler tasks, patients with HIV showed greater activation in the parietal regions. However, with more difficult tasks, patients with HIV showed greater activation additionally in the frontal lobes. Reaction times during these tasks were slower but accuracy was similar in the patients with HIV compared with control subjects. CONCLUSION: Injury to the neural substrate caused by HIV infection may necessitate greater attentional modulation of the neural circuits, hence a greater use of the brain reserve; additional activation of the frontal lobes is required to perform the more complex tasks. The task-dependent increased frontal activation in patients with HIV suggests that the neural correlate of attentional deficits may be excessive attentional modulation as a result of frontostriatal brain injury.

AIDS Dementia Complex↗

PubMed1999

Functional MRI of the human brain with GRASE-based BOLD contrast.

The application of T2*-weighted gradient and spin-echo (GRASE) imaging was investigated as a method for blood oxygenation level-dependent (BOLD)-based functional magnetic resonance imaging (fMRI). The displaced-echo method was implemented to produce single-shot T2*-weighted GRASE images. This technique removes the requirement that the Carr-Purcell Meiboom-Gill (CPMG) condition be fulfilled. T2*-weighted GRASE images that are free from interference artifacts can thus be obtained, hence allowing the possibility of using single-shot GRASE for BOLD-based functional imaging. The method was demonstrated at 3 T and gave robust and reproducible activation-induced signal changes.

Artifacts↗

PubMed1998

GRASE imaging at 3 Tesla with template interactive phase-encoding.

A new method for ordering the phase-encoding gradient is proposed, and an application for short effective TE gradient- and spin-echo (GRASE) imaging is demonstrated. The proposed method calculates the phase-encoding order from the signal decay of a template scan (hence "template interactive phase-encoding" or TIPE). Computer simulations are used to compare the point spread functions of different phase-encoding orders giving short effective echo times (kb centric GRASE, centric GRASE, centric TIPE). The conventional centric phase-encoding order is also considered for GRASE. The conventional centric method is sensitive to both amplitude and phase modulation of the signal in k-space. The centric TIPE method gives the least amplitude modulation artifacts but is vulnerable to phase artifacts. The TIPE experiment was implemented on a 3 Tesla system. To the best of our knowledge, we present the first in vivo GRASE images at this field strength.

Artifacts↗