fMRI Fluctuations
Monday 20 April 2009
Room 323ABC 16:30-18:30

Moderators:

 Rasmus M. Birn and Mark J. Lowe
 
16:30  120. Resting State FMRI of Retinotopically Defined Sub-Regions in Human Visual Cortex
    Egbert J. W. Bleeker1,2, Hubert Fonteijn1,3, Elena Shumskaya1, Jens Schwarzbach1,4, David G. Norris1,5
1Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands; 2Leiden University Medical Centre, Leiden, Netherlands; 3University College , London, UK; 4Centre for Mind/Brain Science, Trento, Italy; 5Erwin L Hahn Institute for MRI, Essen, Germany
    This study examines the uniqueness of resting state connections between sub-regions of the human visual cortex. The sub-regions are defined using retinotopic mapping: eccentricity for central and peripheral regions; polar mapping for the main visual regions, and also to subdivide these into octants. Connectivity between sub-regions is evaluated using the partial correlation coefficients. Central to central and peripheral to peripheral connections are strong, but central to peripheral connections weaker. Octants generally show significant connections to either the same octant in a hierarchically adjacent or homologous area, or to a different octant in the same retinotopic region.
   

 
16:42 121. Sources of FMRI Signal Variance in the Human Brain at Rest: A 7T Study
    Marta Bianciardi1, Masaki Fukunaga1, Peter van Gelderen1, Silvina G. Horovitz1, Jacco A. de Zwart1, Karin Shmueli1, Jeff H. Duyn1
1Advanced MRI Section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, USA, Bethesda, MD, USA
    To exploit the increased BOLD contrast available at 7T for fMRI studies, it is crucial to identify the various noise sources. We determined the contribution of noise to fMRI signal fluctuations in the visual cortex and in the gray matter at 7T during rest. The following noise sources were considered: scanner instability, motion and BOLD effects due to respiration and cardiac cycles, thermal noise, and other sources, tentatively attributed to spontaneous neuronal activity. Our findings demonstrate that at 7T with a resolution of 3mm3 spontaneous fMRI activity is still one of the major contributors to the total fMRI signal fluctuations.
     
16:54 122. Physiological Noise in Gradient Echo and Spin Echo EPI at 3T and 7T
    Christina Triantafyllou1,2, Jonathan R. Polimeni2, Mattijs Elschot2,3, Lawrence L. Wald2,4
1A.A. Martinos Imaging Center,  McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; 2A.A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH, Charlestown, MA, USA; 3Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands; 4Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, USA
    The physiological noise in both spin echo and gradient echo EPI sequences as a function of (thermal) image SNR (SNR0) is investigated by modulating the spatial resolution, receive coil, and field strength. Our findings demonstrate that physiological noise in both sequences exhibit similar properties and the relationship between time-course SNR (tSNR) and SNR0 is well described by the same model. The largest gains in tSNR as a function of voxel size occurred at the highest spatial resolution. At coarser spatial resolutions, both field strengths and sequences showed asymptotic behavior, with higher field strengths nearing the asymptote at smaller voxel volumes.
     
17:06 123. Insights Into the Origin of Spontaneous Coherent BOLD Fluctuations in a Resting Rat Brain Under Varied Isoflurane Anesthesia Depth
    Xiao Liu1,2, Xiao-Hong Zhu1, Yi Zhang1, Wei Chen1,2
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, USA; 2Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA
   

This study observed the spontaneous coherent BOLD fluctuations in the somatosensory system of isoflurane-anesthetized rats. It was found that both the amplitude and coherence strength of the BOLD fluctuations could be modulated by changing the anesthesia level in the critical range of 1.8% ~ 2.2% isoflurane, and such anesthesia-level-dependent modulation of BOLD fluctuation is very similar to that of CBF fluctuation signal, which has been proven to be tightly coupled with simultaneous-recorded EEG signals. Therefore, the overall results suggest the neural origin of coherent BOLD fluctuations observed in the present study and thus provide an important MRI signal source for mapping resting-state connectivity.
   

 
17:18  124.

Spatiotemporal Correlation Between Alpha Modulation and BOLD Fluctuation in an Eyes-Open-Eyes-Closed Task
    Lin Yang1, Zhongming Liu1, Cristina Rios1, Han Yuan1, Bin He1
1Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA
    The purpose of this study is to investigate the spatial and temporal relationship between the electrophysiological alpha rhythmic modulation and the BOLD fluctuation using an eyes-open-eyes-closed task. We reconstructed the spatiotemporal cortical source activity underlying the task-modulated EEG alpha rhythm. The resulting source activity was compared, in both space and time, with the BOLD signal recorded with the same task. The cortical regions generating alpha modulation were co-localized with the fMRI activations/deactivations within the occipital and parietal lobes, where the alpha modulation was found temporally negatively correlated with the BOLD fluctuation. The results may suggest a common neural origin that accounts for both alpha modulation and BOLD fluctuation due to transitions between two common resting conditions.
     
17:30 125.  Functional MRI Study on Brain Plasticity Induced by Different Peripheral Nerve Injury Patterns: What Makes the Difference?
    Rupeng Li1, Seth Jones2, Christopher Pawela1, Maida Parkins2, Daniel Shefchik1, Mark Bosbous2, Ji-Geng Yan2, Safwan S. Jaradeh3, Hani S. Matloub2, James S. Hyde1
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA; 2Plastic Surgery, Medical College of Wisconsin, Milwaukee, WI, USA; 3Neurology, Medical College of Wisconsin, Milwaukee, WI, USA
    This study reveals, for the first time using (fMRI), brain plasticity patterns that are induced by various peripheral nerve injuries. The methodology provides a laboratory basis for selection of optimum surgical procedures.
     
17:42 126. Development of the Brain Default Mode Network from Wakefulness Into Slow Wave Sleep
    Philipp G. Sämann1, Renate Wehrle1, Victor I. Spoormaker1, David Höhn1, Henning Peters1, Florian Holsboer1, Michael Czisch1
1Max-Planck-Institute of Psychiatry, Munich, Germany
   

We report preserved DMN activity throughout all human NREM sleep stages, including so far unreported human slow wave sleep, from EEG validated group analysis. Vigilance was found a critical determinant of general DMN strength and of posterior and anterior DMN nodes as well as temporomesial contributions. We observed retreat of temporomesial contributions to the DMN, possibly related to reduced access to memory during sleep, reduction of PCC/retrosplenial and thalamic contribution, likely reflecting more the arousal systems, and increasing decoupling of medial prefrontal areas from the DMN, that may reflect reduced self-awareness.
     
17:54 127.   Decoupling of the Default Mode Network During Deep Sleep
    Silvina G. Horovitz1,2, Allen R. Braun3, Walter S. Carr4, Dante Picchioni5, Thomas J. Balkin5, Masaki Fukunaga2, Jeff H. Duyn2
1Human Motor Control Section - MNB, NINDS-NIH, Bethesda, MD, USA; 2Advanced MRI - LFMI, NINDS-NIH, Bethesda, MD, USA; 3Language Section Voice, Speech and Language Branch , NIDCD - NIH, Bethesda, MD, USA; 4MSC USN, Naval Medical Research Center, Silver Srping, MD, USA; 5Department of Behavioral Biology, Walter Reed Army Institute of Research, Silver Srping, MD, USA
    The default-mode-network (DMN) is a collection of brain regions highly active in absence of overt behavior. Its function has been attributed to self-reflective thoughts, though it has also been observed in light-sleep and in anesthetized monkeys. Here, we studied the human DMN connectivity during deep sleep, a condition devoid of self-reflective thoughts and low conscious awareness. We show a decoupling of anterior and posterior portions of the DMN, suggesting that reduction of consciousness is reflected in altered levels of network coherence. The activity in each area remains unchanged suggesting it is not activity per-se but rather the coherent activation of the parts that lead to a conscious experience.
     
18:06 128. Influence of Spontaneous BOLD Fluctuation on Stimulus-Evoked BOLD in Human Visual Cortex Using Event-Related Paradigm
    Xiao Liu1, Xiao-Hong Zhu1, Wei Chen1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, USA
    This study found that the spontaneous BOLD fluctuations account for the trial-to-trial variation of stimulus-evoked BOLD responses in human visual cortex, and thus confirmed the linear superimposition of spontaneous BOLD fluctuation and stimulus-evoked BOLD signal in the event-related fMRI studies. Combined with the results from one previous study using continuous visual stimulation, it also suggested that the instantaneous stimuli used by the event-related studies could probably only perturb the spontaneous brain activity briefly and slightly, and thus result in the linear superimposition of BOLD signals approximately, which however could not hold when continuous stimuli are used to constantly stimulate the brain.
     
18:18 129.  Resting-State Connections in Prefrontal Cortex Indicate Cognitive Network Efficiency During Working Memoryτ
    Jolyn Nicole Alexis D'Andrea1, Bradley G. Goodyear2
1Medical Science, University of Calgary, Calgary, Alberta, Canada; 2Radiology, University of Calgary, Calgary, Alberta, Canada
   

The dorsolateral prefrontal cortex (DLFPC) has been identified as critical for working memory, especially as task difficulty increases. The current study used fMRI to investigate resting-state connectivity between left and right DLPFC, and its relationship to recruitment of right DLFPC during a working memory task. Our results show that subjects exhibiting greater resting-state connectivity recruit DLPFC in the right hemisphere to a lesser degree during the performance of a working memory task, as the task becomes more complex. This suggests that subjects with greater resting-state connectivity may possess more efficient cognitive networks during working memory task performance.