Spatiotemporal model of tripartite synapse with perinodal astrocytic process.

Information transfer may not be limited only to synapses. Therefore, the processes and dynamics of biological neuron-astrocyte coupling and intercellular interaction within this domain are worth investigating. Existing models of tripartite synapse consider an astrocyte as a point process. Here, we extended the tripartite synapse model by considering the astrocytic processes (synaptic and perinodal) as compartments. The scattered extrinsic signals in the extracellular space and the presence of calcium stores in different astrocytic sites create local transient [Ca2+]. We investigated the Ca2+ dynamics and found that the increase in astrocytic intracellular [Ca2+] enhances the probability of neurotransmitter release. However, the period in which the extrasynaptic glutamate lingers in the extracellular space may cause excitotoxicity. We propose further biological investigation on intercellular communication, considering that unconventional sources (nonsynaptic) of glutamate may improve information processing in neuron-astrocyte networks.

A New Mathematical Force Model that Predicts the Force-pulse Amplitude Relationship of Human Skeletal Muscle.

Current functional electrical stimulation (FES) systems vary the stimulation intensity to control the muscle force in order to produce precise functional movements. However, mathematical model that predicts the intensity effect on the muscle force is required for model-based controller design. The most previous force model designed by Ding et al was validated only for a standardized stimulation pulse amplitude (intensity). Thus, the purpose of this study was to adapt the Ding et al model to be able to predict the force-pulse amplitude relationship. The experimental results tested on quadriceps femoris muscles of healthy subjects (N=5) show that our adapted model accurately predicts the force response for trains of a wide range of stimulation intensities (30-100 mA). The accurate predictions indicate that our adapted model could be used for designing model-based control strategies to control the muscle force through FES.

Impact of bipolar electrodes contact on fractionation index measurement.

Signals such as Complex Fractionated Atrial Electrograms (CFAE) are tracked during ablation procedures to locate the arrhythmical substrate regions. Most of CFAE classification tools use fractionation indexes. However, recordings from intracardiac catheter depend on electrode contact quality. This paper investigates the impact of electrode contact area on fractionation indexes. It is assessed through three kinds of arrhythmical activations resulting from a numerical simulation of a small piece of the cardiac tissue. Bipolar electrograms are extracted corresponding to 25 different contact areas and fractionation indexes (Shannon entropy, non linear energy operator and maximum peak ratio) are computed. Results yield that the Shannon entropy offers a good potential discrimination between arrhythmic scenarios and is less sensitive to the electrode contact variation.