title: Inhibition of the primary motor cortex can alter one's "sense of effort": effects of low-frequency rTMS.
abstract: Studies using force-matching tasks have suggested that when we feel a "sense of effort," cortical regions may act to increase motor commands, and thus recruit additional motor units, in order to compensate for the exerted force. We hypothesized that suppressing activity in the primary motor cortex (M1), which is the source of the motor commands, would initiate the same process, and induce the same sense of effort. In a force-matching task, grip force was applied to 'right' hand and 10 healthy participants were asked to try to exert the same amount by using 'left' hand, with no visual feedback. On some trials, low-frequency, repetitive transcranial magnetic stimulation (lf-rTMS) was used to suppress the M1 and the primary somatosensory cortex (SI) in the left hemisphere, separately. Results showed that participants tended to overestimate the level of exerted force by up to 24%. In contrast, sham stimulation of the M1 and lf-rTMS over the SI did not significantly affect participants' estimations. Further, the M1 suppression resulted in a 42% reduction in motor-evoked potentials. Thus, the M1 suppression can affect our sense of effort, suggesting that compensatory neural mechanisms that increase the MI activity may play an important role in producing senses of effort.
authors.affiliation: Faculty of Sport Sciences, Waseda University, Saitama 359-1192, Japan. Electronic address: takarada@waseda.jp.
authors.forename: Yudai
authors.initials: Y
authors.lastname: Takarada
authors.affiliation: Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Mima
authors.affiliation: Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
authors.forename: Mitsunari
authors.initials: M
authors.lastname: Abe
authors.affiliation: Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nakatsuka
authors.affiliation: Department of Cognitive Neurobiology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8549, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Taira
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor; D005260:Female; D018737:Hand Strength; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition; D005082:Physical Exertion; D055698:Touch Perception / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods
keywords: Force perception; Motor command; Primary motor cortex; Primary sensory cortex; Spinal motoneuron