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Default mode network (DMN) deactivation has been shown to be functionally relevant for goal-directed cognition. In this study, the DMN's role during olfactory processing was investigated using two complementary functional magnetic resonance imaging (fMRI) paradigms with identical timing, visual-cue stimulation, and response monitoring protocols. Twenty-nine healthy, non-smoking, right-handed adults (mean age = 26 ± 4 years, 16 females) completed an odor-visual association fMRI paradigm that had two alternating odor + visual and visual-only trial conditions. During odor + visual trials, a visual cue was presented simultaneously with an odor, while during visual-only trial conditions the same visual cue was presented alone. Eighteen of the twenty-nine participants (mean age = 27.0 ± 6.0 years, 11 females) also took part in a control no-odor fMRI paradigm that consisted of a visual-only trial condition which was identical to the visual-only trials in the odor-visual association paradigm. Independent Component Analysis (ICA), extended unified structural equation modeling (euSEM), and psychophysiological interaction (PPI) were used to investigate the interplay between the DMN and olfactory network. In the odor-visual association paradigm, DMN deactivation was evoked by both the odor + visual and visual-only trial conditions. In contrast, the visual-only trials in the no-odor paradigm did not evoke consistent DMN deactivation. In the odor-visual association paradigm, the euSEM and PPI analyses identified a directed connectivity between the DMN and olfactory network which was significantly different between odor + visual and visual-only trial conditions. The results support a strong interaction between the DMN and olfactory network and highlights the DMN's role in task-evoked brain activity and behavioral responses during olfactory processing. Hum Brain Mapp 38:1125-1139, 2017. © 2016 Wiley Periodicals, Inc.

Purpose To evaluate the dynamic characteristics of T2* -weighted signal change in exercising skeletal muscle of healthy subjects and peripheral artery disease (PAD) patients under a low-intensity exercise paradigm. Materials and Methods Nine PAD patients and nine age- and sex-matched healthy volunteers underwent a low-intensity exercise paradigm while magnetic resonance imaging (MRI) (3.0T) was obtained. T2*-weighted signal time-courses in lateral gastrocnemius, medial gastrocnemius, soleus, and tibialis anterior were acquired and analyzed. Correlations were performed between dynamic T2*-weighted signal and changes in heart rate, mean arterial pressure, leg pain, and perceived exertion. Results A significant signal decrease was observed during exercise in soleus and tibialis anterior of healthy participants (P = 0.0007–0.04 and 0.001–0.009, respectively). In PAD, negative signals were observed (P = 0.008–0.02 and 0.003–0.01, respectively) in soleus and lateral gastrocnemius during the early exercise stage. Then the signal gradually increased above the baseline in the lateral gastrocnemius during and after exercise in six of the eight patients who completed the study. This signal increase in patients' lateral gastrocnemius was significantly greater than in healthy subjects' during the later exercise stage (two-sample t-tests, P = 0.001–0.03). Heart rate and mean arterial pressure responses to exercise were significantly higher in PAD than healthy subjects (P = 0.036 and 0.008, respectively) and the patients experienced greater leg pain and exertion (P = 0.006 and P = 0.0014, respectively). Conclusion During low-intensity exercise, there were different dynamic T2*-weighted signal behavior in the healthy and PAD exercising muscles. Level of Evidence 2 J. Magn. Reson. Imaging 2016;00:000–000

The study of human olfaction is complicated by the myriad of processing demands in conscious perceptual and emotional experiences of odors. Combining functional magnetic resonance imaging with convergent multivariate network analyses, we examined the spatiotemporal behavior of olfactory-generated blood-oxygenated-level-dependent signal in healthy adults. The experimental functional magnetic resonance imaging (fMRI) paradigm was found to offset the limitations of olfactory habituation effects and permitted the identification of five functional networks. Analysis delineated separable neuronal circuits that were spatially centered in the primary olfactory cortex, striatum, dorsolateral prefrontal cortex, rostral prefrontal cortex/anterior cingulate, and parietal-occipital junction. We hypothesize that these functional networks subserve primary perceptual, affective/motivational, and higher order olfactory-related cognitive processes. Results provided direct evidence for the existence of parallel networks with top-down modulation for olfactory processing and clearly distinguished brain activations that were sniffing-related versus odor-related. A comprehensive neurocognitive model for olfaction is presented that may be applied to broader translational studies of olfactory function, aging, and neurological disease.

Purpose To elucidate differences in the disruption of language network function, as measured by blood oxygenation level-dependent (BOLD) contrast functional MRI (fMRI), attributable to two common sedative agents administered to infants under clinical imaging protocols. Materials and Methods The sedatives pentobarbital (Nembutal) and Propofol, administered clinically to infants at 1 year of age, were compared with respect to BOLD activation profiles in response to passive story-listening stimulation. An intermittent event-related imaging protocol was used with which the temporal evolution of language processing resulting from this stimulation was explored. Results Propofol and Nembutal were found to have distinct and complementary responses to story-listening. Propofol exhibited more activation in higher processing networks with increasing response toward the end of narrative stimulus. Nembutal, in contrast, had much more robust activation of primary and secondary sensory cortices but a decreasing response over time in fronto-parietal default-mode regions. This may suggest a breakdown of top-down feedback for Propofol versus the lack of bottom-up feed-forward processing for Nembutal. Conclusion Two popular sedative agents for use in children for clinical fMRI were found to induce distinct alteration of activation patterns from a language stimulus. This has ramifications for clinical fMRI of sedated infants and encourages further study to build a framework for more confident interpretation. J. Magn. Reson. Imaging 2013;38:1184–1195. © 2013 Wiley Periodicals, Inc.

The ability to process an aurally-presented story is supported by a network of auditory and language-processing brain regions (2-5) that changes during development (6,7). Multiple aspects of language processing are engaged during this naturalistic speech task, including speech perception, word recognition, syntactic processing and discourse coherence. Consequently, this task has been cited as one method for effectively mapping eloquent cortical areas (3,4). In patients undergoing resective surgery, language lateralization information is particularly important, with the goal of using non-invasive functional MRI to replace the invasive and risky intracarotid amobarbital procedure (Wada test). A number of studies (8-10)have demonstrated the ability of fMRI to detect the expected left-lateralized activation pattern associated with in typically-developing children. In addition, fMRI has revealed changes in lateralization associated with neuropathology (11,12). However, a standard paradigm optimized for clinical use in the pediatric population has not been established. In the present study, we investigate two versions of the story processing task that are potentially effective procedures for determining language lateralization and localization in children. Previous fMRI studies have examined the neural basis of story processing in children, using a block-periodic, passive listening (PL) design contrasting short stories with tone sequences (7,13,14). These studies were based on data from a large group of children (313) ages 5−18. Results revealed areas of activation in superior temporal gyrus and superior frontal gyrus (bilaterally), and left posterior superior temporal gyrus. Independent components analysis of the same data (ICA) revealed additional activation in angular gyrus together with the precuneus, posterior cingulate, left inferior parietal lobule and inferior frontal gyrus in addition to the regions mentioned above (7). ICA reveals additional areas of activation compared to standard fMRI analysis using model driven methods because it is a data-driven approach that does not rely on a model of the hemodynamic response function to detect changes in BOLD response(15). One drawback associated with the PL story comprehension task is that no on-line measure of task performance is collected. The studies described above (7,13,14) made use of a post-scan comprehension test on which 87% of participants performed above chance level, suggesting that a majority of children were actively engaged in story comprehension. However, this does not address the accuracy of participant's comprehension during the fMRI scan, nor their level of attention to the stimuli. Young pediatric participants, some of whom require sedation to undergo an MRI procedure, may not be capable of actively generating responses to language stimuli. A passive listening task has already been demonstrated to activate bilateral auditory processing areas in such patients (16). Therefore, examining whether passive listening and active-response tasks evoke similar activation patterns, especially in children, is relevant for application of fMRI in these patients. Continuous fMRI scanning throughout the passive listening task generates acoustic noise that may interfere with participants’ comprehension of the stories. This may also make the identification of task-related activation patterns more difficult due to the presence of background noise (17-19). Schmidt et al. (19) compared BOLD activation in response to identical auditory sentence stimuli tested during continuous fMRI scanning versus sparse fMRI acquisition, and found increased levels of BOLD response in superior temporal regions with the sparse acquisition technique, suggesting that this technique may be more sensitive for detecting activation associated with auditory language stimuli. The present study examines these issues by comparing the PL story paradigm to an active-response (AR) version that includes on-line performance monitoring and utilizes a clustered fMRI acquisition technique that eliminates scanner noise during auditory presentation (20,21). Our goal in developing the AR task was to potentially improve upon the PL version of the task as much as possible since it is regularly used in the clinical setting.

Complex physiological signals are neither deterministic nor random, showing a mixture of long-range dependencies and irregularities (i.e., information) over multiple time scales. In humans, aging and pathology are associated with diminished CNS neurophysiological complexity and impaired cognition. In this study, we computed multiscale entropy (MSE) to measure the time scale dependent complexity (i.e., information) of the resting state BOLD fMRI signal in humans over a large age span (N=138; ages 8-83; 58 male). Physiological noise (heart rate, respiration, head motion and local white matter [WM] signals) was removed from fMRI time courses using linear regression. Data were then bandpass filtered (.008-.1 Hz) to isolate low frequency fluctuations. MSE was computed with parameters m=2 and r=.2 for temporal scales 1-18. BOLD signal in gray matter (GM) and WM gained information with increasing temporal scale and exceeded the information gain from bandpass filtered white and 1/f noise. GM sustained the informa...