Corticomuscular synchronization with small and large dynamic force output

BACKGROUND: Over the last years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC) during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study [1] that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic) generated by a manipulandum. The CMC, the cortical EEG spectral power (SP), the EMG SP and the errors in motor performance (as the difference between target and exerted force) were analyzed. RESULTS: For the static force condition we found the well-documented, significant beta-range CMC (15-30Hz) over the contralateral sensorimotor cortex. Gamma-band CMC (30-45Hz) occurred in both small and large dynamic force conditions without any significant difference between both conditions. Although in some subjects beta-range CMC was observed during both dynamic force conditions no significant difference between conditions could be detected. With respect to the motor performance, the lowest errors were obtained in the static force condition and the highest ones in the dynamic condition with large amplitude. However, when we normalized the magnitude of the errors to the amplitude of the applied force (relative errors) no significant difference between both dynamic conditions was observed. CONCLUSIONS: These findings confirm that during dynamic force output the corticomuscular network oscillates at gamma frequencies. Moreover, we show that amplitude modulation of dynamic force has no effect on the gamma CMC in the low force range investigated. We suggest that gamma CMC is rather associated with the internal state of the sensorimotor system as supported by the unchanged relative error between both dynamic conditions

Corticomuscular synchronization with small and large dynamic force output-3

<p><b>Copyright information:</b></p><p>Taken from "Corticomuscular synchronization with small and large dynamic force output"</p><p>http://www.biomedcentral.com/1471-2202/8/101</p><p>BMC Neuroscience 2007;8():101-101.</p><p>Published online 27 Nov 2007</p><p>PMCID:PMC2245954.</p><p></p> panel) and during force output (right panel) for single subjects and as grand average. The beta-range (15–30 Hz) is marked in light grey. The gamma-range (30–45 Hz) is marked in dark grey

Corticomuscular synchronization with small and large dynamic force output-0

<p><b>Copyright information:</b></p><p>Taken from "Corticomuscular synchronization with small and large dynamic force output"</p><p>http://www.biomedcentral.com/1471-2202/8/101</p><p>BMC Neuroscience 2007;8():101-101.</p><p>Published online 27 Nov 2007</p><p>PMCID:PMC2245954.</p><p></p> electrooculogram (EOG) and the EMG. (b) Manipulandum. (c) Visual feedback about the position of the ring displayed on a monitor in front of the subject. (d) Force profile generated by the manipulandum during static (), (e) small dynamic () and (f) large dynamic () condition. After a gradual increase of force to 4% MVC, the subject has to maintain the ring in its central position for 12 seconds. Both dynamic conditions have a superimposed sinusoidal function

Corticomuscular synchronization with small and large dynamic force output-4

<p><b>Copyright information:</b></p><p>Taken from "Corticomuscular synchronization with small and large dynamic force output"</p><p>http://www.biomedcentral.com/1471-2202/8/101</p><p>BMC Neuroscience 2007;8():101-101.</p><p>Published online 27 Nov 2007</p><p>PMCID:PMC2245954.</p><p></p> panel) and during force output (right panel) for single subjects and as grand average. The beta-range (15–30 Hz) is marked in light grey. The gamma-range (30–45 Hz) is marked in dark grey. Note the highest EMG SP during condition

Corticomuscular synchronization with small and large dynamic force output-5

<p><b>Copyright information:</b></p><p>Taken from "Corticomuscular synchronization with small and large dynamic force output"</p><p>http://www.biomedcentral.com/1471-2202/8/101</p><p>BMC Neuroscience 2007;8():101-101.</p><p>Published online 27 Nov 2007</p><p>PMCID:PMC2245954.</p><p></p>error (the error after normalization to the amplitude of the force) for 8 subjects (Grand average). The static force () condition is marked as grey line, the small dynamic () condition as dotted black line and large dynamic () condition as thick black line

Corticomuscular synchronization with small and large dynamic force output-1

<p><b>Copyright information:</b></p><p>Taken from "Corticomuscular synchronization with small and large dynamic force output"</p><p>http://www.biomedcentral.com/1471-2202/8/101</p><p>BMC Neuroscience 2007;8():101-101.</p><p>Published online 27 Nov 2007</p><p>PMCID:PMC2245954.</p><p></p>dition (left panel) during small dynamic () condition (middle panel) and large dynamic () condition (right panel) for single subjects and as grand average. The beta-range (15–30 Hz) is marked in light grey, the gamma-range (30–45 Hz) in dark grey. Note that during the condition the most prominent activity occurs in the beta-range. During both dynamic conditions previous beta-range coherence is decreased and the general activity is shifted towards high frequencies, principally in gamma-range. During condition remains significant beta-range CMC, which is absent during condition