|M.Sc Student||Rabinovitch Eshed|
|Subject||Stability of Propagation Patterns over Prolonged Time|
Scales in Cultured Neural Networks
|Department||Department of Medicine||Supervisor||Professor Noam Ziv|
An important aspect of network function concerns pathways of activity propagation - the identities, firing times, and/or firing rates of neurons downstream from points at which activity enters the network. Propagation pathways are sensitive to many dynamic variables, the most important ones being neuronal excitability, synaptic plasticity and relative strengths of excitation and inhibition. Prior studies carried out in cortical networks in primary culture suggest that these variables fluctuate considerably. As neuronal and network excitability are combinatorial and highly non-linear, the effects of such fluctuations on activity propagation pathways on long time scales (5-6 days) are difficult to predict. In this study we set out to characterize and quantify spontaneous changes in activity propagation pathways in cortical neuron networks over time scales of days. To that end, we used primary cultures of rat cortical neurons plated on multi-electrode arrays (MEAs). The networks (16 days in vitro) were mounted in setups that allowed for continuous recording and stimulation and were stimulated electrically at low frequency (0.1Hz) from four spatially separated sources to trigger network responses. Several well-established measures as well as a measure we devised were used to quantify similarities between individual propagation pathways evoked by stimuli delivered from the same (and different) sources. We found that networks exhibit a variety of behaviors. In some networks, propagation pathways were relatively stable for days. In others, these changed gradually, yet in others, we found that propagation pathways could change abruptly, effectively resulting in networks shifting among multiple discrete propagation pathways. In some cases such shifts involved reversions to previously used pathways or alternations among different stimulation sources. Our findings thus suggest that the stability of propagation pathways can vary qualitatively and quantitatively across apparently similar networks, for reasons that are yet to be understood.