Entrainment of spontaneous cerebral hemodynamic oscillations to behavioral responses
Entrainment in physiological systems can be manifest in cases where phase-coupling (synchronization) between slow intrinsic oscillations and periodic motor responses, or vice versa, takes place. To test whether voluntary movement has something in common with entrainment of slow hemodynamic oscillations to motor responses, we studied blood pressure (BP), heart rate beat-to-beat intervals (RRI) and prefrontal (de)oxyhemoglobin (Hb/HbO2) during 5 min of rest, 10 min of self-paced, voluntary movements and 10 min of stimulus-paced movements at 10 s intervals in 9 subjects. Subjects were divided into 2 groups according to the timing of voluntary finger movements. It appeared that these movements occurred at relatively regular intervals of approximately 10 s in 5 subjects (group A); while 4 subjects showed random or very short inter-movement intervals (group B).
Two remarkable results were obtained: first, the phase coupling (COH2) between BP and RRI showed a significant (p = 0.0061) interaction between activity (rest vs. movement) and group (A vs. B), with an increased (p = 0.0003) coupling in group A. Second, the COH2 between BP and Hb oscillations showed a significant (p = 0.034) interaction between activity and group, with a decreased (p = 0.079) coupling in group B.
These results suggest that subjects able to initiate self-paced, voluntary movements at relatively regular intervals of ∼10 s show an entrainment potential between physiological oscillations and motor responses. This also provides the first evidence that not only physiological oscillations can be entrained to motor responses, but also motor responses (voluntary movements) can be entrained to slow intrinsic oscillations.