NeuroImage
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The position and extent of individual fiber tracts within the white matter of human brains can be identified in vivo using diffusion tensor imaging (DTI) and fiber tracking methods. Previous to this study, however, the lack of three-dimensional (3-D) probability maps precluded comparing the anatomical precision of MRI studies with microscopically defined fiber tracts in human postmortem brains. The present study provides 3-D registered maps of the topography, course and intersubject variability of major fiber tracts, which were identified at microscopic resolution. ⋯ The individual fiber tracts and nuclei were superimposed in the reference space, and probability maps were generated as a quantitative measure of intersubject variability for each voxel of the stereotaxic space. This study presents the first stereotaxic atlas of the course, location and extent of fiber tracts and related nuclei based on microscopically defined localization and topographic data taken at multiple levels on each of the three orthogonal planes. The maps are useful for evaluating and identifying fiber bundles in DTI, for localizing subcortical lesions visible in anatomical MR images and for studying neuronal connectivity.
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Speech production introduces signal changes in fMRI data that can mimic or mask the task-induced BOLD response. Rapid event-related designs with variable ISIs address these concerns by minimizing the correlation of task and speech-related signal changes without sacrificing efficiency; however, the increase in residual variance due to speech still decreases statistical power and must be explicitly addressed primarily through post-processing techniques. We investigated the timing, magnitude, and location of speech-related variance in an overt picture naming fMRI study with a rapid event-related design, using a data acquisition system that time-stamped image acquisitions, speech, and a pneumatic belt signal on the same clock. ⋯ If left unmodeled, speech-related variance can result in regional detection bias that affects some areas critically implicated in language function. The results establish the feasibility of detecting and mitigating speech-related variance in rapid event-related fMRI experiments with single word utterances. They further demonstrate the utility of precise timing information about speech and respiration for this purpose.
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Functional magnetic resonance imaging (fMRI) studies of the human brain have suggested that low-frequency fluctuations in resting fMRI data collected using blood oxygen level dependent (BOLD) contrast correspond to functionally relevant resting state networks (RSNs). Whether the fluctuations of resting fMRI signal in RSNs are a direct consequence of neocortical neuronal activity or are low-frequency artifacts due to other physiological processes (e.g., autonomically driven fluctuations in cerebral blood flow) is uncertain. In order to investigate further these fluctuations, we have characterized their spatial and temporal properties using probabilistic independent component analysis (PICA), a robust approach to RSN identification. ⋯ The RSNs appear to reflect "default" interactions related to functional networks related to those recruited by specific types of cognitive processes. RSNs are a major source of non-modeled signal in BOLD fMRI data, so a full understanding of their dynamics will improve the interpretation of functional brain imaging studies more generally. Because RSNs reflect interactions in cognitively relevant functional networks, they offer a new approach to the characterization of state changes with pathology and the effects of drugs.
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Evidence suggests that we use the same mechanisms for both producing and perceiving actions. Such 'shared representations' may also underlie social perception and empathy. However, this idea raises some important and as yet unresolved questions: (i) how do we distinguish other-orientated empathic responses from a self-orientated reactions such as personal distress and (ii) what are the neural substrates underpinning these processes? We employed event-related functional magnetic resonance imaging (fMRI) to explore whether 'shared representations' were recruited to decode dynamic social stimuli in 12 healthy volunteers. ⋯ Brain activation specific to the main experimental condition was found in the inferior frontal gyrus (BA44) and premotor areas (BA6) consistent with the use of 'shared representations'. Somatosensory areas such as the insula and supramarginal gyrus (BA40) were also activated suggesting that participants constructed a qualitative representation of the target state. Activity in the rostral anterior cingulate was associated with self-reports of personal distress and increased blood flow to the anterior cingulate (BA24) and inferior parietal cortex (BA40) was related to self-other overlap.
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Controlled Clinical Trial
Mode and site of acupuncture modulation in the human brain: 3D (124-ch) EEG power spectrum mapping and source imaging.
This study determined: (a) if acupuncture stimulation at a traditional site might modulate ongoing EEG as compared with stimulation of a control site; (b) if high-frequency vs. low-frequency stimulation could exert differential effects of acupuncture; (c) if the observed effects of acupuncture were specific to certain EEG bands; and (d) if the acupuncture effect could be isolated at a specific scalp field, with its putative underlying intracranial source. Twelve healthy male volunteers (age range 22-35) participated in two experimental sessions separated by 1 week, which involved transcutaneous acupoint stimulation at selected acupoint (Li 4, HeGu) vs. a mock point at the fourth interosseous muscle area on the left hand in high (HF: 100 Hz) vs. low-frequency (LF: 2 Hz) stimulation by counter-balanced order. 124-ch EEG data were used to analyze the Delta, Theta, Alpha-1, Alpha-2, Beta, and Gamma bands. The absolute EEG powers (muv2) at focal maxima across three stages (baseline, stimulation, post) were examined by two-way (condition, stage) repeated measures ANOVA. ⋯ The topographic Theta activity was tentatively identified to originate from the intracranial current source in cingulate cortex, likely ACC. It is likely that short-term cortical plasticity occurs during high-frequency but not low-frequency stimulation at the HeGu point, but not mock point. We suggest that HeGu acupuncture stimulation modulates limbic cingulum by a frequency modulation mode, which then may damp nociceptive processing in the brain.