Traditional Posters : Functional MRI
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
fMRI Characteristics

Thursday May 12th
Exhibition Hall  13:30 - 15:30

1539.   Spin Echo Hemodynamic Impulse Response at 7 T  
Jeroen Cornelis Willem Siero1,2, Nick F Ramsey1, Johannes Marinus Hoogduin1,2, Peter R Luijten2, and Natalia Petridou1,2
1Rudolf Magnus Institute, University Medical Center Utrecht, Utrecht, Netherlands, 2Radiology, University Medical Center Utrecht, Utrecht, Netherlands

Understanding the neurovascular coupling mechanism underlying the BOLD fMRI signal is contingent on the accurate spatial and temporal characterization of the hemodynamic impulse response (HIR), linked to the microvasculature. We obtained the spin-echo (SE) HIR at 7T using very short visual stimuli and high temporal resolution, and compared it to gradient-echo (GE) HIR obtained near the pial surface and deeper gray matter (dGM). SE HIR delay matched that of GE HIR in dGM, but the width was much narrower. The SE HIR can lead to new insights to the factors that contribute to the GE HIR.

1540.   Correlation of post-stimulus undershoot with BOLD response in event-related fMRI 
Xiaopeng Zong1, and Jie Huang1,2
1Department of Radiology, Michigan State University, East Lansing, MI, United States, 2Neuroscience Program, Michigan State University, East Lansing, MI, United States

Event-related (ER) BOLD-fMRI offers a means for quantitatively investigating the relationship between the elicited BOLD response and the corresponding brief neural events. The dynamic ER-BOLD response increases for a few seconds and then decreases to baseline, followed by a negative undershoot before returning to the baseline. Using an ER paradigm with voxelwise analysis, this study found that the dynamic BOLD response was highly homogeneous across V1, V2 and V3 and the negative undershoot was correlated with the positive BOLD response in each visual area, suggesting a common impulse hemodynamic response across the visual areas.

1541.   Stimulus-evoked response in cutaneous veins as measured by whole brain fMRI 
Evgeniya Kirilina1, Ruediger Bruehl2, Bernd Ittermann2, and Arthur Jacobs1
1Free University of Berlin, Berlin, Germany, 2Physikalisch-Technische Bundesanstalt, Berlin, Germany

An increasing number of fMRI studies are complemented by measurements of task-evoked changes of the heart rate, the pupil size or the skin conductance. These parameters reflect changes in the autonomic nervous system and may be employed as indicators of emotional and cognitive processes and regressors for fMRI analysis. Here we show that task-evoked changes in sympathetic outflow can be detected exploiting physiological information, which is already contained in the fMRI scan. We demonstrate that by analyzing signal changes induced by stimulus evoked venous constriction in the scalp, information about bodily arousal can be extracted.

1542.   Quantitative OEF Determination by Separate T2 and T2* Mapping 
Moritz Bernhard Mie1, and Lothar Rudi Schad1
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany

Knowledge about tissue oxygen supply provides important information about the viability of the tissue. In this study a modification of a model of static dephasing magnetization has been used to measure the oxygen extraction fraction (OEF). The advantage of this technique is the robustness of the values of the reversible relaxation rate R2’, the irreversible relaxation rate R2 and the deoxygenated blood volume DBV, because all parameters were determined in separate measurements.

1543.   Subtle physiologic rate differences affect group fMRI studies 
Erik B Beall1, Lael Stone2, Robert J Fox2, Michael D Phillips1, and Mark J Lowe1
1Imaging Institute, Cleveland Clinic, Cleveland, OH, United States, 2Neurologic Institute, Cleveland Clinic, Cleveland, OH, United States

Various preprocessing steps have been shown to affect results of fMRI group analyses, however physiologic noise correction is commonly assumed to have little or no effect due to the orthogonality between pulse/respiration and experimental paradigm. Certain populations have systematically different pulse/respiration rates than the general population, and it is possible that this will affect noise variance, thereby affecting activation statistics. We show in a group analysis of Multiple Sclerosis patients that this is indeed the case, and that group analyses comparing populations with subtly different rates must take physiologic noise into account to avoid biased results.

1544.   Error analysis of qBOLD technique for measurement brain hemodynamics 
Xiaoqi Wang1, Alexander L Sukstanskii2, and Dmitriy A Yablonskiy1,2
1Department of Physics, Washington University, St. Louis, Missouri, United States, 2Department of Radiology, Washington University, St. Louis, Missouri, United States

qBOLD (quantitative Blood Oxygenation Level Depend) technique provides an MRI-based method to measure tissue hemodynamic parameters such as oxygen extraction fraction (OEF) and deoxyhemoglobin-containing cerebral blood volume fraction (dCBV). It is based on a theory of MR signal dephasing in the presence of blood vessel network and experimental method – Gradient Echo Sampling of Spin Echo (GESSE). Herein, using Bayesian approach we present a comprehensive analysis of uncertainties in OEF and dCBV estimates and their dependence on GESSE sequence parameters, thus allowing optimization of qBOLD technique for optimum dCBV and OEF evaluation. Theoretical results are validated in phantom studies.

1545.   Relationship between fMRI signals in the resting-state (R-fMRI) and task (T-fMRI) 
Sridhar Kannurpatti1, Bart Rypma2, and Bharat Biswal1
1Radiology, UMDNJ-New Jersey Medical School, Newark, New Jersey, United States, 2School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, Texas, United States

We test the hypothesis that functional Magnetic Resonance Imaging (fMRI) blood oxygenation (BOLD) activity generated during the resting state (R-fMRI) and task-induced states (T-fMRI)originate from a common system. In other words, the activity is equivalent and independent of whether the subject performs a task or remains at rest in the MRI scanner. Using healthy human subjects for the study, we obtained linear relationships between resting signal and task-induced signal amplitudes (defined as the R-T relationship) on a voxel-wise basis and across subjects. Such a result reflects the resting- and task-induced BOLD-fMRI responses to arise from a common system.

1546.   Cerebral arterial blood R2* and volume measurements during stimulation 
Tae Kim1, and Soeng-Gi Kim1
1Neuroimaging Laboratory, Radiology, University of Pittsburgh, Pittsburgh, PA, United States

cerebral arterial blood R2* and volume, and their changes during stimulation was measured by arterial spin labeling technique with a short labeling duration of 700 ms. R2* of arterial blood (53.5 plus-or-minus sign15.3 s-1) is larger than tissue R2* (37.1 plus-or-minus sign 7.1 s-1) at 9.4 T, and the R2* change in arterial blood is not significant during stimulation. Arterial blood volume increased from 0.64 plus-or-minus sign 0.23 ml/100g to 0.93 plus-or-minus sign 0.23 ml/100g during stimulation.

1547.   Arterial contribution to the BOLD fMRI response to somatosensory stimulation in rats 
Yoshiyuki Hirano1, and Afonso C Silva1
1Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States

Biophysical models of BOLD contrast assume that the arterial vasculature is fully saturated with oxygen, so that BOLD originates in capillaries and veins. Here, we measured the BOLD and CBF fMRI response to somatosensory stimulation in lower case Greek alpha-chloralose anesthetized rats under different levels of arterial oxygenation. The CBF response was not affected by arterial oxygenation, while the onset time of the BOLD response in hypoxia was significantly longer than those in normoxia or hyperoxia. The onset time difference between BOLD-CBF was significantly smaller than the arteriole-venule transit time, suggesting that a measurable fraction of the BOLD response is of arterial origin.

1548.   Functional Changes in Cerebral Blood Flow and Transit-Time to Somatosensory Stimulation Measured with Dynamic Arterial Spin Labeling 
Renata Ferranti Leoni1,2, Draulio Barros de Araujo2, and Afonso Costa Silva1
1Cerebral Microcirculation Unit, National Institute of Neurological Disorders and Stroke - NIH, Bethesda, Maryland, United States, 2Department of Physics and Mathematics, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil

Compared to other arterial spin labeling (ASL) methods, the dynamic ASL (DASL) technique is an efficient way to obtain information about cerebral hemodynamics. The improved temporal resolution of DASL allows its use in functional MRI experiments. Here we used DASL in combination with somatosensory stimulation in rats, to show that resting cerebral blood flow (CBF), perfusion territories of the major cerebral arteries, transit-times, and both BOLD and CBF responses to functional brain stimulation can be measured simultaneously in a single experiment. This capability makes DASL an efficient and comprehensive technique to investigate the cerebral hemodynamics in scientific and clinical studies.

Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Traditional Posters : Functional MRI

Monday May 9th
Exhibition Hall  14:00 - 16:00

1549.   Thalamic and Cortical Substrates of Large-Scale Neuronal Oscillations Assessed with Simultaneous EEG-fMRI 
Zhongming Liu1, Jacco A de Zwart1, Peter van Gelderen1, Li-Wei Kuo1, and Jeff H Duyn1
1Advanced MRI section, Laboratory of Functional and Molecular Imaging, NINDS, National Institutes of Health, Bethesda, Maryland, United States

Synchronized neuronal oscillations govern the dynamic behavior of neuronal networks. At rest, we used EEG to detect large-scale neuronal oscillations, whose spontaneous fluctuations were correlated with BOLD to reveal underlying sub-cortical and cortical substrates. Between BOLD and posterior alpha and central mu rhythms, we found positive correlations in anterior thalamus and negative correlations in visual and sensorimotor cortical areas. Positive BOLD-BOLD correlations to visual cortex were found at the same cortical regions. Results suggest that thalamus plays a central role orchestrating cortical oscillations within- or cross-modality, and that intrinsic functional connectivity reflects in part the interplay between cortex and thalamus.

1550.   The electrophysiological basis of negative BOLD in default mode network 
Joanne R Hale1, Peter G Morris1, and Matthew J Brookes1
1SPMMRC, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

The default mode network (DMN) has been widely investigated using BOLD fMRI; studies show it to be most ‘active’ in the resting state with BOLD decreasing on task initiation. In this study, we employ parallel fMRI and magnetoencephalography (MEG) experiments to investigate electrophysiological processes that underlie negative BOLD changes. Using a working-memory task we characterise negative BOLD in DMN. Using MEG we show that marked decreases in high beta and gamma oscillations underlie negative haemodynamic change. Our study confirms a neural basis to BOLD in DMN, and adds weight to arguments suggesting that gamma oscillations and BOLD are intimately linked.

1551.   Neuroelectrical basis of the resting-state BOLD global signal as determined with simultaneous EEG-fMRI 
Chi Wah Wong1, Valur Olafsson1, Omer Tal1, Anna Leigh Rack-Gomer1, and Thomas T Liu1
1Center for Functional MRI, University of California San Diego, La Jolla, CA, United States

Recent work in monkeys suggests that the BOLD global signal typically removed as a nuisance term in resting-state studies may have a neural origin. In this study we used simultaneous EEG-fMRI in humans to show that the global signal has a significant component of neuroelectrical origin. In addition, we show that the detection of the anti-correlated relation between the default mode network and the task positive network seems to depend on the removal of this neuroelectrical global signal component.

1552.   Identifying the sources of the pulse artefact in EEG recordings made inside an MR scanner. 
Karen J Mullinger1, Jade Havenhand1, and Richard W Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Electroencephalography data recorded during simultaneous functional magnetic resonance imaging are compromised by large artefact voltages. The pulse artefact (PA) is particularly troublesome because of its variability and persistence after artefact correction. By isolating the effects of the different putative sources of the PA (pulse-driven head rotation, Hall voltages due to blood flow and scalp expansion) we identify the main contributions to the PA’s amplitude and variance. The results indicate that the dominant source of the PA is pulse-driven head rotation with the Hall voltages causing the largest variation in the PA across cardiac cycles.

1553.   Morphology of the eMRI Magnitude Response to Interictal Spikes: Timing, Amplitude and the Dip 
Padmavathi Sundaram1,2, William M Wells2, Robert V Mulkern1, Mukund Balasubramanian1, Ellen J Bubrick3, and Darren B Orbach1,2
1Radiology, Children's Hospital Boston, Boston, MA, United States, 2Radiology, Brigham and Women's Hospital, Boston, MA, United States, 3Neurology, Brigham and Women's Hospital, Boston, MA, United States

An investigation of the MR magnitude response to interictal spikes. We report morphology of the spike-related response - amplitudes, duratiosn and the prolonged post-spike MR signal undershoot.

1554.   A Spatiotemporal Signal Space Projection Method for Artifact Reduction in Simultaneous EEG-fMRI Acquisitions 
Valur Olafsson1, Omer Tal1, Chi Wah Wong1, and Thomas Liu1
1Department of Radiology, University of California San Diego, La Jolla, CA, United States

When acquiring simultaneous EEG-fMRI data, there are artifacts in the EEG data due to the MRI environment. It is common to use template based subtractions to remove these artifacts. However, these methods tend to leave residual artifacts in the EEG data. Here we propose to use a fully automated spatiotemporal signal source projection (SSP) to remove the residual artifacts. We show that the method performs well to remove the residual artifacts due to the MRI environment and from sources outside the brain.

1555.   Simultaneous intracranial EEG-fMRI in humans: data quality 
David William Carmichael1, Serge Vulliemoz1,2, Roman Rodionov1, Karin Rosenkranz1, Andrew McEvoy3, and Louis Lemieux1,4
1Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, United Kingdom, 2Epilepsy Unit, University Hospital and University of Geneva, Geneva, Switzerland, 3Victor Horsley Dept. Neurosurgery, National Hospital for Neurology and Neurosurgery, London, United Kingdom, 4MRI Unit, National Society for Epilepsy, Chalfont St. Peter, United Kingdom

We aimed to record intracranial EEG and fMRI concurrently to study physiological and pathological activity at a greater range of spatial and temporal scales. However, technical challenges of safety and data quality remain. In this abstract, we report first results in two patients with epilepsy, implanted for presurgical evaluation, with reference to safety and data quality. Intracranial EEG quality was high with standard scalp EEG scanner-artifact correction methods, in particular cardiac-related artifacts were small compared to epileptic events. Although fMRI data quality was reduced close to electrode contacts on average >50% signal was observed 5mm from the electrode contact locations.

1556.   An Empirical Investigation of Motion Effects During eMRI of Interictal Epileptiform Spikes 
Padmavathi Sundaram1,2, Robert V Mulkern1, William M Wells2, Christina Triantafyllou3, Tobias Loddenkemper4, Ellen J Bubrick5, and Darren B Orbach1,2
1Radiology, Children's Hospital Boston, Harvard Medical School, Boston, MA, United States, 2Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, 3Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Neurology, Children's Hospital Boston, Harvard Medical School, Boston, MA, United States,5Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States

We recently developed a functional neuroimaging technique called encephalographic MRI. Our method acquires concurrent scalp electroencephalography and rapid gradient echo EPI. We imaged fast (20-200 ms), high amplitude (> 50 uV) cortical discharges in a cohort of focal epilepsy patients. We found easily detectable MR magnitude and phase changes concurrent with the interictal spike with a lag of milliseconds. Due to the time scale of the responses, localized changes in blood flow are unlikely to cause the MR signal changes. While the precise underlying mechanisms are unclear, in this study we empirically investigate one potentially important confound – motion.

1557.   EEG Acquisition in Ultra-High Static Magnetic Field up to 9.4T 
Irene Neuner1,2, Tracy Warbrick1, Martina Reske1, Jörg Felder1, Avdo Celik1, and Nadim Jon Shah1,3
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Juelich, Juelich, Germany, 2Department of Psychiatry and Psychotherapy, JARA, RWTH Aachen University, Aachen, Germany,3Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

We recorded EEG data in 5 young healthy volunteers in ultra-high static magnetic fields up to 9.4T. The EEG-data acquisition was reliable and reproducible. The cardioballistic artefacts increase with the strength of the B0 field and in particular from 8T to 9.4T. The cardioballistic artefacts show a high interindividual variability.

1558.   Delayed BOLD in the somatosensory cortex and its possible relationship to beta band event related synchronisation 
Fan Wang1, Claire Stevenson1, Matthew Brookes1, and Peter Morris1
1Sir Peter Mansfield MR Centre, Nottingham, Nottinghamshire, United Kingdom

In this work we employ a multi-model neuroimaging approach to investigate the relationship between neural oscillations and the BOLD response. We use MEG to measure the temporal profile of beta band oscillations including the characteristic event related desynchronisation (ERD) and the post stimulus synchronisation (ERS). We derive BOLD models based on the timing of ERD/ERS. Our ERS model highlights voxels with a significant delayed BOLD response. We speculate that such responses are not simply a result of haemodynamic lag, but rather that they could reflect the post stimulus beta rebound.

1559.   Spatial and Temporal Characteristics of Evoked and Induced Neural and Vascular Responses Assessed with Simultaneous EEG-fMRI 
Zhongming Liu1, Jacco A de Zwart1, Peter van Gelderen1, Li-Wei Kuo1, and Jeff H Duyn1
1Advanced MRI section, Laboratory of Functional and Molecular Imaging, NINDS, National Institutes of Health, Bethesda, Maryland, United States

Both evoked and induced neural activities contribute to the observed BOLD signal change in response to stimulus or task. By using simultaneous fMRI-EEG and frequency-tagging techniques, we found within visual cortex positive correlation between BOLD and evoked EEG power change tagged with the stimulus frequency, and negative partial correlation between BOLD and induced alpha power change in extended occipital and parietal cortices. Results suggest that stimulus (or task) yields spatially and temporally specific evoked response, as well as much less specific alteration in baseline spontaneous activity.

1560.   Evoked and induced somatosensory EEG responses predict activity in resting state networks in simultaneous fMRI data during median nerve stimulation. 
Stephen D. Mayhew1, Karen J Mullinger2, Andrew P Bagshaw1, Richard W Bowtell2, and Susan T Francis2
1Birmingham University Imaging Centre, School of Psychology, University of Birmingham, Birmingham, United Kingdom, 2Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Here we investigate the interaction of resting state networks with both somatosensory evoked potentials (SEP) and induced mu oscillatory EEG responses during sustained median nerve stimulation recorded using simultaneous EEG-fMRI. The default-mode-network (DFM) and dorsal attention network (DAN) were identified from group ICA of the BOLD data. Strong spatial overlap was observed between: 1) DFM IC and positive BOLD-SEP correlation; 2) DAN IC and negative BOLD-mu rhythm correlations. Fluctuations in BOLD signal in the DFM and DAN were found to correlate with SEPs and mu rhythm, suggesting that these reflect functionally relevant variations in task engagement and attention.

Traditional Posters : Functional MRI
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Human fMRI

Tuesday May 10th
Exhibition Hall  13:30 - 15:30

1561.   Effects of autonomic stimulation on the brain at rest and engaged by cognitive task: an fMRI investigation 
Barbara Basile1, Andrea Bassi2, Giovanni Calcagnini3, Pietro Cortelli4, Carlo Caltagirone2,5, and Marco Bozzali1
1Neuroimaging Laboratory, Santa Lucia Foundation, Rome, Italy, 2Department of Clinical and Behavioural Neurology, Santa Lucia Foundation, Rome, Italy, 3Department of Technology and Health, Italian Institute of Health, Rome, Italy, 4Department of Neurological Science, University of Bologna, Bologna, Italy, 5Department of Neuroscience, University of Rome ‘Tor Vergata', Rome, Italy

The autonomic nervous system (ANS) is well known in its peripheral functioning, while its central aspects are still rather obscure. We present here a novel method that, using fMRI and a parasympathetic stimulation of the carotid baroreceptors, allows to investigate brain activity by a direct perturbation of the ANS. We provide here new evidence that ANS perturbation induces expected peripheral responses together with modulation of brain activity in both, regions associated with the autonomic control and regions implicated in higher level functions. Moreover, we show that the parasympathetic stimulation modulates brain networks engaged during high-level cognitive tasks.

1562.   Effects of inspiratory and expiratory loading upon global and stimulus evoked CBF 
Anja Hayen1,2, Mari Herigstad1,2, Richard G. Wise3, and Kyle T S Pattinson1,2
1Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, Oxford, Oxfordshire, United Kingdom, 3School of Psychology, Cardiff University, CUBRIC, Cardiff, United Kingdom

Altered intrathoracic pressure affects cerebral blood flow (CBF) and may confound CBF based measurements of neuronal activity. In 13 healthy human volunteers, with transcranial Doppler (TCD) and ASL, we evaluated the effects of inspiratory and expiratory loading on CBF, and upon the stimulus-evoked CBF response. Transient effects of CBF were observed for 30 seconds following load application that subsequently normalised to baseline. The stimulus-evoked CBF response was unaltered. Therefore, altered intrathoracic pressure seen in respiratory disease is unlikely to adversely affect CBF. We conclude that longer stimulus blocks are better suited for volunteer models investigating neural processing of breathlessness perception.

1563.   Relationship of Basal Cerebral Blood Flow, Thickness of Cortical Gray Matter and Fractional Anisotropy of Cerebral White Matter in Adolescents 
Ai-Ling Lin1, Peter Kochunov1, Peter T Fox1, Amy Ramage1, Hsiao-Ying Wey1, Timothy Q Duong1, and Douglas Williamson2
1Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States, 2Department of Psychiastry, University of Texas Health Science Center, San Antonio, TX, United States

The purpose of the study was to determine the relationship between the basal cerebral blood flow (CBF), cortical gray matter thickness (GMT) and white matter myelination in adolescents using MRI methods. Our results showed that gray matter pruning and white matter myelination occurred in parallel and the CBF reduction was mainly contributed by the reduced rate of myelination.

1564.   Cerebral blood flow and BOLD MRI during Isometric Exercise-Induced Increase in Blood Pressure 
David a Ravaee1, Claudia Huerta1, Hsiao-Ying Wey1, Ai-ling Lin1, and Timothy Duong1
1University of Texas Health Science Center, San Antonio, TX, United States

This study investigated the relation between perfusion pressure and cerebral blood flow (CBF) in the human brain using MRI during rest and isometric handgrip exercise. Basal CBF was 37 ± 4 mL/100mL/min (N=4). Isometric exercise increased mean CBF, heart rate and mean arterial pressure (P<0.05), but not O2 saturation, end tidal CO2, or respiratory rate (P>0.1). A MRI approach provides objective quantitative CBF with a large field of view without depth limitation. fMRI during isometric exercise provides a unique means to study brain physiology and autoregulation free of potential adverse pharmacological effects.

1565.   Transient Neural Plasticity in Human Motor Cortex 
Kuang-Chi Tung1, Feng Xu1, Jinsoo Uh1, and Hanzhang Lu1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States

Brain¡¯s plasticity forms the basis of many of our daily functions including memory and learning. However, the exact neuronal processes that underlie the plasticity are poorly understood. The present elucidated the temporal course functional connectivity in response to training and its return to baseline level upon training termination. These data suggest that the brain is constantly re-organizing itself based on life experiences and that a short-duration task is sufficient to leave a ¡°foot-print¡± on the brain. However, if not maintained or consolidated, such alterations will disappear within a matter of a few minutes.

1566.   Performance related brain differences in real-time fMRI neurofeedback of imagined hand motor activity 
Mark Chiew1,2, Stephen M LaConte3, and Simon James Graham1,4
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 2Rotman Research Institute, Toronto, Ontario, Canada, 3School of Biomedical Engineering, Virginia Tech, Blacksburg, Virginia, United States, 4Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

Neurofeedback (NF) using real-time functional magnetic resonance imaging (fMRI) is an emerging technique for the self regulation of brain activity, and has been shown to be successful in motor imagery applications. However, in imagined hand motor activity NF experiments on young healthy adults, we show that there is a large range of NF ability observed across the subjects. Here we use a behavioural partial least squares (PLS) analysis to investigate the spatial distribution of brain differences during NF with respect to performance, to identify regions and networks that mediate successful self-regulation.

1567.   Between-group racial differences in the relation of brain function to intelligence 
Vincent Jerome Schmithorst1, and Scott Kerry Holland1
1Radiology, Children's Hospital Medical Center, Cincinnati, OH, United States

To date, there is no published data examining between-group racial differences in the neurobiological correlates of intelligence. We performed a retrospective analysis of fMRI data obtained as part of a study of normal language development in children ages 5-18 to investigate this question. In a cohort of African-American and Caucasian children matched for IQ, age, and socio-economic status, specific regions with race-X-IQ interactions on brain activation were found on two out of the four tasks examined. Results suggest such differences are subtle and not widespread and may relate to differences in the relation between executive function and intelligence.

1568.   Is BA 44 part of the human Mirror Neuron System? A fMRI Study.
Monia Cabinio1,2, Gabriella Cerri3, Paola Borroni4, Valeria Blasi1, Antonella Iadanza1, and Andrea Falini1,2
1Neuroradiology - CERMAC, San Raffaele Scientific Institute, Milan, Italy, 2Vita-Salute San Raffaele University, Milan, Italy, 3Department of Human Physiology, University of Milan, Milan, Italy,4Department of Medicine, Surgery and Dental Sciences, University of Milan, Milan, Italy

Mirror Neurons are bimodal neurons active both during action observation and execution. In humans the observation of actions induces the activation of a fronto-parietal network (Mirror Neuron System, MNS). Some authors found that BA44, a fundamental language area, is part of the MNS. This evidence lead to the hypothesis that MNS is important in the evolution of language. However this data is controversial. With this work we assess if BA44 is active during observation/execution of hand and mouth movements. We did not find activation of BA44 for hand actions and only a minimal, if any, involvement for mouth actions, thus challenging the over mentioned theory.

1569.   The functional selectivity for lexical search guided by letter, semantic category and sentential cues: An fMRI Investigation 
Yunqing Li1,2, Prasanna Karunanayaka1, Jianli Wang1, Paul J Eslinger3, Dana M Lochman1, Ping Li4, and Qing Yang1,5
1Radiology, The Pennsylvania State University, Hershey, Pennsylvania, United States, 2Radiology, Tianjin Medical University, Tianjin, China, People's Republic of, 3Neural & Behavioral Sciences, The Pennsylvania State University, Hershey, Pennsylvania, United States, 4Psychology, The Pennsylvania State University, University Park, Pennsylvania, United States, 5Neurosurgery, The Pennsylvania State University, Hershey, Pennsylvania, United States

Lexical-semantic knowledge undergoes prolonged developmental changes throughout childhood and provides an ideal case for developmental research. Both neuropsychological and fMRI investigations of verbal fluency have been widely used to evaluate language and executive control processes in the human cortex. Our findings show that both the location and amount of cortical activity associated with Lexical-semantic tasks can be modulated by varying the task demands of the verbal fluency paradigm. These results provide convincing evidence for brain connectivity differences in neural networks subserving verbal fluency, depending upon efficient task initiation, planning, organization, and flexibility.

1570.   Probing the brainprime or minutes valuation and choice systems with 7T fMRI 
Fabian Grabenhorst1, Stefan Maderwald2, Frank P. Schulte2,3, and Matthias Brand2,3
1University of Cambridge, Department of Physiology, Development and Neuroscience, Cambridge, United Kingdom, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany,3University Duisburg-Essen, General Psychology: Cognition, Duisburg, Germany

High-field MRI at 7T inherently offers higher signal-to-noise and enhanced soft tissue as well as BOLD contrasts compared to 1.5T or even 3T. Here we used 7T functional MRI to investigate neural representations of valuation and decision variables while subjects performed a food evaluation task. We identified neural representations of key valuation and decision variables such as subjective taste pleasantness and decision confidence in different parts of the brain’s valuation system including orbitofrontal, dorsolateral and ventromedial prefrontal cortex, amygdala and striatum. Our results demonstrate that reward-related effects can be detected with 7T fMRI even simultaneously in anatomically separate artifact-prone areas.

1571.   Brain Activation in Response to Visually Evoked Sexual Arousal ln Male-to-Female Transsexuals: 3.0 Tesla Functional MRI 
Seok-kyun Oh1, Gwang-Won Kim2, Jong-Chul Yang3, Seok-Kwun Kim4, and Gwang-Woo Jeong2,5
1Research Institute for Medical Imaging (RIMI), Department of Radiology, Chonnam National University Hospital, Gwangju, Korea, Republic of, 2Interdisciplinary Program of Biomedical Engineering, Chonnam National University, Gwangju, Korea, Republic of, 3Department of Psychiatry, Chonbuk National University Medical School, Jeonju, Korea, Republic of, 4Department of Plastic and Reconstructive Surgery, Dong-A University College of Medicine, Busan, Korea, Republic of, 5Department of Radiology, Chonnam National University Medical School and Hospital, Gwangju, Korea, Republic of

Transsexualism is a type of the gender identity disorder and it is defined by a desire to be accepted as a member of the opposite sex. Neuroimaging studies for the male-to-female (MTF) transsexuals with a sex reassignment surgery and hormone supplementary therapy have not yet been reported. This study utilized a functional magnetic resonance imaging (fMRI) to contrast the differential brain activation patterns in response to visual stimulation with each male and female erotic nude pictures in MTF transsexuals.

1572.   Cortical Activation in Superior Temporal Gyrus and Fusiform Gyrus Modulated by Congruence of Emotional Content in Music and Face 
Jeong-Won Jeong1, Vaibhav Diwadkar2, Carla D. Chugani3, Harry T. Chugani4, and Diane C. Chugani5
1Pediatrics, Neurology, Wayne State University, Detroit, Michigan, United States, 2Psychiatry, Behavioral Neuroscience, Wayne State University, Detroit, Michigan, United States, 3Florida Gulf Coast University, 4Pediatrics, Neurology, Radiology, Wayne State University, Detroit, Michigan, United States, 5Pediatrics, Radiology, Wayne State University, Detroit, Michigan, United States

Emotional cues from the environment are obtained through multiple sensory modalities, and the integration of these emotionally laden sensory signals might enhance or diminish the emotional experience conveyed by each sense alone. This study hypothesizes that neural mechanisms involved in listening to music may differ when presented together with visual stimuli that conveyed the same emotion as the music when compared to visual stimuli with incongruent emotional content. Based on above hypothesis, we present a novel functinal MRI paradigm combining happy and sad music with happy and sad faces to examine the response of superior temporal gyrus (STG) and fusiform gyrus (FG).

Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Traditional Posters : Functional MRI
Non-Human fMRI

Wednesday May 11th
Exhibition Hall  13:30 - 15:30

1573.   Resting functional connectivity between amygdala and dlPFC predicts anxious temperament in the rhesus monkey 
Rasmus Matthias Birn1, Steven E Shelton1, Jonathan A Oler1, Andrew S Fox2, Richard J Davidson1,2, and Ned H Kalin1
1Department of Psychiatry, University of Wisconsin, Madison, WI, United States, 2Department of Psychology, University of Wisconsin, Madison, WI, United States

In this study we investigate the resting-state functional connectivity of the amygdala and its relation to individual differences in anxious temperament (AT) in a large cohort of young rhesus macaque monkeys (n=107). Significant functional connectivity was found between the right central nucleus of the amygdala (CeA ; where PET imaging shows correlation between metabolism and AT) and left amygdala, bilateral dorsolateral prefrontal cortex (dlPFC), ventromedial prefrontal cortex, and bilateral bed nucleus of the stria terminalis (BNST) regions. Across subjects, AT was significantly correlated with the functional connectivity between right CeA and right dlPFC with more anxious subjects exhibiting lower connectivity.

1574.   Functional Interpretations of the Resting-State Networks in Nonhuman Primates 
Hsiao-Ying Wey1,2, Angela R. Laird1,2, Peter T. Fox1,2, and Timothy Q. Duong1,2
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, 2Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States

Resting-state networks also exist in nonhuman primates. Due to the nature of resting-state data (lack of external stimuli or goal-directed behavior) and the difficulties to map brain functions by evoked responses in nonhuman primates, we explored the possibility to provide functional interpretations of resting-state networks in baboons by finding spatially similar functional networks in humans with known behavioral domains.

1575.   Optimizing negative fMRI response in the rat striatum under isoflurane anesthesia 
Yen-Yu Ian Shih1, Shiliang Huang1, and Timothy Q Duong1
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States

Subcortical activation in anesthetized animal models is challenging. This study introduces a novel approach to evoke negative fMRI response in the rat striatum using forepaw stimulation under isoflurane anesthesia, allowing longitudinal investigation of striatal function. The fMRI responses to nine different stimulus pulse durations of forepaw were analyzed. Robust positive fMRI responses were observed in the contralateral primary somatosensory cortex, but bilateral negative fMRI responses were observed in the striatum. We also demonstrate this approach on a unilateral focal ischemia. Our findings make survival animal fMRI with robust subcortical responses become reality.

1576.   Layer-specific fMRI of visual stimulation in the rat retina: responses to different stimulation luminance, frequency, and color 
Yen-Yu Ian Shih1, Bryan H De La Garza1, Eric R Muir1, Li Guang1, and Timothy Q Duong1
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States

This study reports a novel application of very high resolution (60 µm) fMRI using MION at an 11.7 T scanner to image the rat retina associated with various visual stimulations. The retinal layer responses to flickering light of different luminance, frequency and wavelength were greater than in the choroidal layer. The retinal layer responses were dependent on luminance, frequency and wavelength revealing characteristic tuning curves, whereas the outer layer responses were not, suggesting differential neurovascular coupling between the two vascular layers. This is the first report of vascular layer-specific fMRI during visual stimulation in the retina in vivo.

1577.   Flow-metabolism Uncoupling and Extended Longevity as Observed with a Transgenic Mice Model 
Ai-Ling Lin1, Peter T Fox1, Holly Van Remmen2, Arlan G Richardson2, and Timothy Q Duong1
1Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States, 2Barshop Institute for Logevity and Aging Studies, University of Texas Health Science Center, San Antonio, TX, United States

Increased lifespan is observed in mice with a mitochondrial mutation in an assembly protein (Surf1 knockout; Surf1-/-) for electron-transport-chain complex IV, which results in a reduction in the level of cytochrome c oxidase (COX). The pupose of the study, therefore, was to determine the basal flo-metabolism coupling relationship and the metabolic pathway in the Surf1-/- mice. Cerebral blood flow (CBF) and cerebral metabolic rate of glucose (CMRGlc) were measured with MRI and PET, respectively. The results showed that basal flow and metabolism were uncoupled in the Surf1-/- mice (the basal CBF of the Surf1-/- was observed 20% lower than that of the WT (P < 0.05), while the cerebral glucose uptake of the Surf1-/- mice increased 85% compared to the WT (P < 0.001). The data further demonstrated that the metabolic pathway of the Surf1-/- mice has shifted from oxidative to glycolytic metabolism (with decreased oxygen consumption, but with increased glucose uptake).

1578.   Facilitation of the BOLD response to bilateral somatosensory stimulation in awake marmosets 
Yoshiyuki Hirano1, Junjie Liu1, and Afonso C Silva1
1Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States

The use of fMRI to understand the cortical representation of tactile information of the hands is of current interest. Here, we used BOLD fMRI to measure the hemodynamic response to unilateral and bilateral somatosensory stimulation paradigms in awake marmosets. Robust responses were obtained in contralateral SI to 4 and 40 Hz unilateral stimulation. However, the ipsilateral cortex yielded negative and positive responses, respectively. Moreover, bilateral stimuli produced positive responses of higher amplitudes than the summation of the responses to unilateral stimuli. These findings suggest that bilateral stimulation always facilitates the hemodynamic response in S1 through transcallosal interactions.

1579.   BOLD fMRI of the mouse barrel cortex 
Nathalie Just1,2, Carl Petersen3, and Rolf Gruetter1,4
1LIFMET, CIBM/EPFL, Lausanne, Switzerland, 2Department of Radiology, UNIL, Lausanne, Switzerland, 3LSENS, EPFL, Lausanne, Switzerland, 4Department of Radiology, UNIL& HUG, Lausanne & Geneve, Switzerland

The barrel cortex of the rodent represents the equivalent of the visual area in humans. The mouse barrel cortex is highly organized for processing somatosensory information and represents an attractive model for the development of functional Magnetic Resonance Imaging methods of small structures. However, MR functional investigations remain challenging due to a poor signal to noise ratio. In the present study, we propose to address the feasibility of high field fMRI methods to obtain BOLD responses in the mouse barrel cortex following electrical stimulation of the whisker pad under controlled physiological conditions.

1580.   Resting-state Functional Connectivity across Primate Species: Implications of Evolutionary Hemispheric Asymmetry 
Hsiao-Ying Wey1,2, Peter Kochunov1,2, Peter T. Fox1,2, Angela R. Laird1,2, and Timothy Q. Duong1,2
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, 2Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States

We aim to investigate evolutionary differences of functional connectivity between humans and nonhuman primates. Specifically, we identified resting-state networks in a large nonhuman primate (baboons, Old World monkeys) who is evolutionary close to humans, and we compared the similarities and discrepancies with networks found in humans. We observed similar networks associated with primary functions in both species, however, networks were more asymmetric in baboons.

1581.   Analgesic action sites of pregabalin by fMRI of spinal cord and brain in anesthetized rats, and its qualification against behavioral assay in awake rats 
Fuqiang Zhao1, Denise Welsh1, Mangay Williams1, Hongyu Annie Liang2, Alexandre Coimbra1, Mark O. Urban2, Mark Bowlby2, Richard Hargreaves2, Jeffrey L Evelhoch1, and Donald S Williams1
1Imaging, Merck, West Point, PA, United States, 2Neuroscience, Merck, West Point, PA, United States

Pregabalin (Lyrica) is used for the treatments of epilepsy and pain. Both its anatomical targets and its mechanism of action are poorly understood. In this study, the suppression effects of pregabalin on noxious electrical stimulation (NES) induced responses were investigated by BV fMRI in anesthetized rats, and by behavioral assay (vocalization) in awake rats. Our fMRI and behavioral results suggest that 1) pregabalin has efficacy on NES-induced pain in naïve rats; and 2) the analgesic action sites of pregabalin are not in the primary somatosensory pathway (spinal cord, dorsal column nuclei, thalamic relay, S1), but in other activated regions.

1582.   Comparing results of median nerve stimulation between healthy and C7 donor rats utilizing BOLD fMRI at 9.4T 
Jack B Stephenson, IV1, Rupeng Li2, Patrick Hettinger1, Matthew Runquist2, Christopher P Pawela2, Ji Geng Yan1, Hani Matloub1, and James Hyde2
1Plastic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin, United States, 2Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, United States

It is unclear how the brain is affected after C7 root coaptation in brachial plexus nerve transfer procedures. In this 9.4T BOLD-fMRI rat survival study, the cortices of healthy and donor C7 rat brains are compared using images and voxel counting. Preliminary results show early decreased activation in donor rats' sensorimotor cortex.

1583.   TRPV1-mediated entry of QX-314 leads to inhibition of nociceptive input as measured by BOLD fMRI in mice using thermal stimulation 
Simone Claudia Bosshard1, Florian Stuker1, Constantin von Deuster1, and Markus Rudin1,2
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, 2Institute of Pharmacology and Toxicology, University Zürich, Zurich, Switzerland

To study nociceptive processing in mice, a thermal stimulation paradigm using an infrared laser source for forepaw stimulation was developed. The skin of the forepaws was heated to 45°C or 46°C for 60s, using a feedback system to control the temperature. The stimulation led to significant BOLD changes in the somatosensory cortex and the thalamus. For modulation, a combination of QX-314 and capsaicin was injected into the forepaws, inducing a selective nociceptor block, which led to an abolishment of the BOLD signal. Either solution applied alone did not lead to a decrease in BOLD signal changes.

1584.   Characterization of somatosensory BOLD response deficit and recovery after traumatic brain injury in rat 
Juha-Pekka Niskanen1,2, Antti M Airaksinen1, Alejandra Sierra1, Joanna K Huttunen1, Pasi A Karjalainen2, Jari Nissinen1, Asla Pitkänen1,3, and Olli Gröhn1
1Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland, 2Department of Physics and Mathematics, University of Eastern Finland, Kuopio, Finland, 3Department of Neurology, Kuopio University Hospital, Kuopio, Finland

Previously, we have detected deficit and recovery of the rat somatosensory BOLD response following TBI, although SI appeared normal in structural MRI. To further investigate this phenomenon, simultaneous LFP/fMRI and histology were performed 2 and 35 days after TBI in rats. The ipsilateral BOLD and LFP responses were lost at 2d, but only partially at 35d. Furthermore, histology revealed gliosis in the ipsilateral ventral posterolateral (VPL) thalamic nucleus. Our results show that hemodynamic uncoupling is not the cause for the detected functional deficit in the rat SI after TBI, but rather neurodegeneration in the thalamic VPL.

1585.   Cocaine-Induced Activity in the Rat Hippocampus using phMRI 
S K Hekmatyar1, Madhu M Keralapurath2, Jason Clark2, Sherri Hammond2, and John J Wagner2
1BioImaging Research Center, University of Georgia, Athens, GA, United States, 2Department of Physiology and Pharmacology, University of Georgia, Athens, GA, United States

The temporal pattern of brain activation induced by cocaine in the regions of brain (dHF and vHF) that are associated with memory and learning were studied using functional MRI techniques in three groups of urethane anesthetized (i) cocaine naive (ii) self administered and (iii) in saline injected control rats.

1586.   Evaluation of pharmacological responses by quantitative T2 fMRI 
Joanna K Huttunen1, Antti M Airaksinen1, Kimmo Lehtimäki2, Juha-Pekka Niskanen1,3, Juha Yrjänheikki2, and Olli Gröhn1
1A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland, 2Discovery and Imaging Services, Cerebricon Ltd / Charles River Labs, Kuopio, Finland,3Department of Physics and Mathematics, University of Eastern Finland, Kuopio, Finland

Detection of small pharmacological responses relies on the stability of the measured signal intensity in time. Calculation of T2 maps from two sequential images diminishes fluctuations in the signal, and therefore allows more subtle activations to be detected. Positive apomorfine responses in T2 maps were detected in the lateral entorhinal cortex with increased T2 values of 3-4 ms. Negative apomorfine responses in T2 maps were detected in the motor cortices with decreased T2 values of 1-2 ms. The T2 map method in pharmacological studies could be beneficial in studying new pharmacological agents with small or unknown responses in the brain.

1587.   Pain fMRI response in anesthetized rats correlates with behavioral response to pain in awake rats 
Fuqiang Zhao1, Denise Welsh1, Mangay Williams1, Hongyu Annie Liang2, Alexandre Coimbra1, Mark O. Urban2, Mark Bowlby2, Richard Hargreaves2, Jeffrey L Evelhoch1, and Donald S Williams1
1Imaging, Merck, West Point, PA, United States, 2Neuroscience, Merck, West Point, PA, United States

Anesthesia is necessary for pain fMRI studies in animals. The relationship between fMRI responses under anesthesia and behavioral responses in awake animals is unknown. The effect of systemic lidocaine on the pain-induced fMRI signals and on the vocalization threshold was compared. While the pain fMRI signal in the primary somatosensory cortex is not altered, pain signals in all other activated regions were suppressed by lidocaine, with the temporal profiles showing a striking similarity to that for lidocaine-caused behavioral responses. Results suggest that 1) pain fMRI results from anesthetized animals are associated with the behavioral response in awake animals and 2) S1 may not be involved in the pain processing.

1588.   Neural source of laminar fMRI responses examined with temporal frequency visual stimuli 
Cecil Chern-Chyi Yen1, Hiro Fukuda2, and Seong-Gi Kim2
1Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States, 2Neuroimaging Lab Radiology, University of Pittsburgh, Pittsburgh, PA, United States

Neuroscientists have been interested in cortical laminar neural response for decades. If hemodynamic responses are sensitive to laminar neural activity, then high resolution fMRI may provide a non-invasive way to probe these activity. To investigate this issue, we intentionally modulated layer-dependent changes in neural activity during fMRI studies by manipulating the temporal characteristic of the visual stimuli. All laminar response of BOLD or CBV fRMI behaved similarly, even though spiking activity was reported to have different response in lower cortical layer. Our result suggests that it is currently very difficult for hemodynamic-based fMRI to differentiate layer-specific neural activity.

1589.   Direct Imaging of Microvascular and Macrovasular contributions by Time Resolved BOLD fMRI Allows Better Separation of Whisker Rows in the Rodent Barrel Cortex 
Xin Yu1, Stephen Dodd1, Afonso Silva1, and Alan Koretsky1
1NINDS, NIH, Bethesda, MD, United States

High spatial resolution EPI images could visualize the intracortical vasculature and allow separation of voxels containing large intracortical veins from surrounding voxels enriched with microvasculature. Early positive BOLD response at 0.8 s following stimulus onset mainly encompassed voxels containing the microvasculature. By 1.6 s activation was more prominent in veins even at cortical layer 4. Functional maps of whisker-row specific barrel areas were clearly separated at 0.8s, but were overlapped by large vessels at later times. These results demonstrate that early positive BOLD fMRI response has better spatial specificity to active regions due to exclusion of contributions from cortical veins.

1590.   Functional Magnetic Resonance Spectroscopy of the rat barrel cortex 
Nathalie Just1, and Rolf Gruetter1
1LIFMET, CIBM/EPFL, Lausanne, Switzerland

In the past, Trigeminal nerve electrical stimulation was shown to be a robust model for the investigation of the BOLD fMRI changes in the rat barrel cortex. In the present study, reproducible BOLD fMRI changes were obtained during sustained 10-minute trigeminal nerve stimulation. Current observations suggest that sustained neuronal activation of the rat barrel cortex permits the investigation of the neurochemical consequences of cortical activation.

1591.   Orthogonal diffusion measurements in the mouse hypothalamus by MRI reveal cerebral activity in the fed or fasted states 
Blanca Lizarbe1, Ania Benitez1, Pilar Lopez-Larrubia1, and Sebastian Cerdan1
1Instituto Investigaciones Biomedicas "Alberto Sols", Madrid, Spain

We investigate the functional mechanisms underlying hypothalamic activation by fasting using Diffusion Weighted MR Imaging. We used eight C57 mice, acquiring DWI from axial sections of the brain containing the hypothalamus, in three orthogonal directions, with increasing diffusion weightings (10less than or equal tobless than or equal to90 and 200less than or equal tobless than or equal to1200), from the same fed or fasted mouse. The data set was fitted to biexponential model yielding parameter values for the relative contributions of the fast (FDP, Dfast) and slow (SDP, Dslow) diffusion phases. Fasting induced, among other effects, a directional dependent increase in the relative contribution of SDP, compatible with neurocellular swelling during activation.