fMRI Fluctuations & Connectivity

Buprenorphine is commonly prescribed to treat pain. We implemented blood oxygenated-level dependent (BOLD) functional MRI to characterize and compare the effects of 2.0 mg (sublingual), 0.1 mg/70kg (intravenous) and 0.2 mg/70kg (intravenous) doses of buprenorphine on the central nervous system during pain processing and during the resting state. During pain processing, the 2.0 mg (sublingual) and 0.2 mg/70kg (intravenous) doses significantly (p<0.01) potentiated the BOLD response in regions such as the striatum, while attenuated the BOLD response in somatosensory cortices. Furthermore, the resting-state connectivity for sublingual and intravenous doses of buprenorphine were also altered among structures that mediate pain processing.

While voxels as small as 0.75 mm isotropic provide sufficient SNR for high-field fMRI, voxels falling within cortical gray matter voxels are still influenced by partial-volume contamination with white matter and CSF, which contribute different levels of physiological noise. Here we characterize the impact of partial-volume effects as a function of cortical depth on the resting-state fluctuation amplitudes at 7T. Even after partial-volume effects are taken into account, the magnitude of resting state fluctuations increases with proximity to the pial surface. This suggests that laminar differences in the resting-state fluctuations exist and may reflect increasing dominance of extravascular BOLD signal changes surrounding large pial vessels.

Memory consolidation is a process which stabilizes a short-term memory into a long-term memory. Consolidation occurs after the initial learning lasting for a period of time. In this study, we employed resting-state experiment design to reveal the functional connectivity among hippocampus, PCC, and MTG during consolidation of memorizing easy and difficult words that would result in good and poor memory respectively. As seeds set at three ROIs, we detected increase connection with cuneus in the hard condition, implying the engagement of visual analysis; increment in connection with cerebellum and frontal cortex in the easy condition, reflecting the on-going consolidated activity.

Functional connectivity, implied by inter-region correlation, has been reported in resting state BOLD activity. It is well known that as magnetic field strength is increased, BOLD contrast to noise is improved, implying that a move to high field would benefit functional connectivity measurement. However, fMRI signals are affected by non-neuronal artifacts which increase with field strength making the advantage of 7T questionable. Here, we assess non-neuronal physiological artifacts in 3T and 7T resting state data. Results show that sensorimotor cortex connectivity can be measured accurately and at high spatial resolution at 7T with little contribution from non-neuronal physiological artifact.

Studies that examine the relationship of functional and structural connectivity are important in interpreting neurophysiological data. Although, a linear relationship between functional and structural connectivity has been demonstrated, there is no explicit attempt to quantitatively measure how well functional data can be predicted from structural data. Here, we predict functional connectivity from structural connectivity by utilizing a predictive model based on principal component analysis (PCA) and canonical correlation analysis (CCA).

Interpretation of inter-subject differences in resting-state functional connectivity is complicated by the BOLD signal’s dependence on vascular factors. We found functional connectivity strength to be correlated with resting-state fluctuation amplitude (RSFA) across healthy subjects, where RSFA has previously been shown to correspond to vascular reactivity within subjects. However, we did not find RSFA to be related to either the task-related cerebral blood flow (CBF) response or baseline CBF, suggesting that RSFA does not indicate vascular differences across subjects. Instead, RSFA may reflect true differences in spontaneous neural activity, which contribute to the normal variability found in resting-state functional connectivity.

Recent studies have demonstrated large amplitude spontaneous slow (< 0.1 Hz) fluctuations in functional-MRI (fMRI) signals in humans in the resting state. Despite the large body of human imaging literature on spontaneous activity and functional-connectivity in the resting state, the link to underlying neural activity remains tenuous. We show that spontaneous neurophysiological activity in rat S1FL includes events in which changes in local field potentials across cortical layers resemble the corresponding changes in response to sensory stimulation. These spontaneous neurophysiological events are accompanied by increases in blood oxygenation that peak approximately 5 s following the events.

Hemispherectomy is a last resort treatment for catastrophic hemispheric epilepsy. The remarkable motor recovery after hemispherectomy reflects the plastic capacities of the brain. We studied the remaining brain in hemispherectomized rats, 7 and 49 days post surgery using resting-state fMRI, graph analysis and interregional connectivity. The sensorimotor cortex and striatum in the healthy contralesional hemisphere exhibited significantly increased functional connectivity after surgery. The graph analysis results assume a shift toward a more regular network organization. We have shown that rs-fMRI, connectivity analyses and specific network measures can provide unique insights into functional reorganization in the remaining brain after experimental hemispherectomy.

This study examined the dynamic nonlinear BOLD response pattern in the primary olfactory cortex (POC) and associated brain structures during an olfactory fMRI paradigm. An intricate relationship among perception threshold, sensitivity, and habituation of the human olfactory system challenges the fundamental assumption of linearity in BOLD response. The goal of this study was to emphasize an unconventional nonlinear model of BOLD response through the use of olfactory fMRI and to suggest that such dynamic characteristics may extend to other neuronal systems with a feedback mechanism, profoundly impacting fMRI data acquisition/analysis and its clinical applications.

We evaluated the effect task demand for visual processing on the age-related change of the brain activation in healthy subjects. In the elderly subjects, the % HRF in V1 was reduced by the flickering checkerboard stimuli. By a visuo-motor translation task the % HRF in BA19/7/39 was increased in the elderly, while no significant difference of % HRF was detected between the two age groups in V1. HRF analysis suggested that age-related change of % HRF may depend on the existence of neuronal network to compensate the potential functional decline according to aging.

The cerebral representation of acute pain is well established, whereas that of tonic pain is not due to difficulties in applying functional imaging to prolonged stimuli. We used arterial spin labeling (ASL) to investigate the neural activation associated with tonic muscular pain. The use of ASL allows direct comparison between studies. Compared to our previous study incorporating both acute and tonic phases, we observed smaller CBF changes, and only in bilateral insula and frontal gyrus, despite similar pain levels. A likely explanation is that the acute phase of the previous study induced anxiety and distress, whereas our tonic pain stimulus did not.

Both gender and have long been assumed to have effects on brain function and cerebral blood flow (CBF). However, the effects of gender and age on CBF have not well explored in adolescents. To increase our knowledge in this area, MRI techniques were employed to measure global CBF with 267 adolescents. Our result shows that significant difference in CBF was observed between 12 and 15 years of age. However, no significant main effects of gender were found in the study. The results provide better understanding of brain functions for adolescent across age and gender.

Several empirical studies have shown, that long lasting acoustic noise exposure causes on humans effect called Temporary Hearing Threshold Shift (TTS). This work presents results from 15 healthy subjects participating in a fMRI study of TTS consisting of two runs: ⣣pre⣣ with silent GE EPI scanning and ⣣post⣣ identical to ⣣⣣pre⣣, but after 15min high volume noise exposure (causing a mean 12 dB TTS effect). Group level analysis showed activations in auditory cortex (T=13.3 in lh, and 10.45 in rh). A two-sample T-test fails for post>pre contrast, however detailed ROI analysis shows differences in sub-auditory areas.

Although the mirror neuron system has been extensively studied, no functional imaging data are currently available to gain insight in the possible difference of the mirror system between experts and novices. Therefore, the aim of the present study is to investigate the differences of activation in the mirror neuron system during viewing tool use familiar to experts between expert archers and novice subjects. Our results demonstrated that expert archers showed strong activation in the mirror neuron system during viewing videos of Western-style archery relative to inexpert control subjects. Taken together, our data consistent with previous reports suggest that human mirror neuron system could contain representations of tool use and expand motor repertoire with tool use experiences.

Previous studies have shown that ASL-based fMRI exhibits better spatial specificity than the most commonly used BOLD contrast. Here, we compared the localization of the hand motor area obtained by simultaneous ASL-BOLD fMRI and standard BOLD fMRI at 3T with well established anatomical landmarks, in a group of 15 healthy subjects. Our results indicate that the localization of the hand motor area obtained using ASL fMRI is significantly less variable and closer to the hand motor cortex anatomical landmarks than the one produced by BOLD fMRI. This supports the notion that ASL may more accurately localize brain activation than BOLD.

Understanding the neural mechanisms of consciousness requires identification of the nature of contributions from each of the potential neural correlates, which together generate a complete cognitive experience. We examined the specific and nonspecific thalamic connections in the brain based on the neuroanatomical findings implicating their respective functional roles in sustaining information and integration, which are essential to consciousness. Our results endorse the view that the thalamocortical system is essential to consciousness, and support the hypothesis that the nonspecific thalamic connections largely reflect brain regions that are responsible for information integration, potentially sustaining various awareness functions.

Structure and function are examined in the language network with DT-MRI and BOLD fMRI during a cognitive task. Activated cortical regions are identified and used to determine activation levels in each subject. Additionally, the regions are used to identify fiber tracts of interest. Canonical correlation analysis is used to identify correlations between functional activation and average fractional anisotropy in the fiber tracts. For each correlation found, the highest weightings are found for cortical regions and a tract that connects to that region.

Scanner acoustic noise may detrimentally affect stimulus/task-evoked neural responses in fMRI. This has been reported for the unimodal and associative auditory systems, but also for the default mode network and other brain systems.

In the current experiment, the effects of scanner noise in resting state fMRI are studied. We find that similar independent components may be extracted with and without background scanner noise, both during active and resting states. However, the overall strength, spatial extent, and temporal dynamics of various neural components are affected by the presence of background noise. Our results both corroborate and extend previous findings in literature. More detailed specific findings for various brain systems will be presented.

1185. Neural Correlates of Feigned Hearing

Bradley McPherson¹, Wayne Wilson², David Copland^3,4, Katie McMahon<sup>5

1</sup>Division of Speech and Hearing Sciences, Hong Kong University, China; ²Division of Audiology, University of Queensland, Australia; ³Centre for Clinical Research, University of Queensland, Australia; ⁴School of Health and Rehabilitation Sciences, University of Queensland, Australia; ⁵Centre for Magnetic Resonance, University of Queensland, Brisbane, Queensland, Australia

Can we use patterns of brain activity to detect when someone is feigning a hearing loss? To answer this question, we asked 15 adult participants to respond to pure tones and simple words correctly, incorrectly, randomly, or with the intent to feign a hearing loss.

Type 2 Diabetes mellitus (DM) is linked to a greater risk of dementia, but the underlying mechanisms and brain regions involved are unknown. We conducted a co-twin (DM/non DM) case-control study of fMRI activation during a visual memory task. Non DM twins showed greater activation of temporal, parietal and occipital cortices suggesting involvement of these areas in DM pathology.