A computer simulation of the electrophysiological behavior of neural elements interacting via extracellular potassium ion (K+) concentration variations in a shared extracellular space has been developed.
The aim of the proposed project is to integrate current experimental data that characterize these activity dependent K+ variations with a predictive scheme for exploring their potential functional significance. The generality of ionic coupling between active and inactive cellular elements of the CNS will be studied by modeling particular regional geometries. To be considered are: (1) the effects that such coupling may have on stability of firing patterns of adjacent neurons, (2) K+-mediated depolarization as a presynaptic modulator of classic chemical neurotransmission, (3) activity-dependent ion gradient variations as a locally nonspecific signaling parameter in dense cell assemblies and (4) application of these concepts to formalized models of learning in neural """"""""networks"""""""". The physiological variables to be explored are (1) the width and local geometry of the extracellular environment, (2) the relative distribution of glial and neural membrane in that locale, (3) the degree of driven (extrinsic or spontaneous intrinsic) neural activity, and (4) the degree of coincidence (synchronicity) of driven AP activity among near neighbors. The results will be extended to include dynamic variations in the transmembrane gradients of other relevant ions (Na+, Ca+, and to explore the relation of the above concepts to pathologic states, such as epileptiform activity. Although k-mediated ionic-coupling has implications with respect to instability and epileptiform activity in neural networks, a major conceptual application will be to information processing in general. The novelty of the dynamics resides in the fact that in addition to fixed structural synaptic interactions, the cells of a circumscribed locale may be linked by their proximity in a geometric sense and by the relative synchronicity of exogenous driving such that the traces of activity that are provided by extracellular potassium transients becomes a basis for local neuronal integration. This theoretical investigation will facilitate consideration of small scale cooperative interactions that resist study with current techniques but may be considered to play a role in functional information processing in discrete CNS locales.
| Lebovitz, R M (1996) Quantitative examination of dynamic interneuronal coupling via single-spike extracellular potassium ion transients. J Theor Biol 180:11-25 |
