Runaway Activity Generated by Mutual Excitation Among Neurons.
Rosebrock, Daniel T.
- Neurons in the brain excite each other. Why does this not lead to a chain reaction, with faster firing generating yet faster firing, and so fourth -- or does it, sometimes? We study this question first for a single integrate-and-fire neuron with synaptic self-excitation and self-inhibition, in essence modelling recurrent synaptic connections in a network. Even for this simple model, we supplement ... read moreanalytic results with numerical ones. We then study the same question, using numerical simulations, for a single Hodgkin-Huxley-like model neuron with synaptic self-excitation and self-inhibition, and finally for a network of Hodgkin-Huxley-like excitatory and inhibitory model neurons. We found that in cases when there would be runaway activity with purely self-excitatory, non-saturating synaptic currents in both the integrate-and-fire and Hodgkin-Huxley-like models, adding inhibition tends to create bi-stability, i.e. a situation in which stable rhythmic firing can be ``shocked'' into runaway activity by a strong external drive. This bi-stability was also reproduced in a neuronal network of excitatory and inhibitory model neurons. In neuronal networks, in which excitatory synapses were modelled by saturating synaptic currents, this transition appeared to be dependent on the species of excitatory chemical synapse, as well as the strength of those synapses. From these findings, we may gain a better understanding of the mechanisms behind runaway activity in a single neuron, as well as runaway circuit activity in a neuronal network.read less