= Tonic firing
<Tonic firing> is a sustained pattern of individual <action potentials> rather than brief, separated clusters characteristic of <burst firing>. In a specified preparation it may be relatively regular, but tonic does not require perfectly equal <interspike intervals> or one universal firing frequency. The term concerns timing, not a permanently fixed identity of the <neuron>.
For an invented one-second recording, ten <action potentials> at $0.05,0.15,\ldots,0.95$ seconds give a mean count rate of $10\,\mathrm{s}^{-1}$ and consecutive <interspike intervals> of $0.1$ seconds. Two clusters containing five spikes each can have the same total count with very different intervals. The average rate therefore does not specify whether a train is tonic or bursting.
Recordings from the <lateral habenula> in a 2018 study distinguished tonic and bursting modes and examined changes associated with <membrane potential> and receptor-dependent currents.<Ketamine blocks bursting in the lateral habenula to rapidly relieve depression by Yan Yang and others>[Figures2–4 and Extended Data Figure6; firing modes, current manipulations and model comparisons]{ref} The same cell can change its temporal pattern under changed conditions. This illustrates why a firing-mode label must be attached to the recorded interval and experimental state, rather than inferred solely from the cell's name.
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