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° 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

The Controversy of Vaccinations

Recently vaccination has become a controversial topic. There is a growing number of people who believe that vaccines carry great health risks to patients and therefore refuse to be vaccinated or to vaccinate their children. This ill-informed view of immunizations is beginning to cause serious problems in the United States as growing numbers of disease cases are being seen. A closer look into the science of vaccines and the benefits they have brought, clearly show that not only do vaccines carry very little risk to patients, but they are responsible for the eradication and reduction of multiple debilitating diseases

Digital reference services

A guest editorial in a special issue edited by G Chowdhury focusing on digital library services