ABSTRACT
Although recent work suggests that cortical processing can be involved in the control of balance responses, the central mechanisms involved in these reactions remain unclear. We presently investigated the characteristics of scalp-recorded perturbation-evoked responses (PERs) following a balance disturbance. Eight young adults stabilized an inverted pendulum using their ankle musculature while seated. When perturbations were applied to the pendulum, subjects were instructed to return (active condition) or not return (passive condition) the pendulum to its original stable position. Primary measures included peak latency and amplitude of early PERs (the first negative peak between 100 and 150 ms, N1), amplitude of late PERs (between 200 and 400 ms) and onset and initial amplitude of ankle muscle responses. Based on the timing of PERs, we hypothesized that N1 would represent sensory processing of the balance disturbance and that late PERs would be linked to the sensorimotor processing of balance corrections. Our results revealed that N1 was maximal over frontal-central electrode sites (FCz and Cz). Average N1 measures at FCz, Cz, and CPz were comparable between active and passive tasks ( p>0.05). In contrast, the amplitude of late PERs at Cz was less positive for the active condition than for the passive ( p<0.05). The similarity in N1 between tasks suggests a sensory representation of early PERs. Differences in late PERs may represent sensorimotor processing related to the execution of balance responses.
Subject(s)
Postural Balance/physiology , Somatosensory Cortex/physiology , Adult , Electrodes , Electroencephalography , Electromyography , Evoked Potentials, Somatosensory/physiology , Female , Functional Laterality/physiology , Humans , Male , Muscle, Skeletal/physiology , Psychomotor Performance/physiologyABSTRACT
This study investigated the influence of rhythmic lower-limb activity on the timing of upper-limb balance reactions. Compensatory grasping reactions were evoked in healthy subjects by rapid sagittal tilts of a chair under three conditions: (1) active leg pedaling, (2) passive (motor-driven) leg pedaling, and (3) no lower-limb movement (control task). Compared with control trials, both active and passive pedaling resulted in similar delays in the initiation (43-47 ms) and execution (12-17 ms) of grasping reactions. The similarity between effects due to active and passive movement suggests that the conditioning arose predominantly from sensory discharge associated with lower-limb movement. These results may have important implications for understanding the influence of locomotion or other ongoing movement on the control of stability.
Subject(s)
Arm/physiology , Central Nervous System/physiology , Gait/physiology , Leg/physiology , Periodicity , Postural Balance/physiology , Reaction Time/physiology , Adult , Afferent Pathways/physiology , Arm/innervation , Feedback/physiology , Female , H-Reflex/physiology , Hand Strength/physiology , Humans , Leg/innervation , Locomotion/physiology , Male , Muscle Contraction/physiology , Muscle, Skeletal/innervation , Muscle, Skeletal/physiology , Neural Conduction/physiology , Neural Inhibition/physiology , Proprioception/physiologyABSTRACT
A new experiment for the measurement of nJ(C,P) coupling constants along the phosphodiester backbone in RNA and DNA based on a quantitative-J HCP experiment is presented. In addition to coupling constants, in which a carbon atom couples to only one phosphorus atom, both the intraresidual 3J(C4'i,Pi) and the sequential 3J(C4'i,Pi+1) for the C4' resonances that couple to two phosphorus atoms can be obtained. Coupling constants obtained by this new method are compared to values obtained from the P-FIDS experiment. Together with 3J(H,P) coupling constants measured using the P-FIDS experiment, the backbone angles ß and ∈ can be determined.
