Methodological Considerations in Conducting an Olfactory fMRI Study

Abstract

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.

Functional MRI as an Objective Measure of Olfaction Deficit in Patients with Traumatic Anosmia

“…26 Our finding of decreased brain activation in the bilateral temporal cortex and left superior parietal lobule of patients with traumatic anosmia in response to an unpleasant odor is consistent with previous observations. [27][28][29] Although olfaction primarily functions as a means for odor perception and identification, it also serves an additional function in understanding and integrating multimodal actions. 27 A previous fMRI study that used visual and olfactory stimuli reported increased activation in the middle temporal gyrus and parietal cortex (areas of multisensory integration) during stimulation, supporting the idea that olfaction serves multiple functions.…”

“…[27][28][29] Although olfaction primarily functions as a means for odor perception and identification, it also serves an additional function in understanding and integrating multimodal actions. 27 A previous fMRI study that used visual and olfactory stimuli reported increased activation in the middle temporal gyrus and parietal cortex (areas of multisensory integration) during stimulation, supporting the idea that olfaction serves multiple functions. 28 Furthermore, activation in the temporoparietal cortex has also been associated with odor-recognition memory, a task with a high cognitive demand.…”

“…31,32 Second, previous studies have shown that the piriform cortex and other parts of the primary olfactory cortex are only briefly activated in response to odor stimulation (Ͻ10 -15 seconds), with BOLD signal decreasing to baseline shortly thereafter. 27,33 Although our study design used a brief 10-second odor stimulus, a habituation effect would still be possible and may have obscured differences between the HC and anosmia groups in the pleasant odor condition (ie, in the condition evoking inherently weaker activation). Finally, while the unpleasant olfactory stimulation we used in this study is not known to cause trigeminal stimulation, clearly the pleasant odor of citral is related to trigeminal stimulation to a certain degree.…”

Severity of olfactory deficits is reflected in functional brain networks—An fMRI study

“…Studies that investigate the effects of olfactory disorders on functional activity in the olfactory system during the administration of odors in general show decreased activation in olfactory areas of the brain (Vedaei et al, ). Changes in brain activity after smell loss have been investigated extensively in patients suffering from neurodegenerative disorders, like Alzheimer's disease (Cerf‐Ducastel & Murphy, ; Wang et al, ) and Parkinson's disease (Welge‐Lüssen et al, ), and in aging patients (Welge‐Lüssen, ).…”

Improved low-cost, MR-compatible olfactometer to deliver tobacco smoke odor

“…Another innovative approach employs pinch valves and miniature valve terminal assemblies located close to the participant, both reducing transition times and device footprint (Bestgen et al, 2016). Finally, Vedaei et al (2013) present a review of issues involved in conducting fMRI studies of olfaction. These authors address expected response times and brain locations; issues of habituation, adaptation, concentration, and number of odor presentations; and applications to diseases such as Alzheimer’s disease, Parkinson’s disease, schizophrenia, and clinical depression.…”