Objetive assessment of olfactory function using functional magnetic resonance (fMRI)

Abstract

In this work, a device for generating automated olfactory stimuli in functional magnetic resonance imaging (fMRI) studies is described. The novel issues of our design are: synchronization between the acquisition and the olfactory task, automated control of experimental parameters (odorants sequences, frequency, time and concentration of stimuli). Finally, we present the preliminary results obtained on a General Electric 3 Tesla MRI scanner belong to The Alzheimer Project of the Fundación Reina Sofía.

Methodological Considerations in Conducting an Olfactory fMRI Study

“…Borromeo has shown that there is a lag between administration and presentation of odor in fMRI studies. Also a delay time of 12 seconds after the deactivation of stimuli has been reported in this study [36]. In general, activation of primary olfactory cortex could be missed due to habituation of these areas and lack of synchronization between presentation and administration of odor [11].…”

“…Also, utilization of appropriate oil odorants with adjusted concentration can obtain a delay time less than 3 seconds. This time is more longer for liquid odorants [36].…”

“…One of the most important features in utilizing fMRI tasks is the synchronization between acquisition of the MR signal and stimuli transference [36]. Synchronization is especially important in complex designs to avoid loss of information.…”

“…Two different models can be used in fMRI studies to design stimulation paradigm. "Block designs" and "event-related" models are the two normative approaches to present the stimulus [36]. These two methods are also commonly used to activate neural networks of olfactory system during functional brain imaging.…”

The Human Olfactory System: Cortical Brain Mapping Using fMRI

“…The majority of fMRI studies take advantage of block-designed tasks, which compare alternating intervals of stimulus and no-stimulus epochs with regard to increasing statistically significant changes in blood oxygen level-dependent (BOLD) signal intensity. In olfaction studies, one condition can be odor presentation (an experimental phase), while the other in-volves a no-odor condition (a control phase) (1,(7)(8)(9). In order to produce a precise and adequate delivery of the odor stimulus in both phases, the majority of recent studies have utilized an olfactometer device (7).…”