Bursting

Bursting, or burst firing, is an extremely diverse[1] general phenomenon of the activation patterns of neurons in the central nervous system[2][3] and spinal cord[4] where periods of rapid action potential spiking are followed by quiescent periods much longer than typical inter-spike intervals.

Bursting is thought to be important in the operation of robust central pattern generators,[5][6][7] the transmission of neural codes,[8][9] and some neuropathologies such as epilepsy.

There are many discovered mechanisms of slow subsystems including voltage-[6][12][13] and Ca2+-gated[14] currents and spiking interplay between dendrites and the cell body.

So long as internal calcium ion concentrations remain at an elevated level, the neuron will continue to undergo periods of rapid spiking.

As calcium concentrations decline, the period of rapid bursting ceases, and the phase of quiescence begins.

[16] In isolation or in mathematical models bursting can be recognized since the environment and state of the neuron can be carefully observed and modulated.

In order to recognize bursting patterns in these contexts statistical methods are used to determine threshold parameters.

Bursting is characterized by a coefficient of variation (CV) of the interspike intervals (ISI) that is larger than one, or a Fano factor of the spike count that is larger than one, because bursting leads to spike patterns that are more irregular than a Poisson process (which has a CV and Fano factor equal to unity).

[11] Models of neuron dynamics generally exhibit a number of stable and unstable attractors in phase space which represent resting states.

When the system is sufficiently perturbed by input stimuli it may follow a complex return path back to the stable attractor representing an action potential.

The fold/homoclinic, also called square-wave, burster is so named because the shape of the voltage trace during a burst looks similar to a square wave due to fast transitions between the resting state attractor and the spiking limit cycle.

Due to the all-or-nothing nature of action potentials, single spikes can only encode information in their interspike intervals (ISI).

This is an inherently low fidelity method of transferring information as it depends on very accurate timing and is sensitive to noisy loss of signal: if just a single spike is mistimed or not properly received at the synapse it leads to a possibly unrecoverable loss in coding[citation needed].

The subiculum, a component of the hippocampal formation, is thought to perform relaying of signals originating in the hippocampus to many other parts of the brain.

[25] The pre-Bötzinger complex (preBötC) is located in ventrolateral medulla and is proposed to generate the rhythm underlying inspiratory efforts in mammals.

Intrinsically bursting neurons are thought to make the preBötC oscillations more robust to changing frequencies and the regularity of inspiratory efforts.

[27] Purkinje neurons may utilise these bursting forms in information coding to the deep cerebellar nuclei.