P 48. Supplementary motor area plays a causal role in automatic inhibition of motor response

• Published in: Clinical neurophysiology Vol. 124; no. 10; pp. e86 - e87
• Main Authors: Shirota, Y, Hanajima, R, Ohminami, S, Tsutsumi, R, Ugawa, Y, Terao, Y
• Format: Journal Article
• Language: English
• Published: Elsevier Ireland Ltd 01.10.2013
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2013.04.126

Introduction Negative compatibility effect (NCE) is a phenomenon that reflects automatic self-inhibition of a motor response. NCE is tested by the masked prime paradigm where participants have to respond to right or left oriented arrowhead (“target”) as fast as possible, which is preceded by a “prime” that has the same shape and the same (“compatible” task) or reversed (“incompatible” task) direction as the target, and a “mask” preventing overt perception of the prime. Under certain durations of masking, reaction time (RT) for the incompatible task is shorter than that for the compatible task. This counter-intuitive RT difference is called NCE, and its mechanism has been proposed to lie in the self-inhibition of an automatic response to the masked prime. A lesion study indicated that the supplementary motor area (SMA) is involved in NCE. Objectives To elucidate the causal role of SMA in NCE using repetitive transcranial magnetic stimulation (rTMS) in a healthy population. Materials and methods NCE was tested using the masked prime paradigm described above. In this study, participants responded to the target by clicking the right or left mouse button with their right or left index finger. According to previous reports, a mask duration of 150 ms was used to test NCE. In contrast, when the mask has a shorter duration such as 50 ms, the compatible task has shorter reaction time, called positive CE (PCE). NCE, PCE, and choice reaction time (CRT) was measured before and after quadripulse stimulation (QPS)-5 ms, a newly devised rTMS protocol which produces long-term potentiation (LTP) like aftereffect. QPS over SMA, QPS over the primary motor cortex (M1), and sham QPS were compared. In addition, amplitude of motor evoked potential (MEP) from the first dorsal interosseous (FDI) muscles, resting and active motor thresholds (RMT and AMT) were measured as a physiological parameter. Results QPS over SMA diminished NCE of both hands, whereas QPS over M1 and sham QPS had no effect. CRT was similar among the QPS protocols, but PCE with the right hand tended to be enhanced by QPS over SMA. With regard to the physiological markers, MEP amplitude of right FDI tended to be increased by QPS. RMT and AMT were unchanged in any conditions. Conclusions The present results indicate that SMA plays a causal role to express NCE. The mechanism of PCE enhancement and its relation to NCE decrease needs to be studied in a future research.