| Associated contractions (CAC) can originate in the contralateral muscle during unilateral voluntary contractions of the ipsilateral muscle (Westphal, 1874; Curshmann 1906). In literature this phenomenon is also known as irradiation, motor overflow, synkinesis or mirror movements. CAC has several special features, one interesting feature of CAC is that its occurrence is more pronounced in children (Curshmann, 1906; Todor and Lazarus, 1986). The disappearance of CAC is associated with the maturity of the corpus callosum in the brain. In healthy adults, during fatiguing (Zijdewind, 2001) or strenuous movements (Armatas, 1994)CAC becomes more apparent. Thus, during high effort contractions the level of contralateral activation is increased. The amount of CAC in a fatigued muscle, however, is significantly declined (Zijdewind, Broeders, Steens and Kernell, in preparation). CAC is also more prominent in contractions of distal muscles (fingers or toes) than in contractions of proximal muscles (Durwen, 1989). Some authors suggest that the appearance of CAC in healthy adults is a remainder of childhood coordination. However, the origin of CAC is still unclear. The observation that an increased effort results in an increase of CAC suggest a direct connection between the voluntary muscle activation and the associated movements. The question is, however, where in the central nervous system this interaction takes place. The aim of this study is to get more insight into the origin of CAC. In a pilot study Functional Magnetic Resonance Imaging (fMRI) is used to gain information about the brain activity during associated movements. The subjects had to produce a force with their index finger. Electromyography (EMG) was used to measure the activity in the first dorsal interosseus (FDI) muscle, the most important muscle for index finger abduction. The data of this brain imaging study is now under analyses. |
