Olfactory Cognitive Response Using Odorant Odd-ball Paradigm by Magnetoencephalography
Mitsuo Tonoike, Masahiko Yamaguchi, and Isao Kaetsu
The aim of this study is to measure and analyze perception and cognition in human olfaction. In this magnetoencephalographic (MEG) study the event-related magnetic fields were measured by a whole-cortex biomagnetometer (a 122-channel, first-order planar SQUID gradiometer which can cover the entire head of a subject). We have already reported that the response of olfactory event-related magnetic fields were obtained as a broad peak at 300-500 ms latency on bilateral frontal lobe, whose generators were located symmetrically on bilateral frontal area near the orbito-frontal sulcus. In this experiments we applied an odd-ball paradigm to study olfactory event-related magnetic fields. Three volunteers participated in this study. The odd-ball paradigm using two kinds (amyl acetate, and isovaleric acid) of odorant pulse stimuli were applied. The subjects were instructed to count the number of rare odorant stimuli as a target.
In this odd-ball study, three responding peaks were analyzed by a SSP method. The first component was the trigeminal response of about 270 ms latency. The second components were olfactory responses of 350-450 ms latency which were composed from two generators estimated at the bilateral orbito-frontal regions. These latest components with latency more than 500 ms were evoked by the odorant odd-ball task only and these generators were firstly estimated on a few superior-temporal areas or near in the right and left insula regions. These late MEG components by the olfactory odd-ball paradigm suggest the activities of cognitive response of human olfaction. From these two olfactory MEG experiments and analyses, we found the perception and recognition mechanism in human olfactory system objectively.
Key words: 122-channel whole-cortex biomagnetometer, planar SQUID gradiometer, olfactory stimulator, olfactory event-related magnetic fields, dipole model, olfactory odd-ball paradigm, SSP method, olfactory perception and recognition