Under these circumstances the neuron acts as a detector and encoder of coherence in its input. When however the ISW is incoherent, the activation potential becomes steady or slowly varying in time and the neuron's behavior reverts to the usual sigmoidal dependence of firing frequency on activation without any phase-locking involved. Numerical simulations of a network of bifurcation neurons, show that neurons in the network tend to usually phase-lock their firing and this results in the emergence of coherence in the ISWs of the individual neurons. At first glance such hypothesis may induce skepticism. Noise in cortical neurons, as in other neurons, originates in the synapses, the very sites of communication between neurons.
Synaptic noise has two causes.
These events occur with probability of less than one, meaning that not every nerve impulse reaching the terminal point of an axonal branch forming a synapse junction with another neuron, succeeds in the release of neurotransmitters into the synaptic gap separating a presynaptic neuron from a postsynaptic neuron. Neurotransmitter molecules released into the synaptic gap activate ionic channels in the postsynaptic membrane allowing ions to flow into the postsynaptic neuron altering thereby its potential. This, incidently, is the basic mechanism for electrochemical communication employed by neurons. Recent work carried out by Farhat and Hernandez5, shows bifurcation neuron networks exhibit a phenomenon they call clustering that neutralizes the noise caused by the probabilistic nature of exocytosis. In reference 5 they show that an externally driven network of bifurcation neurons exhibits under certain input conditions clustering, synchronicity, and phase-locking.