Mild traumatic brain injury (mTBI) accounts for more than 80% of people experiencing brain injuries. Symptoms of mTBI include short-term and long-term adverse clinical outcomes. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) was conducted to measure voxel-based indices including fractional amplitude of low-frequency fluctuation (fALFF), regional homogeneity (ReHo), and functional connectivity (FC) in patients suffering from chronic mTBI; 64 patients with chronic mTBI at least 3 months post injury and 40 healthy controls underwent rs-fMRI scanning. Partial correlation analysis controlling for age and gender was performed within mTBI cohort to explore the association between rs-fMRI metrics and neuropsychological scores. Compared with controls, chronic mTBI patients showed increased fALFF in the left middle occipital cortex (MOC), right middle temporal cortex (MTC), and right angular gyrus (AG), and increased ReHo in the left MOC and left posterior cingulate cortex (PCC). Enhanced FC was observed from left MOC to right precuneus; from right MTC to right superior temporal cortex (STC), right supramarginal, and left inferior parietal cortex (IPC); and from the seed located at right AG to left precuneus, left superior medial frontal cortex (SMFC), left MTC, left superior temporal cortex (STC), and left MOC. Furthermore, the correlation analysis revealed a significant correlation between neuropsychological scores and fALFF, ReHo, and seed-based FC measured from the regions with significant group differences. Our results demonstrated that alterations of low-frequency oscillations in chronic mTBI could be representative of disruption in emotional circuits, cognitive performance, and recovery in this cohort.

The sense of smell is a complex chemosensory processing in human and animals that allows them to connect with the environment as one of their chief sensory systems. In the field of functional brain imaging, many studies have focused on locating brain regions that are involved during olfactory processing. Despite wealth of literature about brain network in different olfactory tasks, there is a paucity of data regarding task design. Moreover, considering importance of olfactory tasks for patients with variety of neurological diseases, special contemplations should be addressed for patients. In this article, we review current olfaction tasks for behavioral studies and functional neuroimaging assessments, as well as technical principles regarding utilization of these tasks in functional magnetic resonance imaging studies.

Background: Functional magnetic resonance imaging (fMRI) is a non-invasive and convenient method of mapping brain activity associated with the human sensory systems. Among these systems there is a lack of data from olfactory studies, which could be attributed to technical difficulties in odor delivery during scanning. The current study took advantage of an olfactometer to evaluate brain activity during the odor-smelling process.Objectives: This study aimed to investigate the brain regions of the human olfactory system via fMRI brain imaging. A speculative survey was used to highlight the differences between studies conducted in healthy populations using olfactory tasks, as well as conducting literature survey in terms of the technical principles applying through these tasks in fMRI studies. Subjects and Methods: A functional map of the olfactory system that used a block design, alternating between odor and non-odor phases, was examined in 15 healthy volunteers. The general linear model was used to identify statistically significant voxels that showed activation during the activation blocks. Results: Primary and secondary olfactory regions, including the piriformis, insula, amygdala, parahippocampal gyrus, caudate nucleus, inferior frontal gyrus, middle frontal gyrus, superior temporal gyrus, and cerebellum, demonstrated significant activation in response to odor stimulation. Conclusion: Activation of the aforementioned brain areas, and the pattern of activation, is largely in accordance with previous published olfactory studies carried out in healthy individuals.