Mutual nervous influences between breathing and precision finger movements.

The precision of short-term finger tracking flexions has been shown to vary with the respiratory cycle. In the present study, we analysed the mutual effects between breathing and short-term finger tracking movements (SFTM)--both flexions and extensions. Moreover, we investigated the preferred phase relationships between breathing and spontaneous single finger flexions and extensions. Two types of experiments were carried out. Fifteen volunteers participated in the finger tracking experiments. In one experimental session, a square-wave function served as a tracking signal that required a rapid finger flexion, and in another session it required a finger extension. In the second type of experiment, 14 volunteers performed spontaneous short-term finger flexions and extensions of a pre-defined amplitude, with the starting point chosen at their convenience. SFTM were associated with modulations in the time course of the respiratory cycle. These were more pronounced for finger flexions than for extensions. Likewise, the precision of finger flexions, but not extensions, showed significant respiratory-phase-dependent differences. The largest tracking errors occurred at the end of expiration in finger flexions and at the end of inspiration in finger extensions. Spontaneous finger flexions tended to start at around the respiratory phase transitions. Spontaneous extensions, however, tended to start at early expiration (12.5-37.5% of expiration time). The results demonstrate that both spontaneous and tracking finger flexions and extensions are influenced by different stages of a breath. However, spontaneous finger movements did not tend to start at the stages of breaths that were associated with the highest movement precision in the tracking tests. Moreover, these results suggest that finger flexions are more closely related to the respiratory rhythm than are finger extensions.