The strength of the corticospinal coherence depends on the predictability of modulated isometric forces

Abstract

The strength of the corticospinal coherence depends on the predictability of modulated isometric forces. J Neurophysiol 109: 1579 -1588, 2013. First published December 19, 2012 doi:10.1152/jn.00187.2012.-Isometric compensation of predictably frequency-modulated low forces is associated with corticomuscular coherence (CMC) in beta and low gamma range. It remains unclear how the CMC is influenced by unpredictably modulated forces, which create a mismatch between expected and actual sensory feedback. We recorded electroencephalography from the contralateral hand motor area, electromyography (EMG), and the motor performance of 16 subjects during a visuomotor task in which they had to isometrically compensate target forces at 8% of the maximum voluntary contraction with their right index finger. The modulated forces were presented with predictable or unpredictable frequencies. We calculated the CMC, the cortical motor alpha-, beta-, and gamma-range spectral powers (SP), and the taskrelated desynchronization (TRD), as well as the EMG SP and the performance. We found that in the unpredictable condition the CMC was significantly lower and associated with lower cortical motor SP, stronger TRD, higher EMG SP, and worse performance. The findings suggest that due to the mismatch between predicted and actual sensory feedback leading to higher computational load and less stationary motor state, the unpredictable modulation of the force leads to a decrease in corticospinal synchrony, an increase in cortical and muscle activation, and a worse performance. coherence; human; predictable; oscillations; unpredictable THE BETA AND GAMMA OSCILLATIONS over the sensorimotor cortex are known to synchronize with oscillations in the contralateral motoneuronal pool that can be computed by coherence. Previous primate and human studies showed that beta-range corticomuscular coherence (CMC) is mainly associated with isometric compensation of steady-state forces (Baker and Baker 2003; Baker et al. 1997Baker et al. , 2006 Bressler 2009; Brown 2000; Cheyne et al. 2008;Conway et al. 1995; Engel and Fries 2010; Feige et al. 2000;Gross et al. 2000;Halliday et al. 1998;Houweling et al. 2010;Kristeva-Feige et al. 1993;Murthy and Fetz 1992, 1996a, 1996bPerez et al. 2006;Riddle and Baker 2006;Salenius et al. 1997;Sanes and Donoghue 1993;Tecchio et al. 2006;Witham et al. 2010). The CMC is most likely mediated by monosynaptic connections to the motoneurons (Baker et al. 2003;Conway et al. 1995). However, a large body of evidence was accumulated indicating that the CMC also represents sensory feedback from the moving part of the body (Baker et al. 2006). We have reported that the beta-range CMC is not specific for static forces only. The sensorimotor system may resort to stronger and also broader beta-range CMC to generate stable corticospinal interaction at higher force levels than 4% maximum voluntary contraction (MVC) when compensating for dynamic predictable frequency-modulated forces (from 8 to 16 and to 24% MVC) (Chakarov et al. 2009). Interesti...

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