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PubMed1973

Quantifying Rhythmic Movements of Albizzia julibrissin Pinnules.

The cosinor technique, previously applied to studies of animal rhythms, is used to assess the circadian rhythm in pinnule movement of Albizzia julibrissin. The method provides a quantitative approach for studying rhythm properties of either intact or excised pinnules. Phase shifting in A. julibrissin, as compared to the usually slower phase shifts of various circadian phenomena in the insect, bird, and mammal, occurs within 1 day or two. Rhythm adjustment in the pinnules takes place more rapidly when the lighting regiment is advanced than when it is delayed.

Journal Article↗
PubMed2006

Force and time control in the production of rhythmic movement sequences in Parkinson's disease.

This study investigated force and time control in rhythm production in Parkinson's disease. Patients and age-matched controls reproduced rhythms consisting of equal (600 ms) or alternating (400 and 800 ms) intervals, produced with equal (12 N) or alternating (8 and 16 N) forces, under paced (synchronization) and unpaced (continuation) conditions. Performance was assessed in terms of accuracy and variability. Reproduction of force amplitudes was less accurate in patients than in controls when either time or force alternated but did not deteriorate further when force and time alternated. In contrast, interval timing was least accurate in patients compared with controls when rhythm alternated on both dimensions. The ratio between alternating force levels was better maintained by controls than by patients, without influence of timing requirements in either group. In contrast, the ratio between alternating intervals was relatively preserved in patients when force remained constant but was severely compromised when force alternated. Timing variability was greater in the patient group, especially in the more affected side, but there was no difference in timing variability between groups as a function of rhythm, and there were no differences between groups in variability of force. The results show that force and time control in patients are affected in different ways. We interpret the preserved timing of rhythms with alternation on one dimension as evidence of intact ability to organize movements in a sequence. The data are compatible with a basal ganglia role in the coregulation of time and force, but do not support a general timing function of the basal ganglia.

Aged↗
PubMed1984

On controlling force and time in rhythmic movement sequences: the effect of stress location.

Accentuation involves modulation of motor intensity. It differentiates a movement from others within a motor sequence. Does the serial position of the accent characterize the whole sequence as a particular response? How are the control of time and force coordinated in the motor sequence? Subjects produced sequences of four fingertaps on a key. Time of onset and force of each tap were recorded. Tapping rate was imposed by a string of four clicks delivered at 180-msec intervals before each trial. A flashed digit served as go signal. It indicated to the subject which of the four taps had to be tapped stronger (stress +) or weaker (stress -) than all the others. These conditions were run in separate series. Reaction time (RT) of the sequence increased when the number of equally likely locations of the stress increased from 2 to 4. RT was also longer under the stress - than under the stress + condition. Tapping intervals were longer before and after the stressed tap than elsewhere in the series. The first and last intervals tended to be longer than the second one. These effects were the same under both stress conditions. The RT data indicate that the motor sequence is identified as a particular response before it starts. Timing is partly force-independent, but is modulated by central processes that control force.

Attention↗
PubMed2005

Bimanual coordination during rhythmic movements in the absence of somatosensory feedback.

We investigated the role of somatosensory feedback during bimanual coordination by testing a bilaterally deafferented patient, a unilaterally deafferented patient, and three control participants on a repetitive bimanual circle-drawing task. Circles were drawn symmetrically or asymmetrically at varying speeds with full, partial, or no vision of the hands. Strong temporal coupling was observed between the hands at all movement rates during symmetrical drawing and at the comfortable movement rate during asymmetrical drawing in all participants. When making asymmetric movements at the comfortable and faster rates, the patients and controls exhibited similar evidence of pattern instability, including a reduction in temporal coupling and trajectory deformation. The patients differed from controls on measures of spatial coupling and variability. The amplitudes and shapes of the two circles were less similar across limbs for the patients than the controls and the circles produced by the patients tended to drift in extrinsic space across successive cycles. These results indicate that somatosensory feedback is not critical for achieving temporal coupling between the hands nor does it contribute significantly to the disruption of asymmetrical coordination at faster movement rates. However, spatial consistency and position, both within and between limbs, were disrupted in the absence of somatosensory feedback.

Aged↗
PubMed1996

Coupling the neural and physical dynamics in rhythmic movements.

A pair of coupled oscillators simulating a central pattern generator (CPG) interacting with a pendular limb were numerically integrated. The CPG was represented as a van der Pol oscillator and the pendular limb was modeled as a linearized, hybrid spring-pendulum system. The CPG oscillator drove the pendular limb while the pendular limb modulated the frequency of the CPG. Three results were observed. First, sensory feedback influenced the oscillation frequency of the coupled system. The oscillation frequency was lower in the absence of sensory feedback. Moreover, if the muscle gain was decreased, thereby decreasing the oscillation amplitude of the pendular limb and indirectly lowering the effect of sensory feedback, the oscillation frequency decreased monotonically. This is consistent with experimental data (Williamson and Roberts 1986). Second, the CPG output usually led the angular displacement of the pendular limb by a phase of 90 degrees regardless of the length of the limb. Third, the frequency of the coupled system tuned itself to the resonant frequency of the pendular limb. Also, the frequency of the coupled system was highly resistant to changes in the endogenous frequency of the CPG. The results of these simulations support the view that motor behavior emerges from the interaction of the neural dynamics of the nervous system and the physical dynamics of the periphery.

Computer Simulation↗