O2-D-35. High frequency activity (HFA) is enhanced in the frontal region during free choice of favorite product photos

We studied neural mechanisms of affect-guided choice or oddball choice by measuring magnetoencephalography (MEG) from twenty subjects. Four-hundred product-photos comprising a wide selection of commodities of various kinds such as a chair, kettle, cup, etc. were successively presented. The subjects underwent MEG during a free choice task of favorite products by pressing a switch-button with their left index (mean choice ratio = 29.7%). On another occasion, they performed an odd-ball task with 30%-target (favorite products in their previous free choice tasks) and 70%-nontarget (non-favorite ones). Using a spatial filtering algorithm, we calculated 3-D distribution of MEG power-changes due to selection (the ratio of favorite/non-favorite products and that of target/nontarget) by successively sliding a 300 ms time-window for each photo presentation period (3s). When subjects chose favorite products, high frequency activity (HFA, 22–100 Hz) was enhanced in the left orbitofrontal cortex (OFC, mean latency = 445 ms poststimulus), the right ACC and SMA (641 ms), and the right parietal areas associated with the left finger movement (778 ms). When they selected the same products as oddball or compulsory choices, HFA was absent in OFC, ACC and SMA. The sequent OFC-SMA high-frequency activation probably reflects affect-guided decision-making of favorite products by free will.