Gary Glover

YNIMG Journal 2013 Journal Article

Ferumoxytol enhanced resting state fMRI and relative cerebral blood volume mapping in normal human brain

• Helen D'Arceuil
• Alexandre Coimbra
• Pamela Triano
• Margaret Dougherty
• Julie Mello
• Michael Moseley
• Gary Glover
• Maarten Lansberg

The brain demonstrates spontaneous low-frequency (<0. 1Hz) cerebral blood flow (CBF) fluctuations, measurable by resting state functional MRI (rs-fMRI). Ultra small superparamagnetic iron oxide particles have been shown to enhance task-based fMRI signals (cerebral blood volume fMRI or CBV-fMRI), compared to the BOLD effect, by a factor of ≈2. 5 at 3T in primates and humans. We evaluated the use of ferumoxytol for steady state, resting state FMRI (CBV-rs-fMRI) and relative cerebral blood volume (rCBV) mapping, at 3T, in healthy volunteers. All standard resting state networks (RSNs) were identified in all subjects. On average the RSN Z statistics (MELODIC independent components) and volumes of the visual and default mode (DMN) networks were comparable. rCBV values were averaged for the visual (Vis) and DMN networks and correlated with the corresponding DMN and visual network Z statistics. There was a negative correlation between the rCBV and the Z statistics for the DMN, for both BOLD and CBV-rs-fMRI contrast (R2 =0. 63, 0. 76). A similar correlation was not found for the visual network. Short repetition time rs-fMRI data were Fourier transformed to evaluate the effect of ferumoxytol on cardiac and respiratory fluctuations in the brain rs-BOLD, CBV signals. Cardiac and respiratory fluctuations decreased to baseline within large vessels post ferumoxytol. Robust rs-fMRI and CBV mapping is possible in normal human brain.

YNIMG Journal 2011 Journal Article

Multisite reliability of cognitive BOLD data

• Gregory G. Brown
• Daniel H. Mathalon
• Hal Stern
• Judith Ford
• Bryon Mueller
• Douglas N. Greve
• Gregory McCarthy
• James Voyvodic

Investigators perform multi-site functional magnetic resonance imaging studies to increase statistical power, to enhance generalizability, and to improve the likelihood of sampling relevant subgroups. Yet undesired site variation in imaging methods could off-set these potential advantages. We used variance components analysis to investigate sources of variation in the blood oxygen level-dependent (BOLD) signal across four 3-T magnets in voxelwise and region-of-interest (ROI) analyses. Eighteen participants traveled to four magnet sites to complete eight runs of a working memory task involving emotional or neutral distraction. Person variance was more than 10 times larger than site variance for five of six ROIs studied. Person-by-site interactions, however, contributed sizable unwanted variance to the total. Averaging over runs increased between-site reliability, with many voxels showing good to excellent between-site reliability when eight runs were averaged and regions of interest showing fair to good reliability. Between-site reliability depended on the specific functional contrast analyzed in addition to the number of runs averaged. Although median effect size was correlated with between-site reliability, dissociations were observed for many voxels. Brain regions where the pooled effect size was large but between-site reliability was poor were associated with reduced individual differences. Brain regions where the pooled effect size was small but between-site reliability was excellent were associated with a balance of participants who displayed consistently positive or consistently negative BOLD responses. Although between-site reliability of BOLD data can be good to excellent, acquiring highly reliable data requires robust activation paradigms, ongoing quality assurance, and careful experimental control.

YNIMG Journal 2009 Journal Article

The bivalent side of the nucleus accumbens

• Liat Levita
• Todd A. Hare
• Henning U. Voss
• Gary Glover
• Douglas J. Ballon
• B.J. Casey

An increasing body of evidence suggests that the nucleus accumbens (NAcc) is engaged in both incentive reward processes and in adaptive responses to conditioned and unconditioned aversive stimuli. Yet, it has been argued that NAcc activation to aversive stimuli may be a consequence of the rewarding effects of their termination, i. e. , relief. To address this question we used fMRI to delineate brain response to the onset and offset of unpleasant and pleasant auditory stimuli in the absence of learning or motor response. Increased NAcc activity was seen for the onset of both pleasant and unpleasant stimuli. Our results support the expanded bivalent view of NAcc function and call for expansion of current models of NAcc function that are solely focused on reward.

YNIMG Journal 2007 Journal Article

Sensitivity of the nucleus accumbens to violations in expectation of reward

• Julie Spicer
• Adriana Galvan
• Todd A. Hare
• Henning Voss
• Gary Glover
• BJ Casey

This study examined whether ventral frontostriatal regions differentially code expected and unexpected reward outcomes. We parametrically manipulated the probability of reward and examined the neural response to reward and nonreward for each probability condition in the ventral striatum and the orbitofrontal cortex (OFC). By late trials of the experiment, subjects showed slower behavioral responses for the condition with the lowest probability of reward, relative to the condition with the highest probability of reward. At the neural level, both the nucleus accumbens (NAcc) and OFC showed greater activation to rewarded relative to nonrewarded trials, but the accumbens appeared to be most sensitive to violations in expected reward outcomes. These data suggest distinct roles for frontostriatal circuitry in reward prediction and in responding to violations in expectations.

YNIMG Journal 2005 Journal Article

Contributions of the hippocampus and the striatum to simple association and frequency-based learning

• Dima Amso
• Matthew C. Davidson
• Scott P. Johnson
• Gary Glover
• B.J. Casey

Using fMRI and a learning paradigm, this study examined the independent contributions of the hippocampus and striatum to simple association and frequency-based learning. We scanned 10 right-handed young adult subjects using a spiral in/out sequence on a GE 3. 0 T scanner during performance of the learning paradigm. The paradigm consisted of 2 cues that predicted each of 3 targets with varying probabilities. Simultaneously, we varied the frequency with which each target was presented throughout the task, independent of cue associations. Subjects had shorter response latencies to frequently occurring and highly associated target stimuli and longer response latencies to infrequent target stimuli, indicating learning. Imaging results showed increased caudate activity to infrequent relative to frequent targets and increased hippocampal activity to infrequent relative to frequent cue–target associations. This work provides evidence of different neural mechanisms underlying learning based on simple frequencies versus associations within a single paradigm.

YNIMG Journal 2001 Journal Article

Analysis of noise reduction using independent component analysis

• Toshiharu Nakai
• Shigeru Muraki
• Kayako Matsuo
• Chikako Kato
• Gary Glover
• Tetsuo Moriya

YNIMG Journal 2000 Journal Article

The auditory attention system during dual listening task performance

• Toshi Nakai
• Kayako Matsuo
• Chikako Kato
• Shigeki Tanaka
• Gary Glover
• Tetsuo Moriya
• Tomohisa Okada

YNIMG Journal 1999 Journal Article

A FAIR Study of Motor Cortex Activation under Normo- and Hypercapnia Induced by Breath Challenge

• Tie-Qiang Li
• Michael E. Moseley
• Gary Glover

In this study an arterial spin-tagging technique based on flow-sensitive alternating inversion recovery (FAIR) with single-shot spiral data acquisition was used to study how the basal cerebral blood flow (CBF) elevated by breath holding affects the regional cerebral blood flow (rCBF) response to focal brain activation in the motor cortex. Six subjects were examined using three types of activation studies. These were (a) bilateral finger tapping paced at 4 Hz under normal breathing, (b) repeated expiration breath holding of 30 s, and (c) simultaneous breath holding and finger tapping. It was found that in five of six subjects the prevailing CBF level adjusted by breath challenge and the increase in rCBF in motor cortex associated with bilateral finger tapping were completely additive. This finding from FAIR-based functional magnetic resonance imaging is in accordance with that reported from published positron emission tomography studies. The results indicate that in the majority of the subjects examined the regulatory mechanisms for vasodilatory reaction to CO2 and rCBF response to neural activation in motor cortex region are independent.