Abstract
To further investigate the mechanism of surround inhibition (SI) and to determine whether adopting different attentional strategies might have an impact on the modulation of SI, the effects of adopting an external (EF) or internal focus of attention (IF) on SI and motor performance were investigated. While performing an index flexion with either an EF or IF, transcranial magnetic stimulation was applied at various time points in 14 healthy subjects. When adopting an EF compared to an IF, the results show an improved motor performance (+14.7% in MVC) and a reduced bEMG in the adjacent APB (−22.3%) during maximal index flexion. This was accompanied by an increased SI in the APB with an EF (+26.4%). Additionally, the decrease in bEMG correlated with the magnitude of SI in APB. The current results demonstrate an efficient way to modulate SI by changing the attentional focus in healthy subjects and might, at least in part, explain the better motor performance being associated with an EF. The present findings help to better understand the positive mechanisms of an EF on SI in the healthy motor system and may also points towards a treatment strategy in pathologies with disturbed SI such as focal hand dystonia.
Highlights
The present study aimed to investigate the immediate influence of different attentional strategies (EF vs internal focus of attention (IF)) on (i) motor performance when executing maximal voluntary contractions (MVC) of the first dorsal interosseous muscle (FDI) and (ii) on the amount of surround inhibition (SI) within M1 influencing the activity of the adjacent muscle abductor pollicis brevis (APB)
Subjects showed less Background EMG (bEMG) activity in the adjacent muscle APB (t13 = −2.48, P = 0.02, Fig. 3A) when executing the maximal force task with an EF (0.059 ± 0.05 mV) compared to an IF (0.076 ± 0.07 mV). They showed smaller MNF and median frequencies (MDF) in the adjacent APB muscle when adopting an EF contrasted to an IF (MNF: t13 = −2.99, P = 0.01, EF = 77.67 ± 13.28 Hz, IF = 93.95 ± 28.39 Hz; MDF: t13 = −3.99, P = 0.001, EF = 61.05 ± 10.92 Hz, IF = 73.87 ± 17.67 Hz, Fig. 3B and C)
The results showed a significant coefficient of correlation between the difference in bEMG in the APB muscle during the maximal contraction and the amount of SI in the APB muscle during the premotor phase (r = 0.61, P = 0.001, Fig. 5)
Summary
In the prime mover FDI muscle, there was no significant main effect of focus (F1,11 = 1.78, P = 0.20, η2 < 0.001). Post hoc comparisons revealed that background EMG in all phases was bigger than the control phase (premotor, P = 0.01; phasic, P < 0.001; tonic, P < 0.001), showing that FDI was active during the movement (see Fig. 1D). Background EMG was significantly enhanced during the phasic (P < 0.001) and tonic (P = 0.003) phases compared with the premotor phase. Background EMG was significantly enhanced in the phasic phase compared to the tonic phase (P < 0.001, Table 2 for details). No significant interaction effect of focus x phase (F3,33 = 1.36, P = 0.27, η2 = 0.001) was found
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