Steady state visual evoked potential (SSVEP) changes in response to olfactory stimulation.

Abstract

The location, nature and characteristics of brain activity during detection and identification of odors are of importance if brain function techniques are to be of value to sensory systems. Steady state probe topography (SSPT) has been used in our laboratory to record steady state visual evoked potentials (SSVEP), which have demonstrated cognitive task-related changes in a variety of testing paradigms. The enhanced spatial (when using 64 channels) and temporal resolution (380 ms) of the system enable the brain electrical activity changes occurring before, during and after delivery of an odor to be examined. We have developed a system which can deliver odors during normal respiration and the accurate timing needed for SSVEP recordings. The system is based on the premise that a subject breathing butanol compared with filtered medical air will demonstrate SSVEP topographic changes associated with detection and identification of butanol. During our experiments the subject has either an air sample or an equal volume of butanol injected into the inspiratory airflow. These are randomized, and every breath has the same stimulus system with no known clues as to the differences apart from detection. The results from a panel of 10 female subjects--who all identified the butanol correctly--showed that butanol delivery resulted in sequences of changes in SSVEP topography (amplitude and latencies) which involved parietal, frontal and temporal regions. While consistent with other studies (parietal changes), our results revealed more dynamic temporal changes involving prefrontal and parietal regions at different periods around odor delivery.